WO2014069208A1 - Platinum core shell catalyst, manufacturing method for same, and fuel cell using same - Google Patents
Platinum core shell catalyst, manufacturing method for same, and fuel cell using same Download PDFInfo
- Publication number
- WO2014069208A1 WO2014069208A1 PCT/JP2013/077617 JP2013077617W WO2014069208A1 WO 2014069208 A1 WO2014069208 A1 WO 2014069208A1 JP 2013077617 W JP2013077617 W JP 2013077617W WO 2014069208 A1 WO2014069208 A1 WO 2014069208A1
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- WIPO (PCT)
- Prior art keywords
- platinum
- core
- shell
- catalyst
- ruthenium
- Prior art date
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- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical group [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 title claims abstract description 420
- 239000003054 catalyst Substances 0.000 title claims abstract description 160
- 239000011258 core-shell material Substances 0.000 title claims abstract description 52
- 239000000446 fuel Substances 0.000 title claims abstract description 16
- 238000004519 manufacturing process Methods 0.000 title claims description 18
- 229910052697 platinum Inorganic materials 0.000 claims abstract description 185
- 239000010931 gold Substances 0.000 claims abstract description 134
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical group [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims abstract description 103
- 229910052741 iridium Inorganic materials 0.000 claims abstract description 70
- 229910052707 ruthenium Inorganic materials 0.000 claims abstract description 67
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 claims abstract description 66
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 claims abstract description 60
- 239000007771 core particle Substances 0.000 claims abstract description 50
- 239000002245 particle Substances 0.000 claims abstract description 44
- 229910052737 gold Inorganic materials 0.000 claims abstract description 43
- 239000010949 copper Substances 0.000 claims description 59
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 35
- 239000010410 layer Substances 0.000 claims description 35
- 229910052802 copper Inorganic materials 0.000 claims description 34
- 238000000034 method Methods 0.000 claims description 31
- 239000007864 aqueous solution Substances 0.000 claims description 24
- -1 platinum ions Chemical class 0.000 claims description 17
- 239000007787 solid Substances 0.000 claims description 15
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 13
- 239000001301 oxygen Substances 0.000 claims description 13
- 229910052760 oxygen Inorganic materials 0.000 claims description 13
- 150000002500 ions Chemical class 0.000 claims description 10
- 238000006722 reduction reaction Methods 0.000 claims description 8
- 239000003575 carbonaceous material Substances 0.000 claims description 7
- 239000002356 single layer Substances 0.000 claims description 7
- 238000003756 stirring Methods 0.000 claims description 6
- 230000002378 acidificating effect Effects 0.000 claims description 5
- 150000001875 compounds Chemical class 0.000 claims description 5
- 239000000463 material Substances 0.000 claims description 3
- 238000006467 substitution reaction Methods 0.000 claims 1
- 230000003197 catalytic effect Effects 0.000 abstract description 16
- 239000011257 shell material Substances 0.000 description 84
- 239000011162 core material Substances 0.000 description 36
- 230000000052 comparative effect Effects 0.000 description 20
- 239000006104 solid solution Substances 0.000 description 19
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 description 16
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 15
- 239000002105 nanoparticle Substances 0.000 description 15
- 238000012360 testing method Methods 0.000 description 13
- 229910002849 PtRu Inorganic materials 0.000 description 10
- 239000000084 colloidal system Substances 0.000 description 10
- 230000000694 effects Effects 0.000 description 10
- 239000000203 mixture Substances 0.000 description 10
- 239000000243 solution Substances 0.000 description 10
- 238000004458 analytical method Methods 0.000 description 9
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 8
- 239000013078 crystal Substances 0.000 description 8
- 239000010419 fine particle Substances 0.000 description 8
- 239000012298 atmosphere Substances 0.000 description 7
- 239000000126 substance Substances 0.000 description 7
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 6
- 229910052751 metal Inorganic materials 0.000 description 6
- 239000002184 metal Substances 0.000 description 6
- 238000002156 mixing Methods 0.000 description 6
- 238000002360 preparation method Methods 0.000 description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- 229910052799 carbon Inorganic materials 0.000 description 5
- 239000000306 component Substances 0.000 description 5
- 238000010438 heat treatment Methods 0.000 description 5
- 230000014759 maintenance of location Effects 0.000 description 5
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 4
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 4
- 230000008901 benefit Effects 0.000 description 4
- 230000005587 bubbling Effects 0.000 description 4
- 230000007423 decrease Effects 0.000 description 4
- ZSIAUFGUXNUGDI-UHFFFAOYSA-N hexan-1-ol Chemical compound CCCCCCO ZSIAUFGUXNUGDI-UHFFFAOYSA-N 0.000 description 4
- 238000007254 oxidation reaction Methods 0.000 description 4
- VLTRZXGMWDSKGL-UHFFFAOYSA-N perchloric acid Chemical compound OCl(=O)(=O)=O VLTRZXGMWDSKGL-UHFFFAOYSA-N 0.000 description 4
- 150000003058 platinum compounds Chemical class 0.000 description 4
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 4
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 3
- 239000003929 acidic solution Substances 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 229910052786 argon Inorganic materials 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- 239000003638 chemical reducing agent Substances 0.000 description 3
- WNAHIZMDSQCWRP-UHFFFAOYSA-N dodecane-1-thiol Chemical compound CCCCCCCCCCCCS WNAHIZMDSQCWRP-UHFFFAOYSA-N 0.000 description 3
- 239000011261 inert gas Substances 0.000 description 3
- 238000011068 loading method Methods 0.000 description 3
- 229910044991 metal oxide Inorganic materials 0.000 description 3
- 150000004706 metal oxides Chemical class 0.000 description 3
- 229910000510 noble metal Inorganic materials 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 239000012071 phase Substances 0.000 description 3
- 230000009467 reduction Effects 0.000 description 3
- 230000035882 stress Effects 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- 230000010757 Reduction Activity Effects 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 239000002253 acid Substances 0.000 description 2
- 239000008346 aqueous phase Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 239000011888 foil Substances 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 229910021397 glassy carbon Inorganic materials 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 230000001965 increasing effect Effects 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 239000003223 protective agent Substances 0.000 description 2
- 230000035484 reaction time Effects 0.000 description 2
- 238000006479 redox reaction Methods 0.000 description 2
- 239000000725 suspension Substances 0.000 description 2
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 2
- 229910001887 tin oxide Inorganic materials 0.000 description 2
- 238000012546 transfer Methods 0.000 description 2
- 229910021591 Copper(I) chloride Inorganic materials 0.000 description 1
- JPVYNHNXODAKFH-UHFFFAOYSA-N Cu2+ Chemical compound [Cu+2] JPVYNHNXODAKFH-UHFFFAOYSA-N 0.000 description 1
- 229910003771 Gold(I) chloride Inorganic materials 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 1
- 238000003917 TEM image Methods 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 239000006230 acetylene black Substances 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 229940045985 antineoplastic platinum compound Drugs 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 239000002041 carbon nanotube Substances 0.000 description 1
- 229910021393 carbon nanotube Inorganic materials 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 229910001431 copper ion Inorganic materials 0.000 description 1
- OXBLHERUFWYNTN-UHFFFAOYSA-M copper(I) chloride Chemical compound [Cu]Cl OXBLHERUFWYNTN-UHFFFAOYSA-M 0.000 description 1
- 239000008358 core component Substances 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 230000009881 electrostatic interaction Effects 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- QUCZBHXJAUTYHE-UHFFFAOYSA-N gold Chemical group [Au].[Au] QUCZBHXJAUTYHE-UHFFFAOYSA-N 0.000 description 1
- FDWREHZXQUYJFJ-UHFFFAOYSA-M gold monochloride Chemical compound [Cl-].[Au+] FDWREHZXQUYJFJ-UHFFFAOYSA-M 0.000 description 1
- 150000002430 hydrocarbons Chemical group 0.000 description 1
- 230000009545 invasion Effects 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- GSNZLGXNWYUHMI-UHFFFAOYSA-N iridium(3+);trinitrate Chemical compound [Ir+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O GSNZLGXNWYUHMI-UHFFFAOYSA-N 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 239000003273 ketjen black Substances 0.000 description 1
- 239000002082 metal nanoparticle Substances 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 150000002894 organic compounds Chemical class 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 238000007747 plating Methods 0.000 description 1
- 150000003057 platinum Chemical class 0.000 description 1
- 231100000572 poisoning Toxicity 0.000 description 1
- 230000000607 poisoning effect Effects 0.000 description 1
- 239000005518 polymer electrolyte Substances 0.000 description 1
- 239000010970 precious metal Substances 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- GTCKPGDAPXUISX-UHFFFAOYSA-N ruthenium(3+);trinitrate Chemical compound [Ru+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O GTCKPGDAPXUISX-UHFFFAOYSA-N 0.000 description 1
- YBCAZPLXEGKKFM-UHFFFAOYSA-K ruthenium(iii) chloride Chemical compound [Cl-].[Cl-].[Cl-].[Ru+3] YBCAZPLXEGKKFM-UHFFFAOYSA-K 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000000967 suction filtration Methods 0.000 description 1
- 239000006228 supernatant Substances 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 238000001308 synthesis method Methods 0.000 description 1
- QBVXKDJEZKEASM-UHFFFAOYSA-M tetraoctylammonium bromide Chemical compound [Br-].CCCCCCCC[N+](CCCCCCCC)(CCCCCCCC)CCCCCCCC QBVXKDJEZKEASM-UHFFFAOYSA-M 0.000 description 1
- 238000002411 thermogravimetry Methods 0.000 description 1
- 125000003396 thiol group Chemical group [H]S* 0.000 description 1
- DANYXEHCMQHDNX-UHFFFAOYSA-K trichloroiridium Chemical compound Cl[Ir](Cl)Cl DANYXEHCMQHDNX-UHFFFAOYSA-K 0.000 description 1
- 238000004758 underpotential deposition Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Images
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
- B01J23/48—Silver or gold
- B01J23/52—Gold
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
- B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
- B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
- B01J23/8926—Copper and noble metals
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- B01J35/397—
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- B01J35/40—
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- B01J35/50—
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/02—Impregnation, coating or precipitation
- B01J37/03—Precipitation; Co-precipitation
- B01J37/031—Precipitation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/02—Impregnation, coating or precipitation
- B01J37/03—Precipitation; Co-precipitation
- B01J37/031—Precipitation
- B01J37/035—Precipitation on carriers
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/05—Metallic powder characterised by the size or surface area of the particles
- B22F1/054—Nanosized particles
- B22F1/0549—Hollow particles, including tubes and shells
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/17—Metallic particles coated with metal
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/16—Making metallic powder or suspensions thereof using chemical processes
- B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
- B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C5/00—Alloys based on noble metals
- C22C5/02—Alloys based on gold
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C5/00—Alloys based on noble metals
- C22C5/04—Alloys based on a platinum group metal
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/8647—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites
- H01M4/8657—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites layered
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/88—Processes of manufacture
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/90—Selection of catalytic material
- H01M4/9041—Metals or alloys
- H01M4/905—Metals or alloys specially used in fuel cell operating at high temperature, e.g. SOFC
- H01M4/9058—Metals or alloys specially used in fuel cell operating at high temperature, e.g. SOFC of noble metals or noble-metal based alloys
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/90—Selection of catalytic material
- H01M4/92—Metals of platinum group
- H01M4/925—Metals of platinum group supported on carriers, e.g. powder carriers
- H01M4/926—Metals of platinum group supported on carriers, e.g. powder carriers on carbon or graphite
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/10—Fuel cells with solid electrolytes
- H01M8/1007—Fuel cells with solid electrolytes with both reactants being gaseous or vaporised
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- the present invention relates to a platinum core-shell catalyst suitable for use as a catalyst for oxygen reduction reaction in a fuel cell, a method for producing the same, and a fuel cell using the catalyst.
- a polymer electrolyte fuel cell is a clean energy device that generates only water by causing an oxidation reaction of hydrogen on the anode side and a reduction reaction of oxygen on the cathode side.
- a catalyst using platinum (Pt) as a catalyst on the cathode side is known.
- a catalyst using platinum, which is a noble metal has high catalytic activity and high electrical conductivity, and has an advantage that it is less susceptible to corrosion and poisoning due to the state of the surrounding environment and substances present in the surrounding environment.
- Patent Document 1 Japanese Patent Application Laid-Open No. 2012-41581 discloses core particles made of ruthenium having a face-centered cubic crystal structure as core-shell fine particles that reduce the amount of platinum used and improve catalytic activity, A core-shell fine particle having a shell made of platinum having a face-centered cubic crystal structure formed on the surface is disclosed.
- the main object of the present invention is to increase the catalyst efficiency of platinum by improving the surface density of platinum atoms on the surface of the catalyst fine particles, thereby reducing the amount used, and the center of the surface where the surface density of platinum atoms in the shell is maximized.
- the inventors have found that a cubic crystal structure is used.
- gold is known as a core metal for the platinum shell.
- Gold is a precious metal, has a lower ionization tendency than platinum, is stable against oxidation, and has a much larger amount of resources than platinum, and thus is expected as one of core metals.
- Patent Document 2 Japanese Patent Laid-Open No. 2011-212666 discloses a method for producing a platinum surface catalyst layer on the surface of a gold core particle without using a reducing agent.
- a gold layer is immersed in a solution containing divalent or tetravalent platinum ions to deposit a platinum layer directly on the gold core.
- a catalyst having a gold core / platinum shell can be obtained by a simple method.
- the durability and catalytic efficiency of the catalyst are not examined.
- Patent Document 3 Japanese Patent Laid-Open No. 2010-92725 discloses a catalyst in which a shell of Pt or an alloy thereof is formed on the surface of core particles made of Au or an alloy thereof.
- Au having a large lattice constant is used as a core
- Pt having a small lattice constant is used as a shell.
- the core or shell may be an alloy of Au or Pt.
- a base metal such as Fe and Co and a noble metal such as Ag, Ru, Pd and Ir can be added to Pt of the shell by 40 atomic% or less.
- the Au core particle size is 1 to 10 nm and the Pt shell thickness is 2 nm or less.
- the lattice constant referred to in this document is a lattice constant in a single crystal, and an interatomic distance in an actual nanoparticle is not considered.
- Non-Patent Document 1 when the Pt monolayer catalyst constructed on Au single crystal is compared with the Pt monolayer catalyst constructed on Au nanoparticles having a particle size of 3 nm, the latter oxygen reduction activity is observed. It has been reported to be about 2.5 times better.
- the Pt monolayer has acquired an electronic state (binding force with oxygen species) suitable for the oxygen reduction reaction and exhibits high oxygen reduction activity.
- an object of the present invention is to provide a platinum core-shell catalyst having gold core particles having excellent durability and catalytic efficiency.
- the inventors have the property that platinum dissolves in gold, so that the platinum atoms on the surface of the catalyst particles become a gold core as the potential cycle is repeated. Considering that the catalytic activity decreases due to the decrease in platinum atoms on the surface of the catalyst particles due to the solid solution, investigations have been conducted.
- the inventors focused on the thermodynamic properties of the shell component and the core component in the study to solve the above-mentioned problems, and from a thermodynamic point of view, a state in which solid solution burying of platinum atoms in the gold core is difficult to occur.
- iridium (Ir) or ruthenium (Ru) which is an element having a property that is difficult to mix with gold compared to platinum and easy to mix with platinum compared to gold.
- the inventors have found that a platinum core-shell catalyst having excellent durability and catalytic efficiency can be obtained, and have completed the present invention.
- the present invention has a core particle containing gold and a shell containing platinum and iridium and / or ruthenium formed on the surface of the core and having a diameter of 1.6 to 6.8 nm.
- the present invention relates to a platinum core-shell catalyst for a fuel cell.
- the core particles preferably have a particle size of 1.0 to 5.0 nm and a shell thickness of 0.3 to 0.9 nm.
- the platinum core-shell catalyst of the present invention since the platinum shell is formed on the surface of the gold core particle, all or most of the platinum atoms are present on the surface of the catalyst particle and can exhibit catalytic activity. That is, the utilization efficiency of platinum atoms as a catalyst is extremely high.
- the shell contains iridium (Ir) and / or ruthenium (Ru) in addition to platinum. With this configuration, the platinum core-shell catalyst having excellent durability is obtained by suppressing the solid-solution burying of platinum shell atoms in the gold core. Furthermore, since the particle size of the catalyst is as small as 1.6 to 6.8 nm, the surface area per catalyst weight is increased, and the amount of gold used is also reduced. Furthermore, since the maximum amount of platinum that can be dissolved in the gold core is determined by the volume of the gold core, the loss of platinum due to the solid solution can be kept small by using a gold core having a small particle diameter.
- the core particle size is in the range of 1.0 to 5.0 nm and the shell thickness is in the range of 0.3 to 0.9 nm
- the shell is substantially changed from a monolayer (monoatomic layer) to a triatomic layer, and a gold core.
- the particles are small enough.
- a more suitable platinum core-shell catalyst can be obtained.
- the platinum core-shell catalyst of the present invention can simultaneously provide high mass activity based on high platinum utilization efficiency and high durability based on a structure in which the platinum shell is prevented from dissolving in the gold core. .
- the composition of the catalyst is set from a thermodynamic viewpoint, specifically, by adding a specific type of metal to the shell component, the solidification of platinum in the shell to the core is performed.
- Deterring sunk invasion is an unprecedented new idea.
- the catalyst of the present invention set based on this idea is a novel catalyst having a gold core having a particle size in a specific range and a platinum shell containing iridium and / or ruthenium, In comparison, even if the covering ratio of the shell is low, the catalyst activity retention rate is extremely excellent.
- the ratio of iridium and / or ruthenium to platinum is preferably 0.1 to 50% at.%, And more preferably 5 to 30% at.%. With this ratio, iridium and / or ruthenium effectively suppresses the solid solution of platinum in the gold core and does not inhibit the platinum atom coverage and catalytic activity in the shell. And a catalyst having high durability can be obtained.
- platinum and iridium and / or ruthenium may be mixed in the same layer, and iridium and / or ruthenium may be interposed between the platinum shell and the gold core particle.
- the catalyst in which platinum and iridium and / or ruthenium are mixed in the same layer can be manufactured by a simple manufacturing process because the shell can be formed in one step. There is an advantage of being.
- the catalyst in which iridium and / or ruthenium is interposed between the platinum shell and the gold core particle surface has iridium and / or ruthenium between the platinum shell and the gold core particle. Since it also functions as a barrier, the effect of suppressing the solid solution burying of platinum becomes higher, and at the same time, the surface of the core can be covered only with platinum, so that higher catalytic efficiency can be obtained.
- the platinum core-shell catalyst of the present invention is preferably supported on a carrier made of a carbonaceous material.
- a metal oxide carrier such as tin oxide (SnOx) or titanium oxide (TiOx) having high oxidation resistance, or a carrier obtained by mixing these metal oxides with a carbonaceous material. May be used.
- the platinum core-shell catalyst of the present invention can be suitably used as a catalyst for oxidation-reduction reactions in fuel cells.
- the present invention also includes (1) a step of forming a monoatomic layer made of copper on the surface of a gold core particle supported on a carbonaceous support, and (2) a monoatomic layer made of copper obtained in step (1). And replacing the layer with platinum and iridium and / or ruthenium.
- gold core particles supported on a carbonaceous support are put into an acidic aqueous solution containing Cu ions in which a solid made of copper is immersed, and inert gas such as argon or nitrogen gas is used.
- step (2) removes the solid made of copper from the aqueous solution, and then introduces a substance that gives platinum ions and iridium and / or ruthenium ions;
- the step comprises replacing the copper on the product surface obtained in 1) with platinum and ruthenium and / or iridium.
- a platinum core-shell catalyst having a desired particle size and shell composition is formed by forming a shell containing platinum, iridium and ruthenium in a desired ratio on the surface of a gold core particle having a desired particle size.
- a step (1) the method using an acidic aqueous solution containing Cu ions in which a solid made of copper is immersed is more precise than the conventional UPD method, and precise potential control using an external power source and a counter electrode or reference No need for poles, etc., and since the process and equipment are simple, mass production is possible and the practical use value is extremely high.
- the ratio of iridium and / or ruthenium to platinum is preferably 0.1 to 50% at.%, More preferably 5 to 30% at.%. Is more preferable.
- the present invention is a method in which a compound that gives platinum ions and a compound that gives iridium and / or ruthenium ions are simultaneously added, so that platinum and iridium and / or ruthenium are mixed in the same layer. Is preferably formed. According to this method, a shell containing platinum and iridium and / or ruthenium can be easily formed on the surface of the gold core particle in one step.
- the platinum core-shell catalyst produced by each of the above methods can be suitably used as a catalyst for an oxidation-reduction reaction in a fuel cell.
- the platinum core-shell catalyst of the present invention contains iridium and / or ruthenium in addition to platinum in the shell, and iridium or ruthenium is present in the vicinity of the platinum atom. This suppresses the solid dissolution of platinum atoms in the gold core. That is, the durability of the catalyst is excellent, and the catalytic activity can be maintained for a long time.
- the platinum core-shell catalyst of the present invention has iridium or ruthenium in the shell, and the gold core has a small particle size even when the platinum coverage is low and the solid solution in the gold core particles tends to be large. Therefore, it is possible to maintain good durability and high catalyst efficiency with less solid solution of platinum in the gold core.
- the present invention effectively suppresses solid solution of platinum in the core and improves the durability of the catalyst by a simple measure of adding iridium or ruthenium as a shell component of a platinum shell / gold core catalyst having a known configuration.
- the main purpose is to improve the utilization efficiency of the platinum catalyst by improving the catalytic activity of platinum or by producing a platinum layer by a more efficient method.
- the present invention has improved durability in a simple manner in addition to the utilization efficiency of the catalyst.
- the present invention has an effect that not only the amount of platinum used during the production of the catalyst can be reduced, but also the amount of platinum used can be reduced by enhancing its durability. Since the platinum core-shell catalyst of the present invention can be used as a catalyst for a fuel cell, the cost of the fuel cell can be drastically reduced.
- the core of the platinum core-shell catalyst of the present invention is a gold-containing nanoparticle, and a known gold nanoparticle can be used, or can be produced by a known gold nanoparticle production method.
- the gold core particles may contain other elements other than gold, such as platinum.
- other substances may be included as long as the effects of the present invention are not affected. For example, a residue or part of an additive (reducing agent, fine particle agent, etc.) used in the manufacturing process is included. You may go out.
- the size of the gold core particle is 1.0 to 5.0 nm. It is substantially difficult to synthesize Au core particles having a particle size of less than 1.0 mm.
- the particle size exceeds 5.0 nm, the number of Pt atoms for forming a Pt shell increases, and the amount of gold used for obtaining a unit area also increases, which raises the problem of an increase in catalyst cost.
- the particle size is 5.0 nm or less, a large surface area can be obtained per unit weight of the catalyst, and the amount of gold and platinum required per unit area of the catalyst can be reduced.
- gold is even more expensive than platinum, but the combined material cost of the core material (gold) and shell material (platinum) is the current when the particle size of the gold core is around 2.5 mm.
- the material cost is higher than the current platinum catalyst. For this reason, there is an advantage in using a smaller-sized gold core particle.
- the particle size of the gold core particle is the average particle size obtained from a transmission electron microscope (TEM) image or the Scherrer equation applied to the X-ray diffraction peak of the (220) plane of Au. This means the value calculated by
- the shell of the platinum core-shell catalyst of the present invention contains platinum and iridium and / or ruthenium. Specifically, a shell containing platinum and iridium may be formed on the surface of the gold core particle, or a shell containing platinum and ruthenium may be formed on the surface of the gold core particle. In addition to platinum, iridium and / or ruthenium, other atoms and / or molecules may be contained within a range satisfying a desired catalytic activity. For example, noble metals such as gold and silver, platinum compounds added in the manufacturing process, and residues of organic compounds may be included.
- the ratio of iridium and / or ruthenium to platinum is preferably 0.1 to 50 at.%, More preferably 5 to 30 at.%.
- iridium or ruthenium may be contained at a minimum level capable of suppressing the solid solution of platinum in the gold core, and is appropriate so as not to hinder the coverage of platinum atoms in the shell and the catalytic activity of platinum. Selected.
- the average thickness of the platinum shell is preferably a monoatomic layer to a triatomic layer (about 0.3 nm to 0.9 nm), and more preferably a monoatomic layer to a diatomic layer (about 0.3 nm to 0.6 nm).
- platinum atoms that exhibit activity as an oxygen reduction catalyst are only platinum atoms located in the outermost layer (outermost surface) of the shell, there is no particular advantage in increasing the thickness of the shell.
- Iridium and / or ruthenium may be mixed with platinum to constitute the surface layer of the catalyst, or may be interposed between the gold core and the platinum shell.
- platinum core-shell catalyst of the present invention contains iridium and / or ruthenium in the platinum shell, platinum is prevented from being solid-solution-embedded in the gold core particles.
- Table 1 shows heats of mixing ⁇ H (kJ / mol) when platinum (Pt), gold (Au), iridium (Ir), and ruthenium (Ru) are mixed at a ratio of 50:50.
- the smaller the value the more stable the mixture of the A component and the B component.
- the heat of mixing iridium and ruthenium with respect to platinum is +1 kJ / mol and -1 kJ / mol, respectively, which is smaller than the heat of mixing gold and platinum (+7 kJ / mol).
- the heat of mixing of iridium and ruthenium with gold is + 19 + kJ / mol and +22 kJ / mol, respectively, which is larger than the heat of mixing of gold and platinum (+7 kJ / mol). That is, iridium and ruthenium are easier to mix with platinum than gold, and iridium and ruthenium are harder to mix with gold than platinum.
- the platinum core-shell catalyst of the present invention is preferably dispersed and supported on the surface of a carrier made of a carbonaceous material.
- the carbonaceous material include carbon black, ketjen black, acetylene black, and carbon nanotube.
- metal oxide carriers such as tin oxide (SnOx) and titanium oxide (TiOx) having high oxidation resistance may be used.
- SiOx tin oxide
- TiOx titanium oxide
- the support preferably has a specific surface area of about 10 to 1000 m 2 / g. It is considered that the platinum core-shell catalyst is supported on the surface of the support mainly by electrostatic interaction. A chemical bond can also be formed between the platinum core-shell catalyst and the support in order to more firmly support it and reduce the dropping of the catalyst from the support surface.
- the coverage of the gold core particle surface with platinum and ruthenium and / or iridium can be 50-100%, preferably 60-100%, more preferably 70-100%. Since the amount of platinum solid solution in the gold core is determined by the volume of the gold core particle, if the gold core particle has the same particle size, the higher the platinum coverage, the lower the proportion of platinum lost due to solid solution in gold (that is, When the platinum coverage is low, the proportion of platinum lost by solid solution in gold is high (that is, the durability as a catalyst is low).
- the gold core particle having the same particle size has a platinum shell amount of about 1/2 to 1/4 of that of a conventional platinum core-shell catalyst (a catalyst having a shell made only of platinum).
- a conventional platinum core-shell catalyst a catalyst having a shell made only of platinum.
- durability equivalent to that of the conventional platinum core-shell catalyst see Examples. That is, although the catalyst of the present invention has a low surface coverage of platinum (the number of platinum atoms on the surface), it does not easily cause solid solution in gold. This is presumably because the presence of iridium and / or ruthenium suppresses solid solution of platinum. This is an effect peculiar to the present invention different from the conventional platinum core-shell catalyst.
- the method for producing the platinum core-shell catalyst of the present invention is not particularly limited.
- the copper monoatomic layer obtained in step (1) can be preferably produced by a method including a step of replacing platinum with iridium and / or ruthenium.
- Gold core particles supported on a carbonaceous carrier can be synthesized by a known synthesis method. For example, tetrachloroauric acid (HAuCl 4 ) or the like is added to alkanethiol as a protective agent in an aqueous solution, an organic solution, or a mixed solution thereof, and then reduced to form gold nanoparticles. There is a method of obtaining gold core particles supported on a carbonaceous support by adsorbing to a carbonaceous support via alkanethiol chemisorbed on the carbon, and subsequently removing a part of the thiol group and hydrocarbon chain by heat treatment. .
- a known method can be used to form a monoatomic layer made of copper on the surface of the gold core particle.
- the UPD method disclosed in Non-Patent Document 1 can be followed, or the method can be changed as appropriate.
- an improved Cu-UPD method that does not require precise potential control using an external power source and a counter electrode or a reference electrode.
- gold core particles supported on a carbonaceous support are put into an acidic aqueous solution containing Cu ions in which a solid made of copper is immersed, and an inert gas atmosphere such as argon or nitrogen is used.
- an inert gas atmosphere such as argon or nitrogen is used.
- a monoatomic film made of copper is formed on the surface of the gold core by stirring in the medium.
- the copper monoatomic film is not necessarily a uniform film composed of a monoatomic film on the entire surface, but includes a film in which two or more atoms overlap each other.
- the solid made of copper used in the improved Cu-UPD method is an object that at least has a surface made of copper and is ionized to produce copper ions (Cu 2+ ) when contacted with gold nanoparticles.
- a copper mesh, a copper wire, a copper grain, a copper plate, a copper lump, etc. are mentioned.
- CuSO 4 , CuCl 2 , Cu (CH 3 COO) 2 , Cu (NO 3 ) 2 and the like can be cited as substances that give Cu ions used in acidic aqueous solutions containing Cu ions. By doing so, Cu ions are dissociated.
- the Cu ion concentration is not particularly limited, but can be, for example, 0.1 mM to 100 mM, and is preferably about 1 mM to 50 mM from the viewpoint of the reaction rate and the stability of the reaction solution.
- the acid that gives the acidic solution is not particularly limited as long as it can dissolve copper, and examples thereof include nitric acid, sulfuric acid, hydrochloric acid, perchloric acid, and the like.
- the concentration can be set to 10 mM to 1 M. From the viewpoint of controlling the speed and the potential of the copper solid, it can be set to about 20 mm to 0.5 mm.
- Gold core particles supported on a carbonaceous support are introduced into an acidic solution containing the above Cu ions immersed in the above copper solid, and stirred, for example, at 0 to 45 ° C. for 1 to 50 hours under an inert gas flow. By doing so, a copper monoatomic film is formed on the gold core surface.
- the copper on the product surface obtained is replaced with platinum and ruthenium and / or iridium.
- This step can be performed by a displacement plating method used in a known UPD method or the like.
- platinum ions include platinum salts (K 2 PtCl 4 , K 2 PtBr 4 ), and examples of substances that give ruthenium ions and / or iridium ions include ruthenium chloride, ruthenium nitrate, and iridium chloride. And iridium nitrate.
- the step of replacing the monoatomic film made of copper with platinum and ruthenium and / or iridium is performed by removing the copper solid from the above-described acidic solution containing Cu ions soaked in the copper solid,
- a compound containing ruthenium and / or iridium can be added to the aqueous solution simultaneously or sequentially and stirred. That is, for example, a platinum compound and an iridium and / or ruthenium ion compound may be simultaneously introduced to form a shell in which platinum and iridium and / or ruthenium are mixed in the same layer.
- the addition of the platinum compound and the iridium and / or ruthenium ion compound is preferably carried out with as little time as possible after removing the copper solid.
- the reaction time and temperature can be appropriately selected.
- the reaction time is 0 to 45 ° C. for 1 minute to 50 hours (preferably 1 minute to 1 hour). It is.
- the gold core particles having a shell containing platinum and iridium and / or ruthenium obtained by the above method are washed, dried and the like as required by a known method, and the platinum core-shell catalyst for fuel cells of the present invention Is obtained.
- the production method of the present invention can include separation, purification, washing steps and the like as necessary.
- Example 1 Preparation of iridium-containing platinum shell / gold core catalyst
- i Preparation of Au / C core 7.619 ⁇ 10 ⁇ 4 mol of HAuCl 4 was dissolved in 80 ml of pure water.
- a separatory funnel Using a separatory funnel, a toluene solution of 625 mg of tetraoctylammonium bromide as a phase transfer agent and an aqueous HAuCl 4 solution were mixed and allowed to stand to move [AuCl 4 ] ⁇ to the toluene phase. The aqueous phase was removed and the toluene phase was transferred to an Erlenmeyer flask and placed in a thermostatic bath at 30 ° C.
- the solution was transferred to a separatory funnel to remove the aqueous phase, the Au colloid solution was transferred to a round bottom flask, and toluene was distilled off using an evaporator. 30 ml of n-hexane was added to the round bottom flask after the toluene was distilled off, and the Au colloid was redispersed by irradiation with ultrasonic waves for 30 minutes. Thereafter, 80 ml of ethanol was added to increase the polarity of the solvent to precipitate Au colloid. Using a centrifuge, Au colloid was precipitated and separated by treatment at 12000 rpm for 15 minutes.
- the supernatant was removed and the Au colloid was redispersed in n-hexane. Then, n-hexane was distilled off using an evaporator, 10 ml of n-hexane was added, and ultrasonic waves were irradiated for 30 minutes. Thereafter, 80 ml of ethanol was added to precipitate Au colloid. The colloidal Au was washed by repeating this operation four times. The washed Au colloid was dispersed in 30 ml of n-hexane.
- 350 mg of carbon support (Ketjen black EC 300 J, specific surface area 800 m 2 / g) is ultrasonically dispersed in 350 ml of n-hexane for 1 hour, then added with Au colloid n-hexane dispersion, and then for another 30 minutes Ultrasonic irradiation was performed. Thereafter, the solution was stirred for a whole day and night using a magnetic stirrer at room temperature to support Au colloid on the carbon support. The carbon-supported Au core (Au / C core) was filtered off with suction by stirring the n-hexane solution stirred overnight, and dried in an oven at 60 ° C. for 6 hours in the atmosphere to obtain an Au / C core.
- carbon support Karljen black EC 300 J, specific surface area 800 m 2 / g
- FIG. 2 shows the structure of the rotating ring disk electrode. A catalyst was applied and supported on the disk portion, and the working electrode was rotated to generate a constant convection in the electrolyte, thereby controlling mass transfer.
- Example 2 Preparation of ruthenium-containing platinum shell / gold core catalyst
- i Preparation of PtRu / Au / C catalyst Au / C core after the same heat treatment as used in Example 1 (support rate 28.4 wt.%, 200 mg (particle size 2.8 nm) was dispersed in a 300 ml aqueous solution containing 50 mM H 2 SO 4 and 10 mM CuSO 4 .
- Ar was flowed at a flow rate of 100 ml / min., And the Cu mesh was allowed to coexist in the aqueous solution, and then stirred at 30 ° C. for 10 hours to form a Cu shell on the surface of the Au core particles.
- Table 2 summarizes the results of composition analysis of the catalysts of Examples 1 and 2 and Comparative Example 1 using a fluorescent X-ray analyzer (SEA1200VX, manufactured by SII).
- the catalyst of Example 1 contains iridium (Ir), and the catalyst of Example 2 contains ruthenium (Ru). Was confirmed.
- FIG. 3 shows changes in the electrochemical surface area of Example 1 and Comparative Example 1 accompanying the durability test.
- the horizontal axis indicates the number of potential cycles, and the vertical axis indicates the surface area retention rate (%) with the electrochemical surface area before the cycle test as 100%.
- Example 1 showed an electrochemical surface area retention substantially equivalent to that of Comparative Example 1.
- the catalyst of Example 1 has a smaller number of platinum shell atoms than Comparative Example 1 (about 1/4).
- the platinum shell coverage number of atoms
- the proportion of platinum lost from the surface as a solid solution embedded in the gold core is relatively high, and the durability is reduced.
- the catalyst of Example 1 of the present invention has the same durability as that of Comparative Example 1 even if the number of platinum shell atoms is about 1/4 that of the Pt / Au / C catalyst of Comparative Example 1. That is, the result of FIG. 3 shows that the durability of platinum atoms existing on the catalyst surface of Example 1 is dramatically improved in the durability test of 10,000 cycles. This is probably because the solid solution of platinum was suppressed by the presence of iridium, thereby improving the durability of the catalyst.
- FIG. 4 shows the durability test of Example 2, Comparative Example 1 and the reference platinum fine particle catalyst (platinum fine particle catalyst supported on a carbonaceous carrier, not a core shell, particle size 2.8 nm, loading rate 48 wt.%).
- the change of the electrochemical surface area accompanying with is shown.
- the horizontal axis indicates the number of potential cycles, and the vertical axis indicates the surface area retention rate (%) with the electrochemical surface area before the cycle test as 100%.
- Example 2 showed a higher electrochemical surface area retention than Comparative Example 1 and Reference Example.
- the catalyst of Example 2 of the present invention has high durability exceeding that of the conventional platinum catalyst even though the number of platinum shell atoms is about half that of the Pt / Au / C catalyst of Comparative Example 1. . That is, the results of FIG. 4 show that the durability of platinum atoms existing on the catalyst surface of Example 2 is dramatically improved in the 10,000 cycles durability test. This is probably because the presence of ruthenium suppresses the solid dissolution of platinum and improves the durability of the catalyst.
Abstract
The problem of the present invention is to provide a platinum core shell catalyst that has superior durability and catalytic efficiency, and has gold core particles with an extremely small diameter (5 nm or less). The present invention is a platinum core shell catalyst for fuel cells, characterized in that the particle size thereof is 1.6 -6.8 nm, and by having core particles that include gold, and a shell formed on the surface of the core and comprising platinum and iridium and/or ruthenium.
Description
本発明は、燃料電池において酸素還元反応の触媒として用いるのに適した、白金コアシェル触媒とその製造方法、及び当該触媒を用いた燃料電池に関する。
The present invention relates to a platinum core-shell catalyst suitable for use as a catalyst for oxygen reduction reaction in a fuel cell, a method for producing the same, and a fuel cell using the catalyst.
固体高分子形燃料電池（ＰＥＦＣ）は、アノード側で水素の酸化反応を、カソード側で酸素の還元反応を起こすことにより、水のみを生成するクリーンエネルギーデバイスである。カソード側の触媒として白金（Pt）を使用するものが知られている。貴金属である白金を用いる触媒は、触媒活性や電気伝導性が高く、また、周辺環境の状態や周辺環境に存在する物質による腐食や被毒を受けにくいという利点を有する。
A polymer electrolyte fuel cell (PEFC) is a clean energy device that generates only water by causing an oxidation reaction of hydrogen on the anode side and a reduction reaction of oxygen on the cathode side. A catalyst using platinum (Pt) as a catalyst on the cathode side is known. A catalyst using platinum, which is a noble metal, has high catalytic activity and high electrical conductivity, and has an advantage that it is less susceptible to corrosion and poisoning due to the state of the surrounding environment and substances present in the surrounding environment.
一方で、白金は資源量が少なく価格が高いという問題があるため、その利用効率や耐久性を向上させて使用量を低減するために種々の検討が進められている。検討の一つとして、異種金属上に白金を被覆してなる白金コアシェル触媒が注目されている。白金コアシェル触媒は、触媒活性を発揮する白金原子は触媒粒子の最外層に露出した白金原子のみであることに着目して考案されたもので、白金原子層（シェル）で被覆された異種金属微粒子（コア）が、カーボン等の担体に高分散担持された構成を有する。
On the other hand, since platinum has a problem that the amount of resources is small and the price is high, various studies are being conducted to improve the utilization efficiency and durability and reduce the amount of use. As one of the studies, a platinum core-shell catalyst obtained by coating platinum on a different metal has attracted attention. The platinum core-shell catalyst was devised by focusing on the fact that the platinum atoms exhibiting catalytic activity are only the platinum atoms exposed in the outermost layer of the catalyst particles. The dissimilar metal fine particles covered with the platinum atomic layer (shell) The (core) is configured to be highly dispersed and supported on a carrier such as carbon.
特許文献１（特開２０１２－４１５８１号公報）には、白金の使用量を低減し、触媒活性を向上させるコアシェル微粒子として、面心立方結晶構造を有するルテニウムからなるコア粒子と、当該コア粒子の表面に形成された、面心立方結晶構造を有する白金からなるシェルとを有するコアシェル微粒子が開示されている。この発明は、触媒微粒子表面の白金原子の面密度を向上させることによって白金の触媒効率を上げ、もって使用量を削減することが主旨であり、シェルの白金原子の面密度が最大となる面心立方結晶構造を用いることを見出したものである。
Patent Document 1 (Japanese Patent Application Laid-Open No. 2012-41581) discloses core particles made of ruthenium having a face-centered cubic crystal structure as core-shell fine particles that reduce the amount of platinum used and improve catalytic activity, A core-shell fine particle having a shell made of platinum having a face-centered cubic crystal structure formed on the surface is disclosed. The main object of the present invention is to increase the catalyst efficiency of platinum by improving the surface density of platinum atoms on the surface of the catalyst fine particles, thereby reducing the amount used, and the center of the surface where the surface density of platinum atoms in the shell is maximized. The inventors have found that a cubic crystal structure is used.
また、白金シェルに対するコア金属として、金（Au）が知られている。金は貴金属であり、白金よりもイオン化傾向が小さく酸化に対して安定であり、また白金よりもはるかに資源量が多いことから、コア金属の一つとして期待されている。
Also, gold (Au) is known as a core metal for the platinum shell. Gold is a precious metal, has a lower ionization tendency than platinum, is stable against oxidation, and has a much larger amount of resources than platinum, and thus is expected as one of core metals.
特許文献２（特開２０１１－２１２６６６号公報）には、還元剤を用いることなく、金コア粒子の表面上に白金の表面触媒層を作製する方法が開示されている。この発明は従来のＵＰＤ法（Under-Potential Deposition法）に代替して、二価又は四価白金イオンを含む溶液に金コア粒子を浸漬することによって、金コア上に直接に白金層を析出させる方法に関する。この発明の方法によれば、簡潔な方法で金コア/白金シェルを有する触媒を得ることができることが開示されている。
しかしながらこの文献では、触媒の耐久性や触媒効率は検討されていない。 Patent Document 2 (Japanese Patent Laid-Open No. 2011-212666) discloses a method for producing a platinum surface catalyst layer on the surface of a gold core particle without using a reducing agent. In the present invention, instead of the conventional UPD method (Under-Potential Deposition method), a gold layer is immersed in a solution containing divalent or tetravalent platinum ions to deposit a platinum layer directly on the gold core. Regarding the method. According to the method of the present invention, it is disclosed that a catalyst having a gold core / platinum shell can be obtained by a simple method.
However, in this document, the durability and catalytic efficiency of the catalyst are not examined.
しかしながらこの文献では、触媒の耐久性や触媒効率は検討されていない。 Patent Document 2 (Japanese Patent Laid-Open No. 2011-212666) discloses a method for producing a platinum surface catalyst layer on the surface of a gold core particle without using a reducing agent. In the present invention, instead of the conventional UPD method (Under-Potential Deposition method), a gold layer is immersed in a solution containing divalent or tetravalent platinum ions to deposit a platinum layer directly on the gold core. Regarding the method. According to the method of the present invention, it is disclosed that a catalyst having a gold core / platinum shell can be obtained by a simple method.
However, in this document, the durability and catalytic efficiency of the catalyst are not examined.
特許文献３（特開２０１０－９２７２５号公報）には、Auまたはその合金で構成したコア粒子の表面に、Ptまたはその合金のシェルを形成した触媒が開示されている。この発明では、AuやPtの格子定数に着目し、格子定数の大きいAuをコア、格子定数の小さいPtをシェルとする。このように構成することで、下地のAuによってPtが引っ張り応力を受け、また、この引っ張り応力によってPtの電子状態が変化し、イオン化ポテンシャルが増大したことによって、Ptの優れた触媒活性と耐久性が得られたものと考えられている。
当該文献ではまた、コアやシェルはAuやPtの合金であってもよいことが開示されている。例えば、シェルのPtには、Fe，Co等の卑金属や、Ag，Ru，Pd，Ir等の貴金属が、40原子％以下追加されうることが開示されている。しかしながら、コアやシェルにこれらの金属を追加することの効果や機能については何ら考察されていない。
またこの文献には、Auコア粒子の大きさは1～10 nm、Ptシェルの厚さは2 nm以下との記載がある。しかしながら、実施例に開示されているのは粒径6 nmのAuコア粒子を有する粒径10 nmのコアシェル触媒粒子１種類のみである。すなわち、より小粒径の場合については実質的に検討されていない。また、この文献で言及されている格子定数は単結晶における格子定数であって、実際のナノ粒子における原子間距離については考慮されていない。 Patent Document 3 (Japanese Patent Laid-Open No. 2010-92725) discloses a catalyst in which a shell of Pt or an alloy thereof is formed on the surface of core particles made of Au or an alloy thereof. In the present invention, focusing on the lattice constants of Au and Pt, Au having a large lattice constant is used as a core, and Pt having a small lattice constant is used as a shell. With this configuration, Pt is subjected to tensile stress by the underlying Au, and the electronic state of Pt is changed by this tensile stress, resulting in an increase in ionization potential, resulting in excellent catalytic activity and durability of Pt. Is believed to have been obtained.
The document also discloses that the core or shell may be an alloy of Au or Pt. For example, it is disclosed that a base metal such as Fe and Co and a noble metal such as Ag, Ru, Pd and Ir can be added to Pt of the shell by 40 atomic% or less. However, no consideration has been given to the effects and functions of adding these metals to the core and shell.
This document also states that the Au core particle size is 1 to 10 nm and the Pt shell thickness is 2 nm or less. However, only one type of core-shell catalyst particle with a particle size of 10 nm having an Au core particle with a particle size of 6 nm is disclosed in the examples. That is, the case of a smaller particle size is not substantially studied. Further, the lattice constant referred to in this document is a lattice constant in a single crystal, and an interatomic distance in an actual nanoparticle is not considered.
当該文献ではまた、コアやシェルはAuやPtの合金であってもよいことが開示されている。例えば、シェルのPtには、Fe，Co等の卑金属や、Ag，Ru，Pd，Ir等の貴金属が、40原子％以下追加されうることが開示されている。しかしながら、コアやシェルにこれらの金属を追加することの効果や機能については何ら考察されていない。
またこの文献には、Auコア粒子の大きさは1～10 nm、Ptシェルの厚さは2 nm以下との記載がある。しかしながら、実施例に開示されているのは粒径6 nmのAuコア粒子を有する粒径10 nmのコアシェル触媒粒子１種類のみである。すなわち、より小粒径の場合については実質的に検討されていない。また、この文献で言及されている格子定数は単結晶における格子定数であって、実際のナノ粒子における原子間距離については考慮されていない。 Patent Document 3 (Japanese Patent Laid-Open No. 2010-92725) discloses a catalyst in which a shell of Pt or an alloy thereof is formed on the surface of core particles made of Au or an alloy thereof. In the present invention, focusing on the lattice constants of Au and Pt, Au having a large lattice constant is used as a core, and Pt having a small lattice constant is used as a shell. With this configuration, Pt is subjected to tensile stress by the underlying Au, and the electronic state of Pt is changed by this tensile stress, resulting in an increase in ionization potential, resulting in excellent catalytic activity and durability of Pt. Is believed to have been obtained.
The document also discloses that the core or shell may be an alloy of Au or Pt. For example, it is disclosed that a base metal such as Fe and Co and a noble metal such as Ag, Ru, Pd and Ir can be added to Pt of the shell by 40 atomic% or less. However, no consideration has been given to the effects and functions of adding these metals to the core and shell.
This document also states that the Au core particle size is 1 to 10 nm and the Pt shell thickness is 2 nm or less. However, only one type of core-shell catalyst particle with a particle size of 10 nm having an Au core particle with a particle size of 6 nm is disclosed in the examples. That is, the case of a smaller particle size is not substantially studied. Further, the lattice constant referred to in this document is a lattice constant in a single crystal, and an interatomic distance in an actual nanoparticle is not considered.
一方で、金属ナノ粒子においては、直径数nmを境界として物理化学的性質が大きく変化することが知られている。発明者らによって、直径8 nmのAuナノ粒子とバルクであるAuホイルとを比較すると、Auナノ粒子はAuホイルよりもAu-Au原子間距離が短く、また、その原子間距離はAuナノ粒子のサイズ減少に伴って短くなることが見いだされている（[図１]）。また、非特許文献１では、Au単結晶上に構成されたPtモノレイヤー触媒と、粒径3 nmのAuナノ粒子上に構成されたPtモノレイヤー触媒とを比較すると、後者の酸素還元活性が2.5倍程度優れることが報告されている。
これは、極めて小粒径のAuナノ粒子ではAu-Au原子間距離が減少し、Au単結晶上のPtモノレイヤーと比較して、Auナノ粒子表面に設けたPtモノレイヤーの受ける応力が変化し、これによってPtモノレイヤーに酸素還元反応に適した電子状態（酸素種との結合力）が獲得され、高い酸素還元活性を示したものと考えられている。 On the other hand, in metal nanoparticles, it is known that physicochemical properties change greatly with a diameter of several nm as a boundary. According to the inventors, when comparing Au nanoparticles with a diameter of 8 nm and Au foil, which is a bulk, Au nanoparticles have a shorter Au-Au interatomic distance than Au foil, and the interatomic distance is smaller than Au nanoparticles. It has been found that the length decreases with decreasing size ([Fig. 1]). In Non-Patent Document 1, when the Pt monolayer catalyst constructed on Au single crystal is compared with the Pt monolayer catalyst constructed on Au nanoparticles having a particle size of 3 nm, the latter oxygen reduction activity is observed. It has been reported to be about 2.5 times better.
This is because the Au-Au interatomic distance decreases for Au nanoparticles of extremely small particle size, and the stress applied to the Pt monolayer on the Au nanoparticle surface changes compared to the Pt monolayer on the Au single crystal. As a result, it is considered that the Pt monolayer has acquired an electronic state (binding force with oxygen species) suitable for the oxygen reduction reaction and exhibits high oxygen reduction activity.
これは、極めて小粒径のAuナノ粒子ではAu-Au原子間距離が減少し、Au単結晶上のPtモノレイヤーと比較して、Auナノ粒子表面に設けたPtモノレイヤーの受ける応力が変化し、これによってPtモノレイヤーに酸素還元反応に適した電子状態（酸素種との結合力）が獲得され、高い酸素還元活性を示したものと考えられている。 On the other hand, in metal nanoparticles, it is known that physicochemical properties change greatly with a diameter of several nm as a boundary. According to the inventors, when comparing Au nanoparticles with a diameter of 8 nm and Au foil, which is a bulk, Au nanoparticles have a shorter Au-Au interatomic distance than Au foil, and the interatomic distance is smaller than Au nanoparticles. It has been found that the length decreases with decreasing size ([Fig. 1]). In Non-Patent Document 1, when the Pt monolayer catalyst constructed on Au single crystal is compared with the Pt monolayer catalyst constructed on Au nanoparticles having a particle size of 3 nm, the latter oxygen reduction activity is observed. It has been reported to be about 2.5 times better.
This is because the Au-Au interatomic distance decreases for Au nanoparticles of extremely small particle size, and the stress applied to the Pt monolayer on the Au nanoparticle surface changes compared to the Pt monolayer on the Au single crystal. As a result, it is considered that the Pt monolayer has acquired an electronic state (binding force with oxygen species) suitable for the oxygen reduction reaction and exhibits high oxygen reduction activity.
上記のとおり、極めて小粒径のナノ粒子における原子の状態は、単結晶の状態とは異なっているために、極めて小粒径のナノ粒子に対して単結晶の考え方をそのまま適用することはできないと考えられる。すなわちAuコア/Ptシェル触媒において未だ最適な形態は見出されておらず、耐久性と触媒効率の向上についてさらなる検討が要請されている。
As described above, the state of atoms in nanoparticles having a very small particle size is different from the state of single crystals, so the concept of single crystal cannot be applied to nanoparticles having a very small particle size. it is conceivable that. In other words, an optimum form has not yet been found in the Au core / Pt shell catalyst, and further studies are required for improving durability and catalyst efficiency.
したがって本発明は、耐久性と触媒効率に優れた金コア粒子を有する白金コアシェル触媒を提供することを課題とする。
Therefore, an object of the present invention is to provide a platinum core-shell catalyst having gold core particles having excellent durability and catalytic efficiency.
発明者らは、Auコア/Ptシェル触媒の耐久性を損なう要因の一つとして、白金が金に固溶する性質を有するために、電位サイクルを繰り返すに従って触媒粒子表面の白金原子が金コアに固溶埋没し、触媒粒子表面の白金原子が減少することで触媒活性が低下すると考え、検討を進めてきた。
As one of the factors that impair the durability of the Au core / Pt shell catalyst, the inventors have the property that platinum dissolves in gold, so that the platinum atoms on the surface of the catalyst particles become a gold core as the potential cycle is repeated. Considering that the catalytic activity decreases due to the decrease in platinum atoms on the surface of the catalyst particles due to the solid solution, investigations have been conducted.
発明者らは前記課題を解決するための検討において、シェル成分とコア成分との熱力学的性質に着目し、熱力学的観点から、白金原子の金コアへの固溶埋没が生じ難い状態を作り出すことに着想した。そして、白金シェル中に、白金と比較して金と混合しにくく、かつ、金と比較して白金と混合しやすい性質を有する元素である、イリジウム（Ir）やルテニウム（Ru）を添加すると、耐久性と触媒効率に優れた白金コアシェル触媒が得られることを見出し、本発明を完成した。
The inventors focused on the thermodynamic properties of the shell component and the core component in the study to solve the above-mentioned problems, and from a thermodynamic point of view, a state in which solid solution burying of platinum atoms in the gold core is difficult to occur. Inspired to create. And, in the platinum shell, when adding iridium (Ir) or ruthenium (Ru), which is an element having a property that is difficult to mix with gold compared to platinum and easy to mix with platinum compared to gold, The inventors have found that a platinum core-shell catalyst having excellent durability and catalytic efficiency can be obtained, and have completed the present invention.
すなわち本発明は、金を含有するコア粒子と、当該コアの表面に形成された、白金と、イリジウム及び／又はルテニウムとを含有するシェルとを有し、直径が1.6 nm～6.8 nmであることを特徴とする、燃料電池用の白金コアシェル触媒に関する。前記触媒においては、コア粒子の粒径が1.0 nm～5.0 nmであり、シェルの厚みが0.3 nm～0.9 nmであればより好ましい。
That is, the present invention has a core particle containing gold and a shell containing platinum and iridium and / or ruthenium formed on the surface of the core and having a diameter of 1.6 to 6.8 nm. The present invention relates to a platinum core-shell catalyst for a fuel cell. In the catalyst, the core particles preferably have a particle size of 1.0 to 5.0 nm and a shell thickness of 0.3 to 0.9 nm.
本発明の白金コアシェル触媒は、金コア粒子の表面に白金シェルが形成されているので、白金原子の全部ないし大半が触媒粒子の表面に存在し、触媒活性を発揮することができる。すなわち白金原子の触媒としての利用効率が極めて高い。またシェルには、白金に加えて、イリジウム（Ir）及び／又はルテニウム（Ru）が含まれる。この構成によって白金シェル原子の金コアへの固溶埋没が抑制され、耐久性に優れた白金コアシェル触媒が得られる。さらに、触媒の粒径が1.6 nm～6.8 nmと極めて小粒径であることによって、触媒重量当たりの表面積が大きくなり、同時に金の使用量も削減される。さらにまた、金コアに固溶しうる白金の最大量は金コアの体積によって決まるため、小粒径の金コアを用いることで、固溶による白金の損失を少量に留めることができる。
In the platinum core-shell catalyst of the present invention, since the platinum shell is formed on the surface of the gold core particle, all or most of the platinum atoms are present on the surface of the catalyst particle and can exhibit catalytic activity. That is, the utilization efficiency of platinum atoms as a catalyst is extremely high. The shell contains iridium (Ir) and / or ruthenium (Ru) in addition to platinum. With this configuration, the platinum core-shell catalyst having excellent durability is obtained by suppressing the solid-solution burying of platinum shell atoms in the gold core. Furthermore, since the particle size of the catalyst is as small as 1.6 to 6.8 nm, the surface area per catalyst weight is increased, and the amount of gold used is also reduced. Furthermore, since the maximum amount of platinum that can be dissolved in the gold core is determined by the volume of the gold core, the loss of platinum due to the solid solution can be kept small by using a gold core having a small particle diameter.
また、コア粒子の粒径を1.0 nm～5.0 nm、シェルの厚みを0.3 nm～0.9 nmの範囲とすると、シェルは実質的にモノレイヤー（単原子層）から三原子層となり、かつ、金コア粒子は十分に小さい。このことによって、より好適な白金コアシェル触媒が得られる。このように、本発明の白金コアシェル触媒は、高い白金利用効率に基づく高い質量活性と、白金シェルが金コア内に固溶することを抑止した構造に基づく高い耐久性を同時に提供することができる。
In addition, if the core particle size is in the range of 1.0 to 5.0 nm and the shell thickness is in the range of 0.3 to 0.9 nm, the shell is substantially changed from a monolayer (monoatomic layer) to a triatomic layer, and a gold core. The particles are small enough. As a result, a more suitable platinum core-shell catalyst can be obtained. Thus, the platinum core-shell catalyst of the present invention can simultaneously provide high mass activity based on high platinum utilization efficiency and high durability based on a structure in which the platinum shell is prevented from dissolving in the gold core. .
燃料電池触媒の白金削減技術において、熱力学的観点から触媒の組成を設定すること、具体的には、シェル成分に特定種の金属を添加することによって、シェルに存在する白金のコアへの固溶埋没を抑止することは、従来に無い新しい考えである。そして、この考えに基づいて設定された本発明の触媒は、特定範囲の粒径である金コアと、イリジウム及び／又はルテニウムを含有する白金シェルとを有する新規な触媒であり、従来の触媒と比べてシェルの被覆率が低くても触媒活性の保持率に極めて優れるという格別の効果を有する。
In the platinum reduction technology for fuel cell catalysts, the composition of the catalyst is set from a thermodynamic viewpoint, specifically, by adding a specific type of metal to the shell component, the solidification of platinum in the shell to the core is performed. Deterring sunk invasion is an unprecedented new idea. The catalyst of the present invention set based on this idea is a novel catalyst having a gold core having a particle size in a specific range and a platinum shell containing iridium and / or ruthenium, In comparison, even if the covering ratio of the shell is low, the catalyst activity retention rate is extremely excellent.
前記シェルにおいて、白金に対するイリジウム及び／又はルテニウムの割合は、0.1～50 at.%であることが好ましく、5～30 at.％であることがより好ましい。この割合とすれば、イリジウム及び／又はルテニウムが白金の金コアへの固溶を効果的に抑制し、かつ、シェルにおける白金原子の被覆率や触媒活性を阻害することがないため、より質量活性が高く耐久性に優れた触媒を得ることができる。
In the shell, the ratio of iridium and / or ruthenium to platinum is preferably 0.1 to 50% at.%, And more preferably 5 to 30% at.%. With this ratio, iridium and / or ruthenium effectively suppresses the solid solution of platinum in the gold core and does not inhibit the platinum atom coverage and catalytic activity in the shell. And a catalyst having high durability can be obtained.
前記シェルにおいて、白金とイリジウム及び／又はルテニウムは、同一層内で混在していてもよく、イリジウム及び／又はルテニウムが、白金シェルと金コア粒子との間に介在していてもよい。
In the shell, platinum and iridium and / or ruthenium may be mixed in the same layer, and iridium and / or ruthenium may be interposed between the platinum shell and the gold core particle.
白金とイリジウム及び／又はルテニウムが同一層内で混在している触媒には、上述の効果に加えて、シェルをワンステップで形成することが可能であるために簡潔な製造工程によって製造が可能であるという利点がある。
また、イリジウム及び／又はルテニウムが、白金シェルと金コア粒子表面との間に介在している触媒には、上述の効果に加えて、イリジウム及び／又はルテニウムが白金シェルと金コア粒子の間のバリアとしても機能するため、白金の固溶埋没の抑制効果がより高くなると同時に、コアの表面を白金のみで被覆することが可能になるため、より高い触媒効率を得ることができる。 In addition to the above-mentioned effects, the catalyst in which platinum and iridium and / or ruthenium are mixed in the same layer can be manufactured by a simple manufacturing process because the shell can be formed in one step. There is an advantage of being.
In addition to the above-described effects, the catalyst in which iridium and / or ruthenium is interposed between the platinum shell and the gold core particle surface has iridium and / or ruthenium between the platinum shell and the gold core particle. Since it also functions as a barrier, the effect of suppressing the solid solution burying of platinum becomes higher, and at the same time, the surface of the core can be covered only with platinum, so that higher catalytic efficiency can be obtained.
また、イリジウム及び／又はルテニウムが、白金シェルと金コア粒子表面との間に介在している触媒には、上述の効果に加えて、イリジウム及び／又はルテニウムが白金シェルと金コア粒子の間のバリアとしても機能するため、白金の固溶埋没の抑制効果がより高くなると同時に、コアの表面を白金のみで被覆することが可能になるため、より高い触媒効率を得ることができる。 In addition to the above-mentioned effects, the catalyst in which platinum and iridium and / or ruthenium are mixed in the same layer can be manufactured by a simple manufacturing process because the shell can be formed in one step. There is an advantage of being.
In addition to the above-described effects, the catalyst in which iridium and / or ruthenium is interposed between the platinum shell and the gold core particle surface has iridium and / or ruthenium between the platinum shell and the gold core particle. Since it also functions as a barrier, the effect of suppressing the solid solution burying of platinum becomes higher, and at the same time, the surface of the core can be covered only with platinum, so that higher catalytic efficiency can be obtained.
また、本発明の白金コアシェル触媒は、炭素質材料からなる担体に担持されていることが好ましい。一方、炭素質材料担体の酸化劣化の観点から、耐酸化性の高い酸化錫（SnOx）や酸化チタン（TiOx）などの金属酸化物担体、あるいはこれらの金属酸化物と炭素質材料を混合した担体を使用してもよい。また、本発明の白金コアシェル触媒は、燃料電池における酸化還元反応の触媒として好適に利用することができる。
The platinum core-shell catalyst of the present invention is preferably supported on a carrier made of a carbonaceous material. On the other hand, from the viewpoint of oxidative deterioration of the carbonaceous material carrier, a metal oxide carrier such as tin oxide (SnOx) or titanium oxide (TiOx) having high oxidation resistance, or a carrier obtained by mixing these metal oxides with a carbonaceous material. May be used. Moreover, the platinum core-shell catalyst of the present invention can be suitably used as a catalyst for oxidation-reduction reactions in fuel cells.
また本発明は、（１）炭素質担体に担持された金コア粒子の表面に銅からなる単原子層を形成させるステップと、（２）前記ステップ（１）で得られた銅からなる単原子層を、白金と、イリジウム及び／又はルテニウムとに置換するステップと、を含むことを特徴とする、前記触媒の製造方法に関する。
前記の方法は、ステップ（１）が、炭素質担体に担持された金コア粒子を、銅からなる固体が浸漬されたCuイオンを含有する酸性水溶液に投入し、アルゴンや窒素ガス等の不活性雰囲気中で撹拌することを含むステップであり、ステップ（２）が、前記水溶液から前記銅からなる固体を除いた後、白金イオンとイリジウム及び／又はルテニウムイオンを与える物質を投入し、前記ステップ（１）で得られた生成物表面の銅を、白金とルテニウム及び／又はイリジウムと置換することを含むステップであることが好ましい。 The present invention also includes (1) a step of forming a monoatomic layer made of copper on the surface of a gold core particle supported on a carbonaceous support, and (2) a monoatomic layer made of copper obtained in step (1). And replacing the layer with platinum and iridium and / or ruthenium.
In the above-described method, in step (1), gold core particles supported on a carbonaceous support are put into an acidic aqueous solution containing Cu ions in which a solid made of copper is immersed, and inert gas such as argon or nitrogen gas is used. A step including stirring in an atmosphere, wherein step (2) removes the solid made of copper from the aqueous solution, and then introduces a substance that gives platinum ions and iridium and / or ruthenium ions; Preferably, the step comprises replacing the copper on the product surface obtained in 1) with platinum and ruthenium and / or iridium.
前記の方法は、ステップ（１）が、炭素質担体に担持された金コア粒子を、銅からなる固体が浸漬されたCuイオンを含有する酸性水溶液に投入し、アルゴンや窒素ガス等の不活性雰囲気中で撹拌することを含むステップであり、ステップ（２）が、前記水溶液から前記銅からなる固体を除いた後、白金イオンとイリジウム及び／又はルテニウムイオンを与える物質を投入し、前記ステップ（１）で得られた生成物表面の銅を、白金とルテニウム及び／又はイリジウムと置換することを含むステップであることが好ましい。 The present invention also includes (1) a step of forming a monoatomic layer made of copper on the surface of a gold core particle supported on a carbonaceous support, and (2) a monoatomic layer made of copper obtained in step (1). And replacing the layer with platinum and iridium and / or ruthenium.
In the above-described method, in step (1), gold core particles supported on a carbonaceous support are put into an acidic aqueous solution containing Cu ions in which a solid made of copper is immersed, and inert gas such as argon or nitrogen gas is used. A step including stirring in an atmosphere, wherein step (2) removes the solid made of copper from the aqueous solution, and then introduces a substance that gives platinum ions and iridium and / or ruthenium ions; Preferably, the step comprises replacing the copper on the product surface obtained in 1) with platinum and ruthenium and / or iridium.
本発明の方法によれば、所望の粒径の金コア粒子の表面に、白金、イリジウム、ルテニウムを所望の割合で含有するシェルを形成して、所望の粒径とシェル組成を有する白金コアシェル触媒を得ることができる。特に、ステップ（１）として、銅からなる固体が浸漬されたCuイオンを含有する酸性水溶液を用いる方法は、従来のＵＰＤ法と比較して、外部電源を用いた精密な電位制御と対極や参照極等を必要とせず、工程や設備が簡潔であるために大量生産も可能であり、実用上の使用価値が極めて高い。
According to the method of the present invention, a platinum core-shell catalyst having a desired particle size and shell composition is formed by forming a shell containing platinum, iridium and ruthenium in a desired ratio on the surface of a gold core particle having a desired particle size. Can be obtained. In particular, as a step (1), the method using an acidic aqueous solution containing Cu ions in which a solid made of copper is immersed is more precise than the conventional UPD method, and precise potential control using an external power source and a counter electrode or reference No need for poles, etc., and since the process and equipment are simple, mass production is possible and the practical use value is extremely high.
前記ステップ（２）で置換された白金とルテニウム及び／又はイリジウムにおいて、白金に対するイリジウム及び／又はルテニウムの割合は、0.1～50 at.％であることが好ましく、5～30 at.％であることがより好ましい。
In the platinum and ruthenium and / or iridium substituted in the step (2), the ratio of iridium and / or ruthenium to platinum is preferably 0.1 to 50% at.%, More preferably 5 to 30% at.%. Is more preferable.
また本発明は、前記方法のステップ（２）において、白金イオンを与える化合物とイリジウム及び／又はルテニウムイオンを与える化合物を同時に投入し、白金と、イリジウム及び／又はルテニウムが同一層内で混在するシェルを形成することが好ましい。
この方法によれば、金コア粒子の表面に、白金とイリジウム及び／又はルテニウムを含むシェルをワンステップで簡単に形成することができる。 In the step (2) of the above method, the present invention is a method in which a compound that gives platinum ions and a compound that gives iridium and / or ruthenium ions are simultaneously added, so that platinum and iridium and / or ruthenium are mixed in the same layer. Is preferably formed.
According to this method, a shell containing platinum and iridium and / or ruthenium can be easily formed on the surface of the gold core particle in one step.
この方法によれば、金コア粒子の表面に、白金とイリジウム及び／又はルテニウムを含むシェルをワンステップで簡単に形成することができる。 In the step (2) of the above method, the present invention is a method in which a compound that gives platinum ions and a compound that gives iridium and / or ruthenium ions are simultaneously added, so that platinum and iridium and / or ruthenium are mixed in the same layer. Is preferably formed.
According to this method, a shell containing platinum and iridium and / or ruthenium can be easily formed on the surface of the gold core particle in one step.
上記の各方法で製造された白金コアシェル触媒は、燃料電池における酸化還元反応の触媒として好適に利用することができる。
The platinum core-shell catalyst produced by each of the above methods can be suitably used as a catalyst for an oxidation-reduction reaction in a fuel cell.
本発明の白金コアシェル触媒は、シェルにおいて白金に加えてイリジウム及び／又はルテニウムが含有され、白金原子の近傍にイリジウムやルテニウムが存在する。このことによって、白金原子の金コアへの固溶埋没が抑制される。すなわち触媒の耐久性に優れ、触媒活性を長期間に渡って維持することが可能である。本発明の白金コアシェル触媒は、白金による被覆率が低く金コア粒子への固溶が大きくなりやすい場合であっても、シェルにイリジウムやルテニウムが存在し、また金コアが小粒径であることによって、白金の金コアへの固溶が少なく、良好な耐久性と高い触媒効率を維持することが可能である。
The platinum core-shell catalyst of the present invention contains iridium and / or ruthenium in addition to platinum in the shell, and iridium or ruthenium is present in the vicinity of the platinum atom. This suppresses the solid dissolution of platinum atoms in the gold core. That is, the durability of the catalyst is excellent, and the catalytic activity can be maintained for a long time. The platinum core-shell catalyst of the present invention has iridium or ruthenium in the shell, and the gold core has a small particle size even when the platinum coverage is low and the solid solution in the gold core particles tends to be large. Therefore, it is possible to maintain good durability and high catalyst efficiency with less solid solution of platinum in the gold core.
本発明は、公知の構成である白金シェル・金コア触媒のシェル成分としてイリジウムやルテニウムを添加するという簡便な方策によって、効果的に白金のコアへの固溶を抑制し、触媒の耐久性向上を実現した。従来の白金削減技術では、白金の触媒活性を向上させることや、より効率的な方法で白金層を作製することによって、白金触媒の利用効率を向上させることを主旨としていた。これに対して本発明は、触媒の利用効率に加えて、簡便な方策で耐久性を向上させた。すなわち本発明は、触媒の作製時における白金の使用量削減だけでなく、その耐久性を高めることにより白金使用量を削減できるという効果がある。
なお本発明の白金コアシェル触媒は燃料電池の触媒として用いることができるため、燃料電池のコストの飛躍的低減も可能となる。 The present invention effectively suppresses solid solution of platinum in the core and improves the durability of the catalyst by a simple measure of adding iridium or ruthenium as a shell component of a platinum shell / gold core catalyst having a known configuration. Realized. In the conventional platinum reduction technology, the main purpose is to improve the utilization efficiency of the platinum catalyst by improving the catalytic activity of platinum or by producing a platinum layer by a more efficient method. On the other hand, the present invention has improved durability in a simple manner in addition to the utilization efficiency of the catalyst. In other words, the present invention has an effect that not only the amount of platinum used during the production of the catalyst can be reduced, but also the amount of platinum used can be reduced by enhancing its durability.
Since the platinum core-shell catalyst of the present invention can be used as a catalyst for a fuel cell, the cost of the fuel cell can be drastically reduced.
なお本発明の白金コアシェル触媒は燃料電池の触媒として用いることができるため、燃料電池のコストの飛躍的低減も可能となる。 The present invention effectively suppresses solid solution of platinum in the core and improves the durability of the catalyst by a simple measure of adding iridium or ruthenium as a shell component of a platinum shell / gold core catalyst having a known configuration. Realized. In the conventional platinum reduction technology, the main purpose is to improve the utilization efficiency of the platinum catalyst by improving the catalytic activity of platinum or by producing a platinum layer by a more efficient method. On the other hand, the present invention has improved durability in a simple manner in addition to the utilization efficiency of the catalyst. In other words, the present invention has an effect that not only the amount of platinum used during the production of the catalyst can be reduced, but also the amount of platinum used can be reduced by enhancing its durability.
Since the platinum core-shell catalyst of the present invention can be used as a catalyst for a fuel cell, the cost of the fuel cell can be drastically reduced.
本発明の白金コアシェル触媒のコアは、金を含有するナノ粒子であって、公知の金ナノ粒子を用いることができ、公知の金ナノ粒子の製造方法で製造することもできる。金コア粒子には金以外の他種元素、例えば白金を含んでいてもよい。また、本発明の効果に影響を与えない範囲で、他の物質を含んでいてもよく、例えば製造の過程で使用される添加剤（還元剤、微粒子化剤等）の残渣或いは一部を含んでいてもよい。
The core of the platinum core-shell catalyst of the present invention is a gold-containing nanoparticle, and a known gold nanoparticle can be used, or can be produced by a known gold nanoparticle production method. The gold core particles may contain other elements other than gold, such as platinum. In addition, other substances may be included as long as the effects of the present invention are not affected. For example, a residue or part of an additive (reducing agent, fine particle agent, etc.) used in the manufacturing process is included. You may go out.
金コア粒子の大きさは1.0 nm～5.0 nmである。粒径1.0 nm未満のAuコア粒子の合成は実質的に困難である。粒径が5.0 nmを超えるとPtシェルを形成するためのPt原子数が増加し、また、単位面積を得るための金使用量も増加するため、触媒コストが上昇する問題がある。粒径を5.0 nm以下とすると特に、触媒単位重量当たりで大きな表面積を得ることができ、触媒単位面積当たりに必要な金および白金の使用量を低減することができる。またコストの点でも、2012年現在、金は白金よりもさらに高価であるところ、コア材料（金）とシェル材料（白金）を合わせた材料費は金コアの粒径が約2.5 mm付近で現行の白金触媒（粒径約2.8 nm）に拮抗し、それよりも大きな金コアを使用した場合では、現行の白金触媒よりも材料費が高くなってしまう。このため、より小粒径の金コア粒子を用いることに利点がある。
The size of the gold core particle is 1.0 to 5.0 nm. It is substantially difficult to synthesize Au core particles having a particle size of less than 1.0 mm. When the particle size exceeds 5.0 nm, the number of Pt atoms for forming a Pt shell increases, and the amount of gold used for obtaining a unit area also increases, which raises the problem of an increase in catalyst cost. Particularly when the particle size is 5.0 nm or less, a large surface area can be obtained per unit weight of the catalyst, and the amount of gold and platinum required per unit area of the catalyst can be reduced. Also, in terms of cost, as of 2012, gold is even more expensive than platinum, but the combined material cost of the core material (gold) and shell material (platinum) is the current when the particle size of the gold core is around 2.5 mm. When using a larger gold core than the platinum catalyst (particle size of about 2.8 nm), the material cost is higher than the current platinum catalyst. For this reason, there is an advantage in using a smaller-sized gold core particle.
なお、本明細書中で金コア粒子の粒径とは、透過型電子顕微鏡（ＴＥＭ）画像から求めた平均粒径、或いは、Auの（220）面のＸ線回折ピークにシェラー式を適用して算出した値を意味している。
In this specification, the particle size of the gold core particle is the average particle size obtained from a transmission electron microscope (TEM) image or the Scherrer equation applied to the X-ray diffraction peak of the (220) plane of Au. This means the value calculated by
本発明の白金コアシェル触媒のシェルは、白金と、イリジウム及び／又はルテニウムを含む。具体的には、金コア粒子の表面に白金及びイリジウムを含むシェルが形成されていてもよく、金コア粒子の表面に白金及びルテニウムを含むシェルが形成されていてもよい。白金、イリジウム及び／又はルテニウムの他、所望の触媒活性を満たす範囲で他の原子及び／又は分子を含有していてもよい。例えば、金、銀等の貴金属、製造過程で添加される白金化合物や有機化合物の残渣等が含まれていてもよい。
The shell of the platinum core-shell catalyst of the present invention contains platinum and iridium and / or ruthenium. Specifically, a shell containing platinum and iridium may be formed on the surface of the gold core particle, or a shell containing platinum and ruthenium may be formed on the surface of the gold core particle. In addition to platinum, iridium and / or ruthenium, other atoms and / or molecules may be contained within a range satisfying a desired catalytic activity. For example, noble metals such as gold and silver, platinum compounds added in the manufacturing process, and residues of organic compounds may be included.
白金に対するイリジウム及び／又はルテニウムの割合は、0.1～50 at.%であることが好ましく、5～30 at.%がより好ましい。本発明においてイリジウムやルテニウムは、白金の金コアへの固溶を抑制しうる最低限度で含有されていればよく、シェルにおける白金原子の被覆率や白金の触媒活性を阻害することがないよう適切に選択される。
白金シェルの平均的厚みは、単原子層～三原子層（0.3 nm～0.9 nm程度）であることが好ましく、単原子層～二原子層（0.3 nm～0.6 nm程度）がより好ましい。酸素還元触媒として活性を発揮する白金原子は、シェルの最外層（最表面）に位置する白金原子のみであるので、シェルの厚みを増すことには特段の利点がない。イリジウム及び／又はルテニウムは、白金と混在して触媒の表面層を構成していてもよいし、金コアと白金シェルとの間に介在していてもよい。 The ratio of iridium and / or ruthenium to platinum is preferably 0.1 to 50 at.%, More preferably 5 to 30 at.%. In the present invention, iridium or ruthenium may be contained at a minimum level capable of suppressing the solid solution of platinum in the gold core, and is appropriate so as not to hinder the coverage of platinum atoms in the shell and the catalytic activity of platinum. Selected.
The average thickness of the platinum shell is preferably a monoatomic layer to a triatomic layer (about 0.3 nm to 0.9 nm), and more preferably a monoatomic layer to a diatomic layer (about 0.3 nm to 0.6 nm). Since the platinum atoms that exhibit activity as an oxygen reduction catalyst are only platinum atoms located in the outermost layer (outermost surface) of the shell, there is no particular advantage in increasing the thickness of the shell. Iridium and / or ruthenium may be mixed with platinum to constitute the surface layer of the catalyst, or may be interposed between the gold core and the platinum shell.
白金シェルの平均的厚みは、単原子層～三原子層（0.3 nm～0.9 nm程度）であることが好ましく、単原子層～二原子層（0.3 nm～0.6 nm程度）がより好ましい。酸素還元触媒として活性を発揮する白金原子は、シェルの最外層（最表面）に位置する白金原子のみであるので、シェルの厚みを増すことには特段の利点がない。イリジウム及び／又はルテニウムは、白金と混在して触媒の表面層を構成していてもよいし、金コアと白金シェルとの間に介在していてもよい。 The ratio of iridium and / or ruthenium to platinum is preferably 0.1 to 50 at.%, More preferably 5 to 30 at.%. In the present invention, iridium or ruthenium may be contained at a minimum level capable of suppressing the solid solution of platinum in the gold core, and is appropriate so as not to hinder the coverage of platinum atoms in the shell and the catalytic activity of platinum. Selected.
The average thickness of the platinum shell is preferably a monoatomic layer to a triatomic layer (about 0.3 nm to 0.9 nm), and more preferably a monoatomic layer to a diatomic layer (about 0.3 nm to 0.6 nm). Since the platinum atoms that exhibit activity as an oxygen reduction catalyst are only platinum atoms located in the outermost layer (outermost surface) of the shell, there is no particular advantage in increasing the thickness of the shell. Iridium and / or ruthenium may be mixed with platinum to constitute the surface layer of the catalyst, or may be interposed between the gold core and the platinum shell.
本発明の白金コアシェル触媒は、白金シェルにイリジウム及び／又はルテニウムを含有することによって、白金が金コア粒子中に固溶埋没することが抑制されるが、その理由は次のように考えられる。
白金（Pt）、金（Au）、イリジウム（Ir）、ルテニウム（Ru）の其々を50:50の割合で混合する場合の混合熱ΔＨ（kJ/mol）を表１に示す。表中、数値が小さいほど、Ａ成分とＢ成分とを混合した方が安定であることを意味している。 When the platinum core-shell catalyst of the present invention contains iridium and / or ruthenium in the platinum shell, platinum is prevented from being solid-solution-embedded in the gold core particles. The reason is considered as follows.
Table 1 shows heats of mixing ΔH (kJ / mol) when platinum (Pt), gold (Au), iridium (Ir), and ruthenium (Ru) are mixed at a ratio of 50:50. In the table, the smaller the value, the more stable the mixture of the A component and the B component.
白金（Pt）、金（Au）、イリジウム（Ir）、ルテニウム（Ru）の其々を50:50の割合で混合する場合の混合熱ΔＨ（kJ/mol）を表１に示す。表中、数値が小さいほど、Ａ成分とＢ成分とを混合した方が安定であることを意味している。 When the platinum core-shell catalyst of the present invention contains iridium and / or ruthenium in the platinum shell, platinum is prevented from being solid-solution-embedded in the gold core particles. The reason is considered as follows.
Table 1 shows heats of mixing ΔH (kJ / mol) when platinum (Pt), gold (Au), iridium (Ir), and ruthenium (Ru) are mixed at a ratio of 50:50. In the table, the smaller the value, the more stable the mixture of the A component and the B component.
表１のとおり、イリジウム及びルテニウムの白金に対する混合熱は其々+1 kJ/mol、-1 kJ/molであり、金と白金の混合熱（+7 kJ/mol）よりも小さい。また、イリジウム及びルテニウムの金に対する混合熱は其々+19 kJ/mol、+22 kJ/molであり、金と白金の混合熱（+7 kJ/mol）よりも大きい。すなわち、イリジウム及びルテニウムは、金と比べて白金と混合しやすく、またイリジウム及びルテニウムは、白金と比べて金と混合しにくい。
As shown in Table 1, the heat of mixing iridium and ruthenium with respect to platinum is +1 kJ / mol and -1 kJ / mol, respectively, which is smaller than the heat of mixing gold and platinum (+7 kJ / mol). The heat of mixing of iridium and ruthenium with gold is + 19 + kJ / mol and +22 kJ / mol, respectively, which is larger than the heat of mixing of gold and platinum (+7 kJ / mol). That is, iridium and ruthenium are easier to mix with platinum than gold, and iridium and ruthenium are harder to mix with gold than platinum.
このことから、シェルである白金原子の近傍に、白金と親和性が高くかつ金との親和性が低い元素であるイリジウムやルテニウムを存在させると、これらの元素は金に固溶せずに白金と相互作用するために、白金シェルが金コアに固溶埋没することが抑制されると考えられる。
Therefore, when iridium or ruthenium, which has high affinity with platinum and low affinity with gold, is present in the vicinity of the platinum atom, which is a shell, these elements do not dissolve in gold but are dissolved in platinum. Therefore, it is considered that the platinum shell is suppressed from being solid-solution buried in the gold core.
本発明の白金コアシェル触媒は、炭素質材料からなる担体の表面に分散されて担持されていることが好ましい。炭素質材料としてはカーボンブラック、ケッチェンブラック、アセチレンブラック、カーボンナノチューブ等が挙げられる。また、炭素質材料担体の酸化劣化の観点から、耐酸化性の高い酸化錫（SnOx）や酸化チタン（TiOx）などの金属酸化物担体を使用してもよく、炭素質材料担体と金属酸化物担体とを混合して使用してもよい。担体は、比表面積が10～1000 m2/g程度であることが好ましい。白金コアシェル触媒は、主に静電的相互作用によって担体の表面に担持されていると考えられる。より強固に担持させて担体表面からの触媒の脱落を低減するために、白金コアシェル触媒と担体との間に、化学結合を形成することもできる。
The platinum core-shell catalyst of the present invention is preferably dispersed and supported on the surface of a carrier made of a carbonaceous material. Examples of the carbonaceous material include carbon black, ketjen black, acetylene black, and carbon nanotube. From the viewpoint of oxidative deterioration of the carbonaceous material carrier, metal oxide carriers such as tin oxide (SnOx) and titanium oxide (TiOx) having high oxidation resistance may be used. You may mix and use a support | carrier. The support preferably has a specific surface area of about 10 to 1000 m 2 / g. It is considered that the platinum core-shell catalyst is supported on the surface of the support mainly by electrostatic interaction. A chemical bond can also be formed between the platinum core-shell catalyst and the support in order to more firmly support it and reduce the dropping of the catalyst from the support surface.
白金とルテニウム及び／又はイリジウムとによる金コア粒子表面の被覆率は、50～100 %とすることができ、60～100 %が好ましく、70～100 %とすることがより好ましい。金コアへの白金固溶量は金コア粒子の体積によって決まるため、同粒径の金コア粒子であれば、白金被覆率が高いほど金への固溶によって失われる白金の割合が低く（つまり、触媒としての耐久性が高く）、白金被覆率が低いと、金への固溶によって失われる白金の割合が高く（つまり、触媒としての耐久性が低く）なる。
The coverage of the gold core particle surface with platinum and ruthenium and / or iridium can be 50-100%, preferably 60-100%, more preferably 70-100%. Since the amount of platinum solid solution in the gold core is determined by the volume of the gold core particle, if the gold core particle has the same particle size, the higher the platinum coverage, the lower the proportion of platinum lost due to solid solution in gold (that is, When the platinum coverage is low, the proportion of platinum lost by solid solution in gold is high (that is, the durability as a catalyst is low).
しかしながらまた、本発明の白金コアシェル触媒では、同粒径の金コア粒子において、従来型白金コアシェル触媒（白金のみからなるシェルを有する触媒）の1/2～1/4程度の白金シェル量であっても、従来型白金コアシェル触媒と同等の耐久性を有することが見いだされている（実施例を参照）。つまり、本発明の触媒は、白金の表面被覆率（表面の白金原子数）が低いにも関わらず、金への固溶が生じにくい。これは、イリジウム及び／又はルテニウムの存在が、白金の固溶を抑制しているためであると考えられる。これは、従来の白金コアシェル触媒と異なる本発明に特有の効果である。
However, in the platinum core-shell catalyst of the present invention, the gold core particle having the same particle size has a platinum shell amount of about 1/2 to 1/4 of that of a conventional platinum core-shell catalyst (a catalyst having a shell made only of platinum). However, it has been found to have durability equivalent to that of the conventional platinum core-shell catalyst (see Examples). That is, although the catalyst of the present invention has a low surface coverage of platinum (the number of platinum atoms on the surface), it does not easily cause solid solution in gold. This is presumably because the presence of iridium and / or ruthenium suppresses solid solution of platinum. This is an effect peculiar to the present invention different from the conventional platinum core-shell catalyst.
本発明の白金コアシェル触媒の製造方法は特に制限されるものではないが、例えば、（１）炭素質担体に担持された金コア粒子の表面に銅からなる単原子層を形成させるステップと、（２）ステップ（１）で得られた銅単原子層を、白金と、イリジウム及び／又はルテニウムとに置換するステップとを含む方法によって好適に製造することができる。
The method for producing the platinum core-shell catalyst of the present invention is not particularly limited. For example, (1) a step of forming a monoatomic layer made of copper on the surface of a gold core particle supported on a carbonaceous support; 2) The copper monoatomic layer obtained in step (1) can be preferably produced by a method including a step of replacing platinum with iridium and / or ruthenium.
炭素質担体に担持された金コア粒子は公知の合成法によって合成することが可能である。一例としては、四塩化金酸（HAuCl4）等を水溶液、有機溶液、又はそれらの混合溶液中、保護剤としてアルカンチオールを添加し、その後還元して金ナノ粒子を形成させ、金ナノ粒子表面に化学吸着したアルカンチオールを介して炭素質担体に吸着させ、続いて熱処理によってチオール基と炭化水素鎖の一部を除去することによって、炭素質担体に担持された金コア粒子を得る方法がある。
Gold core particles supported on a carbonaceous carrier can be synthesized by a known synthesis method. For example, tetrachloroauric acid (HAuCl 4 ) or the like is added to alkanethiol as a protective agent in an aqueous solution, an organic solution, or a mixed solution thereof, and then reduced to form gold nanoparticles. There is a method of obtaining gold core particles supported on a carbonaceous support by adsorbing to a carbonaceous support via alkanethiol chemisorbed on the carbon, and subsequently removing a part of the thiol group and hydrocarbon chain by heat treatment. .
金コア粒子の表面に銅からなる単原子層を形成させるには、公知の方法を用いることができる。例えば、非特許文献１に開示されているＵＰＤ法に従うこと、或いは、当該方法を適宜変更して行うことができる。
A known method can be used to form a monoatomic layer made of copper on the surface of the gold core particle. For example, the UPD method disclosed in Non-Patent Document 1 can be followed, or the method can be changed as appropriate.
また本発明の製造方法では、外部電源を使用した精密な電位制御と対極や参照極を必要としない、改良型Ｃｕ－ＵＰＤ法を用いることがより好ましい。改良型Ｃｕ－ＵＰＤ法とは、炭素質担体に担持された金コア粒子を、銅からなる固体が浸漬されたCuイオンを含有する酸性水溶液中に投入し、アルゴンや窒素等の不活性ガス雰囲気中で撹拌することで、金コア表面に銅からなる単原子膜を形成させる方法である。銅単原子膜は必ずしも膜の全面が単原子膜からなる均一膜でなく、部分的に二原子或いはそれ以上の重複が生じているものも含む。
In the production method of the present invention, it is more preferable to use an improved Cu-UPD method that does not require precise potential control using an external power source and a counter electrode or a reference electrode. In the improved Cu-UPD method, gold core particles supported on a carbonaceous support are put into an acidic aqueous solution containing Cu ions in which a solid made of copper is immersed, and an inert gas atmosphere such as argon or nitrogen is used. In this method, a monoatomic film made of copper is formed on the surface of the gold core by stirring in the medium. The copper monoatomic film is not necessarily a uniform film composed of a monoatomic film on the entire surface, but includes a film in which two or more atoms overlap each other.
改良型Ｃｕ－ＵＰＤ法に用いられる、銅からなる固体としては、少なくとも表面が銅で構成されており、金ナノ粒子と接触した際にイオン化して銅イオン（Cu2+）を生じる物体であれば制限されない。例えば、銅メッシュ、銅ワイヤ、銅粒、銅板、銅塊等が挙げられる。
The solid made of copper used in the improved Cu-UPD method is an object that at least has a surface made of copper and is ionized to produce copper ions (Cu 2+ ) when contacted with gold nanoparticles. There is no limit. For example, a copper mesh, a copper wire, a copper grain, a copper plate, a copper lump, etc. are mentioned.
Cuイオンを含有する酸性水溶液に用いられるCuイオンを与える物質としては、CuSO4、CuCl2、Cu(CH3COO)2、Cu(NO3)2等が挙げられ、これらのCu塩を水溶液とすることによってCuイオンが解離する。Cuイオン濃度は特に制限されるものではないが、例えば0.1 mM～100 mMとすることができ、反応速度と反応溶液の安定性等の観点からは1 mM～50 mM程度とすることが好ましい。
CuSO 4 , CuCl 2 , Cu (CH 3 COO) 2 , Cu (NO 3 ) 2 and the like can be cited as substances that give Cu ions used in acidic aqueous solutions containing Cu ions. By doing so, Cu ions are dissociated. The Cu ion concentration is not particularly limited, but can be, for example, 0.1 mM to 100 mM, and is preferably about 1 mM to 50 mM from the viewpoint of the reaction rate and the stability of the reaction solution.
酸性溶液を与える酸としては、銅を溶解可能であれば特に制限されないが、例えば、硝酸、硫酸、塩酸、過塩素酸等が挙げられ、濃度は10 mM～1 Mとすることができ、反応速度と銅固体の電位制御の観点からは20 mM～0.5 M程度とすることができる。
The acid that gives the acidic solution is not particularly limited as long as it can dissolve copper, and examples thereof include nitric acid, sulfuric acid, hydrochloric acid, perchloric acid, and the like. The concentration can be set to 10 mM to 1 M. From the viewpoint of controlling the speed and the potential of the copper solid, it can be set to about 20 mm to 0.5 mm.
上記銅固体を浸漬した上記のCuイオンを含む酸性溶液に、炭素質担体に担持された金コア粒子を投入し、例えば、0～45 ℃において1～50時間、不活性ガス通気下で撹拌を行うことによって、金コア表面に銅の単原子膜が形成される。
Gold core particles supported on a carbonaceous support are introduced into an acidic solution containing the above Cu ions immersed in the above copper solid, and stirred, for example, at 0 to 45 ° C. for 1 to 50 hours under an inert gas flow. By doing so, a copper monoatomic film is formed on the gold core surface.
続いて、得られた生成物表面の銅を、白金とルテニウム及び／又はイリジウムと置換する。このステップは、公知のＵＰＤ法等で用いられている置換めっき法で行うことができる。白金イオンを与える物質としては、白金酸塩（K2PtCl4、K2PtBr4）等が挙げられ、ルテニウムイオン及び／又はイリジウムイオンを与える物質としては例えば、塩化ルテニウム、硝酸ルテニウム、塩化イリジウム酸、硝酸イリジウム等が挙げられる。
Subsequently, the copper on the product surface obtained is replaced with platinum and ruthenium and / or iridium. This step can be performed by a displacement plating method used in a known UPD method or the like. Examples of substances that give platinum ions include platinum salts (K 2 PtCl 4 , K 2 PtBr 4 ), and examples of substances that give ruthenium ions and / or iridium ions include ruthenium chloride, ruthenium nitrate, and iridium chloride. And iridium nitrate.
銅からなる単原子膜を、白金とルテニウム及び／又はイリジウムで置換するステップは、前述の銅固体を浸漬した上記のCuイオンを含む酸性溶液から、銅固体を除いた上で、前記の白金、ルテニウム及び／又はイリジウムを含む化合物を、同時に又は順次水溶液に添加し、撹拌することによって行うことができる。すなわち例えば、白金化合物とイリジウム及び又はルテニウムイオン化合物を同時に投入し、白金とイリジウム及び／又はルテニウムとが同一層内で混在するシェルを形成してもよい。白金化合物とイリジウム及び又はルテニウムイオン化合物の添加は、銅固体を取り除いた後、可能な限り時間をあけずに行うことが好ましい。操作の過程で大気中の酸素が溶液中に侵入すると、金コア上に生成した銅単原子膜が溶解するため、銅固体を取り除いた後、直ちに白金化合物とイリジウム及び又はルテニウムイオン化合物を添加することが好ましい。
反応時間、温度は適宜選択することができるが、例えば、0～45 ℃において1分～50時間（好ましくは1分～1時間）であり、不活性ガス通気下、撹拌しながら行うことが可能である。 The step of replacing the monoatomic film made of copper with platinum and ruthenium and / or iridium is performed by removing the copper solid from the above-described acidic solution containing Cu ions soaked in the copper solid, A compound containing ruthenium and / or iridium can be added to the aqueous solution simultaneously or sequentially and stirred. That is, for example, a platinum compound and an iridium and / or ruthenium ion compound may be simultaneously introduced to form a shell in which platinum and iridium and / or ruthenium are mixed in the same layer. The addition of the platinum compound and the iridium and / or ruthenium ion compound is preferably carried out with as little time as possible after removing the copper solid. When oxygen in the atmosphere enters into the solution during the operation, the copper monoatomic film formed on the gold core dissolves, so after removing the copper solid, immediately add platinum compound and iridium and / or ruthenium ion compound It is preferable.
The reaction time and temperature can be appropriately selected. For example, the reaction time is 0 to 45 ° C. for 1 minute to 50 hours (preferably 1 minute to 1 hour). It is.
反応時間、温度は適宜選択することができるが、例えば、0～45 ℃において1分～50時間（好ましくは1分～1時間）であり、不活性ガス通気下、撹拌しながら行うことが可能である。 The step of replacing the monoatomic film made of copper with platinum and ruthenium and / or iridium is performed by removing the copper solid from the above-described acidic solution containing Cu ions soaked in the copper solid, A compound containing ruthenium and / or iridium can be added to the aqueous solution simultaneously or sequentially and stirred. That is, for example, a platinum compound and an iridium and / or ruthenium ion compound may be simultaneously introduced to form a shell in which platinum and iridium and / or ruthenium are mixed in the same layer. The addition of the platinum compound and the iridium and / or ruthenium ion compound is preferably carried out with as little time as possible after removing the copper solid. When oxygen in the atmosphere enters into the solution during the operation, the copper monoatomic film formed on the gold core dissolves, so after removing the copper solid, immediately add platinum compound and iridium and / or ruthenium ion compound It is preferable.
The reaction time and temperature can be appropriately selected. For example, the reaction time is 0 to 45 ° C. for 1 minute to 50 hours (preferably 1 minute to 1 hour). It is.
前記の方法によって得た、白金とイリジウム及び／又はルテニウムとを含有するシェルを有する金コア粒子は、公知の方法によって洗浄、乾燥等を必要に応じて行い、本発明の燃料電池用白金コアシェル触媒が得られる。なお、本発明の製造方法には、前述のステップのほかにも必要に応じて、分離、精製、洗浄工程等を含むことができる。
The gold core particles having a shell containing platinum and iridium and / or ruthenium obtained by the above method are washed, dried and the like as required by a known method, and the platinum core-shell catalyst for fuel cells of the present invention Is obtained. In addition to the steps described above, the production method of the present invention can include separation, purification, washing steps and the like as necessary.
以下、実施例を用いて本発明をより具体的に説明するが、本発明は実施例に限定されるものではない。
Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to the examples.
［実施例１］イリジウム含有白金シェル／金コア触媒の作製
（ｉ）Au/Cコアの作製
7.619×10-4モルのHAuCl4を純水80 mlに溶解させた。分液ロートを用いて、相間移動剤であるテトラオクチルアンモニウムブロミド625 mgのトルエン溶液とHAuCl4水溶液とを混合後、静置し、トルエン相に[AuCl4]-を移動させた。水相を除去し、トルエン相を三角フラスコに移し、30 ℃の恒温槽に設置した。Arガスを500 ml/min.の流量で流し、撹拌しながら保護剤であるドデカンチオールを1.904×10-3モル添加した。ドデカンチオール添加後、Arバブリングを1時間行なった。その後、三角フラスコを60 ℃の恒温槽に移動させた。還元剤であるNaBH4 288 mgを純水25 mlに溶解し、チューブポンプを用いて15分で三角フラスコに滴下し、金イオンを還元してAuコロイド粒子を得た。60 ℃で合計1時間撹拌後、30 ℃の恒温槽に移動し、3時間撹拌してAuコロイドを熟成した。熟成後、溶液を分液ロートに移して水相を除去し、Auコロイド溶液を丸底フラスコに移動し、エバポレーターを用いてトルエンを留去した。
トルエン留去後の丸底フラスコに30 mlのn-ヘキサンを添加し、超音波を30分間照射してAuコロイドを再分散させた。その後、80 mlのエタノールを添加し、溶媒の極性を高めてAuコロイドを沈殿させた。遠心分離機を用い、12000回転で15分間処理してAuコロイドを沈降分離した。上澄み液を除去し、Auコロイドをn-ヘキサン中に再分散させた。その後、エバポレーターを用いてn-ヘキサンを留去し、n-ヘキサンを10 ml添加して超音波を30分間照射した。その後、エタノールを80 ml添加してAuコロイドを沈殿させた。この操作を4回繰り返すことによってAuコロイドを洗浄した。
洗浄処理したAuコロイドを30 mlのn-ヘキサンに分散させた。350 mgのカーボン担体（Ketjen black EC 300 J, 比表面積800 m2/g）を350 mlのn-ヘキサン中で1時間超音波分散し、Auコロイドのn-ヘキサン分散液を加え、さらに30分間超音波照射を行なった。その後、室温でマグネチックスタラーを用いて溶液を一昼夜撹拌し、Auコロイドをカーボン担体上に担持させた。
一昼夜攪拌したn-ヘキサン溶液を吸引濾過してカーボン担持Auコア(Au/Cコア)を濾別し、大気中60 ℃のオーブンで6時間乾燥してAu/Cコアを得た。
（ii）Au/Cコアの熱処理
大気中330 ℃で1時間Au/Cを熱処理し、Auコア粒子表面に化学吸着したドデカンチオールを除去した。
（iii）Au/Cコアの分析
熱処理後のAu/Cコアを電子顕微鏡（日本電子株式会社製、JEM2100F）で観察したところ、カーボン担体に担持されたAu微粒子が確認された。TEM像中の200個のAuコア粒子の直径を測定した結果、平均粒径は2.8 nmであった。また、金属Auの担持率を熱重量分析（リガク製、Thermo Plus TG-8120）で調べた結果、28.4 wt.%であった。
（iv）Au/Cコア上へのIr含有Ptシェルの形成
担持率28.4 wt.%、粒径2.8 nmのAu/Cコア200 mgを、濃度50 mMのH2SO4と濃度10 mMのCuSO4を含む300 mlの水溶液中に分散させた。Arを100 ml/min.の流量で流し、Cuメッシュを水溶液中に共存させた後、30 ℃で10時間撹拌してAuコア粒子表面にCuシェルを形成した。その後、Cuメッシュを水溶液から除去し、予めArバブリングして溶存酸素を除去したK2PtCl4水溶液とH2IrCl6水溶液をそれぞれ1 mMの濃度となるよう直ちに加え、Cuシェル層をPtIrシェル層に置換させてAuコア/PtIrシェル触媒（PtIr/Au/C）を得た。生成したPtIr/Au/C触媒を純水300 ml中に分散撹拌した後、吸引濾過した。この操作を3回繰り返して触媒を洗浄した。その後、大気中60 ℃のオーブンで6時間乾燥した。
（v）PtIr/Au/C触媒の分析
得られたPtIr/Au/C触媒の組成を、蛍光X線装置(SII社製、SEA1200VX)で分析した結果、Pt:Ir:Au=18.6:5.7:75.7 (at.%)であった。また、(220)のXRDピークにシェラー式を適用して算出したPtIr/Auの平均粒径は3.4 nmであった。
Au/Cコアの分析結果及びPtIr/Au/C触媒の分析結果から、平均粒径2.8 nmのAuコアの表面に、Pt及びIr（PtとIrの原子数割合は18.6:5.7）が混在する平均層厚0.3 nmのシェルを有する、白金コアシェル触媒が得られたと考察された。 [Example 1] Preparation of iridium-containing platinum shell / gold core catalyst (i) Preparation of Au / C core 7.619 × 10 −4 mol of HAuCl 4 was dissolved in 80 ml of pure water. Using a separatory funnel, a toluene solution of 625 mg of tetraoctylammonium bromide as a phase transfer agent and an aqueous HAuCl 4 solution were mixed and allowed to stand to move [AuCl 4 ] − to the toluene phase. The aqueous phase was removed and the toluene phase was transferred to an Erlenmeyer flask and placed in a thermostatic bath at 30 ° C. Ar gas was flowed at a flow rate of 500 ml / min., And 1.904 × 10 −3 mol of dodecanethiol as a protective agent was added while stirring. After dodecanethiol addition, Ar bubbling was performed for 1 hour. Thereafter, the Erlenmeyer flask was moved to a constant temperature bath at 60 ° C. NaBH 4 288 mg as a reducing agent was dissolved in 25 ml of pure water and dropped into an Erlenmeyer flask in 15 minutes using a tube pump to reduce gold ions to obtain Au colloidal particles. After stirring at 60 ° C. for a total of 1 hour, the mixture was transferred to a constant temperature bath at 30 ° C. and stirred for 3 hours to age the Au colloid. After aging, the solution was transferred to a separatory funnel to remove the aqueous phase, the Au colloid solution was transferred to a round bottom flask, and toluene was distilled off using an evaporator.
30 ml of n-hexane was added to the round bottom flask after the toluene was distilled off, and the Au colloid was redispersed by irradiation with ultrasonic waves for 30 minutes. Thereafter, 80 ml of ethanol was added to increase the polarity of the solvent to precipitate Au colloid. Using a centrifuge, Au colloid was precipitated and separated by treatment at 12000 rpm for 15 minutes. The supernatant was removed and the Au colloid was redispersed in n-hexane. Then, n-hexane was distilled off using an evaporator, 10 ml of n-hexane was added, and ultrasonic waves were irradiated for 30 minutes. Thereafter, 80 ml of ethanol was added to precipitate Au colloid. The colloidal Au was washed by repeating this operation four times.
The washed Au colloid was dispersed in 30 ml of n-hexane. 350 mg of carbon support (Ketjen black EC 300 J, specific surface area 800 m 2 / g) is ultrasonically dispersed in 350 ml of n-hexane for 1 hour, then added with Au colloid n-hexane dispersion, and then for another 30 minutes Ultrasonic irradiation was performed. Thereafter, the solution was stirred for a whole day and night using a magnetic stirrer at room temperature to support Au colloid on the carbon support.
The carbon-supported Au core (Au / C core) was filtered off with suction by stirring the n-hexane solution stirred overnight, and dried in an oven at 60 ° C. for 6 hours in the atmosphere to obtain an Au / C core.
(Ii) Au / C core heat treatment Au / C was heat-treated in air at 330 ° C. for 1 hour to remove dodecanethiol chemically adsorbed on the surface of the Au core particles.
(Iii) Analysis of Au / C core When the Au / C core after heat treatment was observed with an electron microscope (JEM2100F, manufactured by JEOL Ltd.), Au fine particles supported on the carbon support were confirmed. As a result of measuring the diameter of 200 Au core particles in the TEM image, the average particle size was 2.8 nm. Further, the loading ratio of metallic Au was examined by thermogravimetric analysis (Rigaku, Thermo Plus TG-8120), and as a result, it was 28.4 wt.%.
(Iv) Formation of Ir-containing Pt shell on Au / C core 200% Au / C core with a loading rate of 28.4 wt.% And a particle size of 2.8 nm, 50 mM H 2 SO 4 and 10 mM CuSO Dispersed in 300 ml of aqueous solution containing 4 . Ar was flowed at a flow rate of 100 ml / min., And the Cu mesh was allowed to coexist in the aqueous solution, and then stirred at 30 ° C. for 10 hours to form a Cu shell on the surface of the Au core particles. After that, remove Cu mesh from aqueous solution, add K 2 PtCl 4 aqueous solution and H 2 IrCl 6 aqueous solution, which have been dissolved in oxygen by bubbling Ar in advance, so that each concentration becomes 1 mM, Cu shell layer is added to PtIr shell layer To obtain an Au core / PtIr shell catalyst (PtIr / Au / C). The produced PtIr / Au / C catalyst was dispersed and stirred in 300 ml of pure water, followed by suction filtration. This operation was repeated 3 times to wash the catalyst. Thereafter, it was dried in an oven at 60 ° C. for 6 hours in the atmosphere.
(V) Analysis of PtIr / Au / C catalyst The composition of the obtained PtIr / Au / C catalyst was analyzed with a fluorescent X-ray apparatus (SEA1200VX, manufactured by SII). As a result, Pt: Ir: Au = 18.6: 5.7: 75.7 (at.%). The average particle size of PtIr / Au calculated by applying the Scherrer equation to the XRD peak of (220) was 3.4 nm.
Based on the analysis results of the Au / C core and the PtIr / Au / C catalyst, Pt and Ir (Pt and Ir atomic ratio is 18.6: 5.7) are mixed on the surface of the Au core with an average particle size of 2.8 nm. It was considered that a platinum core-shell catalyst having a shell with an average layer thickness of 0.3 nm was obtained.
（ｉ）Au/Cコアの作製
7.619×10-4モルのHAuCl4を純水80 mlに溶解させた。分液ロートを用いて、相間移動剤であるテトラオクチルアンモニウムブロミド625 mgのトルエン溶液とHAuCl4水溶液とを混合後、静置し、トルエン相に[AuCl4]-を移動させた。水相を除去し、トルエン相を三角フラスコに移し、30 ℃の恒温槽に設置した。Arガスを500 ml/min.の流量で流し、撹拌しながら保護剤であるドデカンチオールを1.904×10-3モル添加した。ドデカンチオール添加後、Arバブリングを1時間行なった。その後、三角フラスコを60 ℃の恒温槽に移動させた。還元剤であるNaBH4 288 mgを純水25 mlに溶解し、チューブポンプを用いて15分で三角フラスコに滴下し、金イオンを還元してAuコロイド粒子を得た。60 ℃で合計1時間撹拌後、30 ℃の恒温槽に移動し、3時間撹拌してAuコロイドを熟成した。熟成後、溶液を分液ロートに移して水相を除去し、Auコロイド溶液を丸底フラスコに移動し、エバポレーターを用いてトルエンを留去した。
トルエン留去後の丸底フラスコに30 mlのn-ヘキサンを添加し、超音波を30分間照射してAuコロイドを再分散させた。その後、80 mlのエタノールを添加し、溶媒の極性を高めてAuコロイドを沈殿させた。遠心分離機を用い、12000回転で15分間処理してAuコロイドを沈降分離した。上澄み液を除去し、Auコロイドをn-ヘキサン中に再分散させた。その後、エバポレーターを用いてn-ヘキサンを留去し、n-ヘキサンを10 ml添加して超音波を30分間照射した。その後、エタノールを80 ml添加してAuコロイドを沈殿させた。この操作を4回繰り返すことによってAuコロイドを洗浄した。
洗浄処理したAuコロイドを30 mlのn-ヘキサンに分散させた。350 mgのカーボン担体（Ketjen black EC 300 J, 比表面積800 m2/g）を350 mlのn-ヘキサン中で1時間超音波分散し、Auコロイドのn-ヘキサン分散液を加え、さらに30分間超音波照射を行なった。その後、室温でマグネチックスタラーを用いて溶液を一昼夜撹拌し、Auコロイドをカーボン担体上に担持させた。
一昼夜攪拌したn-ヘキサン溶液を吸引濾過してカーボン担持Auコア(Au/Cコア)を濾別し、大気中60 ℃のオーブンで6時間乾燥してAu/Cコアを得た。
（ii）Au/Cコアの熱処理
大気中330 ℃で1時間Au/Cを熱処理し、Auコア粒子表面に化学吸着したドデカンチオールを除去した。
（iii）Au/Cコアの分析
熱処理後のAu/Cコアを電子顕微鏡（日本電子株式会社製、JEM2100F）で観察したところ、カーボン担体に担持されたAu微粒子が確認された。TEM像中の200個のAuコア粒子の直径を測定した結果、平均粒径は2.8 nmであった。また、金属Auの担持率を熱重量分析（リガク製、Thermo Plus TG-8120）で調べた結果、28.4 wt.%であった。
（iv）Au/Cコア上へのIr含有Ptシェルの形成
担持率28.4 wt.%、粒径2.8 nmのAu/Cコア200 mgを、濃度50 mMのH2SO4と濃度10 mMのCuSO4を含む300 mlの水溶液中に分散させた。Arを100 ml/min.の流量で流し、Cuメッシュを水溶液中に共存させた後、30 ℃で10時間撹拌してAuコア粒子表面にCuシェルを形成した。その後、Cuメッシュを水溶液から除去し、予めArバブリングして溶存酸素を除去したK2PtCl4水溶液とH2IrCl6水溶液をそれぞれ1 mMの濃度となるよう直ちに加え、Cuシェル層をPtIrシェル層に置換させてAuコア/PtIrシェル触媒（PtIr/Au/C）を得た。生成したPtIr/Au/C触媒を純水300 ml中に分散撹拌した後、吸引濾過した。この操作を3回繰り返して触媒を洗浄した。その後、大気中60 ℃のオーブンで6時間乾燥した。
（v）PtIr/Au/C触媒の分析
得られたPtIr/Au/C触媒の組成を、蛍光X線装置(SII社製、SEA1200VX)で分析した結果、Pt:Ir:Au=18.6:5.7:75.7 (at.%)であった。また、(220)のXRDピークにシェラー式を適用して算出したPtIr/Auの平均粒径は3.4 nmであった。
Au/Cコアの分析結果及びPtIr/Au/C触媒の分析結果から、平均粒径2.8 nmのAuコアの表面に、Pt及びIr（PtとIrの原子数割合は18.6:5.7）が混在する平均層厚0.3 nmのシェルを有する、白金コアシェル触媒が得られたと考察された。 [Example 1] Preparation of iridium-containing platinum shell / gold core catalyst (i) Preparation of Au / C core 7.619 × 10 −4 mol of HAuCl 4 was dissolved in 80 ml of pure water. Using a separatory funnel, a toluene solution of 625 mg of tetraoctylammonium bromide as a phase transfer agent and an aqueous HAuCl 4 solution were mixed and allowed to stand to move [AuCl 4 ] − to the toluene phase. The aqueous phase was removed and the toluene phase was transferred to an Erlenmeyer flask and placed in a thermostatic bath at 30 ° C. Ar gas was flowed at a flow rate of 500 ml / min., And 1.904 × 10 −3 mol of dodecanethiol as a protective agent was added while stirring. After dodecanethiol addition, Ar bubbling was performed for 1 hour. Thereafter, the Erlenmeyer flask was moved to a constant temperature bath at 60 ° C. NaBH 4 288 mg as a reducing agent was dissolved in 25 ml of pure water and dropped into an Erlenmeyer flask in 15 minutes using a tube pump to reduce gold ions to obtain Au colloidal particles. After stirring at 60 ° C. for a total of 1 hour, the mixture was transferred to a constant temperature bath at 30 ° C. and stirred for 3 hours to age the Au colloid. After aging, the solution was transferred to a separatory funnel to remove the aqueous phase, the Au colloid solution was transferred to a round bottom flask, and toluene was distilled off using an evaporator.
30 ml of n-hexane was added to the round bottom flask after the toluene was distilled off, and the Au colloid was redispersed by irradiation with ultrasonic waves for 30 minutes. Thereafter, 80 ml of ethanol was added to increase the polarity of the solvent to precipitate Au colloid. Using a centrifuge, Au colloid was precipitated and separated by treatment at 12000 rpm for 15 minutes. The supernatant was removed and the Au colloid was redispersed in n-hexane. Then, n-hexane was distilled off using an evaporator, 10 ml of n-hexane was added, and ultrasonic waves were irradiated for 30 minutes. Thereafter, 80 ml of ethanol was added to precipitate Au colloid. The colloidal Au was washed by repeating this operation four times.
The washed Au colloid was dispersed in 30 ml of n-hexane. 350 mg of carbon support (Ketjen black EC 300 J, specific surface area 800 m 2 / g) is ultrasonically dispersed in 350 ml of n-hexane for 1 hour, then added with Au colloid n-hexane dispersion, and then for another 30 minutes Ultrasonic irradiation was performed. Thereafter, the solution was stirred for a whole day and night using a magnetic stirrer at room temperature to support Au colloid on the carbon support.
The carbon-supported Au core (Au / C core) was filtered off with suction by stirring the n-hexane solution stirred overnight, and dried in an oven at 60 ° C. for 6 hours in the atmosphere to obtain an Au / C core.
(Ii) Au / C core heat treatment Au / C was heat-treated in air at 330 ° C. for 1 hour to remove dodecanethiol chemically adsorbed on the surface of the Au core particles.
(Iii) Analysis of Au / C core When the Au / C core after heat treatment was observed with an electron microscope (JEM2100F, manufactured by JEOL Ltd.), Au fine particles supported on the carbon support were confirmed. As a result of measuring the diameter of 200 Au core particles in the TEM image, the average particle size was 2.8 nm. Further, the loading ratio of metallic Au was examined by thermogravimetric analysis (Rigaku, Thermo Plus TG-8120), and as a result, it was 28.4 wt.%.
(Iv) Formation of Ir-containing Pt shell on Au / C core 200% Au / C core with a loading rate of 28.4 wt.% And a particle size of 2.8 nm, 50 mM H 2 SO 4 and 10 mM CuSO Dispersed in 300 ml of aqueous solution containing 4 . Ar was flowed at a flow rate of 100 ml / min., And the Cu mesh was allowed to coexist in the aqueous solution, and then stirred at 30 ° C. for 10 hours to form a Cu shell on the surface of the Au core particles. After that, remove Cu mesh from aqueous solution, add K 2 PtCl 4 aqueous solution and H 2 IrCl 6 aqueous solution, which have been dissolved in oxygen by bubbling Ar in advance, so that each concentration becomes 1 mM, Cu shell layer is added to PtIr shell layer To obtain an Au core / PtIr shell catalyst (PtIr / Au / C). The produced PtIr / Au / C catalyst was dispersed and stirred in 300 ml of pure water, followed by suction filtration. This operation was repeated 3 times to wash the catalyst. Thereafter, it was dried in an oven at 60 ° C. for 6 hours in the atmosphere.
(V) Analysis of PtIr / Au / C catalyst The composition of the obtained PtIr / Au / C catalyst was analyzed with a fluorescent X-ray apparatus (SEA1200VX, manufactured by SII). As a result, Pt: Ir: Au = 18.6: 5.7: 75.7 (at.%). The average particle size of PtIr / Au calculated by applying the Scherrer equation to the XRD peak of (220) was 3.4 nm.
Based on the analysis results of the Au / C core and the PtIr / Au / C catalyst, Pt and Ir (Pt and Ir atomic ratio is 18.6: 5.7) are mixed on the surface of the Au core with an average particle size of 2.8 nm. It was considered that a platinum core-shell catalyst having a shell with an average layer thickness of 0.3 nm was obtained.
［試験電極の作製］
PtIr/Au/C触媒のn-ヘキサノール懸濁液を調製し、回転リングディスク電極のグラッシーカーボンディスク（直径6 mm）上に、Auコアが14.1 μg/cm2となるよう塗布担持し、試験電極を作製した。図２に回転リングディスク電極の構造を示す。ディスク部分に触媒を塗布担持させ、作用電極を回転させることにより電解液中に一定の対流を発生させ、物質移動を制御した。 [Production of test electrode]
Prepare an n-hexanol suspension of PtIr / Au / C catalyst and apply and support it on a glassy carbon disk (diameter 6 mm) of a rotating ring disk electrode so that the Au core is 14.1 μg / cm 2. Was made. FIG. 2 shows the structure of the rotating ring disk electrode. A catalyst was applied and supported on the disk portion, and the working electrode was rotated to generate a constant convection in the electrolyte, thereby controlling mass transfer.
PtIr/Au/C触媒のn-ヘキサノール懸濁液を調製し、回転リングディスク電極のグラッシーカーボンディスク（直径6 mm）上に、Auコアが14.1 μg/cm2となるよう塗布担持し、試験電極を作製した。図２に回転リングディスク電極の構造を示す。ディスク部分に触媒を塗布担持させ、作用電極を回転させることにより電解液中に一定の対流を発生させ、物質移動を制御した。 [Production of test electrode]
Prepare an n-hexanol suspension of PtIr / Au / C catalyst and apply and support it on a glassy carbon disk (diameter 6 mm) of a rotating ring disk electrode so that the Au core is 14.1 μg / cm 2. Was made. FIG. 2 shows the structure of the rotating ring disk electrode. A catalyst was applied and supported on the disk portion, and the working electrode was rotated to generate a constant convection in the electrolyte, thereby controlling mass transfer.
［実施例２］ルテニウム含有白金シェル／金コア触媒の作製
（i）PtRu/Au/C触媒の作製
実施例１で使用したものと同じ熱処理後のAu/Cコア（担持率28.4 wt.%、粒径2.8 nm）200 mgを、濃度50 mMのH2SO4と濃度10 mMのCuSO4を含む300 mlの水溶液中に分散させた。Arを100 ml/min.の流量で流し、Cuメッシュを水溶液中に共存させた後、30 ℃で10時間撹拌してAuコア粒子表面にCuシェルを形成した。その後、Cuメッシュを水溶液から除去し、予めArバブリングして溶存酸素を除去したK2PtCl4水溶液とRuCl3水溶液をそれぞれ1 mMの濃度となるよう直ちに加え、Cuシェル層をPtRuシェル層に置換させてAuコア/PtRuシェル触媒（PtRu/Au/C）を得た。生成したPtRu/Au/C触媒を純水300 ml中に分散撹拌した後、吸引濾過した。この操作を3回繰り返して触媒を洗浄した。その後、大気中60 ℃のオーブンで6時間乾燥した。
（ii）PtRu/Au/C触媒の分析
得られたPtRu/Au/C触媒の組成を、蛍光X線装置(SII社製、SEA1200VX)で分析した結果、Pt:Ru:Au=32.7:4.1:63.2 (at.%)であった。また、(220)のXRDピークにシェラー式を適用して算出したPtRu/Auの平均粒径は3.4 nmであった。
Au/Cコアの分析結果及びPtRu/Au/C触媒の分析結果から、平均粒径2.8 nmのAuコアの表面に、Pt及びRu（PtとRuの原子数割合は32.7:4.1）が混在する平均層厚0.3 nmのシェルを有する、白金コアシェル触媒が得られたと考察された。 [Example 2] Preparation of ruthenium-containing platinum shell / gold core catalyst (i) Preparation of PtRu / Au / C catalyst Au / C core after the same heat treatment as used in Example 1 (support rate 28.4 wt.%, 200 mg (particle size 2.8 nm) was dispersed in a 300 ml aqueous solution containing 50 mM H 2 SO 4 and 10 mM CuSO 4 . Ar was flowed at a flow rate of 100 ml / min., And the Cu mesh was allowed to coexist in the aqueous solution, and then stirred at 30 ° C. for 10 hours to form a Cu shell on the surface of the Au core particles. Then remove the Cu mesh from the aqueous solution, and immediately add the K 2 PtCl 4 aqueous solution and RuCl 3 aqueous solution, each of which has been dissolved in oxygen by bubbling Ar in advance to a concentration of 1 mM, and replace the Cu shell layer with the PtRu shell layer. To obtain an Au core / PtRu shell catalyst (PtRu / Au / C). The produced PtRu / Au / C catalyst was dispersed and stirred in 300 ml of pure water, and then suction filtered. This operation was repeated 3 times to wash the catalyst. Thereafter, it was dried in an oven at 60 ° C. for 6 hours in the atmosphere.
(Ii) Analysis of PtRu / Au / C catalyst As a result of analyzing the composition of the obtained PtRu / Au / C catalyst with a fluorescent X-ray apparatus (SEA1200VX, manufactured by SII), Pt: Ru: Au = 32.7: 4.1: 63.2 (at.%). The average particle diameter of PtRu / Au calculated by applying the Scherrer equation to the XRD peak of (220) was 3.4 nm.
Based on the analysis results of the Au / C core and the PtRu / Au / C catalyst, Pt and Ru (the atomic ratio of Pt and Ru is 32.7: 4.1) are mixed on the surface of the Au core with an average particle size of 2.8 nm. It was considered that a platinum core-shell catalyst having a shell with an average layer thickness of 0.3 nm was obtained.
（i）PtRu/Au/C触媒の作製
実施例１で使用したものと同じ熱処理後のAu/Cコア（担持率28.4 wt.%、粒径2.8 nm）200 mgを、濃度50 mMのH2SO4と濃度10 mMのCuSO4を含む300 mlの水溶液中に分散させた。Arを100 ml/min.の流量で流し、Cuメッシュを水溶液中に共存させた後、30 ℃で10時間撹拌してAuコア粒子表面にCuシェルを形成した。その後、Cuメッシュを水溶液から除去し、予めArバブリングして溶存酸素を除去したK2PtCl4水溶液とRuCl3水溶液をそれぞれ1 mMの濃度となるよう直ちに加え、Cuシェル層をPtRuシェル層に置換させてAuコア/PtRuシェル触媒（PtRu/Au/C）を得た。生成したPtRu/Au/C触媒を純水300 ml中に分散撹拌した後、吸引濾過した。この操作を3回繰り返して触媒を洗浄した。その後、大気中60 ℃のオーブンで6時間乾燥した。
（ii）PtRu/Au/C触媒の分析
得られたPtRu/Au/C触媒の組成を、蛍光X線装置(SII社製、SEA1200VX)で分析した結果、Pt:Ru:Au=32.7:4.1:63.2 (at.%)であった。また、(220)のXRDピークにシェラー式を適用して算出したPtRu/Auの平均粒径は3.4 nmであった。
Au/Cコアの分析結果及びPtRu/Au/C触媒の分析結果から、平均粒径2.8 nmのAuコアの表面に、Pt及びRu（PtとRuの原子数割合は32.7:4.1）が混在する平均層厚0.3 nmのシェルを有する、白金コアシェル触媒が得られたと考察された。 [Example 2] Preparation of ruthenium-containing platinum shell / gold core catalyst (i) Preparation of PtRu / Au / C catalyst Au / C core after the same heat treatment as used in Example 1 (support rate 28.4 wt.%, 200 mg (particle size 2.8 nm) was dispersed in a 300 ml aqueous solution containing 50 mM H 2 SO 4 and 10 mM CuSO 4 . Ar was flowed at a flow rate of 100 ml / min., And the Cu mesh was allowed to coexist in the aqueous solution, and then stirred at 30 ° C. for 10 hours to form a Cu shell on the surface of the Au core particles. Then remove the Cu mesh from the aqueous solution, and immediately add the K 2 PtCl 4 aqueous solution and RuCl 3 aqueous solution, each of which has been dissolved in oxygen by bubbling Ar in advance to a concentration of 1 mM, and replace the Cu shell layer with the PtRu shell layer. To obtain an Au core / PtRu shell catalyst (PtRu / Au / C). The produced PtRu / Au / C catalyst was dispersed and stirred in 300 ml of pure water, and then suction filtered. This operation was repeated 3 times to wash the catalyst. Thereafter, it was dried in an oven at 60 ° C. for 6 hours in the atmosphere.
(Ii) Analysis of PtRu / Au / C catalyst As a result of analyzing the composition of the obtained PtRu / Au / C catalyst with a fluorescent X-ray apparatus (SEA1200VX, manufactured by SII), Pt: Ru: Au = 32.7: 4.1: 63.2 (at.%). The average particle diameter of PtRu / Au calculated by applying the Scherrer equation to the XRD peak of (220) was 3.4 nm.
Based on the analysis results of the Au / C core and the PtRu / Au / C catalyst, Pt and Ru (the atomic ratio of Pt and Ru is 32.7: 4.1) are mixed on the surface of the Au core with an average particle size of 2.8 nm. It was considered that a platinum core-shell catalyst having a shell with an average layer thickness of 0.3 nm was obtained.
［試験電極の作製］
PtRu/Au/C触媒のn-ヘキサノール懸濁液を調製し、回転リングディスク電極のグラッシーカーボンディスク（直径6 mm）上に、Auコアが14.1 μg/cm2となるよう塗布担持し、試験電極を作製した。 [Production of test electrode]
Prepare an n-hexanol suspension of PtRu / Au / C catalyst, and apply and support it on a glassy carbon disk (diameter 6 mm) of a rotating ring disk electrode so that the Au core is 14.1 μg / cm 2. Was made.
PtRu/Au/C触媒のn-ヘキサノール懸濁液を調製し、回転リングディスク電極のグラッシーカーボンディスク（直径6 mm）上に、Auコアが14.1 μg/cm2となるよう塗布担持し、試験電極を作製した。 [Production of test electrode]
Prepare an n-hexanol suspension of PtRu / Au / C catalyst, and apply and support it on a glassy carbon disk (diameter 6 mm) of a rotating ring disk electrode so that the Au core is 14.1 μg / cm 2. Was made.
［比較例１］白金シェル／金コア触媒の作製
（i）Pt/Au/C触媒の作製
実施例１で使用したものと同じ熱処理後のAu/Cコア（担持率28.4 wt.%、粒径2.8 nm）200 mgを、濃度50 mMのH2SO4と濃度10 mMのCuSO4を含む300 mlの水溶液中に分散させた。Arを100 ml/min.の流量で流し、Cuメッシュを水溶液中に共存させた後、30 ℃で10時間撹拌してAuコア粒子表面にCuシェルを形成した。その後、Cuメッシュを水溶液から除去し、予めArバブリングして溶存酸素を除去したK2PtCl4水溶液を2 mMの濃度となるよう直ちに加え、Cuシェル層をPtシェル層に置換させてAuコア/Ptシェル触媒（Pt/Au/C）を得た。生成したPt/Au/C触媒を純水300 ml中に分散撹拌した後、吸引濾過した。この操作を3回繰り返して触媒を洗浄した。その後、大気中60 ℃のオーブンで6時間乾燥した。
（ii）Pt/Au/C触媒の分析
得られたPt/Au/C触媒の組成を、蛍光X線装置(SII社製、SEA1200VX)で分析した結果、Pt:Au=50.5:49.5 (at.%)であった。また、(220)のXRDピークにシェラー式を適用して算出したPt/Auの平均粒径は3.4 nmであった。
Au/Cコアの分析結果及びPt/Au/C触媒の分析結果から、平均粒径2.8 nmのAuコアの表面に、平均層厚0.3 nmのPtシェルを有する、白金コアシェル触媒が得られたと考察された。 [Comparative Example 1] Preparation of platinum shell / gold core catalyst (i) Preparation of Pt / Au / C catalyst Au / C core after heat treatment same as that used in Example 1 (support rate 28.4 wt.%, Particle size) 2.8 nm) 200 mg was dispersed in a 300 ml aqueous solution containing 50 mM H 2 SO 4 and 10 mM CuSO 4 . Ar was flowed at a flow rate of 100 ml / min., And the Cu mesh was allowed to coexist in the aqueous solution, and then stirred at 30 ° C. for 10 hours to form a Cu shell on the surface of the Au core particles. Thereafter, the Cu mesh is removed from the aqueous solution, and K 2 PtCl 4 aqueous solution in which dissolved oxygen has been removed in advance by bubbling with Ar is immediately added to a concentration of 2 mM, and the Cu shell layer is replaced with the Pt shell layer to form an Au core / A Pt shell catalyst (Pt / Au / C) was obtained. The produced Pt / Au / C catalyst was dispersed and stirred in 300 ml of pure water, and then suction filtered. This operation was repeated 3 times to wash the catalyst. Thereafter, it was dried in an oven at 60 ° C. for 6 hours in the atmosphere.
(Ii) Analysis of Pt / Au / C catalyst The composition of the obtained Pt / Au / C catalyst was analyzed with a fluorescent X-ray apparatus (SEA1200VX, manufactured by SII). As a result, Pt: Au = 50.5: 49.5 (at. %)Met. The average particle size of Pt / Au calculated by applying the Scherrer equation to the XRD peak of (220) was 3.4 nm.
From the analysis results of the Au / C core and the Pt / Au / C catalyst, it was considered that a platinum core-shell catalyst having a Pt shell with an average layer thickness of 0.3 nm on the surface of an Au core with an average particle diameter of 2.8 nm was obtained. It was done.
（i）Pt/Au/C触媒の作製
実施例１で使用したものと同じ熱処理後のAu/Cコア（担持率28.4 wt.%、粒径2.8 nm）200 mgを、濃度50 mMのH2SO4と濃度10 mMのCuSO4を含む300 mlの水溶液中に分散させた。Arを100 ml/min.の流量で流し、Cuメッシュを水溶液中に共存させた後、30 ℃で10時間撹拌してAuコア粒子表面にCuシェルを形成した。その後、Cuメッシュを水溶液から除去し、予めArバブリングして溶存酸素を除去したK2PtCl4水溶液を2 mMの濃度となるよう直ちに加え、Cuシェル層をPtシェル層に置換させてAuコア/Ptシェル触媒（Pt/Au/C）を得た。生成したPt/Au/C触媒を純水300 ml中に分散撹拌した後、吸引濾過した。この操作を3回繰り返して触媒を洗浄した。その後、大気中60 ℃のオーブンで6時間乾燥した。
（ii）Pt/Au/C触媒の分析
得られたPt/Au/C触媒の組成を、蛍光X線装置(SII社製、SEA1200VX)で分析した結果、Pt:Au=50.5:49.5 (at.%)であった。また、(220)のXRDピークにシェラー式を適用して算出したPt/Auの平均粒径は3.4 nmであった。
Au/Cコアの分析結果及びPt/Au/C触媒の分析結果から、平均粒径2.8 nmのAuコアの表面に、平均層厚0.3 nmのPtシェルを有する、白金コアシェル触媒が得られたと考察された。 [Comparative Example 1] Preparation of platinum shell / gold core catalyst (i) Preparation of Pt / Au / C catalyst Au / C core after heat treatment same as that used in Example 1 (support rate 28.4 wt.%, Particle size) 2.8 nm) 200 mg was dispersed in a 300 ml aqueous solution containing 50 mM H 2 SO 4 and 10 mM CuSO 4 . Ar was flowed at a flow rate of 100 ml / min., And the Cu mesh was allowed to coexist in the aqueous solution, and then stirred at 30 ° C. for 10 hours to form a Cu shell on the surface of the Au core particles. Thereafter, the Cu mesh is removed from the aqueous solution, and K 2 PtCl 4 aqueous solution in which dissolved oxygen has been removed in advance by bubbling with Ar is immediately added to a concentration of 2 mM, and the Cu shell layer is replaced with the Pt shell layer to form an Au core / A Pt shell catalyst (Pt / Au / C) was obtained. The produced Pt / Au / C catalyst was dispersed and stirred in 300 ml of pure water, and then suction filtered. This operation was repeated 3 times to wash the catalyst. Thereafter, it was dried in an oven at 60 ° C. for 6 hours in the atmosphere.
(Ii) Analysis of Pt / Au / C catalyst The composition of the obtained Pt / Au / C catalyst was analyzed with a fluorescent X-ray apparatus (SEA1200VX, manufactured by SII). As a result, Pt: Au = 50.5: 49.5 (at. %)Met. The average particle size of Pt / Au calculated by applying the Scherrer equation to the XRD peak of (220) was 3.4 nm.
From the analysis results of the Au / C core and the Pt / Au / C catalyst, it was considered that a platinum core-shell catalyst having a Pt shell with an average layer thickness of 0.3 nm on the surface of an Au core with an average particle diameter of 2.8 nm was obtained. It was done.
［触媒の評価：触媒組成の分析］
実施例１、２及び比較例１の触媒について、蛍光X線分析装置（SII社製、SEA1200VX）を用いて組成分析を行った結果を表2にまとめた。 [Evaluation of catalyst: analysis of catalyst composition]
Table 2 summarizes the results of composition analysis of the catalysts of Examples 1 and 2 and Comparative Example 1 using a fluorescent X-ray analyzer (SEA1200VX, manufactured by SII).
実施例１、２及び比較例１の触媒について、蛍光X線分析装置（SII社製、SEA1200VX）を用いて組成分析を行った結果を表2にまとめた。 [Evaluation of catalyst: analysis of catalyst composition]
Table 2 summarizes the results of composition analysis of the catalysts of Examples 1 and 2 and Comparative Example 1 using a fluorescent X-ray analyzer (SEA1200VX, manufactured by SII).
表２に示されるとおり、白金（Pt）及び金（Au）に加えて、実施例１の触媒にはイリジウム（Ir）、実施例２の触媒にはルテニウム（Ru）がそれぞれ含有されていることが確認された。
As shown in Table 2, in addition to platinum (Pt) and gold (Au), the catalyst of Example 1 contains iridium (Ir), and the catalyst of Example 2 contains ruthenium (Ru). Was confirmed.
［触媒の評価：耐久性試験］
実施例１、２及び比較例１の其々の触媒を用いた試験電極について、アルゴンガス飽和した、60 ℃の0.1 Mの過塩素酸水溶液中で、ＲＨＥ（可逆水素電極）に対して0.6 V (3 s) - 1.0 V (3 s)の電位幅で矩形波電位サイクル試験を行い、白金コアシェル触媒の耐久性を評価した。 [Evaluation of catalyst: durability test]
The test electrodes using the respective catalysts of Examples 1 and 2 and Comparative Example 1 were 0.6 V relative to RHE (reversible hydrogen electrode) in a 0.1 M perchloric acid aqueous solution saturated with argon gas at 60 ° C. A rectangular wave potential cycle test was conducted at a potential width of (3 s)-1.0 V (3 s) to evaluate the durability of the platinum core-shell catalyst.
実施例１、２及び比較例１の其々の触媒を用いた試験電極について、アルゴンガス飽和した、60 ℃の0.1 Mの過塩素酸水溶液中で、ＲＨＥ（可逆水素電極）に対して0.6 V (3 s) - 1.0 V (3 s)の電位幅で矩形波電位サイクル試験を行い、白金コアシェル触媒の耐久性を評価した。 [Evaluation of catalyst: durability test]
The test electrodes using the respective catalysts of Examples 1 and 2 and Comparative Example 1 were 0.6 V relative to RHE (reversible hydrogen electrode) in a 0.1 M perchloric acid aqueous solution saturated with argon gas at 60 ° C. A rectangular wave potential cycle test was conducted at a potential width of (3 s)-1.0 V (3 s) to evaluate the durability of the platinum core-shell catalyst.
図３に実施例１及び比較例１の、耐久性試験に伴う電気化学的表面積の変化を示す。グラフ中、横軸は電位サイクル回数を示し、縦軸はサイクル試験前の電気化学的表面積を100 ％とした表面積の保持率（％）を示している。
図３のとおり、実施例１は、比較例１とほぼ同等の電気化学的表面積の保持率を示した。
ここで上記表２より、実施例１及び比較例１の触媒における金に対する白金原子の割合はそれぞれ、実施例１では18.6/75.7=0.25、比較例１では50.5/49.5=1.02である。すなわち、実施例１の触媒は、比較例１の触媒と比較して金に対する白金原子の割合が約1/4である。これは、実施例１の触媒では、白金シェル原子数が比較例１に比べて少ないこと(約1/4)を意味する。従来、白金コアシェル触媒では、白金シェルの被覆率（原子数）が低いと、金コアに固溶埋没して表面から失われる白金の比率が相対的に高くなり、耐久性が低下することがわかっている（[図５]を参照）。しかし、本発明の実施例１の触媒は、白金シェル原子数が比較例１のPt/Au/C触媒の1/4程度であっても、比較例１と同等の耐久性を有する。つまり、図３の結果は、10000サイクルの耐久性試験において、実施例１の触媒表面に存在する白金原子の耐久性が、飛躍的に高められていることを示すものである。これは、イリジウムの存在によって白金の固溶埋没が抑制されたことによって、触媒の耐久性が向上したものと考えられる。 FIG. 3 shows changes in the electrochemical surface area of Example 1 and Comparative Example 1 accompanying the durability test. In the graph, the horizontal axis indicates the number of potential cycles, and the vertical axis indicates the surface area retention rate (%) with the electrochemical surface area before the cycle test as 100%.
As shown in FIG. 3, Example 1 showed an electrochemical surface area retention substantially equivalent to that of Comparative Example 1.
Here, from Table 2 above, the ratio of platinum atoms to gold in the catalysts of Example 1 and Comparative Example 1 is 18.6 / 75.7 = 0.25 in Example 1 and 50.5 / 49.5 = 1.02 in Comparative Example 1, respectively. That is, the catalyst of Example 1 has a ratio of platinum atoms to gold of about 1/4 as compared with the catalyst of Comparative Example 1. This means that the catalyst of Example 1 has a smaller number of platinum shell atoms than Comparative Example 1 (about 1/4). Conventionally, with platinum core-shell catalysts, when the platinum shell coverage (number of atoms) is low, the proportion of platinum lost from the surface as a solid solution embedded in the gold core is relatively high, and the durability is reduced. (See [Fig. 5]). However, the catalyst of Example 1 of the present invention has the same durability as that of Comparative Example 1 even if the number of platinum shell atoms is about 1/4 that of the Pt / Au / C catalyst of Comparative Example 1. That is, the result of FIG. 3 shows that the durability of platinum atoms existing on the catalyst surface of Example 1 is dramatically improved in the durability test of 10,000 cycles. This is probably because the solid solution of platinum was suppressed by the presence of iridium, thereby improving the durability of the catalyst.
図３のとおり、実施例１は、比較例１とほぼ同等の電気化学的表面積の保持率を示した。
ここで上記表２より、実施例１及び比較例１の触媒における金に対する白金原子の割合はそれぞれ、実施例１では18.6/75.7=0.25、比較例１では50.5/49.5=1.02である。すなわち、実施例１の触媒は、比較例１の触媒と比較して金に対する白金原子の割合が約1/4である。これは、実施例１の触媒では、白金シェル原子数が比較例１に比べて少ないこと(約1/4)を意味する。従来、白金コアシェル触媒では、白金シェルの被覆率（原子数）が低いと、金コアに固溶埋没して表面から失われる白金の比率が相対的に高くなり、耐久性が低下することがわかっている（[図５]を参照）。しかし、本発明の実施例１の触媒は、白金シェル原子数が比較例１のPt/Au/C触媒の1/4程度であっても、比較例１と同等の耐久性を有する。つまり、図３の結果は、10000サイクルの耐久性試験において、実施例１の触媒表面に存在する白金原子の耐久性が、飛躍的に高められていることを示すものである。これは、イリジウムの存在によって白金の固溶埋没が抑制されたことによって、触媒の耐久性が向上したものと考えられる。 FIG. 3 shows changes in the electrochemical surface area of Example 1 and Comparative Example 1 accompanying the durability test. In the graph, the horizontal axis indicates the number of potential cycles, and the vertical axis indicates the surface area retention rate (%) with the electrochemical surface area before the cycle test as 100%.
As shown in FIG. 3, Example 1 showed an electrochemical surface area retention substantially equivalent to that of Comparative Example 1.
Here, from Table 2 above, the ratio of platinum atoms to gold in the catalysts of Example 1 and Comparative Example 1 is 18.6 / 75.7 = 0.25 in Example 1 and 50.5 / 49.5 = 1.02 in Comparative Example 1, respectively. That is, the catalyst of Example 1 has a ratio of platinum atoms to gold of about 1/4 as compared with the catalyst of Comparative Example 1. This means that the catalyst of Example 1 has a smaller number of platinum shell atoms than Comparative Example 1 (about 1/4). Conventionally, with platinum core-shell catalysts, when the platinum shell coverage (number of atoms) is low, the proportion of platinum lost from the surface as a solid solution embedded in the gold core is relatively high, and the durability is reduced. (See [Fig. 5]). However, the catalyst of Example 1 of the present invention has the same durability as that of Comparative Example 1 even if the number of platinum shell atoms is about 1/4 that of the Pt / Au / C catalyst of Comparative Example 1. That is, the result of FIG. 3 shows that the durability of platinum atoms existing on the catalyst surface of Example 1 is dramatically improved in the durability test of 10,000 cycles. This is probably because the solid solution of platinum was suppressed by the presence of iridium, thereby improving the durability of the catalyst.
図４に実施例２、比較例１、及び参考例である白金微粒子触媒（炭素質担体に担持されたコアシェルでない白金微粒子触媒、粒径2.8 nm、担持率48 wt.%）の、耐久性試験に伴う電気化学的表面積の変化を示す。グラフ中、横軸は電位サイクル回数を示し、縦軸はサイクル試験前の電気化学的表面積を100 %とした表面積の保持率（％）を示している。
図４のとおり、実施例２は、比較例１及び参考例よりも高い電気化学的表面積の保持率を示した。
また上記表２より、実施例２及び比較例１の触媒における金に対する白金原子の割合はそれぞれ、実施例２では32.7/63.2=0.52、比較例１では50.5/49.5=1.02である。すなわち、実施例２の触媒は、比較例１の触媒と比較して、金に対する白金原子の割合が約1/2である。これは、実施例２では白金シェル原子数が比較例１に比べて少ないこと（約1/2）を意味する。上述したように、従来の白金コアシェル触媒では、白金シェルの被覆率（原子数）が少ないほど金コアに固溶埋没する割合が高くなるため、耐久性が低下することが示されている。しかし、本発明の実施例２の触媒は、白金シェル原子数が比較例１のPt/Au/C触媒の1/2程度であるにも関わらず、従来の白金触媒を超える高い耐久性を有する。つまり、図４の結果は、10000サイクルの耐久性試験において、実施例２の触媒表面に存在する白金原子の耐久性が、飛躍的に高められていることを示すものである。これは、ルテニウムの存在によって白金の固溶埋没が抑制され、触媒の耐久性が向上したものと考えられる。 FIG. 4 shows the durability test of Example 2, Comparative Example 1 and the reference platinum fine particle catalyst (platinum fine particle catalyst supported on a carbonaceous carrier, not a core shell, particle size 2.8 nm, loading rate 48 wt.%). The change of the electrochemical surface area accompanying with is shown. In the graph, the horizontal axis indicates the number of potential cycles, and the vertical axis indicates the surface area retention rate (%) with the electrochemical surface area before the cycle test as 100%.
As shown in FIG. 4, Example 2 showed a higher electrochemical surface area retention than Comparative Example 1 and Reference Example.
From Table 2 above, the ratio of platinum atom to gold in the catalysts of Example 2 and Comparative Example 1 is 32.7 / 63.2 = 0.52 in Example 2 and 50.5 / 49.5 = 1.02 in Comparative Example 1, respectively. That is, in the catalyst of Example 2, the ratio of platinum atoms to gold is about ½ compared to the catalyst of Comparative Example 1. This means that in Example 2, the number of platinum shell atoms is smaller than that in Comparative Example 1 (about 1/2). As described above, in the conventional platinum core-shell catalyst, the smaller the platinum shell coverage (number of atoms) is, the higher the ratio of solid solution burying in the gold core is. However, the catalyst of Example 2 of the present invention has high durability exceeding that of the conventional platinum catalyst even though the number of platinum shell atoms is about half that of the Pt / Au / C catalyst of Comparative Example 1. . That is, the results of FIG. 4 show that the durability of platinum atoms existing on the catalyst surface of Example 2 is dramatically improved in the 10,000 cycles durability test. This is probably because the presence of ruthenium suppresses the solid dissolution of platinum and improves the durability of the catalyst.
図４のとおり、実施例２は、比較例１及び参考例よりも高い電気化学的表面積の保持率を示した。
また上記表２より、実施例２及び比較例１の触媒における金に対する白金原子の割合はそれぞれ、実施例２では32.7/63.2=0.52、比較例１では50.5/49.5=1.02である。すなわち、実施例２の触媒は、比較例１の触媒と比較して、金に対する白金原子の割合が約1/2である。これは、実施例２では白金シェル原子数が比較例１に比べて少ないこと（約1/2）を意味する。上述したように、従来の白金コアシェル触媒では、白金シェルの被覆率（原子数）が少ないほど金コアに固溶埋没する割合が高くなるため、耐久性が低下することが示されている。しかし、本発明の実施例２の触媒は、白金シェル原子数が比較例１のPt/Au/C触媒の1/2程度であるにも関わらず、従来の白金触媒を超える高い耐久性を有する。つまり、図４の結果は、10000サイクルの耐久性試験において、実施例２の触媒表面に存在する白金原子の耐久性が、飛躍的に高められていることを示すものである。これは、ルテニウムの存在によって白金の固溶埋没が抑制され、触媒の耐久性が向上したものと考えられる。 FIG. 4 shows the durability test of Example 2, Comparative Example 1 and the reference platinum fine particle catalyst (platinum fine particle catalyst supported on a carbonaceous carrier, not a core shell, particle size 2.8 nm, loading rate 48 wt.%). The change of the electrochemical surface area accompanying with is shown. In the graph, the horizontal axis indicates the number of potential cycles, and the vertical axis indicates the surface area retention rate (%) with the electrochemical surface area before the cycle test as 100%.
As shown in FIG. 4, Example 2 showed a higher electrochemical surface area retention than Comparative Example 1 and Reference Example.
From Table 2 above, the ratio of platinum atom to gold in the catalysts of Example 2 and Comparative Example 1 is 32.7 / 63.2 = 0.52 in Example 2 and 50.5 / 49.5 = 1.02 in Comparative Example 1, respectively. That is, in the catalyst of Example 2, the ratio of platinum atoms to gold is about ½ compared to the catalyst of Comparative Example 1. This means that in Example 2, the number of platinum shell atoms is smaller than that in Comparative Example 1 (about 1/2). As described above, in the conventional platinum core-shell catalyst, the smaller the platinum shell coverage (number of atoms) is, the higher the ratio of solid solution burying in the gold core is. However, the catalyst of Example 2 of the present invention has high durability exceeding that of the conventional platinum catalyst even though the number of platinum shell atoms is about half that of the Pt / Au / C catalyst of Comparative Example 1. . That is, the results of FIG. 4 show that the durability of platinum atoms existing on the catalyst surface of Example 2 is dramatically improved in the 10,000 cycles durability test. This is probably because the presence of ruthenium suppresses the solid dissolution of platinum and improves the durability of the catalyst.
Claims (14)
- 金を含有するコア粒子と、当該コアの表面に形成された、白金と、イリジウム及び／又はルテニウムとを含有するシェルとを有し、粒径が1.6 nm～6.8 nmであることを特徴とする、燃料電池用の白金コアシェル触媒。 It has a core particle containing gold and a shell containing platinum and iridium and / or ruthenium formed on the surface of the core, and has a particle size of 1.6 to 6.8 nm. Platinum core shell catalyst for fuel cells.
- 前記触媒において、コア粒子の粒径が1.0 nm～5.0 nmであり、シェルの厚みが0.3 nm～0.9 nmであることを特徴とする、請求項１に記載の白金コアシェル触媒。 The platinum core-shell catalyst according to claim 1, wherein the catalyst has a core particle size of 1.0 to 5.0 nm and a shell thickness of 0.3 to 0.9 nm.
- 前記シェルにおいて、白金に対するイリジウム及び／又はルテニウムの割合が、0.1～50 at.%であることを特徴とする、請求項１又は２に記載の白金コアシェル触媒。 The platinum core-shell catalyst according to claim 1 or 2, wherein a ratio of iridium and / or ruthenium to platinum in the shell is 0.1 to 50 at.%.
- 前記シェルにおいて、白金に対するイリジウム及び／又はルテニウムの割合が、5～30 at.％であることを特徴とする、請求項３に記載の白金コアシェル触媒。 The platinum core-shell catalyst according to claim 3, wherein a ratio of iridium and / or ruthenium to platinum in the shell is 5 to 30% at.%.
- 前記シェルにおいて、白金と、イリジウム及び／又はルテニウムが同一層内で混在していることを特徴とする、請求項１～４のいずれかに記載の白金コアシェル触媒。 The platinum core-shell catalyst according to any one of claims 1 to 4, wherein platinum and iridium and / or ruthenium are mixed in the same layer in the shell.
- 前記シェルにおいて、イリジウム及び／又はルテニウムが、白金と金コア粒子との間に介在していることを特徴とする、請求項１～４のいずれかに記載の白金コアシェル触媒。 The platinum core-shell catalyst according to any one of claims 1 to 4, wherein iridium and / or ruthenium are interposed between platinum and gold core particles in the shell.
- 前記触媒が、炭素質材料からなる坦体に担持されていることを特徴とする、請求項１～６のいずれかに記載の触媒。 The catalyst according to any one of claims 1 to 6, wherein the catalyst is supported on a carrier made of a carbonaceous material.
- 請求項１～７のいずれか１項に記載の触媒を用いた、白金コアシェル触媒を酸素還元反応の触媒として利用する燃料電池。 A fuel cell using the catalyst according to any one of claims 1 to 7 and utilizing a platinum core-shell catalyst as a catalyst for an oxygen reduction reaction.
- （１）炭素質担体に担持された金コア粒子の表面に銅からなる単分子層を形成させるステップと、
（２）前記ステップ（１）で得られた銅単分子層を、白金と、イリジウム及び／又はルテニウムとに置換するステップと、
を含むことを特徴とする、燃料電池用の白金コアシェル触媒の製造方法。 (1) forming a monomolecular layer made of copper on the surface of a gold core particle supported on a carbonaceous support;
(2) replacing the copper monolayer obtained in step (1) with platinum and iridium and / or ruthenium;
A method for producing a platinum core-shell catalyst for a fuel cell, comprising: - 前記ステップ（１）が、炭素質担体に担持された金コア粒子を、銅からなる固体が浸漬されたCuイオンを含む酸性水溶液に投入して撹拌することを含むステップであり、前記ステップ（２）が、前記水溶液から前記銅からなる固体を除いた後、白金イオンとイリジウム及び／又はルテニウムイオンを与える物質を投入し、前記ステップ（１）で得られた生成物表面の銅を、白金とルテニウム及び／又はイリジウムと置換することを含むステップであることを特徴とする、請求項９に記載の製造方法。 The step (1) is a step including putting the gold core particles supported on the carbonaceous support into an acidic aqueous solution containing Cu ions in which a solid made of copper is immersed, and stirring the gold core particles. ), After removing the solid made of copper from the aqueous solution, a material that gives platinum ions and iridium and / or ruthenium ions is added, and copper on the product surface obtained in the step (1) is replaced with platinum. The method according to claim 9, wherein the method comprises a step including substitution with ruthenium and / or iridium.
- 前記ステップ（２）で置換された白金とルテニウム及び／又はイリジウムにおいて、白金に対するイリジウム及び／又はルテニウムの割合が、0.1～50 at.％であることを特徴とする、請求項９又は１０に記載の製造方法。 The platinum and ruthenium and / or iridium substituted in the step (2) are characterized in that the ratio of iridium and / or ruthenium to platinum is 0.1 to 50 at.%. Manufacturing method.
- 前記ステップ（２）で置換された白金とルテニウム及び／又はイリジウムにおいて、白金に対するイリジウム及び／又はルテニウムの割合が、5～30 at.％であることを特徴とする、請求項９又は１０に記載の製造方法。 The platinum and ruthenium and / or iridium substituted in the step (2) are characterized in that the ratio of iridium and / or ruthenium to platinum is 5 to 30 at.%. Manufacturing method.
- 前記ステップ（２）において、白金イオンを与える化合物とイリジウム及び又はルテニウムイオンを与える化合物を同時に投入し、白金とイリジウム及び／又はルテニウムとが同一層内で混在するシェルを形成することを特徴とする、請求項９～１２のいずれかに記載の白金コアシェル触媒の製造方法。 In the step (2), a compound that gives platinum ions and a compound that gives iridium and / or ruthenium ions are simultaneously added to form a shell in which platinum and iridium and / or ruthenium are mixed in the same layer. The method for producing a platinum core-shell catalyst according to any one of claims 9 to 12.
- 請求項９～１３のいずれかに記載の方法によって製造された白金コアシェル触媒を酸素還元反応の触媒として利用する燃料電池。 A fuel cell using the platinum core-shell catalyst produced by the method according to any one of claims 9 to 13 as a catalyst for an oxygen reduction reaction.
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