JP2013058429A - Electrode catalyst having oxygen-reducing property - Google Patents
Electrode catalyst having oxygen-reducing property Download PDFInfo
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- 239000003054 catalyst Substances 0.000 title claims abstract description 120
- WOCIAKWEIIZHES-UHFFFAOYSA-N ruthenium(iv) oxide Chemical compound O=[Ru]=O WOCIAKWEIIZHES-UHFFFAOYSA-N 0.000 claims abstract description 97
- 229910001925 ruthenium oxide Inorganic materials 0.000 claims abstract description 96
- 239000002135 nanosheet Substances 0.000 claims abstract description 91
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims abstract description 78
- 229910052697 platinum Inorganic materials 0.000 claims abstract description 29
- 239000000446 fuel Substances 0.000 claims abstract description 27
- 239000002131 composite material Substances 0.000 claims abstract description 21
- 239000006229 carbon black Substances 0.000 claims abstract description 8
- 229910052760 oxygen Inorganic materials 0.000 claims description 30
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 29
- 239000001301 oxygen Substances 0.000 claims description 29
- 239000005518 polymer electrolyte Substances 0.000 claims description 20
- 230000003197 catalytic effect Effects 0.000 abstract description 5
- 239000007787 solid Substances 0.000 abstract description 4
- 229920000642 polymer Polymers 0.000 abstract description 2
- 230000000694 effects Effects 0.000 description 17
- 239000001257 hydrogen Substances 0.000 description 15
- 229910052739 hydrogen Inorganic materials 0.000 description 15
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 10
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 9
- 239000010411 electrocatalyst Substances 0.000 description 8
- 239000006185 dispersion Substances 0.000 description 7
- -1 hydrogen ions Chemical class 0.000 description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 7
- 238000006479 redox reaction Methods 0.000 description 6
- 239000003792 electrolyte Substances 0.000 description 5
- 239000006228 supernatant Substances 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 4
- 239000002253 acid Substances 0.000 description 4
- 150000001875 compounds Chemical class 0.000 description 4
- 238000002474 experimental method Methods 0.000 description 4
- 239000010410 layer Substances 0.000 description 4
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- 229910052700 potassium Inorganic materials 0.000 description 4
- 239000011591 potassium Substances 0.000 description 4
- 238000003756 stirring Methods 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 3
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 3
- 238000000089 atomic force micrograph Methods 0.000 description 3
- 239000012153 distilled water Substances 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 239000000843 powder Substances 0.000 description 3
- 238000006722 reduction reaction Methods 0.000 description 3
- 229920006395 saturated elastomer Polymers 0.000 description 3
- 239000007784 solid electrolyte Substances 0.000 description 3
- 238000009210 therapy by ultrasound Methods 0.000 description 3
- 229910021642 ultra pure water Inorganic materials 0.000 description 3
- 239000012498 ultrapure water Substances 0.000 description 3
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 229920000557 Nafion® Polymers 0.000 description 2
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 239000004020 conductor Substances 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
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- 230000000977 initiatory effect Effects 0.000 description 2
- 238000005342 ion exchange Methods 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 230000007935 neutral effect Effects 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 239000008188 pellet Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 229910052707 ruthenium Inorganic materials 0.000 description 2
- 229910052708 sodium Inorganic materials 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 239000000725 suspension Substances 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229920000049 Carbon (fiber) Polymers 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- 229910001260 Pt alloy Inorganic materials 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 238000010306 acid treatment Methods 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 229910052783 alkali metal Inorganic materials 0.000 description 1
- 150000001340 alkali metals Chemical class 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 230000005587 bubbling Effects 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000004917 carbon fiber Substances 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 229920001577 copolymer Polymers 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 238000002848 electrochemical method Methods 0.000 description 1
- 238000003411 electrode reaction Methods 0.000 description 1
- 238000001962 electrophoresis Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 238000009830 intercalation Methods 0.000 description 1
- 230000002687 intercalation Effects 0.000 description 1
- 238000010030 laminating Methods 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 1
- 239000011812 mixed powder Substances 0.000 description 1
- 239000004570 mortar (masonry) Substances 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- CFQCIHVMOFOCGH-UHFFFAOYSA-N platinum ruthenium Chemical compound [Ru].[Pt] CFQCIHVMOFOCGH-UHFFFAOYSA-N 0.000 description 1
- 229920006254 polymer film Polymers 0.000 description 1
- 229920005597 polymer membrane Polymers 0.000 description 1
- BWHMMNNQKKPAPP-UHFFFAOYSA-L potassium carbonate Chemical compound [K+].[K+].[O-]C([O-])=O BWHMMNNQKKPAPP-UHFFFAOYSA-L 0.000 description 1
- 229910001414 potassium ion Inorganic materials 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- 238000000527 sonication Methods 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 238000010408 sweeping Methods 0.000 description 1
- 229920002554 vinyl polymer Polymers 0.000 description 1
- 238000004832 voltammetry Methods 0.000 description 1
Classifications
-
- 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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- Catalysts (AREA)
- Inert Electrodes (AREA)
- Fuel Cell (AREA)
Abstract
Description
本発明は、酸素還元能を有する電極触媒に関し、さらに詳しくは、固体高分子形燃料電池用電極の触媒として好ましく用いられ、触媒活性及び耐久性をより向上させることができる酸素還元能を有する電極触媒に関する。 The present invention relates to an electrode catalyst having an oxygen reducing ability, and more specifically, an electrode having an oxygen reducing ability which can be preferably used as a catalyst for an electrode for a polymer electrolyte fuel cell and can further improve catalytic activity and durability. Relates to the catalyst.
固体高分子形燃料電池（ＰＥＦＣ）は、小型軽量で高出力を発揮できるため、主に燃料電池自動車や家庭用のコージェネレーション電源として注目を集めている。こうした固体高分子形燃料電池は、水素と酸素の化学反応を利用した地球に優しい新エネルギー源として期待されている。その基本構造は、負極（燃料極）、電解質（固体高分子膜）及び正極（空気極）を貼り合わせて一体化した膜／電極接合体（Membrane Electrode Assembly：MEAともいう。）を、反応ガスの供給流路が形成されたバイポーラプレート（bipolar plate。「導電板」ともいう。）で挟んで１つの基本単位（「単セル（single cell）」ともいう。）が構成されている。そして、その単セルを積層して直列接続したセルスタック（fuel cell stack）構造にして高電圧を得ている。 The polymer electrolyte fuel cell (PEFC) is attracting attention as a fuel cell vehicle and a cogeneration power source for home use because it is small and lightweight and can exhibit high output. Such a polymer electrolyte fuel cell is expected as a new energy source friendly to the earth using a chemical reaction between hydrogen and oxygen. The basic structure is a membrane / electrode assembly (also referred to as MEA) in which a negative electrode (fuel electrode), an electrolyte (solid polymer membrane), and a positive electrode (air electrode) are bonded together, and a reactive gas. A basic unit (also referred to as a “single cell”) is formed by being sandwiched between bipolar plates (also referred to as “conductive plates”) in which a supply flow path is formed. And the high voltage is obtained with the cell stack (fuel cell stack) structure which laminated | stacked the single cell and connected in series.
負極では、水素やメタノール等の燃料が供給され、水素イオンと電子に分解し、生成した水素イオンは固体電解質膜内を移動し、電子は導線内を通って正極へと移動する。この負極では、一般にカーボンブラック担体上に白金触媒を担持したものや、カーボンブラック担体上にルテニウム−白金合金触媒を担持したものが用いられている。また、固体高分子膜は、負極で生成した水素イオンを正極に移動するように作用し、ナフィオン（Nafion、デュポン社の登録商標）等が用いられている。そして、水素イオンは水和され、固体電解質膜中の水分が負極から正極に移動することになる。また、正極では、固体電解質膜内を移動した水素イオンと、導線内を移動した電子とが空気中の酸素に反応して水を生成する。 In the negative electrode, a fuel such as hydrogen or methanol is supplied and decomposed into hydrogen ions and electrons. The generated hydrogen ions move in the solid electrolyte membrane, and the electrons move through the conductor to the positive electrode. As this negative electrode, those in which a platinum catalyst is supported on a carbon black support or those in which a ruthenium-platinum alloy catalyst is supported on a carbon black support are generally used. The solid polymer film acts to move hydrogen ions generated at the negative electrode to the positive electrode, and Nafion (registered trademark of DuPont) or the like is used. Then, hydrogen ions are hydrated, and moisture in the solid electrolyte membrane moves from the negative electrode to the positive electrode. In the positive electrode, hydrogen ions that have moved in the solid electrolyte membrane and electrons that have moved in the conductive wire react with oxygen in the air to generate water.
こうした構成の固体高分子形燃料電池では、理論上は高い電圧が得られるが、電極反応の損失等で実際の電圧が低くなってしまうという問題がある。また、燃料効率、触媒の耐性を含む電極寿命、触媒として使用する白金コストと入手性等の問題がある。 In the polymer electrolyte fuel cell having such a configuration, a high voltage can be theoretically obtained, but there is a problem that an actual voltage becomes low due to loss of electrode reaction or the like. In addition, there are problems such as fuel efficiency, electrode life including catalyst resistance, platinum cost and availability as a catalyst.
こうした中、本発明者は、固体高分子形燃料電池用電極の触媒（以下「電極触媒」ともいう。）として、カーボンブラック担体上に白金触媒を担持した電極触媒に、酸化ルテニウムナノシート（「ルテニウム酸ナノシート」ともいう。）を添加した複合電極触媒を用い、電極を作製した（特許文献１）。また、本発明者は、その酸化ルテニウムナノシート及びその製造方法についても検討している（特許文献２）。 Under these circumstances, the present inventors have used a ruthenium oxide nanosheet (“ruthenium”) as an electrode catalyst (hereinafter also referred to as “electrode catalyst”) for a polymer electrolyte fuel cell electrode, in which a platinum catalyst is supported on a carbon black carrier. An electrode was produced using a composite electrode catalyst to which "acid nanosheet" was added (Patent Document 1). Moreover, this inventor is also examining the ruthenium oxide nanosheet and its manufacturing method (patent document 2).
上記した固体高分子形燃料電池では、電極触媒に高価な白金を用いることによるコスト削減に対する障害や、電極触媒自体の耐性が十分ではないという問題がある。しかし、電極触媒を構成する白金の実質的な使用量を低減できない場合であっても、できるだけ触媒活性を向上させたり、耐性を向上させたりすることができれば、相対的に白金の使用量を低減させることができることになる。 The polymer electrolyte fuel cell described above has a problem of cost reduction due to the use of expensive platinum as an electrode catalyst and a problem that the resistance of the electrode catalyst itself is not sufficient. However, even if the substantial amount of platinum that constitutes the electrode catalyst cannot be reduced, if the catalytic activity can be improved or the resistance can be improved as much as possible, the amount of platinum used can be relatively reduced. Will be able to.
本発明は、上記課題を解決するためになされたものであって、その目的は、固体高分子形燃料電池用電極の触媒として好ましく用いられ、触媒活性及び耐久性をより向上させることができる酸素還元能を有する電極触媒を提供することにある。 The present invention has been made in order to solve the above-mentioned problems, and the object thereof is oxygen which can be preferably used as a catalyst for a polymer electrolyte fuel cell electrode and can further improve catalytic activity and durability. The object is to provide an electrocatalyst having a reducing ability.
本発明者は、固体高分子形燃料電池用電極に用いる電極触媒について検討している過程で、触媒活性及び耐久性をより向上させることができる電極触媒の寸法依存性を見出した。そして、そうした電極触媒は固体高分子形燃料電池用の電極触媒として効果があるとともに、酸素還元能を有する電極触媒として広く応用可能であることを見出し、本発明を完成させた。 In the course of studying an electrode catalyst used for an electrode for a polymer electrolyte fuel cell, the present inventor has found the dimensional dependence of an electrode catalyst that can further improve the catalytic activity and durability. The inventors have found that such an electrode catalyst is effective as an electrode catalyst for a polymer electrolyte fuel cell and can be widely applied as an electrode catalyst having an oxygen reducing ability, thereby completing the present invention.
上記課題を解決するための本発明の第１の観点に係る酸素還元能を有する電極触媒は、白金系電極触媒とともに用いられる酸化ルテニウムナノシートかならなる電極触媒であって、前記酸化ルテニウムナノシートが、鱗片形状からなり、最大長さと該最大長さの中点で直交する長さとの平均を該酸化ルテニウムナノシートの寸法としたとき、該寸法が５０ｎｍ以上３５０ｎｍ以下のものが全体の６５％以上であり、且つモード径が１００ｎｍ以上２５０ｎｍ以下であることを特徴とする。 The electrode catalyst having oxygen reducing ability according to the first aspect of the present invention for solving the above problems is an electrode catalyst made of a ruthenium oxide nanosheet used together with a platinum-based electrode catalyst, and the ruthenium oxide nanosheet comprises: When the average of the maximum length and the length orthogonal to the midpoint of the maximum length is the dimension of the ruthenium oxide nanosheet, the dimension is 50 nm or more and 350 nm or less, and the dimension is 65% or more of the whole. The mode diameter is 100 nm or more and 250 nm or less.
この発明によれば、上記寸法の酸化ルテニウムナノシートからなる電極触媒を白金系触媒の電極触媒とともに用いて複合電極触媒とすれば、その複合電極触媒からなる電極触媒、好ましくは固体高分子形燃料電池用電極触媒の耐性をより向上させることができる。その結果、この酸化ルテニウムナノシートを用いれば、相対的に白金の使用量を低減させることができる。 According to the present invention, when an electrode catalyst comprising a ruthenium oxide nanosheet having the above dimensions is used together with an electrode catalyst of a platinum-based catalyst to form a composite electrode catalyst, an electrode catalyst comprising the composite electrode catalyst, preferably a polymer electrolyte fuel cell The resistance of the electrode catalyst can be further improved. As a result, if this ruthenium oxide nanosheet is used, the amount of platinum used can be relatively reduced.
上記課題を解決するための本発明の第２の観点に係る酸素還元能を有する電極触媒は、白金系電極触媒と、酸化ルテニウムナノシート触媒とを有する複合電極触媒であって、前記酸化ルテニウムナノシートが、鱗片形状からなり、最大長さと該最大長さの中点で直交する長さとの平均を該酸化ルテニウムナノシートの寸法としたとき、該寸法が５０ｎｍ以上３５０ｎｍ以下のものが全体の６５％以上であり、且つモード径が１００ｎｍ以上２５０ｎｍ以下であることを特徴とする。 The electrode catalyst having oxygen reducing ability according to the second aspect of the present invention for solving the above-mentioned problem is a composite electrode catalyst having a platinum-based electrode catalyst and a ruthenium oxide nanosheet catalyst, wherein the ruthenium oxide nanosheet is , When the average of the maximum length and the length orthogonal to the midpoint of the maximum length is the dimension of the ruthenium oxide nanosheet, the dimension is 50 nm or more and 350 nm or less when the average is 65% or more And the mode diameter is 100 nm or more and 250 nm or less.
この発明によれば、白金系電極触媒と上記寸法の酸化ルテニウムナノシートとを有する複合電極触媒であるので、酸素還元能を有する電極触媒、好ましくは固体高分子形燃料電池用の電極触媒の耐性をより向上させることができる。 According to this invention, since it is a composite electrode catalyst having a platinum-based electrode catalyst and a ruthenium oxide nanosheet having the above dimensions, the resistance of an electrode catalyst having oxygen reducing ability, preferably an electrode catalyst for a polymer electrolyte fuel cell is improved. It can be improved further.
本発明に係る酸素還元能を有する電極触媒において、前記白金系触媒が、カーボンブラック担体上に白金触媒を担持した電極触媒であることが好ましい。 In the electrode catalyst having oxygen reducing ability according to the present invention, the platinum catalyst is preferably an electrode catalyst having a platinum catalyst supported on a carbon black carrier.
本発明に係る酸素還元能を有する電極触媒は、固体高分子形燃料電池用の負極に用いられることが好ましい。 The electrode catalyst having oxygen reducing ability according to the present invention is preferably used for a negative electrode for a polymer electrolyte fuel cell.
本発明に係る酸素還元能を有する電極触媒によれば、その酸化ルテニウムナノシートを白金系電極触媒とともに用いることにより、酸素還元能を有する電極触媒、好ましくは固体高分子形燃料電池用電極触媒の耐性をより向上させることができる。その結果、この酸化ルテニウムナノシートを用いれば、相対的に白金の使用量を低減させることができる。 According to the electrode catalyst having oxygen reducing ability according to the present invention, by using the ruthenium oxide nanosheet together with the platinum-based electrode catalyst, the resistance of the electrode catalyst having oxygen reducing ability, preferably the electrode catalyst for polymer electrolyte fuel cell Can be further improved. As a result, if this ruthenium oxide nanosheet is used, the amount of platinum used can be relatively reduced.
以下、本発明に係る酸素還元能を有する電極触媒について詳しく説明するが、本発明は、その技術的範囲に含まれる範囲において下記の説明に限定されない。 Hereinafter, although the electrode catalyst which has the oxygen reduction ability which concerns on this invention is demonstrated in detail, this invention is not limited to the following description in the range included in the technical scope.
本発明に係る酸素還元能を有する電極触媒は、固体高分子形燃料電池用の電極触媒として好ましく用いられるものであって、（１）酸化ルテニウムナノシートからなる電極触媒、及び、（２）酸化ルテニウムナノシートからなる電極触媒と白金系電極触媒とからなる複合電極触媒、を包含するものである。前者の酸化ルテニウムナノシートからなる電極触媒は、白金系電極触媒の添加触媒として作用する。 The electrode catalyst having oxygen reducing ability according to the present invention is preferably used as an electrode catalyst for a polymer electrolyte fuel cell, and includes (1) an electrode catalyst composed of a ruthenium oxide nanosheet, and (2) ruthenium oxide. It includes a composite electrode catalyst comprising a nanosheet electrode catalyst and a platinum-based electrode catalyst. The former electrode catalyst comprising a ruthenium oxide nanosheet acts as an addition catalyst for a platinum-based electrode catalyst.
酸化ルテニウムナノシートは、厚さが理論的には約０．２５ｎｍ〜０．４０ｎｍであり、測定ではｎｍオーダー〜サブｎｍオーダーの鱗片形状の化合物であり、縦と横がそれぞれ数百ｎｍ〜μｍオーダーのサイズのシート状の結晶性ルテニウム酸化合物である。この酸化ルテニウムナノシートは、電気泳動法等で容易に積層させることができる。本発明では、酸素還元能を有する電極触媒、具体的には固体高分子形燃料電池の負極触媒として利用しているが、正極触媒としても利用でき、さらには擬似二重層キャパシタとしても利用できる。 The ruthenium oxide nanosheet is theoretically about 0.25 nm to 0.40 nm in thickness, and is a scaly compound in the order of nm to sub-nm in the measurement. The length and width are on the order of several hundred nm to μm, respectively. It is a sheet-like crystalline ruthenic acid compound of the size. This ruthenium oxide nanosheet can be easily laminated by electrophoresis or the like. In the present invention, it is used as an electrode catalyst having oxygen reducing ability, specifically, a negative electrode catalyst of a polymer electrolyte fuel cell, but it can also be used as a positive electrode catalyst, and further as a pseudo double layer capacitor.
酸化ルテニウムナノシートは、後述の実施例で説明するように、酸化ルテニウムナノシートが積層して形成された層状ルテニウム酸化合物、例えば層状酸化ルテニウム（水素型：Ｈ0.2ＲｕＯ2.1）の層間にアルキルアンモニウムイオンを含むアルキルアンモニウム−層状ルテニウム酸層間化合物を提供することにより、剥離して得ることができる。 The ruthenium oxide nanosheet has a layered ruthenium acid compound formed by laminating ruthenium oxide nanosheets, for example, an alkylammonium ion between layers of layered ruthenium oxide (hydrogen type: H 0.2 RuO 2.1 ), as will be described in Examples below. By providing the containing alkylammonium-layered ruthenic acid intercalation compound, it can be obtained by peeling.
この酸化ルテニウムナノシートは、最大長さと該最大長さの中点で直交する長さとの平均を該酸化ルテニウムナノシートの寸法としたとき、その寸法が５０ｎｍ以上３５０ｎｍ以下のものが全体の６５％以上であり、且つモード径が１００ｎｍ以上２５０ｎｍ以下であることに特徴がある（以下、この寸法範囲を「寸法Ｃ」ともいう。）。なお、「モード径」とは、出現比率がもっとも大きい粒子径チャンネル、すなわち粒子分布の極大値のことである。 In this ruthenium oxide nanosheet, when the average of the maximum length and the length perpendicular to the midpoint of the maximum length is taken as the dimension of the ruthenium oxide nanosheet, the dimension is 50 nm or more and 350 nm or less with 65% or more of the total. And the mode diameter is 100 nm or more and 250 nm or less (hereinafter, this dimension range is also referred to as “dimension C”). The “mode diameter” is the particle diameter channel with the highest appearance ratio, that is, the maximum value of the particle distribution.
上記範囲内の寸法を持つ酸化ルテニウムナノシートを電極触媒とし、白金系触媒の電極触媒とともに用いて複合電極触媒とすれば、その複合電極触媒からなる酸素還元能を有する電極触媒、具体的には固体高分子形燃料電池用電極触媒の耐性をより向上させることができる。その結果、この酸化ルテニウムナノシートを用いれば、相対的に白金の使用量を低減させることができる。 If a ruthenium oxide nanosheet having a size within the above range is used as an electrode catalyst and is used in combination with an electrode catalyst of a platinum-based catalyst, a composite electrode catalyst, an electrode catalyst having an oxygen reducing ability comprising the composite electrode catalyst, specifically a solid The resistance of the electrode catalyst for polymer fuel cells can be further improved. As a result, if this ruthenium oxide nanosheet is used, the amount of platinum used can be relatively reduced.
一方、酸化ルテニウムナノシートの寸法が上記範囲外の場合には、その範囲内のものと比較して、酸素還元能を有する電極触媒、具体的には固体高分子形燃料電池用の電極触媒の耐性が低下する。具体的には、後述の実験例で詳しく説明するが、寸法が１００ｎｍ以上４５０ｎｍ以下の酸化ルテニウムナノシートが全体の６５％以上であり且つモード径が１５０ｎｍ以上３５０ｎｍ以下である場合（以下、この寸法範囲を「寸法Ｂ」ともいう。）や、寸法が１５０ｎｍ以５５０ｎｍ以下の酸化ルテニウムナノシートが全体の７０％以上であり且つモード径が２００ｎｍ以上４５０ｎｍ以下である場合（以下、この寸法範囲を「寸法Ａ」ともいう。）は、上記本発明の範囲のものと比べて、固体高分子形燃料電池用の電極触媒の耐性が低下する。 On the other hand, when the dimension of the ruthenium oxide nanosheet is out of the above range, the resistance of the electrode catalyst having an oxygen reducing ability, specifically, the electrode catalyst for the polymer electrolyte fuel cell is compared with that in the range. Decreases. Specifically, as will be described in detail in an experimental example described later, when the ruthenium oxide nanosheet having a dimension of 100 nm to 450 nm is 65% or more of the whole and the mode diameter is 150 nm to 350 nm (hereinafter, this dimension range). Or a ruthenium oxide nanosheet having a dimension of 150 nm or more and 550 nm or less and a mode diameter of 200 nm or more and 450 nm or less (hereinafter, this dimension range is referred to as “dimension A”). ”), The resistance of the electrode catalyst for a polymer electrolyte fuel cell is reduced as compared with the above-mentioned range of the present invention.
こうした寸法の酸化ルテニウムナノシートは、酸素還元能を有する電極触媒であれば例えば固体高分子形燃料電池用の電極触媒等に利用できるが、通常は、白金系電極触媒、具体的にはカーボンブラック担体上に白金触媒を担持した電極触媒への添加触媒として好ましく用いられる。 The ruthenium oxide nanosheet having such dimensions can be used as an electrode catalyst for a polymer electrolyte fuel cell, for example, as long as it is an electrode catalyst having an oxygen reducing ability, but is usually a platinum-based electrode catalyst, specifically a carbon black carrier. It is preferably used as an addition catalyst to an electrode catalyst carrying a platinum catalyst thereon.
以下、実験例により本発明を具体的に説明する。 Hereinafter, the present invention will be described in detail by experimental examples.
［酸化ルテニウムナノシートの作製］
最初に、酸化ルテニウムナノシートを得るための層状酸化ルテニウムを作製した。層状酸化ルテニウムは、酸化ルテニウムとアルカリ金属（ナトリウム、カリウム等）との複合酸化物であり、中でもＫ0.2ＲｕＯ2.1・ｎＨ2Ｏ、及びＮａ0.2ＲｕＯ2・ｎＨ2Ｏは、イオン交換能を利用することで層一枚単位にまで層剥離することが可能であるので、これにより酸化ルテニウムナノシートを得ることができる。
[Production of ruthenium oxide nanosheets]
First, layered ruthenium oxide for obtaining a ruthenium oxide nanosheet was prepared. Layered ruthenium oxide is a complex oxide of ruthenium oxide and alkali metals (sodium, potassium, etc.). Among them, K 0.2 RuO 2.1 · nH 2 O and Na 0.2 RuO 2 · nH 2 O utilize ion exchange capacity. By doing so, it is possible to delaminate the layer as a unit, so that a ruthenium oxide nanosheet can be obtained.
具体的には、先ず、酸化ルテニウム（ＲｕＯ2）と炭酸カリウム（Ｋ2ＣＯ3）とをモル比８：５の割合となるように量り取り、メノウ乳鉢を用いてアセトン中で１時間湿式混合した。その後、錠剤成形器を用いて混合粉末をペレット化した。このペレットをアルミナボートにのせ、管状炉にてアルゴン流通下で８５０℃、１２時間焼成した。焼成後、ペレットを粉砕し、イオン交換蒸留水で洗浄し、上澄み液を取り除いた。この操作を上澄み液が中性になるまで繰り返したものを層状酸化ルテニウム（カリウム型）とした。 Specifically, first, ruthenium oxide (RuO 2 ) and potassium carbonate (K 2 CO 3 ) are weighed so as to have a molar ratio of 8: 5, and wet-mixed in acetone for 1 hour using an agate mortar. did. Thereafter, the mixed powder was pelletized using a tablet molding machine. The pellet was placed on an alumina boat and fired at 850 ° C. for 12 hours in a tubular furnace under an argon flow. After firing, the pellets were pulverized, washed with ion exchange distilled water, and the supernatant was removed. A layered ruthenium oxide (potassium type) was obtained by repeating this operation until the supernatant became neutral.
次に、層状酸化ルテニウム（カリウム型）に１ＭのＨＣｌを加え、６０℃のウォーターバス内で７２時間酸処理をして、層状酸化ルテニウム（カリウム型）に含まれるＫ＋イオンを水素イオン（プロトン）に置換した。その後、イオン交換蒸留水で洗浄し上澄み液を取り除いた。この操作を上澄み液が中性になるまで繰り返し、ろ過後に、層状酸化ルテニウム（水素型：Ｈ0.2ＲｕＯ2.1）の粉末を得た。 Next, 1M HCl is added to layered ruthenium oxide (potassium type), and acid treatment is performed in a water bath at 60 ° C. for 72 hours, so that K + ions contained in layered ruthenium oxide (potassium type) are converted into hydrogen ions (protons). ). Thereafter, the supernatant was removed by washing with ion-exchanged distilled water. This operation was repeated until the supernatant became neutral. After filtration, layered ruthenium oxide (hydrogen type: H 0.2 RuO 2.1 ) powder was obtained.
得られた層状酸化ルテニウム(水素型：Ｈ0.2ＲｕＯ2.1）に、酸化ルテニウムナノシートを得る剥離剤としての１０％ＴＢＡＯＨ水溶液を加えた。層状酸化ルテニウム(水素型：Ｈ0.2ＲｕＯ2.1）の濃度を、ＴＢＡＯＨとプロトンとの割合で、ＴＢＡ＋／Ｈ＋＝１．５、５、１０に変えてそれぞれ用いた。それぞれについて、層状酸化ルテニウム(水素型：Ｈ0.2ＲｕＯ2.1）を蒸留水に加え、大きいサイズ（寸法Ａ）のナノシートを得るために５日間振とうさせ、普通サイズ（寸法Ｂ）のナノシートを得るために１０日間振とうさせ、小さいサイズ（寸法Ｃ）のナノシートを得るために１０日間振とうさせた後さらに３時間超音波処理を行った。この方法で単層剥離させた酸化ルテニウムナノシートを２０００ｒｐｍで３０分間遠心分離した後、上澄み液を回収して、超純水にて濃度を０．０２ｇ／Ｌまで希釈した酸化ルテニウムナノシート水分散液を得た。 To the obtained layered ruthenium oxide (hydrogen type: H 0.2 RuO 2.1 ), 10% TBAOH aqueous solution as a release agent for obtaining a ruthenium oxide nanosheet was added. The concentration of layered ruthenium oxide (hydrogen type: H 0.2 RuO 2.1 ) was changed to TBA + / H + = 1.5, 5 and 10 in the ratio of TBAOH and proton, respectively. For each, layered ruthenium oxide (hydrogen type: H 0.2 RuO 2.1 ) is added to distilled water and shaken for 5 days to obtain a large size (dimension A) nanosheet, to obtain a normal size (dimension B) nanosheet And then sonicated for 3 hours after shaking for 10 days in order to obtain a small size (dimension C) nanosheet. The ruthenium oxide nanosheet peeled off by this method was centrifuged at 2000 rpm for 30 minutes, and then the supernatant liquid was recovered, and an aqueous dispersion of ruthenium oxide nanosheet diluted with ultrapure water to a concentration of 0.02 g / L was obtained. Obtained.
［作製された酸化ルテニウムナノシートの寸法］
図１は、この方法で単層剥離させた酸化ルテニウムナノシートのＡＦＭ像である。このＡＦＭ像は、先ず、シリコンウエハを１質量％ポリビニルアルコール−ポリジアリルアミン共重合ポリマー水溶液中に１０分間浸漬した後、水で数回洗浄し、乾燥した。次に、０．０８ｍｇ／ｍＬのナノシート水分散液に２分浸漬後、水で数回洗浄し、乾燥した。この過程をそれぞれの酸化ルテニウムナノシートについて同じように行った。酸化ルテニウムナノシートの寸法Ａ〜Ｃは、このＡＦＭ層の観察画像から測定した。具体的には、鱗片形状の酸化ルテニウムナノシートについて、最大長さとその最大長さの中点で直交する長さとを測定し、それらの平均を出して「寸法」とした。これを７０〜８０箇所繰り返した。
[Dimensions of the produced ruthenium oxide nanosheet]
FIG. 1 is an AFM image of a ruthenium oxide nanosheet peeled by a single layer by this method. In this AFM image, first, a silicon wafer was immersed in a 1% by mass polyvinyl alcohol-polydiallylamine copolymer aqueous solution for 10 minutes, then washed several times with water and dried. Next, it was immersed in a 0.08 mg / mL nanosheet aqueous dispersion for 2 minutes, washed several times with water, and dried. This process was performed in the same manner for each ruthenium oxide nanosheet. The dimensions A to C of the ruthenium oxide nanosheet were measured from the observed image of this AFM layer. Specifically, for the scale-shaped ruthenium oxide nanosheet, the maximum length and the length orthogonal at the midpoint of the maximum length were measured, and the average of them was taken as the “dimension”. This was repeated at 70 to 80 locations.
その結果、大きいサイズ（寸法Ａ）のナノシートを得るために５日間振とうさせた場合の酸化ルテニウムナノシートの寸法は、１５０ｎｍ以５５０ｎｍ以下の酸化ルテニウムナノシートが全体の７０％以上であり且つモード径が２００ｎｍ以上４５０ｎｍ以下であった。また、普通サイズ（寸法Ｂ）のナノシートを得るために１０日間振とうさせた場合の酸化ルテニウムナノシートの寸法は、１００ｎｍ以上４５０ｎｍ以下の酸化ルテニウムナノシートが全体の６５％以上であり且つモード径が１５０ｎｍ以上３５０ｎｍ以下であった。また、小さいサイズ（寸法Ｃ）のナノシートを得るために１０日間振とうさせた後さらに３時間超音波処理を行った場合の酸化ルテニウムナノシートの寸法は、５０ｎｍ以上３５０ｎｍ以下のものが全体の６５％以上であり、且つモード径が１００ｎｍ以上２５０ｎｍ以下であった。 As a result, the size of the ruthenium oxide nanosheet when shaken for 5 days to obtain a nanosheet having a large size (dimension A) is 70% or more of the total ruthenium oxide nanosheet of 150 nm to 550 nm and the mode diameter is It was 200 nm or more and 450 nm or less. The size of the ruthenium oxide nanosheet when shaken for 10 days to obtain a nanosheet of normal size (dimension B) is 100% or more and 450 nm or less of the ruthenium oxide nanosheet is 65% or more of the whole and the mode diameter is 150 nm. It was 350 nm or less. Further, in order to obtain a nanosheet having a small size (dimension C), the size of the ruthenium oxide nanosheet when the ultrasonic treatment is further performed for 3 hours after shaking for 10 days is 65% to 50% of the whole. The mode diameter was 100 nm or more and 250 nm or less.
こうした寸法の酸化ルテニウムナノシートが分散した３種の酸化ルテニウムナノシート水分散液として、下記の実験に用いた。 Three types of ruthenium oxide nanosheet aqueous dispersions in which ruthenium oxide nanosheets having such dimensions were dispersed were used in the following experiments.
［実験１／複合電極触媒の調製］
酸化ルテニウムナノシートをＰｔ／Ｃ（カーボンブラック担体上に白金触媒を担持した電極触媒）と組み合わせるために、先ず、約１０ｍｇ／ｍＬのＰｔ／Ｃを超純水中に加え、攪拌及び超音波処理を行って分散させた。この溶液に、適量の酸化ルテニウム水分散液を、攪拌しながらゆっくり滴下した。酸化ルテニウムナノシート水分散液の濃度は任意に調整できるが、ここでは１０ｍｇ／ｍＬとした。こうした濃度の酸化ルテニウムナノシート水分散液を滴下して、複合電極触媒のモル比が、酸化ルテニウム：Ｐｔ＝０．３：１となるように調整した。
[Experiment 1 / Preparation of composite electrode catalyst]
In order to combine ruthenium oxide nanosheets with Pt / C (electrode catalyst having a platinum catalyst supported on a carbon black support), first, about 10 mg / mL Pt / C is added to ultrapure water, and stirring and sonication are performed. Went and dispersed. An appropriate amount of an aqueous ruthenium oxide dispersion was slowly added dropwise to this solution while stirring. The concentration of the aqueous dispersion of ruthenium oxide nanosheets can be adjusted arbitrarily, but here it was 10 mg / mL. The aqueous dispersion of ruthenium oxide nanosheets having such a concentration was dropped, and the molar ratio of the composite electrode catalyst was adjusted to be ruthenium oxide: Pt = 0.3: 1.
さらに、均一な反応を確保するために、撹拌、超音波処理及び超純水洗浄を行い、過剰なＴＢＡＯＨを除去した後、懸濁液を１２０℃で一晩乾燥させて電極触媒紛体を得た。酸化ルテニウムナノシートとＰｔ／Ｃとの均一化は、懸濁液を攪拌した後、数時間静置して沈殿させ、液の色が黒から透明になることによって判断した。この段階では、酸化ルテニウムナノシートもＰｔ／Ｃも安定していることを確認した。得られた複合電極触媒は、窒素雰囲気下で保存した。 Furthermore, in order to ensure a uniform reaction, stirring, ultrasonic treatment and ultrapure water washing were performed to remove excess TBAOH, and then the suspension was dried overnight at 120 ° C. to obtain an electrode catalyst powder. . The homogenization of the ruthenium oxide nanosheet and Pt / C was judged by stirring the suspension and then allowing it to stand for several hours to precipitate, so that the color of the liquid changed from black to transparent. At this stage, it was confirmed that both the ruthenium oxide nanosheet and Pt / C were stable. The obtained composite electrode catalyst was stored under a nitrogen atmosphere.
このように、ＴＢＡ＋／Ｈ＋比が１．５、５、１０の３種で、ＴＢＡ＋／Ｈ＋＝１．５の場合はナノシートサイズ大（寸法Ａ）、普通（寸法Ｂ）及び小（寸法Ｃ）の３つ、ＴＢＡ＋／Ｈ＋＝５の場合もナノシートサイズ大（寸法Ａ）、普通（寸法Ｂ）及び小（Ｃ）の３つ、ＴＢＡ＋／Ｈ＋＝１０の場合はナノシートサイズ普通（Ｂ）及び小（寸法Ｃ）の２つの、合計８つの異なる酸化ルテニウムナノシート水分散液を用いて、Ｐｔ／Ｃ触媒と混合させて複合電極触媒を得た。 Thus, when the TBA + / H + ratio is 1.5, 5, 10, and 10 and TBA + / H + = 1.5, the nanosheet size is large (dimension A), normal (dimension B), and small In the case of three (dimension C), TBA + / H + = 5, when nanosheet size is large (dimension A), normal (dimension B) and small (C), and TBA + / H + = 10 A total of 8 different ruthenium oxide nanosheet aqueous dispersions of nanosheet size normal (B) and small (dimension C) were mixed with Pt / C catalyst to obtain a composite electrode catalyst.
［実験２／触媒インク及び電極の準備］
イソプロピルアルコール／超純水溶液（７５／２５体積割合）２５ｍＬに、１８．５ｍｇの複合電極触媒を混合して、触媒インクを準備した。電極に対して良好な密着性を確保するために、プロトン伝導性バインダーとして、５質量％のナフィオン（Nafion、デュポン社の登録商標）溶液１００μＬを加えた。この触媒インクを３０分間超音波処理して分散させた。
[Experiment 2: Preparation of catalyst ink and electrode]
18.5 mg of a composite electrode catalyst was mixed with 25 mL of isopropyl alcohol / ultra pure aqueous solution (75/25 volume ratio) to prepare a catalyst ink. In order to ensure good adhesion to the electrode, 100 μL of a 5% by mass Nafion (registered trademark of DuPont) solution as a proton conductive binder was added. This catalyst ink was dispersed by ultrasonic treatment for 30 minutes.
予め０．０５μｍのアルミナ粉末を用いてバフ研磨した直径６ｍｍのグラッシーカーボンを、真空中で６０℃で乾燥させた。こうしたグラッシーカーボンに触媒インクを塗布して固体高分子形燃料電池用の電極を作製した。なお、触媒インクの塗布は、電極上に設けられた複合電極触媒に含まれる酸化ルテニウムナノシートの含有量に関わらず、白金含有量が１７．３μｇとなるように塗布した。 Glassy carbon having a diameter of 6 mm, which was previously buffed with 0.05 μm alumina powder, was dried at 60 ° C. in a vacuum. A catalyst ink was applied to such glassy carbon to produce an electrode for a polymer electrolyte fuel cell. The catalyst ink was applied so that the platinum content was 17.3 μg regardless of the content of the ruthenium oxide nanosheet contained in the composite electrode catalyst provided on the electrode.
［実験３／電気化学的測定］
回転ディスク電極（ＲＤＥ）測定は、標準的な３電極電気化学セルで行った。カウンター電極として、炭素繊維（ＴｏｈｏＴｅｎａｘ社製、ＨＴＡ−３Ｋ、フィラメント番号：３０００）を用い、参照電極として可逆水素電極（ＲＨＥ）を用いた。ＲＤＥ測定は、０．５Ｍの硫酸電解液中で行った。電極表面は、予め掃引速度５０ｍＶ／秒、０．０５Ｖ〜１．２Ｖ（ｖｓＲＨＥ）、窒素バブリング下、２５℃で、３０サイクルした後に試料に供した。この前処理を行った後、脱気した０．５Ｍ硫酸電解液での直線走査ボルタンメトリーを、１０ｍＶ／秒、１．２Ｖ〜０．０５Ｖ（ｖｓＲＨＥ、負方向掃）で、回転速度（ω）３１００、２２００、１６００、１２００、８００及び４００ｒｐｍで行い、耐性テスト前のＬＳＶ曲線を得た。
[Experiment 3 / Electrochemical measurement]
The rotating disk electrode (RDE) measurement was performed on a standard three-electrode electrochemical cell. Carbon fiber (manufactured by Toho Tenax, HTA-3K, filament number: 3000) was used as the counter electrode, and a reversible hydrogen electrode (RHE) was used as the reference electrode. RDE measurement was performed in a 0.5 M sulfuric acid electrolyte. The surface of the electrode was subjected to 30 cycles in advance at a sweep rate of 50 mV / sec, 0.05 V to 1.2 V (vs RHE), and nitrogen bubbling at 25 ° C. After this pretreatment, linear scanning voltammetry with degassed 0.5 M sulfuric acid electrolyte was performed at 10 mV / sec, 1.2 V to 0.05 V (vs RHE, negative sweep), and rotational speed (ω) 3100. 2200, 1600, 1200, 800 and 400 rpm were performed, and LSV curves before the resistance test were obtained.
その後、５０ｍＶ／秒、０．０５Ｖ〜０．９Ｖ（ｖｓＲＨＥ）間で３サイクル繰り返し掃引した。３回目のサイクルは、電気化学活性比表面積（ＥＣＳＡ）評価のために使用した。ＥＣＳＡは、水素吸着波の吸着電気量から算出した。酸化還元反応（ＯＲＲ）は、酸素飽和０．５Ｍ硫酸での１０ｍＶ／秒、１．２Ｖ〜０．０５Ｖ（ｖｓＲＨＥ）、各回転速度でのＬＳＶ（２サイクル）で特定した。脱気電解液で得られたＬＳＶデータを、酸素飽和０．５Ｍ硫酸で得られたデータから差し引いた。 Thereafter, sweeping was repeated for 3 cycles between 50 mV / sec and 0.05 V to 0.9 V (vs RHE). The third cycle was used for electrochemically active specific surface area (ECSA) evaluation. ECSA was calculated from the amount of electricity absorbed by the hydrogen adsorption wave. The oxidation-reduction reaction (ORR) was specified by 10 mV / sec in oxygen-saturated 0.5 M sulfuric acid, 1.2 V to 0.05 V (vs RHE), and LSV (2 cycles) at each rotation speed. The LSV data obtained with the degassed electrolyte was subtracted from the data obtained with oxygen saturated 0.5M sulfuric acid.
電極触媒の耐性は、１００ｍＶ／秒、酸素飽和０．５Ｍ硫酸、１６００ｒｐｍでの１．２〜０．６Ｖ（ｖｓＲＨＥ）の３００ＣＶサイクルを実行することにより評価した。なお、バックグラウンドとしてのＬＳＶを再び窒素下で測定し、酸素下で同じパラメータで測定したＬＳＶによってＯＲＲを評価した。 The resistance of the electrocatalyst was evaluated by performing a 300 CV cycle of 1.2-0.6 V (vs RHE) at 100 mV / sec, oxygen saturated 0.5 M sulfuric acid, 1600 rpm. In addition, LSV as a background was measured again under nitrogen, and ORR was evaluated by LSV measured under the same parameters under oxygen.
［実験結果］
（ＯＲＲ活性に対する酸化ルテニウムナノシートのサイズの影響）
Koutecky-Levitchプロットを式（１）によって得た。式（１）中、ｎは酸素分子の電子数を表し、Ｆはファラデー定数を表し、Ｃはバルク酸素濃度を表し、Ｄは酸素の拡散係数を表し、ｖは電解質の粘性を表し、ωは電極の回転速度を表す。
[Experimental result]
(Effect of size of ruthenium oxide nanosheet on ORR activity)
A Koutecky-Levitch plot was obtained by equation (1). In formula (1), n represents the number of electrons in the oxygen molecule, F represents the Faraday constant, C represents the bulk oxygen concentration, D represents the oxygen diffusion coefficient, v represents the viscosity of the electrolyte, and ω represents Represents the rotation speed of the electrode.
図２は、Ｐｔ／Ｃ系電極触媒の場合の、３１００ｒｐｍ、２２００ｒｐｍ、１６００ｒｐｍ、１２００ｒｐｍ、８００ｒｐｍ及び４００ｒｐｍにおける０．８Ｖ（ｖｓＲＨＥ）の電流密度の逆数を、ω−１／２に対してプロットしたグラフである。ここでの結果は、図２中に黒塗り記号（●、◆、■、▲）で示した。また、図２の活性化支配電流密度ｊｋは、式（１）によるKoutecky-Levichプロットから求めた。 FIG. 2 is a graph in which the reciprocal of the current density of 0.8 V (vs RHE) at 3100 rpm, 2200 rpm, 1600 rpm, 1200 rpm, 800 rpm, and 400 rpm is plotted against ω −1/2 in the case of a Pt / C-based electrode catalyst. It is. The results here are indicated by black symbols (●, ◆, ■, ▲) in FIG. Further, the activation dominant current density jk in FIG. 2 was obtained from the Koutecky-Levich plot according to the equation (1).
表１は、酸化ルテニウムナノシートの寸法とＴＢＡ＋／Ｈ＋比とで影響される初期活性値を示したものである。Ｐｔ／Ｃのみの電極触媒の初期質量活性は２２５ＡｇＰｔ −１であった。ＴＢＡ＋／Ｈ＋比が１．５の場合の初期質量活性は、大（寸法Ａ）、普通（寸法Ｂ）及び小（寸法Ｃ）のそれぞれについて、２４１ＡｇＰｔ −１、３９１ＡｇＰｔ −１及び４０７ＡｇＰｔ −１に増加した。普通サイズ（寸法Ｂ）の酸化ルテニウムナノシートの初期質量活性は、ＴＢＡ＋／Ｈ＋比が１０、５及び１．５のそれぞれについて、２１５ＡｇＰｔ −１、３２７Ａ−１及び３９１ＡｇＰｔ −１に増加した。ＴＢＡ＋／Ｈ＋比が１．５で、小サイズ（寸法Ｃ）の酸化ルテニウムナノシート−Ｐｔ／Ｃが、最も高い質量活性を示し、酸化ルテニウムナノシートを有しない電極触媒よりも８０％高い４０７ＡｇＰｔ −１を示した。ＴＢＡ＋の含有量が少なく、酸化ルテニウムナノシートの寸法が小さいほど質量活性が増加する傾向にあった。 Table 1 shows the initial activity values affected by the dimensions of the ruthenium oxide nanosheet and the TBA + / H + ratio. The initial mass activity of the Pt / C-only electrocatalyst was 225Ag Pt- 1 . The initial mass activity for a TBA + / H + ratio of 1.5 is 241 Ag Pt −1 , 391 Ag Pt −1 and 407 Ag for large (dimension A), normal (dimension B) and small (dimension C), respectively. Increased to Pt- 1 . The initial mass activity of normal size (dimension B) ruthenium oxide nanosheets increased to 215 Ag Pt −1 , 327 A −1 and 391 Ag Pt −1 for TBA + / H + ratios of 10, 5 and 1.5, respectively. . 407Ag Pt with a TBA + / H + ratio of 1.5 and a small size (dimension C) of ruthenium oxide nanosheets—Pt / C showing the highest mass activity and 80% higher than the electrocatalyst without the ruthenium oxide nanosheets -1 was shown. There was a tendency that the mass activity increased as the content of TBA + was smaller and the size of the ruthenium oxide nanosheet was smaller.
（触媒耐性に対する酸化ルテニウムナノシートサイズの影響）
上記した「ＯＲＲ活性に対する酸化ルテニウムナノシートのサイズの影響」の検討と同様にして評価した。１６００ｒｐｍでの耐性テスト（６０℃、酸素下で３００サイクル、０．６〜１．２Ｖ ｖｓＲＨＥ）後のKoutecky-Levichプロットは、図２中に示した。ここでの結果は、図２中に白抜き記号（○、◇、□、△）で示した。
(Effect of ruthenium oxide nanosheet size on catalyst resistance)
The evaluation was performed in the same manner as in the above-described examination of “the influence of the size of the ruthenium oxide nanosheet on the ORR activity”. The Koutecky-Levich plot after a resistance test at 1600 rpm (60 ° C., 300 cycles under oxygen, 0.6-1.2 V vs RHE) is shown in FIG. The results here are indicated by white symbols (◯, ◇, □, Δ) in FIG.
表２は、酸化ルテニウムナノシートの寸法とＴＢＡ＋／Ｈ＋比とで影響される耐性試験後の活性値を示したものである。耐性試験後、ＴＢＡ＋/Ｈ+比が１．５で、寸法Ｃの酸化ルテニウムナノシートを用いた複合電極触媒が最も高い質量活性を示し、酸化ルテニウムナノシートを有さない電極触媒よりも１３０％高い数値である２３４ＡｇＰｔ −１を示した。活性の保持は、耐久後の質量活性を初期質量活性で割って算出した。 Table 2 shows the activity values after the resistance test, which are influenced by the dimensions of the ruthenium oxide nanosheet and the TBA + / H + ratio. After endurance testing, the composite electrocatalyst with a TBA + / H + ratio of 1.5 and using a dimension C ruthenium oxide nanosheet exhibits the highest mass activity and is 130% higher than the electrocatalyst without the ruthenium oxide nanosheet A numerical value of 234Ag Pt −1 was shown. The retention of activity was calculated by dividing the mass activity after endurance by the initial mass activity.
以上の実験結果より、Ｐｔ／Ｃ触媒への酸化ルテニウムナノシートの添加は、初期質量活性と触媒の耐性の両方を向上させた。酸化ルテニウムナノシートは、触媒の全体的な電気抵抗を減少させるとともに、プロトン伝導性を向上する効果を奏し、その結果、好ましい結果が得られたより小さい寸法Ｃの酸化ルテニウムナノシートは、シート自体の重なり合いが減ること、及びその初期活性による三相界面の改善によって、より均一な複合電極触媒をえることができたと考えられた。ＴＢＡ＋/Ｈ+比が１．５で、酸化ルテニウムナノシートの寸法Ｃ（小さい）場合のＰｔ／Ｃ複合電極触媒は、Ｐｔ／Ｃ単独触媒よりも１３０％高い活性を示し、長期耐性に明確な差が認められた。なお、現時点での考察では、酸化ルテニウムナノシートを添加した複合電極触媒の耐性が向上する理由としては、負に帯電した酸化ルテニウムが、陽イオンのＰｔ種の拡散を防ぐためであると考えられる。酸化ルテニウムは、Ｐｔの溶解種として考えられているＰｔｎ＋の捕獲サイトとして作用し得る。また、カーボンが腐食されると、酸化ルテニウムは、良い電子伝導体であり、Ｐｔが沈殿物であるとしても、ＯＲＲに活性とすることができるので、Ｐｔ粒子の二次サポートとして機能することができると考えられる。 From the above experimental results, the addition of ruthenium oxide nanosheets to the Pt / C catalyst improved both initial mass activity and catalyst resistance. Ruthenium oxide nanosheets have the effect of reducing the overall electrical resistance of the catalyst and improving proton conductivity, and as a result, the smaller size C ruthenium oxide nanosheets with favorable results are not overlapping the sheets themselves. It was considered that a more uniform composite electrocatalyst could be obtained by the reduction and improvement of the three-phase interface due to its initial activity. The Pt / C composite electrocatalyst with a TBA + / H + ratio of 1.5 and a ruthenium oxide nanosheet size C (small) shows 130% higher activity than the Pt / C single catalyst, and is clear in long-term resistance Differences were noted. In the present discussion, it is considered that the reason why the composite electrode catalyst to which the ruthenium oxide nanosheet is added is improved is that negatively charged ruthenium oxide prevents the diffusion of Pt species of the cation. Ruthenium oxide can act as a capture site for Pt n + , which is considered as a dissolved species of Pt. Also, when carbon is corroded, ruthenium oxide is a good electron conductor, and even if Pt is a precipitate, it can be activated by ORR, so it can function as a secondary support for Pt particles. It is considered possible.
Claims (4)
前記酸化ルテニウムナノシートが、鱗片形状からなり、最大長さと該最大長さの中点で直交する長さとの平均を該酸化ルテニウムナノシートの寸法としたとき、該寸法が５０ｎｍ以上３５０ｎｍ以下のものが全体の６５％以上であり、且つモード径が１００ｎｍ以上２５０ｎｍ以下であることを特徴とする酸素還元能を有する電極触媒。 An electrode catalyst made of a ruthenium oxide nanosheet used with a platinum-based electrode catalyst,
The ruthenium oxide nanosheet has a scaly shape, and when the average of the maximum length and the length orthogonal to the midpoint of the maximum length is the dimension of the ruthenium oxide nanosheet, the entire dimension is 50 nm to 350 nm. An electrode catalyst having an oxygen reducing ability, wherein the mode diameter is from 100 nm to 250 nm.
前記酸化ルテニウムナノシートが、鱗片形状からなり、最大長さと該最大長さの中点で直交する長さとの平均を該酸化ルテニウムナノシートの寸法としたとき、該寸法が５０ｎｍ以上３５０ｎｍ以下のものが全体の６５％以上であり、且つモード径が１００ｎｍ以上２５０ｎｍ以下であることを特徴とする酸素還元能を有する電極触媒。 A composite electrode catalyst having a platinum-based electrode catalyst and a ruthenium oxide nanosheet catalyst,
The ruthenium oxide nanosheet has a scaly shape, and when the average of the maximum length and the length orthogonal to the midpoint of the maximum length is the dimension of the ruthenium oxide nanosheet, the entire dimension is 50 nm to 350 nm. An electrode catalyst having an oxygen reducing ability, wherein the mode diameter is from 100 nm to 250 nm.
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