WO2020250673A1 - Catalyst for suppressing hydrogen peroxide generation, method for suppressing hydrogen peroxide generation using same, membrane-electrode assembly, and fuel cell using same - Google Patents

Catalyst for suppressing hydrogen peroxide generation, method for suppressing hydrogen peroxide generation using same, membrane-electrode assembly, and fuel cell using same Download PDF

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WO2020250673A1
WO2020250673A1 PCT/JP2020/020823 JP2020020823W WO2020250673A1 WO 2020250673 A1 WO2020250673 A1 WO 2020250673A1 JP 2020020823 W JP2020020823 W JP 2020020823W WO 2020250673 A1 WO2020250673 A1 WO 2020250673A1
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catalyst
hydrogen peroxide
anode
membrane
polymer electrolyte
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PCT/JP2020/020823
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French (fr)
Japanese (ja)
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内田裕之
内田誠
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国立大学法人山梨大学
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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
    • B01J23/70—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
    • 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
    • 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
    • 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
    • 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
    • H01M8/1004—Fuel cells with solid electrolytes characterised by membrane-electrode assemblies [MEA]
    • 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
    • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
    • H01M8/1018—Polymeric electrolyte materials
    • H01M8/1041—Polymer electrolyte composites, mixtures or blends
    • H01M8/1046—Mixtures of at least one polymer and at least one additive
    • H01M8/1051—Non-ion-conducting additives, e.g. stabilisers, SiO2 or ZrO2
    • 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
    • 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 application relates to a catalyst for suppressing hydrogen peroxide generation, a method for suppressing hydrogen peroxide generation using the catalyst, and a membrane-electrode assembly and a fuel cell using the membrane-electrode assembly.
  • PEFC polymer electrolyte fuel cell
  • PEFC of operating temperatures used for fuel cell vehicles (FCV) or stationary is generally from about 100 ° C. from room temperature, in the fuel electrode (anode) hydrogen oxidation reaction (HOR) "H 2 ⁇ 2H + + 2e -" Progresses.
  • HOR hydrogen oxidation reaction
  • Pure platinum is used as a catalyst material having the highest HOR activity (specific activity: current density per actual working area of the catalyst) in a temperature range of about 100 ° C. from room temperature and having corrosion resistance to a strongly acidic polymer electrolyte membrane. (Pt) is widely known.
  • a Pt / C catalyst in which platinum fine particles having a particle size of about 2 to 4 nm are highly dispersed in a carbon carrier is widely used.
  • H 2 gas permeates the polymer electrolyte membrane (PEM) from the cathode side and reacts with the adsorbed H 2 or H atom on the anode catalyst to generate hydrogen peroxide (H 2 O 2 ).
  • H 2 O 2 reacts with impurities such as Fe 2+ ions in the PEM, there is a problem that OH radicals are generated and the PEM is decomposed.
  • Patent Document 1 proposes a technique of adding a radical scavenger such as Ce 3+ to PEM.
  • Patent Document 2 is provided as a technique relating to the anode catalyst of the membrane-electrode assembly of the present application
  • Patent Document 3 is provided as a technique relating to a fuel cell.
  • Patent Document 1 has a problem that a radical scavenger such as Ce 3+ moves to the cathode side during the operation of PEFC and the radical scavenging effect is lowered. Further, when a large amount of radical scavenger is added to PEM, there is a problem that ohm resistance and cathode polarization increase.
  • a membrane-electrode assembly capable of suppressing deterioration of PEM by using a platinum alloy anode catalyst having a low H 2 O 2 production rate as a radical source as a catalyst for suppressing hydrogen peroxide generation and a membrane-electrode assembly thereof can be used.
  • the fuel cell used is provided.
  • the catalyst for suppressing hydrogen peroxide generation disclosed in the present application is a catalyst for suppressing hydrogen peroxide generation, which is composed of alloy particles of platinum and a transition metal and suppresses the generation of hydrogen peroxide at the anode of a fuel cell.
  • the method for suppressing the generation of hydrogen peroxide disclosed in the present application is a method for suppressing the generation of hydrogen peroxide in the anode of the fuel cell using the catalyst for suppressing the generation of hydrogen peroxide disclosed in the present application.
  • the membrane-electrode assembly disclosed in the present application is a membrane-electrode assembly including a polymer electrolyte membrane, an anode, and a cathode, and the anode is a catalyst for suppressing hydrogen peroxide generation disclosed in the present application. Includes.
  • the fuel cell disclosed in the present application is a fuel cell including the membrane-electrode assembly disclosed in the present application.
  • deterioration of the polymer electrolyte membrane of the fuel cell can be suppressed, thereby improving the durability of the fuel cell.
  • FIG. 1 is a schematic view of a membrane-electrode assembly of the embodiment.
  • FIG. 2 is a schematic diagram showing the generation of H 2 O 2 and OH radicals in the anode catalyst.
  • FIG. 3 is a diagram showing the adsorption energies of hydrogen atoms (H) and hydrogen molecules (H 2 ) with respect to various catalyst metals.
  • FIG. 4 is a schematic view showing a channel flow double electrode cell.
  • FIG. 5 is an enlarged schematic view of the test electrode and the detection electrode of FIG.
  • FIG. 6 is a diagram showing a convection voltamogram of the test electrode (lower stage) and a current density of the detection electrode (upper stage) in the channel flow double electrode method.
  • FIG. 7 is a diagram showing the generation rate of H 2 O 2 of various catalysts.
  • the film-electrode junction of the present embodiment includes a polymer electrolyte membrane, an anode, and a cathode, the anode includes an anode catalyst layer, the cathode includes a cathode catalyst layer, and the anode catalyst layer includes a cathode catalyst layer.
  • the cathode catalyst layer is arranged on the first main surface of the polymer electrolyte membrane, the cathode catalyst layer is arranged on the second main surface of the polymer electrolyte film, and the anode catalyst layer contains a platinum alloy catalyst.
  • the membrane-electrode assembly of the present embodiment contains a platinum alloy catalyst having a low H 2 O 2 formation rate as a radical source in its anode catalyst layer, deterioration of the polymer electrolyte membrane can be prevented. As a result, the durability of the fuel cell can be improved. That is, the platinum alloy catalyst functions as a hydrogen peroxide generation suppressing catalyst that suppresses the generation of hydrogen peroxide at the anode of the fuel cell.
  • FIG. 1 is a schematic view of the membrane-electrode assembly of the present embodiment.
  • the membrane-electrode assembly 10 is arranged on the polymer electrolyte membrane 11, the anode 12 arranged on one main surface of the polymer electrolyte membrane 11, and the other main surface of the polymer electrolyte membrane 11. It is provided with a cathode 13.
  • the anode 12 includes an anode catalyst layer 14 and an anode gas diffusion layer 15 from the polymer electrolyte membrane 11 side. Further, an anode gas flow path 16 is arranged outside the anode 12.
  • the cathode 13 includes a cathode catalyst layer 17 and a cathode gas diffusion layer 18 from the polymer electrolyte membrane 11 side. Further, a cathode gas flow path 19 is arranged outside the cathode 13.
  • Figure 1 supplies a fuel gas (hydrogen gas) to the anode gas passage 16, when the cathode gas channel 19 for supplying air (oxygen gas), the anode 12, H 2 ⁇ 2H + + 2e - hydrogen oxidation reaction (HOR) occurs, and proton H + and electron e - are generated.
  • the proton H + moves to the cathode 13 via the polymer electrolyte membrane 11, and the electron e ⁇ moves to the cathode 13 through the wiring.
  • the protons H + and electrons e from the anode 12 - by, O 2 + 4H + + 4e - ⁇ 2H 2 O oxygen reduction reaction of (ORR) occurs. In this way, the electronic e - power can be generated by the flow.
  • the O 2 gas from the cathode 13 permeates the polymer electrolyte membrane 11 and reaches the anode 12.
  • the O 2 gas generates H 2 O 2 on the anode catalyst by the following oxygen reduction reaction.
  • H 2 gas reacts with the H 2 molecule (H 2, ad ) and the H atom (H ad ) adsorbed on the anode catalyst as described below to generate H 2 O 2 .
  • the radical scavenger is regenerated by the following regeneration reaction.
  • FIG. 3 is a diagram showing the adsorption energies of hydrogen atoms (H) and hydrogen molecules (H 2 ) with respect to various catalyst metals.
  • Catalytic metal used Pt alone, PtRu alloy, and, as the platinum skin catalyst described below, Pt 1AL PtNi, Pt 1AL PtCo, a Pt 1AL PtFe. Further, the adsorption energy was obtained by DFT calculation.
  • steps of the hydrogen atom (H) for various catalytic metals - Edge (step-edge) and the size of the adsorption energy in terrace is, Pt>PtRu> Pt 1AL PtNi > Pt 1AL PtCo> Pt 1AL PtFe It can be seen that it becomes smaller in the order of. That, PtRu, Pt 1AL PtNi, Pt 1AL PtCo, platinum alloy catalysts such as Pt 1AL PtFe has a small adsorption energy of hydrogen atoms (H) as compared to Pt alone, a hydrogen atom (H) is considered to hardly adsorbed ..
  • PtRu, Pt 1AL PtNi, Pt 1AL PtCo, platinum alloy catalysts such as Pt 1AL PtFe has a small adsorption energy of hydrogen atoms (H) as compared to Pt alone, a hydrogen atom (H) is a hard adsorbed Therefore, as described above, even if O 2 gas permeates the polymer electrolyte membrane from the cathode and reaches the anode, the O 2 gas reacts with H atoms (H ad ) adsorbed on the anode catalyst. Is extremely reduced, and it is considered that the H 2 O 2 production rate is reduced.
  • the catalyst for suppressing hydrogen peroxide generation of the present embodiment is a platinum alloy catalyst composed of alloy particles of platinum and a transition metal and suppressing the generation of hydrogen peroxide at the anode of a fuel cell. That is, the platinum alloy catalyst contained in the anode catalyst layer of the membrane-electrode assembly described above is the catalyst for suppressing hydrogen peroxide generation disclosed in the present application, which is composed of alloy particles of platinum and a transition metal.
  • transition metal contained in the catalyst for suppressing molybdenum generation examples include iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn), chromium (Cr), vanadium (V), and titanium ( At least one selected from Ti), niobium (Nb), molybdenum (Mo), lead (Pb), and tungsten (W) can be used, but Co is most preferable. This is because the PtCo-based alloy has a large hydrogen oxidation reaction (HOR) activity.
  • HOR hydrogen oxidation reaction
  • the catalyst for suppressing hydrogen peroxide generation composed of the platinum alloy catalyst is Pt 100-n M n (M: transition metal atom, n: atomic percentage of transition metal atom M in the alloy, 5 ⁇ n ⁇ 90). expressed.
  • the platinum alloy catalyst is provided with a platinum skin layer having 1 to 2 atomic layers composed of platinum atoms on the surface of alloy particles of platinum and a transition metal. This is because the H 2 O 2 production rate is further reduced.
  • the catalyst for suppressing hydrogen generation generated by the platinum alloy catalyst provided with the platinum skin layer is Pt xAL ⁇ Pt 100-n M n (M: transition metal atom, x: number of platinum skin layers 1 to 2, AL: atomic-layer, n: Atomic percentage of the transition metal atom M in the alloy, represented by 5 ⁇ n ⁇ 90), such a platinum alloy catalyst is also referred to as a platinum skin catalyst.
  • the platinum skin catalyst and a method for producing the platinum skin catalyst are disclosed in detail in Patent Document 2 (Japanese Unexamined Patent Publication No. 2017-042759).
  • the platinum alloy catalyst is usually used as a supported catalyst supported on a carrier.
  • the carrier is not particularly limited, but in consideration of catalyst supporting ability, electron conductivity, electrochemical stability, etc., it has a high surface area such as carbon black, amorphous carbon, Ketjen black, activated carbon, carbon nanohorns, carbon nanotubes, etc. Carbon is preferred.
  • carbon (C) is used as the carrier, the platinum alloy catalyst is represented by Pt 100-n M n / C, and the platinum skin catalyst is represented by Pt xAL- Pt 100-n M n / C. ..
  • the catalyst for suppressing hydrogen peroxide generation of the present embodiment as the anode of the fuel cell, it is possible to provide a method of suppressing the generation of hydrogen peroxide at the anode of the fuel cell.
  • the anode catalyst layer constituting the membrane-electrode assembly of the present embodiment is arranged on the first main surface of the polymer electrolyte membrane, and the anode catalyst layer comprises the above-mentioned catalyst for suppressing hydrogen peroxide generation and a binder. Includes.
  • the binder is not particularly limited, but an ionic conductive binder is preferable, and a binder made of an ionic conductive fluororesin is preferable.
  • a binder made of an ionic conductive fluororesin include "Nafion” (registered trademark) manufactured by DuPont.
  • the anode catalyst layer is formed by preparing a catalyst ink containing the catalyst for suppressing hydrogen peroxide generation, the binder, and a solvent, applying the catalyst ink to the polymer electrolyte membrane, and then removing the solvent. can do.
  • the cathode catalyst layer constituting the membrane-electrode assembly of the present embodiment is arranged on the second main surface of the polymer electrolyte membrane, and the cathode catalyst layer can be formed from a supported catalyst and a binder.
  • the supported catalyst and the binder are not particularly limited, but the same materials as those used for the anode catalyst layer described above can also be used. Further, the cathode catalyst layer can be formed in the same manner as the anode catalyst layer described above.
  • the polymer electrolyte membrane constituting the membrane-electrode assembly of the present embodiment is formed of a material that exhibits good ion (proton) conductivity in a wet state, and is, for example, an ion (proton) formed of a fluororesin.
  • a conductive ion exchange membrane is used.
  • the fluororesin include "Nafion" (registered trademark) manufactured by DuPont.
  • a radical scavenger can also be used for the membrane-electrode assembly of the present embodiment.
  • the radical trapping agent is preferably disposed at least one selected from the polymer electrolyte membrane, the anode catalyst layer, and between the polymer electrolyte membrane and the anode catalyst layer.
  • the radical scavenger When the radical scavenger is arranged in the polymer electrolyte membrane, it is preferable to arrange the radical scavenger unevenly on the anode side of the polymer electrolyte membrane. When the radical scavenger is arranged in the anode catalyst layer, it is preferable that the radical scavenger is unevenly distributed on the polymer electrolyte membrane side of the anode catalyst layer.
  • the type of the radical scavenger is not particularly limited, but cerium (Ce), manganese (Mn), ruthenium (Ru), silver (Ag), tungsten (W), chromium (Cr), aluminum (Al) and cobalt (Al). It is preferably a compound containing at least one element selected from the group consisting of Co). Of these, cerium compounds such as cerium oxide, cerium hydroxide, and cerium phosphate are preferable.
  • a radical scavenger using cerium phosphate is disclosed in detail in Patent Document 1 (Japanese Unexamined Patent Publication No. 2006-324094).
  • the fuel cell of the present embodiment includes the membrane-electrode assembly of the above-described embodiment. Since the membrane-electrode assembly uses a catalyst for suppressing hydrogen peroxide generation (platinum alloy catalyst, platinum skin catalyst) having a low H 2 O 2 production rate as a radical source as an anode catalyst, it is a polymer electrolyte membrane. Deterioration can be suppressed, and as a result, the durability of the fuel cell can be improved.
  • the gas diffusion layer, gas flow path, and other constituent members used in the fuel cell of the present embodiment are not particularly limited, and for example, those disclosed in Patent Document 3 (Patent No. 6150265) are used. be able to.
  • FIG. 4 shows a schematic diagram of a channel flow double electrode (CFDE) cell used in the CFDE method.
  • FIG. 5 is an enlarged schematic view of the test electrode and the detection electrode of FIG.
  • c-Pt / C (commercial-platinum-supported carbon catalyst) is fixed to a glassy carbon (GC) substrate of a CFDE cell, and the surface thereof is a 0.1 ⁇ m-thick Nafion thin film (DuPont).
  • an electrolytic solution saturated with pure hydrogen in a 0.1 M HClO 4 aqueous solution is flowed at a temperature of 80 ° C. and an average flow rate of 111 cm / s, and a convection voltamogram of a test electrode is measured at a sweep rate of 5 mV / s.
  • the hydrogen oxidation reaction (HOR) characteristics were evaluated.
  • the convection voltamogram is shown in the lower part of FIG.
  • the convection voltamogram of FIG. 6 showed the HOR characteristic shown in A (H 2 ), and the HOR current density increased from 0 V and reached the diffusion limit current density at about 0.06 V.
  • the voltage V here is a voltage for a reversible hydrogen electrode (RHE: Reversible Hydrogen Electrode).
  • the detection electrode located downstream of the test electrode can oxidize the generated H 2 O 2 by diffusion control, and 1.4 V with respect to RHE so that the hydrogen peroxide (HOR) current (background) becomes small.
  • the current density of the detection electrode is shown as j c in the upper part of FIG.
  • the current density j c (H 2 ) by HOR of the detection electrode was about 0.1 mAcm -2 regardless of the test electrode potential.
  • the generation rate j (H 2 O 2 ) of H 2 O 2 at the test electrode was defined as the following equation.
  • j (H 2 O 2 ) [j c (10% air / H 2 ) -j c (H 2 )] / N
  • N is the capture rate of the detection electrode, and an experimentally obtained value of 0.29 was used.
  • Pt (acac) 2 was 0.125 mmol (49 mg)
  • Co (acac) 3 was 0.125 mmol (44 mg)
  • 1,2-hexadecanediol was 1 mmol (260 mg)
  • diphenyl ether was 12.5 ml (13.5 g, 79. 3 mmol) was added to the beaker, the temperature was raised to 100 ° C. using a stirrer, and the mixture was stirred and mixed for 10 minutes.
  • 0.25 mmol (85 ⁇ l) of oleic acid and 0.25 mmol (80 ⁇ l) of oleylamine were added thereto, the temperature was raised to 200 ° C. with stirring, and the mixture was stirred as it was for 20 minutes to obtain a nanocapsule solution.
  • the mixed solution is filtered, vacuum dried at 60 ° C., and then the remaining organic solvent is removed and Pt is precipitated on the surface of the PtCo fine particles at the same time. Therefore, in a 4% hydrogen gas atmosphere, 4 at 400 ° C. subjected to heat treatment time, to obtain a Pt 1AL -PtCo / C.
  • a tetraammine platinum hydroxide solution [Pt (NH 3 ) 4 ] (OH) 2 ) for the Pt1 atomic layer was dissolved in 10 mL of pure water to prepare a Pt skin precursor solution. did.
  • the solution is mixed Pt 1AL -PtCo / C obtained during and after boiling 10 minutes, the reaction solution is allowed to warm to 60 ° C., the hydrogen gas concentration of 5% and a temperature 60 ° C., the time 1H Hydrogen bubbling was performed under the conditions of.
  • Pt skin layer on the surface of the Pt 1AL -PtCo particles are uniformly formed, to obtain a Pt 2AL -PtCo / C catalyst.
  • Example 2 Pt in nanocapsules in the same manner as in Example 1 except that the starting material of Example 1 was Pt (acac) 2 : 0.125 mmol (49 mg) and Co (acac) 3 : 0.042 mmol (15 mg).
  • the Pt 3 Co fine particles were supported on the carbon black particles in the same manner as in Example 1 using the solution B.
  • the mixed solution containing the Pt 3 Co fine particle-supporting carbon black particles is filtered, vacuum dried at 60 ° C., and then heat-treated at a high temperature for a short time in a 4% hydrogen gas atmosphere to contain Co25 atom%.
  • a Pt 3 Co / C catalyst was obtained.
  • H 2 O 2 generation rate j (H 2 O 2 ) [j c (10% air / H 2 ) -j c (H 2 )] /0.29
  • Example 1 Example 2 and Comparative Example 1
  • j (H 2 O 2 ) increased with a decrease in potential and reached a maximum value at 0 V, but j (in Example 1 and Example 2).
  • H 2 O 2) is found to have decreased in comparison with the Comparative example 1 j (H 2 O 2).
  • j (H 2 O 2 ) of Example 1 using a platinum skin catalyst is j (H) of Comparative Example 1 using a conventional commercially available c-Pt / C catalyst in a potential range of 0.06 V or less. Compared with 2 O 2 ), it was suppressed to 1/2 or less.
  • the fuel cell provided with the membrane-electrode assembly using the hydrogen peroxide generation suppressing catalyst disclosed in the present application is made of a polymer due to the H 2 O 2 production suppressing effect of the hydrogen peroxide generation suppressing catalyst. Since deterioration of the electrolyte membrane can be suppressed, the durability of the fuel cell can be improved.
  • a membrane-electrode assembly using the catalyst for suppressing hydrogen peroxide generation disclosed in the present application as an anode catalyst and a fuel cell using the same can prevent deterioration of the polymer electrolyte membrane, and as a result, the durability of the fuel cell can be improved. It can be improved and can be effectively used for fuel cell vehicles and household fuel cells.

Abstract

A membrane-electrode assembly disclosed herein comprises a polymer electrolyte membrane, an anode, and a cathode, wherein: the anode includes an anode catalyst layer; the cathode includes a cathode catalyst layer; the anode catalyst layer is disposed on a first main surface of the polymer electrolyte membrane; the cathode catalyst layer is disposed on a second main surface of the polymer electrolyte membrane; and the anode catalyst layer includes a catalyst which is for suppressing hydrogen peroxide generation and is formed of alloy particles of platinum and a transition metal or a catalyst which is for suppressing hydrogen peroxide generation and further includes 1 or 2 atom layers of platinum skin layers composed of platinum atoms on the surfaces of the alloy particles.

Description

過酸化水素発生抑制用触媒及びそれを用いた過酸化水素の発生を抑制する方法、並びに膜－電極接合体及びそれを用いた燃料電池A catalyst for suppressing hydrogen peroxide generation, a method for suppressing hydrogen peroxide generation using the catalyst, a membrane-electrode assembly, and a fuel cell using the same.
　本願は、過酸化水素発生抑制用触媒及びそれを用いた過酸化水素の発生を抑制する方法、並びに膜－電極接合体及びその膜－電極接合体を用いた燃料電池に関する。 The present application relates to a catalyst for suppressing hydrogen peroxide generation, a method for suppressing hydrogen peroxide generation using the catalyst, and a membrane-electrode assembly and a fuel cell using the membrane-electrode assembly.
　固体高分子形燃料電池（ＰＥＦＣ）は、クリーンで高発電効率な発電システムであるため、燃料電池自動車や家庭用燃料電池等に応用され普及が始まっている。 Since the polymer electrolyte fuel cell (PEFC) is a clean and highly efficient power generation system, it has been applied to fuel cell vehicles, household fuel cells, etc. and has begun to spread.
　燃料電池自動車（ＦＣＶ）や定置用に用いられるＰＥＦＣの作動温度は、一般的に室温から約１００℃であり、燃料極（アノード）では水素酸化反応（ＨＯＲ）「Ｈ2→２Ｈ+＋２ｅ-」が進行する。そして、室温から約１００℃の温度域でのＨＯＲ活性（比活性：触媒の実作動面積当たりの電流密度）が最も高く、強酸性の高分子電解質膜に対する耐蝕性を有する触媒材料として、純白金（Ｐｔ）が広く知られている。例えば、高純度の水素を燃料とするＦＣＶの燃料電池のアノード触媒としては、粒径約２～４ｎｍの白金微粒子を炭素担体に高分散したＰｔ／Ｃ触媒が広く用いられている。 PEFC of operating temperatures used for fuel cell vehicles (FCV) or stationary is generally from about 100 ° C. from room temperature, in the fuel electrode (anode) hydrogen oxidation reaction (HOR) "H 2 → 2H + + 2e -" Progresses. Pure platinum is used as a catalyst material having the highest HOR activity (specific activity: current density per actual working area of the catalyst) in a temperature range of about 100 ° C. from room temperature and having corrosion resistance to a strongly acidic polymer electrolyte membrane. (Pt) is widely known. For example, as an anode catalyst for an FCV fuel cell using high-purity hydrogen as a fuel, a Pt / C catalyst in which platinum fine particles having a particle size of about 2 to 4 nm are highly dispersed in a carbon carrier is widely used.
　従来、ＰＥＦＣでは、カソード側からＯ2ガスが高分子電解質膜（ＰＥＭ）を透過し、アノード触媒上の吸着Ｈ2又はＨ原子と反応して過酸化水素（Ｈ2Ｏ2）が生成し、このＨ2Ｏ2と、ＰＥＭ中のＦｅ2+イオン等の不純物とが反応すると・ＯＨラジカルが発生し、ＰＥＭを分解する問題があった。 Conventionally, in PEFC, O 2 gas permeates the polymer electrolyte membrane (PEM) from the cathode side and reacts with the adsorbed H 2 or H atom on the anode catalyst to generate hydrogen peroxide (H 2 O 2 ). When this H 2 O 2 reacts with impurities such as Fe 2+ ions in the PEM, there is a problem that OH radicals are generated and the PEM is decomposed.
　上記問題を解決するために、ＰＥＭ中にＣｅ3+等のラジカル捕捉剤を添加する技術が特許文献１に提案されている。 In order to solve the above problem, Patent Document 1 proposes a technique of adding a radical scavenger such as Ce 3+ to PEM.
　また、本願の膜－電極接合体のアノード触媒に関する技術として特許文献２があり、燃料電池に関する技術として特許文献３がある。 Further, Patent Document 2 is provided as a technique relating to the anode catalyst of the membrane-electrode assembly of the present application, and Patent Document 3 is provided as a technique relating to a fuel cell.
特開２００６－３２４０９４号公報Japanese Unexamined Patent Publication No. 2006-324094 特開２０１７－０４２７５９号公報Japanese Unexamined Patent Publication No. 2017-042759 特許第６１５０２６５号公報Japanese Patent No. 6150265
　しかし、特許文献１が提案する技術では、ＰＥＦＣの運転中にＣｅ3+等のラジカル捕捉剤がカソード側に移動してラジカル捕捉効果が低下する問題がある。また、ラジカル捕捉剤を多量にＰＥＭに添加するとオーム抵抗やカソード分極が増大する問題もある。 However, the technique proposed by Patent Document 1 has a problem that a radical scavenger such as Ce 3+ moves to the cathode side during the operation of PEFC and the radical scavenging effect is lowered. Further, when a large amount of radical scavenger is added to PEM, there is a problem that ohm resistance and cathode polarization increase.
　本願は、過酸化水素発生抑制用触媒として、ラジカル源となるＨ2Ｏ2生成速度の低い白金合金アノード触媒を用いることにより、ＰＥＭの劣化を抑制することができる膜－電極接合体及びそれを用いた燃料電池を提供する。 In the present application, a membrane-electrode assembly capable of suppressing deterioration of PEM by using a platinum alloy anode catalyst having a low H 2 O 2 production rate as a radical source as a catalyst for suppressing hydrogen peroxide generation and a membrane-electrode assembly thereof can be used. The fuel cell used is provided.
　本願で開示する過酸化水素発生抑制用触媒は、白金と遷移金属との合金粒子からなり、燃料電池のアノードにおける過酸化水素の発生を抑制する過酸化水素発生抑制用触媒である。 The catalyst for suppressing hydrogen peroxide generation disclosed in the present application is a catalyst for suppressing hydrogen peroxide generation, which is composed of alloy particles of platinum and a transition metal and suppresses the generation of hydrogen peroxide at the anode of a fuel cell.
　また、本願で開示する過酸化水素の発生を抑制する方法は、本願で開示する過酸化水素発生抑制用触媒を用いる燃料電池のアノードにおける過酸化水素の発生を抑制する方法である。 Further, the method for suppressing the generation of hydrogen peroxide disclosed in the present application is a method for suppressing the generation of hydrogen peroxide in the anode of the fuel cell using the catalyst for suppressing the generation of hydrogen peroxide disclosed in the present application.
　また、本願で開示する膜－電極接合体は、高分子電解質膜と、アノードと、カソードとを含む膜－電極接合体であって、前記アノードが、本願で開示する過酸化水素発生抑制用触媒を含んでいる。 The membrane-electrode assembly disclosed in the present application is a membrane-electrode assembly including a polymer electrolyte membrane, an anode, and a cathode, and the anode is a catalyst for suppressing hydrogen peroxide generation disclosed in the present application. Includes.
　また、本願で開示する燃料電池は、本願で開示する膜－電極接合体を含む燃料電池である。 Further, the fuel cell disclosed in the present application is a fuel cell including the membrane-electrode assembly disclosed in the present application.
　本願によれば、燃料電池の高分子電解質膜の劣化を抑制することができ、それにより燃料電池の耐久性を向上できる。 According to the present application, deterioration of the polymer electrolyte membrane of the fuel cell can be suppressed, thereby improving the durability of the fuel cell.
図１は、実施形態の膜－電極接合体の模式図である。FIG. 1 is a schematic view of a membrane-electrode assembly of the embodiment. 図２は、アノード触媒でのＨ2Ｏ2とＯＨラジカルの発生を示す模式図である。FIG. 2 is a schematic diagram showing the generation of H 2 O 2 and OH radicals in the anode catalyst. 図３は、各種触媒金属に対する水素原子（Ｈ）と水素分子（Ｈ2）の吸着エネルギーを示す図である。FIG. 3 is a diagram showing the adsorption energies of hydrogen atoms (H) and hydrogen molecules (H 2 ) with respect to various catalyst metals. 図４は、チャンネルフロー二重電極セルを示す模式図である。FIG. 4 is a schematic view showing a channel flow double electrode cell. 図５は、図４の試験極及び検出極の拡大模式図である。FIG. 5 is an enlarged schematic view of the test electrode and the detection electrode of FIG. 図６は、チャンネルフロー二重電極法における試験極の対流ボルタモグラム（下段）及び検出極の電流密度（上段）を示す図である。FIG. 6 is a diagram showing a convection voltamogram of the test electrode (lower stage) and a current density of the detection electrode (upper stage) in the channel flow double electrode method. 図７は、各種触媒のＨ2Ｏ2の発生速度を示す図である。FIG. 7 is a diagram showing the generation rate of H 2 O 2 of various catalysts.
　（膜－電極接合体）
　本願で開示する膜－電極接合体（Membrane Electrode Assembly：ＭＥＡ）の実施形態について説明する。本実施形態の膜－電極接合体は、高分子電解質膜と、アノードと、カソードとを備え、上記アノードは、アノード触媒層を含み、上記カソードは、カソード触媒層を含み、上記アノード触媒層は、上記高分子電解質膜の第１主面に配置され、上記カソード触媒層は、上記高分子電解質膜の第２主面に配置され、上記アノード触媒層は、白金合金触媒を含んでいる。 (Membrane-electrode assembly)
An embodiment of a membrane-electrode assembly (MEA) disclosed in the present application will be described. The film-electrode junction of the present embodiment includes a polymer electrolyte membrane, an anode, and a cathode, the anode includes an anode catalyst layer, the cathode includes a cathode catalyst layer, and the anode catalyst layer includes a cathode catalyst layer. The cathode catalyst layer is arranged on the first main surface of the polymer electrolyte membrane, the cathode catalyst layer is arranged on the second main surface of the polymer electrolyte film, and the anode catalyst layer contains a platinum alloy catalyst.
　本実施形態の膜－電極接合体は、そのアノード触媒層に、ラジカル源となるＨ2Ｏ2生成速度の低い白金合金触媒を含んでいるので、高分子電解質膜の劣化を防止することができ、その結果、燃料電池の耐久性を向上できる。即ち、上記白金合金触媒は、燃料電池のアノードにおける過酸化水素の発生を抑制する過酸化水素発生抑制用触媒として機能する。 Since the membrane-electrode assembly of the present embodiment contains a platinum alloy catalyst having a low H 2 O 2 formation rate as a radical source in its anode catalyst layer, deterioration of the polymer electrolyte membrane can be prevented. As a result, the durability of the fuel cell can be improved. That is, the platinum alloy catalyst functions as a hydrogen peroxide generation suppressing catalyst that suppresses the generation of hydrogen peroxide at the anode of the fuel cell.
　ここで、上記白金合金触媒をアノード触媒層に含めることにより高分子電解質膜の劣化を防止できる理由について説明するが、先ず、図面に基づき高分子電解質膜の劣化メカニズムについて説明する。 Here, the reason why the deterioration of the polymer electrolyte membrane can be prevented by including the platinum alloy catalyst in the anode catalyst layer will be described. First, the deterioration mechanism of the polymer electrolyte membrane will be described based on the drawings.
　＜高分子電解質膜の劣化メカニズム＞
　図１は、本実施形態の膜－電極接合体の模式図である。図１において、膜－電極接合体１０は、高分子電解質膜１１と、高分子電解質膜１１の一方の主面に配置されたアノード１２と、高分子電解質膜１１の他方の主面に配置されたカソード１３とを備えている。 <Degradation mechanism of polymer electrolyte membrane>
FIG. 1 is a schematic view of the membrane-electrode assembly of the present embodiment. In FIG. 1, the membrane-electrode assembly 10 is arranged on the polymer electrolyte membrane 11, the anode 12 arranged on one main surface of the polymer electrolyte membrane 11, and the other main surface of the polymer electrolyte membrane 11. It is provided with a cathode 13.
　アノード１２は、高分子電解質膜１１側からアノード触媒層１４及びアノードガス拡散層１５を備えている。また、アノード１２の外側にはアノードガス流路１６が配置されている。 The anode 12 includes an anode catalyst layer 14 and an anode gas diffusion layer 15 from the polymer electrolyte membrane 11 side. Further, an anode gas flow path 16 is arranged outside the anode 12.
　カソード１３は、高分子電解質膜１１側からカソード触媒層１７及びカソードガス拡散層１８を備えている。また、カソード１３の外側にはカソードガス流路１９が配置されている。 The cathode 13 includes a cathode catalyst layer 17 and a cathode gas diffusion layer 18 from the polymer electrolyte membrane 11 side. Further, a cathode gas flow path 19 is arranged outside the cathode 13.
　図１において、アノードガス流路１６に燃料ガス（水素ガス）を供給し、カソードガス流路１９に空気（酸素ガス）を供給すると、アノード１２では、Ｈ2→２Ｈ+＋２ｅ-の水素酸化反応（ＨＯＲ）が起こり、プロトンＨ+及び電子ｅ-が生じる。このプロトンＨ+が高分子電解質膜１１を介してカソード１３へ移動し、電子ｅ-が配線を通ってカソード１３へ移動する。カソード１３では、アノード１２からのプロトンＨ+及び電子ｅ-により、Ｏ2＋４Ｈ+＋４ｅ-→２Ｈ2Ｏの酸素還元反応（ＯＲＲ）が起こる。このようにして電子ｅ-が流れることにより発電することができる。 In Figure 1, supplies a fuel gas (hydrogen gas) to the anode gas passage 16, when the cathode gas channel 19 for supplying air (oxygen gas), the anode 12, H 2 → 2H + + 2e - hydrogen oxidation reaction (HOR) occurs, and proton H + and electron e - are generated. The proton H + moves to the cathode 13 via the polymer electrolyte membrane 11, and the electron e − moves to the cathode 13 through the wiring. In the cathode 13, the protons H + and electrons e from the anode 12 - by, O 2 + 4H + + 4e - → 2H 2 O oxygen reduction reaction of (ORR) occurs. In this way, the electronic e - power can be generated by the flow.
　一方、図１に示すように、カソード１３からＯ2ガスが高分子電解質膜１１を透過してアノード１２に達する。そのＯ2ガスが、アノード触媒上で下記酸素還元反応によりＨ2Ｏ2を発生させる。
　Ｏ2＋２Ｈ+＋２ｅ-→Ｈ2Ｏ2 On the other hand, as shown in FIG. 1, the O 2 gas from the cathode 13 permeates the polymer electrolyte membrane 11 and reaches the anode 12. The O 2 gas generates H 2 O 2 on the anode catalyst by the following oxygen reduction reaction.
O 2 + 2H + + 2e - → H 2 O 2
　また、上記Ｏ2ガスが、アノード触媒に下記のように吸着したＨ2分子（Ｈ2,ad）やＨ原子（Ｈad）と下記のように反応してＨ2Ｏ2を発生させる。
　Ｈ+＋ｅ-→Ｈad（吸着）
　Ｈ2,ad⇔２Ｈad（吸着状態での変化）
　Ｏ2＋Ｈ2,ad→Ｈ2Ｏ2
　Ｏ2＋２Ｈad→Ｈ2Ｏ2 Further, the O 2 gas reacts with the H 2 molecule (H 2, ad ) and the H atom (H ad ) adsorbed on the anode catalyst as described below to generate H 2 O 2 .
H + + e - → H ad ( adsorption)
H 2, ad ⇔ 2 H ad (change in adsorption state)
O 2 + H 2, ad → H 2 O 2
O 2 + 2H ad → H 2 O 2
　その結果、図２に示すように、上記のように発生したＨ2Ｏ2と、高分子電解質膜中及びアノード触媒層中のＦｅ2+イオン等の不純物とが反応すると・ＯＨラジカルが発生し、この・ＯＨラジカルが高分子電解質膜（ＰＥＭ）を分解する問題がある。 As a result, as shown in FIG. 2, when H 2 O 2 generated as described above reacts with impurities such as Fe 2+ ions in the polymer electrolyte membrane and the anode catalyst layer, OH radicals are generated. There is a problem that this OH radical decomposes the polymer electrolyte membrane (PEM).
　この問題に対処するために、従来からＰＥＭ中にＣｅ3+等のラジカル捕捉剤が添加されている。これにより、下記ラジカル分解反応によりＯＨラジカルを除去できる。
　・ＯＨ＋Ｃｅ3+＋Ｈ+→Ｃｅ4+＋Ｈ2Ｏ In order to deal with this problem, a radical scavenger such as Ce 3+ has been conventionally added to PEM. As a result, OH radicals can be removed by the following radical decomposition reaction.
・ OH + Ce 3+ + H + → Ce 4+ + H 2 O
　また、下記再生反応によりラジカル捕捉剤は再生される。
　Ｃｅ4+＋１／２Ｈ2→Ｃｅ3+＋Ｈ+ In addition, the radical scavenger is regenerated by the following regeneration reaction.
Ce 4+ + 1 / 2H 2 → Ce 3+ + H +
　しかし、燃料電池の運転中にＣｅ3+がカソード側に移動して、ラジカル捕捉効果が低下する問題がある。また、ラジカル捕捉剤を高分子電解質膜中に多量に添加するとオーム抵抗やカソード分極が増大して、発電性能が低下することになる。このため、従来の燃料電池では、その運転に伴いラジカル捕捉剤の効果が低下し、高分子電解質膜が劣化することになる。 However, there is a problem that Ce 3+ moves to the cathode side during the operation of the fuel cell and the radical scavenging effect is reduced. Further, if a large amount of radical scavenger is added to the polymer electrolyte membrane, the ohm resistance and the cathode polarization increase, and the power generation performance deteriorates. Therefore, in the conventional fuel cell, the effect of the radical scavenger is reduced with the operation, and the polymer electrolyte membrane is deteriorated.
　＜高分子電解質膜の劣化を防止できる理由＞
　これに対し、アノード触媒層１４に白金合金触媒を含めると、ラジカル源となるＨ2Ｏ2の生成速度を低下させることができると考えられる。その理由を各種触媒金属に対する水素原子（Ｈ）と水素分子（Ｈ2）の吸着エネルギーの違いにより説明する。図３は、各種触媒金属に対する水素原子（Ｈ）と水素分子（Ｈ2）の吸着エネルギーを示す図である。用いた触媒金属は、Ｐｔ単体、ＰｔＲｕ合金、及び、後述する白金スキン触媒として、Ｐｔ1ALＰｔＮｉ、Ｐｔ1ALＰｔＣｏ、Ｐｔ1ALＰｔＦｅである。また、上記吸着エネルギーは、ＤＦＴ計算で求めた。 <Reason for preventing deterioration of polymer electrolyte membrane>
On the other hand, if a platinum alloy catalyst is included in the anode catalyst layer 14, it is considered that the production rate of H 2 O 2 as a radical source can be reduced. The reason will be explained by the difference in the adsorption energy of hydrogen atom (H) and hydrogen molecule (H 2 ) for various catalyst metals. FIG. 3 is a diagram showing the adsorption energies of hydrogen atoms (H) and hydrogen molecules (H 2 ) with respect to various catalyst metals. Catalytic metal used, Pt alone, PtRu alloy, and, as the platinum skin catalyst described below, Pt 1AL PtNi, Pt 1AL PtCo, a Pt 1AL PtFe. Further, the adsorption energy was obtained by DFT calculation.
　図３から、各種触媒金属に対する水素原子（Ｈ）のステップ－エッジ（step-edge）及びテラス（terrace）における吸着エネルギーの大きさは、Ｐｔ＞ＰｔＲｕ＞Ｐｔ1ALＰｔＮｉ＞Ｐｔ1ALＰｔＣｏ＞Ｐｔ1ALＰｔＦｅの順で小さくなっていることが分かる。即ち、ＰｔＲｕ、Ｐｔ1ALＰｔＮｉ、Ｐｔ1ALＰｔＣｏ、Ｐｔ1ALＰｔＦｅ等の白金合金触媒は、Ｐｔ単体に比べて水素原子（Ｈ）の吸着エネルギーが小さく、水素原子（Ｈ）が吸着しにくいと考えられる。 3, steps of the hydrogen atom (H) for various catalytic metals - Edge (step-edge) and the size of the adsorption energy in terrace (terrace The terrace) is, Pt>PtRu> Pt 1AL PtNi > Pt 1AL PtCo> Pt 1AL PtFe It can be seen that it becomes smaller in the order of. That, PtRu, Pt 1AL PtNi, Pt 1AL PtCo, platinum alloy catalysts such as Pt 1AL PtFe has a small adsorption energy of hydrogen atoms (H) as compared to Pt alone, a hydrogen atom (H) is considered to hardly adsorbed ..
　また、図３から、各種触媒金属に対する水素分子（Ｈ2）のステップ－エッジ（step-edge）における吸着エネルギーの大きさは、Ｐｔ＞ＰｔＲｕ＞Ｐｔ1ALＰｔＮｉ＝Ｐｔ1ALＰｔＣｏ＝Ｐｔ1ALＰｔＦｅの順で小さくなっていることが分かる。即ち、ＰｔＲｕ、Ｐｔ1ALＰｔＮｉ、Ｐｔ1ALＰｔＣｏ、Ｐｔ1ALＰｔＦｅ等の白金合金触媒は、Ｐｔ単体に比べてステップ－エッジ（step-edge）における水素分子（Ｈ2）の吸着エネルギーが小さく、水素分子（Ｈ2）が吸着しにくいと考えられる。 Further, from FIG. 3, the steps of the hydrogen molecules to various metal catalyst (H 2) - Edge (step-edge) the size of the adsorption energy in the, Pt>PtRu> Pt 1AL PtNi = Pt 1AL PtCo = Pt 1AL PtFe order You can see that it is getting smaller. That, PtRu, Pt 1AL PtNi, Pt 1AL PtCo, platinum alloy catalysts such as Pt 1AL PtFe, compared to Pt alone Step - Edge (step-edge) small adsorption energy of the hydrogen molecules (H 2) in the hydrogen molecule It is considered that (H 2 ) is difficult to be adsorbed.
　一方、図３から、各種触媒金属に対する水素分子（Ｈ2）のテラス（terrace）における吸着エネルギーの大きさは、測定した全ての触媒金属において小さいことが分かる。即ち、Ｐｔ、ＰｔＲｕ、Ｐｔ1ALＰｔＮｉ、Ｐｔ1ALＰｔＣｏ、Ｐｔ1ALＰｔＦｅ等の白金系触媒は、全般にテラス（terrace）における水素分子（Ｈ2）の吸着エネルギーが小さく、水素分子（Ｈ2）が吸着しにくいと考えられる。 On the other hand, from FIG. 3, it can be seen that the magnitude of the adsorption energy of the hydrogen molecule (H 2 ) on the terrace with respect to various catalyst metals is small in all the measured catalyst metals. That, Pt, PtRu, Pt 1AL PtNi , Pt 1AL PtCo, platinum-based catalysts such as Pt 1AL PtFe has a small adsorption energy terrace hydrogen molecules in (terrace) (H 2) in general, hydrogen molecules (H 2) is It is thought that it is difficult to adsorb.
　このように、ＰｔＲｕ、Ｐｔ1ALＰｔＮｉ、Ｐｔ1ALＰｔＣｏ、Ｐｔ1ALＰｔＦｅ等の白金合金触媒は、Ｐｔ単体に比べて水素原子（Ｈ）の吸着エネルギーが小さく、水素原子（Ｈ）が吸着しにくいと考えられることから、前述のように、カソードからＯ2ガスが高分子電解質膜を透過してアノードに達しても、そのＯ2ガスがアノード触媒に吸着したＨ原子（Ｈad）と反応することが極度に減少することから、Ｈ2Ｏ2生成速度が低下すると考えられる。 Thus, PtRu, Pt 1AL PtNi, Pt 1AL PtCo, platinum alloy catalysts such as Pt 1AL PtFe has a small adsorption energy of hydrogen atoms (H) as compared to Pt alone, a hydrogen atom (H) is a hard adsorbed Therefore, as described above, even if O 2 gas permeates the polymer electrolyte membrane from the cathode and reaches the anode, the O 2 gas reacts with H atoms (H ad ) adsorbed on the anode catalyst. Is extremely reduced, and it is considered that the H 2 O 2 production rate is reduced.
　このように、アノード触媒層１４に白金合金触媒を含めると、ラジカル源となるＨ2Ｏ2生成速度を低下させることができ、その結果、・ＯＨラジカルの発生も減少し、高分子電解質膜の劣化を防止できると考えられる。 In this way, when the platinum alloy catalyst is included in the anode catalyst layer 14, the H 2 O 2 generation rate as a radical source can be reduced, and as a result, the generation of OH radicals is also reduced, and the polymer electrolyte membrane It is thought that deterioration can be prevented.
　（過酸化水素発生抑制用触媒）
　次に、本願で開示する過酸化水素発生抑制用触媒の実施形態について説明する。本実施形態の過酸化水素発生抑制用触媒は、白金と遷移金属との合金粒子からなり、燃料電池のアノードにおける過酸化水素の発生を抑制する白金合金触媒である。即ち、前述の膜－電極接合体のアノード触媒層に含まれる白金合金触媒は、白金と遷移金属との合金粒子からなる本願で開示する過酸化水素発生抑制用触媒である。 (Catalyst for suppressing hydrogen peroxide generation)
Next, an embodiment of the catalyst for suppressing hydrogen peroxide generation disclosed in the present application will be described. The catalyst for suppressing hydrogen peroxide generation of the present embodiment is a platinum alloy catalyst composed of alloy particles of platinum and a transition metal and suppressing the generation of hydrogen peroxide at the anode of a fuel cell. That is, the platinum alloy catalyst contained in the anode catalyst layer of the membrane-electrode assembly described above is the catalyst for suppressing hydrogen peroxide generation disclosed in the present application, which is composed of alloy particles of platinum and a transition metal.
　上記過酸化水素発生抑制用触媒に含まれる遷移金属としては、例えば、鉄（Ｆｅ）、コバルト（Ｃｏ）、ニッケル（Ｎｉ）、マンガン（Ｍｎ）、クロム（Ｃｒ）、バナジウム（Ｖ）、チタン（Ｔｉ）、ニオブ（Ｎｂ）、モリブデン（Ｍｏ）、鉛（Ｐｂ）、タングステン（Ｗ）から選ばれる少なくとも１種を用いることができるが、Ｃｏが最も好ましい。ＰｔＣｏ系合金は、水素酸化反応（ＨＯＲ）活性が大きいからである。 Examples of the transition metal contained in the catalyst for suppressing molybdenum generation include iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn), chromium (Cr), vanadium (V), and titanium ( At least one selected from Ti), niobium (Nb), molybdenum (Mo), lead (Pb), and tungsten (W) can be used, but Co is most preferable. This is because the PtCo-based alloy has a large hydrogen oxidation reaction (HOR) activity.
　上記白金合金触媒からなる過酸化水素発生抑制用触媒は、Ｐｔ100-nＭn（Ｍ：遷移金属原子、ｎ：合金中の遷移金属原子Ｍの原子パーセントであり、５≦ｎ≦９０）で表される。 The catalyst for suppressing hydrogen peroxide generation composed of the platinum alloy catalyst is Pt 100-n M n (M: transition metal atom, n: atomic percentage of transition metal atom M in the alloy, 5 ≦ n ≦ 90). expressed.
　更に、上記白金合金触媒は、白金と遷移金属との合金粒子の表面に、白金原子からなる１から２原子層の白金スキン層を備えていることがより好ましい。これにより、Ｈ2Ｏ2生成速度がより低下するからである。上記白金スキン層を備えた白金合金触媒からなる過酸化水素発生抑制用触媒は、ＰｔxAL－Ｐｔ100-nＭn（Ｍ：遷移金属原子、ｘ：白金スキン層の数１～２、ＡＬ：atomic-layer、ｎ：合金中の遷移金属原子Ｍの原子パーセントであり、５≦ｎ≦９０）で表され、かかる白金合金触媒を白金スキン触媒ともいう。白金スキン触媒及びその製造方法については、特許文献２（特開２０１７－０４２７５９号公報）に詳細に開示されている。 Further, it is more preferable that the platinum alloy catalyst is provided with a platinum skin layer having 1 to 2 atomic layers composed of platinum atoms on the surface of alloy particles of platinum and a transition metal. This is because the H 2 O 2 production rate is further reduced. The catalyst for suppressing hydrogen generation generated by the platinum alloy catalyst provided with the platinum skin layer is Pt xAL −Pt 100-n M n (M: transition metal atom, x: number of platinum skin layers 1 to 2, AL: atomic-layer, n: Atomic percentage of the transition metal atom M in the alloy, represented by 5 ≦ n ≦ 90), such a platinum alloy catalyst is also referred to as a platinum skin catalyst. The platinum skin catalyst and a method for producing the platinum skin catalyst are disclosed in detail in Patent Document 2 (Japanese Unexamined Patent Publication No. 2017-042759).
　また、上記白金合金触媒は、通常、担体に担持された担持触媒として用いられる。上記担体としては、特に限定されないが、触媒担持能、電子伝導性、電気化学的安定性等を考慮すると、カーボンブラック、アモルファスカーボン、ケッチェンブラック、活性炭、カーボンナノホーン、カーボンナノチューブ等の高表面積のカーボンが好ましい。担体としてカーボン（Ｃ）を用いた場合、上記白金合金触媒は、Ｐｔ100-nＭn／Ｃで表され、上記白金スキン触媒は、ＰｔxAL－Ｐｔ100-nＭn／Ｃで表される。 Further, the platinum alloy catalyst is usually used as a supported catalyst supported on a carrier. The carrier is not particularly limited, but in consideration of catalyst supporting ability, electron conductivity, electrochemical stability, etc., it has a high surface area such as carbon black, amorphous carbon, Ketjen black, activated carbon, carbon nanohorns, carbon nanotubes, etc. Carbon is preferred. When carbon (C) is used as the carrier, the platinum alloy catalyst is represented by Pt 100-n M n / C, and the platinum skin catalyst is represented by Pt xAL- Pt 100-n M n / C. ..
　本実施形態の過酸化水素発生抑制用触媒を燃料電池のアノードに用いることにより、燃料電池のアノードにおける過酸化水素の発生を抑制する方法を提供できる。 By using the catalyst for suppressing hydrogen peroxide generation of the present embodiment as the anode of the fuel cell, it is possible to provide a method of suppressing the generation of hydrogen peroxide at the anode of the fuel cell.
　続いて、前述の実施形態の膜－電極接合体に用いるアノード触媒層、カソード触媒層、高分子電解質膜、及びラジカル捕捉材について説明する。 Subsequently, the anode catalyst layer, the cathode catalyst layer, the polymer electrolyte membrane, and the radical scavenger used for the membrane-electrode assembly of the above-described embodiment will be described.
　＜アノード触媒層＞
　本実施形態の膜－電極接合体を構成するアノード触媒層は、高分子電解質膜の第１主面に配置され、上記アノード触媒層は、前述の過酸化水素発生抑制用触媒と、バインダーとを含んでいる。 <Anode catalyst layer>
The anode catalyst layer constituting the membrane-electrode assembly of the present embodiment is arranged on the first main surface of the polymer electrolyte membrane, and the anode catalyst layer comprises the above-mentioned catalyst for suppressing hydrogen peroxide generation and a binder. Includes.
　上記バインダーとしては特に限定されないが、イオン伝導性バインダーが好ましく、イオン伝導性のフッ素系樹脂からなるバインダーが好ましい。上記イオン伝導性のフッ素系樹脂としては、例えば、デュポン社製の“Ｎａｆｉｏｎ”（登録商標）が挙げられる。 The binder is not particularly limited, but an ionic conductive binder is preferable, and a binder made of an ionic conductive fluororesin is preferable. Examples of the ionic conductive fluororesin include "Nafion" (registered trademark) manufactured by DuPont.
　上記アノード触媒層は、上記過酸化水素発生抑制用触媒と、上記バインダーと、溶媒とを含む触媒インクを作製し、この触媒インクを高分子電解質膜に塗布した後、溶媒を除去することにより形成することができる。 The anode catalyst layer is formed by preparing a catalyst ink containing the catalyst for suppressing hydrogen peroxide generation, the binder, and a solvent, applying the catalyst ink to the polymer electrolyte membrane, and then removing the solvent. can do.
　＜カソード触媒層＞
　本実施形態の膜－電極接合体を構成するカソード触媒層は、高分子電解質膜の第２主面に配置され、上記カソード触媒層は、担持触媒と、バインダーとから形成できる。上記担持触媒及び上記バインダーとしては、特に限定されないが、前述のアノード触媒層に用いたものと同じ材料を用いることもできる。また、上記カソード触媒層は、前述のアノード触媒層と同様にして形成できる。 <Cathode catalyst layer>
The cathode catalyst layer constituting the membrane-electrode assembly of the present embodiment is arranged on the second main surface of the polymer electrolyte membrane, and the cathode catalyst layer can be formed from a supported catalyst and a binder. The supported catalyst and the binder are not particularly limited, but the same materials as those used for the anode catalyst layer described above can also be used. Further, the cathode catalyst layer can be formed in the same manner as the anode catalyst layer described above.
　＜高分子電解質膜＞
　本実施形態の膜－電極接合体を構成する高分子電解質膜は、湿潤状態で良好なイオン（プロトン）伝導性を示す材料で形成されており、例えば、フッ素系樹脂により形成されたイオン（プロトン）伝導性のイオン交換膜が用いられる。上記フッ素系樹脂としては、デュポン社製の“Ｎａｆｉｏｎ”（登録商標）が挙げられる。 <Polymer electrolyte membrane>
The polymer electrolyte membrane constituting the membrane-electrode assembly of the present embodiment is formed of a material that exhibits good ion (proton) conductivity in a wet state, and is, for example, an ion (proton) formed of a fluororesin. ) A conductive ion exchange membrane is used. Examples of the fluororesin include "Nafion" (registered trademark) manufactured by DuPont.
　＜ラジカル捕捉剤＞
　本実施形態の膜－電極接合体には、ラジカル捕捉剤を用いることもできる。上記ラジカル捕捉剤は、高分子電解質膜中、アノード触媒層中、及び、高分子電解質膜とアノード触媒層との間、から選ばれる少なくとも一箇所に配置されることが好ましい。これにより、高分子電解質膜の劣化原因となるＯＨラジカルを直接的に除去できる。また、上記ラジカル捕捉剤がカソード側に移動してその量が減少したとしても、前述の過酸化水素発生抑制用触媒のＨ2Ｏ2生成抑制効果と相まって、残存する少量のラジカル捕捉剤であってもその効果を最大限に発揮でき、確実にＯＨラジカルを除去できる。 <Radical scavenger>
A radical scavenger can also be used for the membrane-electrode assembly of the present embodiment. The radical trapping agent is preferably disposed at least one selected from the polymer electrolyte membrane, the anode catalyst layer, and between the polymer electrolyte membrane and the anode catalyst layer. As a result, OH radicals that cause deterioration of the polymer electrolyte membrane can be directly removed. Further, even if the radical scavenger moves to the cathode side and the amount thereof decreases, it is a small amount of the remaining radical scavenger in combination with the H 2 O 2 production suppressing effect of the hydrogen peroxide generation suppressing catalyst. However, the effect can be maximized and OH radicals can be reliably removed.
　上記ラジカル捕捉剤を高分子電解質膜中に配置する場合には、ラジカル捕捉剤を高分子電解質膜のアノード側に偏在して配置するのが好ましい。また、上記ラジカル捕捉剤をアノード触媒層中に配置する場合には、ラジカル捕捉剤をアノード触媒層の高分子電解質膜側に偏在して配置するのが好ましい。 When the radical scavenger is arranged in the polymer electrolyte membrane, it is preferable to arrange the radical scavenger unevenly on the anode side of the polymer electrolyte membrane. When the radical scavenger is arranged in the anode catalyst layer, it is preferable that the radical scavenger is unevenly distributed on the polymer electrolyte membrane side of the anode catalyst layer.
　上記ラジカル捕捉剤の種類については特に限定されないが、セリウム（Ｃｅ）、マンガン（Ｍｎ）、ルテニウム（Ｒｕ）、銀（Ａｇ）、タングステン（Ｗ）、クロム（Ｃｒ）、アルミニウム（Ａｌ）及びコバルト（Ｃｏ）からなる群から選ばれる少なくとも１種の元素を含む化合物であることが好ましい。中でも、酸化セリウム、水酸化セリウム、リン酸セリウム等のセリウム化合物が好ましい。リン酸セリウムを用いたラジカル捕捉剤については、特許文献１（特開２００６－３２４０９４号公報）に詳細に開示されている。 The type of the radical scavenger is not particularly limited, but cerium (Ce), manganese (Mn), ruthenium (Ru), silver (Ag), tungsten (W), chromium (Cr), aluminum (Al) and cobalt (Al). It is preferably a compound containing at least one element selected from the group consisting of Co). Of these, cerium compounds such as cerium oxide, cerium hydroxide, and cerium phosphate are preferable. A radical scavenger using cerium phosphate is disclosed in detail in Patent Document 1 (Japanese Unexamined Patent Publication No. 2006-324094).
　（燃料電池）
　本願で開示する燃料電池の実施形態について説明する。本実施形態の燃料電池は、前述の実施形態の膜－電極接合体を備えている。上記膜－電極接合体は、アノード触媒として、ラジカル源となるＨ2Ｏ2生成速度の低い過酸化水素発生抑制用触媒（白金合金触媒、白金スキン触媒）を用いているので、高分子電解質膜の劣化を抑制することができ、その結果、燃料電池の耐久性を向上できる。 (Fuel cell)
An embodiment of the fuel cell disclosed in the present application will be described. The fuel cell of the present embodiment includes the membrane-electrode assembly of the above-described embodiment. Since the membrane-electrode assembly uses a catalyst for suppressing hydrogen peroxide generation (platinum alloy catalyst, platinum skin catalyst) having a low H 2 O 2 production rate as a radical source as an anode catalyst, it is a polymer electrolyte membrane. Deterioration can be suppressed, and as a result, the durability of the fuel cell can be improved.
　本実施形態の燃料電池で用いるガス拡散層、ガス流路及びその他の構成部材については、特に制限されるものではなく、例えば、特許文献３（特許第６１５０２６５号公報）に開示のものを使用することができる。 The gas diffusion layer, gas flow path, and other constituent members used in the fuel cell of the present embodiment are not particularly limited, and for example, those disclosed in Patent Document 3 (Patent No. 6150265) are used. be able to.
　以下、本願で開示する過酸化水素発生抑制用触媒及び従来の白金触媒の過酸化水素（Ｈ2Ｏ2）発生速度について、実施例に基づき説明するが、本願は下記の実施例により限定されるものではない。 Hereinafter, the hydrogen peroxide (H 2 O 2 ) generation rate of the catalyst for suppressing hydrogen peroxide generation and the conventional platinum catalyst disclosed in the present application will be described based on examples, but the present application is limited to the following examples. It's not a thing.
　＜過酸化水素（Ｈ2Ｏ2）発生速度の測定方法＞
　過酸化水素（Ｈ2Ｏ2）発生速度は、チャンネルフロー二重電極（ＣＦＤＥ）法により測定した。図４にＣＦＤＥ法に用いるチャンネルフロー二重電極（ＣＦＤＥ）セルの模式図を示す。また、図５は、図４の試験極及び検出極の拡大模式図である。 <Measurement method of hydrogen peroxide (H 2 O 2 ) generation rate>
The rate of hydrogen peroxide (H 2 O 2 ) generation was measured by the channel flow double electrode (CFDE) method. FIG. 4 shows a schematic diagram of a channel flow double electrode (CFDE) cell used in the CFDE method. Further, FIG. 5 is an enlarged schematic view of the test electrode and the detection electrode of FIG.
　図４及び図５において、ｃ－Ｐｔ／Ｃ（市販（commercial）－白金担持カーボン触媒）をＣＦＤＥセルのグラッシーカーボン（ＧＣ）基板に固定し、その表面を厚さ０．１μｍのＮａｆｉｏｎ薄膜（デュポン社製のフッ素系樹脂“Ｎａｆｉｏｎ”（登録商標）からなる薄膜）で被覆して試験極とした。また、試験極の下流には、Ｐｔ板からなる検出極を配置した。 In FIGS. 4 and 5, c-Pt / C (commercial-platinum-supported carbon catalyst) is fixed to a glassy carbon (GC) substrate of a CFDE cell, and the surface thereof is a 0.1 μm-thick Nafion thin film (DuPont). A thin film made of a fluororesin "Nafion" (registered trademark) manufactured by the same company was used as a test electrode. Further, a detection electrode made of a Pt plate was arranged downstream of the test electrode.
　先ず、０．１ＭのＨＣｌＯ4水溶液に純水素を飽和した電解液を、温度８０℃、平均流速１１１ｃｍ／ｓで流して、掃引速度５ｍＶ／ｓで試験極の対流ボルタモグラムを測定して、通常の水素酸化反応（ＨＯＲ）特性を評価した。図６の下段に上記対流ボルタモグラムを示す。図６の対流ボルタモグラムではＡ（Ｈ2）に示すＨＯＲ特性を示し、ＨＯＲ電流密度は、０Ｖから立ち上がり、約０．０６Ｖで拡散限界電流密度に達した。ここでの電圧Ｖは、可逆水素電極（ＲＨＥ：Reversible Hydrogen Electrode）に対する電圧である。 First, an electrolytic solution saturated with pure hydrogen in a 0.1 M HClO 4 aqueous solution is flowed at a temperature of 80 ° C. and an average flow rate of 111 cm / s, and a convection voltamogram of a test electrode is measured at a sweep rate of 5 mV / s. The hydrogen oxidation reaction (HOR) characteristics were evaluated. The convection voltamogram is shown in the lower part of FIG. The convection voltamogram of FIG. 6 showed the HOR characteristic shown in A (H 2 ), and the HOR current density increased from 0 V and reached the diffusion limit current density at about 0.06 V. The voltage V here is a voltage for a reversible hydrogen electrode (RHE: Reversible Hydrogen Electrode).
　一方、試験極の下流に位置する検出極は、発生したＨ2Ｏ2を拡散支配で酸化可能で、水素酸化（ＨＯＲ）電流（バックグラウンド）が小さくなるように、ＲＨＥに対して１．４Ｖに保持した。図６の上段に検出極の電流密度をｊcとして示す。検出極のＨＯＲによる電流密度ｊc（Ｈ2）は、試験極電位によらず約０．１ｍＡｃｍ-2であった。 On the other hand, the detection electrode located downstream of the test electrode can oxidize the generated H 2 O 2 by diffusion control, and 1.4 V with respect to RHE so that the hydrogen peroxide (HOR) current (background) becomes small. Held in. The current density of the detection electrode is shown as j c in the upper part of FIG. The current density j c (H 2 ) by HOR of the detection electrode was about 0.1 mAcm -2 regardless of the test electrode potential.
　次に、高分子電解質膜からのＯ2ガスの透過を模擬して、空気・水素混合ガス（空気濃度：１０％）を飽和した０．１ＭのＨＣｌＯ4水溶液を電解液として上記と同様に上記ＣＦＤＥセルに流して、試験極の対流ボルタモグラムと検出極の電流密度ｊc（１０％ａｉｒ／Ｈ2）を測定した。その結果を図６に示す。図６の下段の対流ボルタモグラムでは、Ｂ（１０％ａｉｒ／Ｈ2）に示すＨＯＲ特性を示し、図６の上段の検出極の電流密度では、ｊc（１０％ａｉｒ／Ｈ2）に示す電流密度を示した。 Next, simulating the permeation of O 2 gas from the polymer electrolyte membrane, 0.1 M HClO 4 aqueous solution saturated with air / hydrogen mixed gas (air concentration: 10%) was used as the electrolytic solution in the same manner as above. It was passed through a CFDE cell, and the convection voltamogram of the test electrode and the current density j c (10% air / H 2 ) of the detection electrode were measured. The result is shown in FIG. The convection voltamogram in the lower part of FIG. 6 shows the HOR characteristic shown in B (10% air / H 2 ), and the current density of the detection electrode in the upper part of FIG. 6 shows the current shown in j c (10% air / H 2 ). The density was shown.
　図６の下段から、酸素還元反応（ＯＲＲ）電流の重畳により、Ｂ（１０％ａｉｒ／Ｈ2）に示すＨＯＲ電流密度は、Ａ（Ｈ2）に示すＨＯＲ電流密度より僅かに減少した。一方、検出極の電流密度では、ｊc（１０％ａｉｒ／Ｈ2）は、試験極電位の低下とともに増加した。この増加分は、試験極で発生したＨ2Ｏ2の酸化反応によるものと考えられる。 From the lower part of FIG. 6, the HOR current density shown in B (10% air / H 2 ) was slightly reduced from the HOR current density shown in A (H 2 ) due to the superposition of the oxygen reduction reaction (ORR) current. On the other hand, in the current density of the detection electrode, j c (10% air / H 2 ) increased as the test electrode potential decreased. This increase is considered to be due to the oxidation reaction of H 2 O 2 generated at the test electrode.
　以上の結果から、試験極でのＨ2Ｏ2の発生速度ｊ（Ｈ2Ｏ2）を下記式のように定義した。
　ｊ（Ｈ2Ｏ2）＝［ｊc（１０％ａｉｒ／Ｈ2）－ｊc（Ｈ2）］／Ｎ
　上記式中でＮは、検出極の捕捉率であり、実験的に求めた値０．２９を用いた。 From the above results, the generation rate j (H 2 O 2 ) of H 2 O 2 at the test electrode was defined as the following equation.
j (H 2 O 2 ) = [j c (10% air / H 2 ) -j c (H 2 )] / N
In the above formula, N is the capture rate of the detection electrode, and an experimentally obtained value of 0.29 was used.
　（実施例１）
　＜Ｐｔ2AL－ＰｔＣｏ／Ｃ触媒の作製＞
　遷移金属Ｍとしてコバルト（Ｃｏ）、担体としてカーボン（Ｃ）を用いた２原子層の白金スキン層で被覆したＰｔ2AL－ＰｔＣｏ／Ｃ触媒を次のようにして作製した。 (Example 1)
< Preparation of Pt 2AL- PtCo / C catalyst>
A Pt 2AL- PtCo / C catalyst coated with a diatomic platinum skin layer using cobalt (Co) as the transition metal M and carbon (C) as the carrier was prepared as follows.
　先ず、Ｐｔ（ａｃａｃ）2を０．１２５ｍｍｏｌ（４９ｍｇ）、Ｃｏ（ａｃａｃ）3を０．１２５ｍｍｏｌ（４４ｍｇ）、１，２－ヘキサデカンジオール１ｍｍｏｌ（２６０ｍｇ）、ジフェニルエーテル１２．５ｍｌ（１３．５ｇ、７９．３ｍｍｏｌ）をビーカーに加え、スターラーを用いて１００℃に昇温して１０分間攪拌混合した。これにオレイン酸０．２５ｍｍｏｌ（８５μｌ）及びオレイルアミン０．２５ｍｍｏｌ（８０μｌ）を加えた後、攪拌しながら２００℃まで昇温し、そのまま２０分間攪拌して、ナノカプセル溶液を得た。 First, Pt (acac) 2 was 0.125 mmol (49 mg), Co (acac) 3 was 0.125 mmol (44 mg), 1,2-hexadecanediol was 1 mmol (260 mg), and diphenyl ether was 12.5 ml (13.5 g, 79. 3 mmol) was added to the beaker, the temperature was raised to 100 ° C. using a stirrer, and the mixture was stirred and mixed for 10 minutes. 0.25 mmol (85 μl) of oleic acid and 0.25 mmol (80 μl) of oleylamine were added thereto, the temperature was raised to 200 ° C. with stirring, and the mixture was stirred as it was for 20 minutes to obtain a nanocapsule solution.
　次に、得られたナノカプセル溶液に１Ｍ（ｍｏｌ／Ｌ）のＬｉＢ（Ｃ2Ｈ5）3Ｈ・ＴＨＦ溶液１．０ｍｌ（１ｍｍｏｌ）を２分間かけて徐々に滴下し、５分間攪拌した後、２６０℃に昇温し、この温度にて２０分間還流加熱して還元反応させ、ナノカプセル内にてＰｔＣｏ粒子（Ｃｏ５０ａｔｏｍ％）を含む溶液Ａを得た。その後、溶液Ａを１００℃付近まで降温し、ＰｔＣｏの担持量がカーボンブラックに対して２７．２ｗｔ％となるようにカーボンブラック（比表面積：１５０ｍ2／ｇ）を混合攪拌し、ＰｔＣｏ微粒子をカーボンブラック粒子に担持させた。 Next, 1.0 ml (1 mmol) of a 1 M (mol / L) LiB (C 2 H 5 ) 3 H / THF solution was gradually added dropwise to the obtained nanocapsule solution over 2 minutes, followed by stirring for 5 minutes. The temperature was raised to 260 ° C., and the mixture was heated under reflux for 20 minutes at this temperature for a reduction reaction to obtain a solution A containing PtCo particles (Co50 atom%) in nanocapsules. Then, the temperature of the solution A is lowered to around 100 ° C., carbon black (specific surface area: 150 m 2 / g) is mixed and stirred so that the amount of PtCo supported is 27.2 wt% with respect to the carbon black, and the PtCo fine particles are carbonized. It was supported on black particles.
　続いて、その混合液を濾過し、６０℃で真空乾燥した後、残存した有機溶媒の除去とＰｔＣｏ微粒子の表面へのＰｔ析出を同時に行なうため、４％水素ガス雰囲気下で、４００℃で４時間の加熱処理を行ない、Ｐｔ1AL－ＰｔＣｏ／Ｃを得た。 Subsequently, the mixed solution is filtered, vacuum dried at 60 ° C., and then the remaining organic solvent is removed and Pt is precipitated on the surface of the PtCo fine particles at the same time. Therefore, in a 4% hydrogen gas atmosphere, 4 at 400 ° C. subjected to heat treatment time, to obtain a Pt 1AL -PtCo / C.
　次に、Ｐｔスキン前駆体として、Ｐｔ１原子層分のテトラアンミン白金水酸塩溶液（［Ｐｔ（ＮＨ3）4］（ＯＨ）2）を純水１０ｍＬに溶解させて、Ｐｔスキン前駆体溶液を作製した。この溶液中に得られたＰｔ1AL－ＰｔＣｏ／Ｃを混合し、１０分の煮沸を行った後に、反応溶液が６０℃になるのを待って、水素ガス濃度５％、温度６０℃、時間１Ｈの条件で、水素バブリングを行った。その結果、各Ｐｔ1AL－ＰｔＣｏ微粒子の表面にＰｔスキン層が均一に形成され、Ｐｔ2AL－ＰｔＣｏ／Ｃ触媒を得た。 Next, as a Pt skin precursor, a tetraammine platinum hydroxide solution ([Pt (NH 3 ) 4 ] (OH) 2 ) for the Pt1 atomic layer was dissolved in 10 mL of pure water to prepare a Pt skin precursor solution. did. The solution is mixed Pt 1AL -PtCo / C obtained during and after boiling 10 minutes, the reaction solution is allowed to warm to 60 ° C., the hydrogen gas concentration of 5% and a temperature 60 ° C., the time 1H Hydrogen bubbling was performed under the conditions of. As a result, Pt skin layer on the surface of the Pt 1AL -PtCo particles are uniformly formed, to obtain a Pt 2AL -PtCo / C catalyst.
　（実施例２）
　実施例１の出発原料を、Ｐｔ（ａｃａｃ）2：０．１２５ｍｍｏｌ（４９ｍｇ）、Ｃｏ（ａｃａｃ）3：０．０４２ｍｍｏｌ（１５ｍｇ）とした以外は実施例１と同様にしてナノカプセル内にてＰｔ3Ｃｏ粒子を含む溶液Ｂを作製した後、その溶液Ｂを用いて実施例１と同様にしてＰｔ3Ｃｏ微粒子をカーボンブラック粒子に担持させた。その後、そのＰｔ3Ｃｏ微粒子担持カーボンブラック粒子を含む混合液を濾過し、６０℃で真空乾燥した後、４％水素ガス雰囲気下で、高温での短時間の加熱処理を行ない、Ｃｏ２５ａｔｏｍ％を含むＰｔ3Ｃｏ／Ｃ触媒を得た。 (Example 2)
Pt in nanocapsules in the same manner as in Example 1 except that the starting material of Example 1 was Pt (acac) 2 : 0.125 mmol (49 mg) and Co (acac) 3 : 0.042 mmol (15 mg). After preparing a solution B containing 3 Co particles, the Pt 3 Co fine particles were supported on the carbon black particles in the same manner as in Example 1 using the solution B. Then, the mixed solution containing the Pt 3 Co fine particle-supporting carbon black particles is filtered, vacuum dried at 60 ° C., and then heat-treated at a high temperature for a short time in a 4% hydrogen gas atmosphere to contain Co25 atom%. A Pt 3 Co / C catalyst was obtained.
　（比較例１）
　触媒金属として白金（Ｐｔ）、担体としてカーボン（Ｃ）を用いた市販のｃ－Ｐｔ／Ｃ触媒を準備した。 (Comparative Example 1)
A commercially available c-Pt / C catalyst using platinum (Pt) as the catalyst metal and carbon (C) as the carrier was prepared.
　＜Ｈ2Ｏ2発生速度ｊ（Ｈ2Ｏ2）の測定＞
　前述のチャンネルフロー二重電極（ＣＦＤＥ）法により、実施例１、実施例２及び比較例１の各触媒のｊc（Ｈ2）、ｊc（１０％ａｉｒ／Ｈ2）を測定し、下記式によりＨ2Ｏ2発生速度ｊ（Ｈ2Ｏ2）を算出した。
　ｊ（Ｈ2Ｏ2）＝［ｊc（１０％ａｉｒ／Ｈ2）－ｊc（Ｈ2）］／０．２９ <Measurement of H 2 O 2 generation rate j (H 2 O 2 )>
The j c (H 2 ) and j c (10% air / H 2 ) of the catalysts of Example 1, Example 2 and Comparative Example 1 were measured by the channel flow double electrode (CFDE) method described above, and described below. The H 2 O 2 generation rate j (H 2 O 2 ) was calculated by the formula.
j (H 2 O 2 ) = [j c (10% air / H 2 ) -j c (H 2 )] /0.29
　その結果を図７に示す。図７から、実施例１、実施例２及び比較例１では、ｊ（Ｈ2Ｏ2）は電位低下とともに増加し、０Ｖで最大値となったが、実施例１及び実施例２のｊ（Ｈ2Ｏ2）は、比較例１のｊ（Ｈ2Ｏ2）に比べて低下していることが分かる。特に、白金スキン触媒を用いた実施例１のｊ（Ｈ2Ｏ2）は、０．０６Ｖ以下の電位域で、従来の市販のｃ－Ｐｔ／Ｃ触媒を用いた比較例１のｊ（Ｈ2Ｏ2）に比べて、１／２以下に抑制されていた。 The result is shown in FIG. From FIG. 7, in Example 1, Example 2 and Comparative Example 1, j (H 2 O 2 ) increased with a decrease in potential and reached a maximum value at 0 V, but j (in Example 1 and Example 2). H 2 O 2) is found to have decreased in comparison with the Comparative example 1 j (H 2 O 2). In particular, j (H 2 O 2 ) of Example 1 using a platinum skin catalyst is j (H) of Comparative Example 1 using a conventional commercially available c-Pt / C catalyst in a potential range of 0.06 V or less. Compared with 2 O 2 ), it was suppressed to 1/2 or less.
　また、図７において、ｊ（Ｈ2Ｏ2）が最大となる０ＶではＨＯＲ電流はゼロであるので、燃料電池の開回路電位（ＯＣＶ）に相当する。従来から、燃料電池の開回路状態での高分子電解質膜の劣化が加速されることはよく知られていたが、上記結果から、その劣化原因が、開回路状態でのｊ（Ｈ2Ｏ2）が最大となることであったことが分かる。 Further, in FIG. 7, since the HOR current is zero at 0 V where j (H 2 O 2 ) is maximized, it corresponds to the open circuit potential (OCV) of the fuel cell. Conventionally, it has been well known that the deterioration of the polymer electrolyte membrane in the open circuit state of the fuel cell is accelerated, but from the above results, the cause of the deterioration is j (H 2 O 2) in the open circuit state. ) Was the maximum.
　上記結果より、本願で開示する過酸化水素発生抑制用触媒を用いた膜－電極接合体を備えた燃料電池は、上記過酸化水素発生抑制用触媒のＨ2Ｏ2生成抑制効果により、高分子電解質膜の劣化を抑制できるため、燃料電池の耐久性を向上できる。 Based on the above results, the fuel cell provided with the membrane-electrode assembly using the hydrogen peroxide generation suppressing catalyst disclosed in the present application is made of a polymer due to the H 2 O 2 production suppressing effect of the hydrogen peroxide generation suppressing catalyst. Since deterioration of the electrolyte membrane can be suppressed, the durability of the fuel cell can be improved.
　本願で開示する過酸化水素発生抑制用触媒をアノード触媒として用いた膜－電極接合体及びそれを用いた燃料電池は、高分子電解質膜の劣化を防止でき、その結果、燃料電池の耐久性を向上でき、燃料電池自動車や家庭用燃料電池等に有効に利用できる。 A membrane-electrode assembly using the catalyst for suppressing hydrogen peroxide generation disclosed in the present application as an anode catalyst and a fuel cell using the same can prevent deterioration of the polymer electrolyte membrane, and as a result, the durability of the fuel cell can be improved. It can be improved and can be effectively used for fuel cell vehicles and household fuel cells.
　１０　膜－電極接合体
　１１　高分子電解質膜
　１２　アノード
　１３　カソード
　１４　アノード触媒層
　１５　アノードガス拡散層
　１６　アノードガス流路
　１７　カソード触媒層
　１８　カソードガス拡散層
　１９　カソードガス流路 10 Membrane-electrode junction 11 Polymer electrolyte membrane 12 Anode 13 Cathode 14 Anode catalyst layer 15 Anode gas diffusion layer 16 Anode gas flow path 17 Cathode catalyst layer 18 Cathode gas diffusion layer 19 Cathode gas flow path

Claims (14)

  1. 　白金と遷移金属との合金粒子からなり、燃料電池のアノードにおける過酸化水素の発生を抑制する過酸化水素発生抑制用触媒。 A catalyst for suppressing hydrogen peroxide generation, which consists of alloy particles of platinum and transition metal and suppresses the generation of hydrogen peroxide at the anode of a fuel cell.
  2. 　Ｐｔ100-nＭn（Ｍ：遷移金属原子、ｎ：合金中の遷移金属原子Ｍの原子パーセントであり、５≦ｎ≦９０）で表される請求項１に記載の過酸化水素発生抑制用触媒。 The hydrogen peroxide generation suppression according to claim 1, which is represented by Pt 100-n M n (M: transition metal atom, n: atomic percentage of transition metal atom M in the alloy, 5 ≦ n ≦ 90). catalyst.
  3. 　前記合金粒子の表面に、白金原子からなる１から２原子層の白金スキン層を更に備えた請求項１に記載の過酸化水素発生抑制用触媒。 The catalyst for suppressing hydrogen peroxide generation according to claim 1, further comprising a platinum skin layer having 1 to 2 atomic layers composed of platinum atoms on the surface of the alloy particles.
  4. 　ＰｔxAL－Ｐｔ100-nＭn（Ｍ：遷移金属原子、ｘ：白金スキン層の数１～２、ＡＬ：atomic-layer、ｎ：合金中の遷移金属原子Ｍの原子パーセントであり、５≦ｎ≦９０）で表される請求項３に記載の過酸化水素発生抑制用触媒。 Pt xAL −Pt 100-n M n (M: transition metal atom, x: number of platinum skin layers 1-2, AL: atomic-layer, n: atomic percentage of transition metal atom M in alloy, 5 ≦ The catalyst for suppressing generation of hydrogen peroxide according to claim 3, which is represented by n ≦ 90).
  5. 　前記遷移金属が、コバルトである請求項１～４のいずれかに記載の過酸化水素発生抑制用触媒。 The catalyst for suppressing hydrogen peroxide generation according to any one of claims 1 to 4, wherein the transition metal is cobalt.
  6. 　担体に担持された担持触媒である請求項１～５のいずれかに記載の過酸化水素発生抑制用触媒。 The catalyst for suppressing hydrogen peroxide generation according to any one of claims 1 to 5, which is a supported catalyst supported on a carrier.
  7. 　前記担体が、カーボンである請求項６に記載の過酸化水素発生抑制用触媒。 The catalyst for suppressing hydrogen peroxide generation according to claim 6, wherein the carrier is carbon.
  8. 　請求項１～７のいずれかに記載の過酸化水素発生抑制用触媒を用いる燃料電池のアノードにおける過酸化水素の発生を抑制する方法。 A method for suppressing the generation of hydrogen peroxide at the anode of a fuel cell using the catalyst for suppressing hydrogen peroxide generation according to any one of claims 1 to 7.
  9. 　高分子電解質膜と、アノードと、カソードとを含む膜－電極接合体であって、
    　前記アノードが、請求項１～７のいずれかに記載の過酸化水素発生抑制用触媒を含む膜－電極接合体。     A membrane-electrode assembly containing a polymer electrolyte membrane, an anode, and a cathode.
    A membrane-electrode assembly in which the anode contains the catalyst for suppressing hydrogen peroxide generation according to any one of claims 1 to 7.
  10. 　前記アノードは、アノード触媒層を含み、
    　前記カソードは、カソード触媒層を含み、
    　前記アノード触媒層は、前記高分子電解質膜の第１主面に配置され、
    　前記カソード触媒層は、前記高分子電解質膜の第２主面に配置されている請求項９に記載の膜－電極接合体。     The anode comprises an anode catalyst layer and
    The cathode includes a cathode catalyst layer.
    The anode catalyst layer is arranged on the first main surface of the polymer electrolyte membrane.
    The membrane-electrode assembly according to claim 9, wherein the cathode catalyst layer is arranged on the second main surface of the polymer electrolyte membrane.
  11. 　前記高分子電解質膜中、前記アノード触媒層中、及び、前記高分子電解質膜と前記アノード触媒層との間、から選ばれる少なくとも一箇所に、ラジカル捕捉剤を更に配置した請求項１０に記載の膜－電極接合体。 The tenth aspect of claim 10, wherein the radical trapping agent is further arranged at at least one selected from the polymer electrolyte membrane, the anode catalyst layer, and between the polymer electrolyte membrane and the anode catalyst layer. Membrane-electrode assembly.
  12. 　前記ラジカル捕捉剤が、Ｃｅ、Ｍｎ、Ｒｕ、Ａｇ、Ｗ、Ｃｒ、Ａｌ、及びＣｏからなる群から選ばれる少なくとも１種の元素を含む化合物である請求項１１に記載の膜－電極接合体。 The membrane-electrode assembly according to claim 11, wherein the radical scavenger is a compound containing at least one element selected from the group consisting of Ce, Mn, Ru, Ag, W, Cr, Al, and Co.
  13. 　前記高分子電解質膜が、フッ素系樹脂により形成されたイオン伝導性のイオン交換膜である請求項９～１２のいずれかに記載の膜－電極接合体。 The membrane-electrode assembly according to any one of claims 9 to 12, wherein the polymer electrolyte membrane is an ion-conducting ion exchange membrane formed of a fluororesin.
  14. 　請求項９～１３のいずれかに記載の膜－電極接合体を含む燃料電池。 A fuel cell comprising the membrane-electrode assembly according to any one of claims 9 to 13.
PCT/JP2020/020823 2019-06-11 2020-05-27 Catalyst for suppressing hydrogen peroxide generation, method for suppressing hydrogen peroxide generation using same, membrane-electrode assembly, and fuel cell using same WO2020250673A1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000012043A (en) * 1998-04-23 2000-01-14 Ne Chemcat Corp Electrode catalyst for solid high-polymer electrolyte- type fuel cell, and electrode, electrolyte film/electrode junction body and solid high-polymer electrolyte-type fuel cell using the catalyst
JP2008192505A (en) * 2007-02-06 2008-08-21 Toyota Motor Corp Fuel cell
JP2017041384A (en) * 2015-08-20 2017-02-23 エヌ・イーケムキャット株式会社 Manufacturing method of catalyst for electrode

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000012043A (en) * 1998-04-23 2000-01-14 Ne Chemcat Corp Electrode catalyst for solid high-polymer electrolyte- type fuel cell, and electrode, electrolyte film/electrode junction body and solid high-polymer electrolyte-type fuel cell using the catalyst
JP2008192505A (en) * 2007-02-06 2008-08-21 Toyota Motor Corp Fuel cell
JP2017041384A (en) * 2015-08-20 2017-02-23 エヌ・イーケムキャット株式会社 Manufacturing method of catalyst for electrode

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