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JP-7855202-B2 - Anode catalyst for polymer electrolyte fuel cells with excellent CO-resistant catalyst toxicity.

JP7855202B2JP 7855202 B2JP7855202 B2JP 7855202B2JP-7855202-B2

Inventors

  • 近野 健人
  • 石田 稔
  • 香川 勝
  • 笠井 秀明
  • 中西 寛
  • スーザン メニェス アスペラ

Assignees

  • 田中貴金属工業株式会社
  • 独立行政法人国立高等専門学校機構

Dates

Publication Date
20260508
Application Date
20240930

Claims (4)

  1. Anode catalyst for a polymer electrolyte fuel cell having catalyst particles for processing fuel gas containing carbon monoxide, The catalyst particles consist of Pt and Ir, with an atomic ratio of Pt to Ir (Pt:Ir) of 2:1 or more and 1:2 or less. The catalyst particles are characterized in that they include regions on their surface in which four or more Ir atoms are clustered adjacent to each other, making them an anode catalyst for polymer electrolyte fuel cells.
  2. The anode catalyst for a polymer electrolyte fuel cell according to claim 1, wherein the catalyst particles are supported on a carbon fine powder carrier.
  3. The anode catalyst for a polymer electrolyte fuel cell according to claim 1 or 2, wherein the loading density of the catalyst particles relative to the entire catalyst is 20% by mass or more and 70% by mass or less.
  4. In a power generation method that includes the step of supplying fuel gas to the anode of a polymer electrolyte fuel cell, The fuel gas contains carbon monoxide. A method for generating electricity, characterized in that the anode comprises the anode catalyst described in claim 1 or claim 2.

Description

This invention relates to an anode catalyst for advancing the anode reaction in a polymer electrolyte fuel cell. In particular, it relates to an anode catalyst for a polymer electrolyte fuel cell with improved catalyst toxicity resistance to CO (carbon monoxide) contained in the fuel gas. The practical application of polymer electrolyte fuel cells (MSF) is progressing for use as power sources for automobiles and homes. MSFs primarily consist of a membrane/electrode assembly (MEA) comprising a hydrogen electrode (anode) supplied with hydrogen-containing fuel gas, an air electrode (cathode) supplied with oxidizing gas such as oxygen or air, and a solid polymer electrolyte membrane sandwiched between these electrodes. The anode and cathode are composed of catalysts in which catalyst particles made of precious metals such as platinum (Pt) are supported on a carrier such as carbon fine powder. In MSFs, the catalysts used in the anode and cathode are primarily required to exhibit catalytic activity to promote the reactions occurring at each electrode. In addition, they are also required to possess additional characteristics depending on the composition of the supplied raw materials (fuel gas and oxidizing gas) and the operating load. In polymer electrolyte fuel cells, anode catalysts generally use Pt catalysts, which exhibit high activity in the hydrogen gas oxidation reaction (HOR: H₂ → 2H⁺ + 2e⁻ ) and are resistant to corrosion in the acidic conditions of polymer electrolyte fuel cells. In addition to this catalytic activity, resistance to CO (carbon monoxide) toxicity is also required. The hydrogen supplied to the anode is sometimes obtained from reformed gases such as gasoline or methanol. These reformed gases often contain trace amounts of CO during their synthesis. CO contained in the fuel gas adsorbs onto the catalyst particles and occupies active sites, leading to catalyst degradation (deactivation) over time. Therefore, anode catalysts are required to be resistant to CO catalyst poisoning. For anode catalysts used in polymer electrolyte fuel cells, catalysts using PtRu alloy (Pt-Ru alloy) as catalyst particles have been conventionally known as those exhibiting excellent resistance to CO catalyst poisoning (Patent Documents 1 and 2, etc.). Catalysts using Pt alloys such as PtRu alloy as catalyst particles can be manufactured by impregnating a carrier such as carbon fine powder with a solution containing Pt and Ru ions, followed by reduction and heat treatment, thereby metallizing and alloying the Pt and Ru ions. The improvement in CO catalyst toxicity resistance achieved by alloying Pt with a dissimilar metal such as Ru (hereinafter, the dissimilar metal alloyed with Pt may be referred to as metal M) can be explained by two mechanisms: (i) the ligand effect and (ii) the bifunctional model. (i) The Ligand effect is the effect caused by the change in electron density resulting from the difference in electronegativity between a Pt atom and a metal M atom when the two atoms are adjacent. When Ru, which has fewer electrons than Pt, alloys with Pt, the electronic state of the catalyst particle surface changes, making electron transfer easier. This leads to a decrease in CO adsorption capacity and accelerated desorption reactions. In other words, alloying with Ru reduces the frequency of CO adsorption to Pt and accelerates the release of the adsorbed state, thereby improving the catalyst particle's resistance to CO catalyst toxicity. Furthermore, the bifunctional model in (ii) is the action of Ru acting as a co-catalyst to remove CO adsorbed on Pt. In this mechanism, CO is adsorbed on Pt in (1) below (the CO adsorbed on Pt will be referred to as CO adsorbents below). On the other hand, the electrolysis (oxidation) of water in (2) causes the adsorption of OH onto Ru (the OH adsorbed on Ru will be referred to as OH adsorbents below). Then, the reaction between the Pt-CO adsorbents and Ru-OH adsorbents produced by these reactions causes CO to be released as CO2 . This action of Ru improves the catalyst particle's resistance to CO catalyst toxicity by releasing the CO adsorbed onto Pt. Pt + CO → Pt-CO ads (1) Ru + H 2 O → Ru-OH ads + H + + e - (2) Pt-CO ads + Ru-OH ads → Pt + Ru + CO 2 + H + + e - (3) Japanese Patent Application Publication No. 9-153366Japanese Patent Publication No. 2000-3712 Simulation results when metal M atoms (Ru, Rh, Pd, Ir) are substituted on the surface of catalyst particles made of Pt.A model diagram of a Pt alloy catalyst for simulating the improvement in CO-resistance catalyst toxicity due to the Ligand effect.A model diagram showing the state of CO and OH adsorbed on the surface of a Pt alloy catalyst, used to simulate the effect of improving CO-resistance catalyst toxicity using a bifunctional model.This figure shows the simulation results of the CO elimination reaction mechanism in a PtRu alloy catalyst.This figure shows the simulation results of the CO elimination reaction mechanism i