Fuel electrode catalyst for fuel cell, electrode/membrane assembly, and fuel cell and fuel cell system provided with the electrode/membrane assembly

An electrode/membrane assembly for a fuel cell, comprising a fuel electrode bonded to one surface of a polymer electrolyte membrane and an air electrode bonded to the other surface of the polymer electrolyte membrane,

• wherein the fuel electrode comprises a mixed catalyst layer prepared by mixing a first catalyst with a second catalyst, said mixed catalyst layer having a mixing ratio by mass of the first catalyst to the second catalyst set to 10:
• 1-10,
• said first catalyst consisting of a platinum-ruthenium alloy and supported by carbon, in which platinum Pt and ruthenium Ru are included at a mass % of Pt:
• Ru=10-95:5-90, wherein Pt+Ru=100 and,
• said second catalyst consisting of a platinum-ruthenium-metal (M) alloy and supported by carbon, in which platinum Pt, ruthenium Ru and the metal M are included at a mass % of Pt:Ru:M=10-95:1-90:0.001-30, wherein:
• Pt+Ru+M=100,
• and
• the metal (M) has a lower dissolving potential than ruthenium.