Process for producing membrane/ electrode assembly for polymer electrolyte fuel cells

A process for producing a membrane/electrode assembly comprising a first electrode having a first catalyst layer and a first gas diffusion layer, a second electrode having a second catalyst layer and a second gas diffusion layer, and an electrolyte membrane interposed between the first electrode and the second electrode, which comprises:

• applying a coating fluid comprising an ion exchange resin on a substrate, followed by annealing at from 100 to 250° C. to form an electrolyte membrane, and applying a coating fluid comprising an electrode catalyst and an ion exchange resin on the surface of the obtained electrolyte membrane to form the first catalyst layer, thereby to prepare a first intermediate consisting of said substrate, the electrolyte membrane and the first catalyst layer;
• applying a coating fluid comprising an electrode catalyst and an ion exchange resin on the surface of the second gas diffusion layer to form the second catalyst layer, thereby to prepare a second intermediate consisting of the second gas diffusion layer and the second catalyst layer;
• and
• bonding the first gas diffusion layer to the first intermediate, so that the first catalyst layer is located between the first gas diffusion layer and the electrolyte membrane,
• peeling said substrate from said first intermediate after bonding said first intermediate and said first gas diffusion layer,
• bonding said second intermediate to the electrolyte membrane so that said second catalyst layer is located between the second gas diffusion layer and the electrolyte membrane, and
• wherein the first gas diffusion layer comprises a gas-diffusing substrate and a first carbon layer formed on the surface of the gas-diffusing substrate by applying a coating fluid comprising a fluorinated ion exchange resin and carbon fiber having a fiber diameter of from 50 to 200 nm and a fiber length of from 1 to 50 μm, and
• the first gas diffusion layer and the first intermediate are bonded, so that the first carbon layer and the first catalyst layer are in contact with each other.