Resin-framed stepped membrane electrode assembly for fuel cell

A resin-framed stepped membrane electrode assembly for a fuel cell, comprising:

• a stepped membrane electrode assembly comprising:
• a solid polymer electrolyte membrane having a first surface and a second surface opposite to the first surface in a stacking direction;
• a first electrode stacked on the first surface in the stacking direction and including a first electrode catalyst layer and a first gas diffusion layer;
• and
• a second electrode stacked on the second surface in the stacking direction and including a second electrode catalyst layer and a second gas diffusion layer, the first electrode being larger than the second electrode viewed in the stacking direction, the second electrode catalyst layer including an outer periphery exposed portion extending from a diffusion outer peripheral end of the second gas diffusion layer in a direction substantially perpendicular to the stacking direction viewed in the stacking direction;
• and
• a resin frame member surrounding a membrane outer periphery end of the solid polymer electrolyte membrane viewed in the stacking direction and including an inner protruding portion protruding from the membrane outer periphery end toward the second electrode viewed in the stacking direction and joined to the stepped membrane electrode assembly with an adhesive, the inner protruding portion comprising:
• a bank portion disposed between the diffusion outer peripheral end and the membrane outer periphery end in the direction viewed in the stacking direction and having a bank surface opposite to the outer periphery exposed portion in the stacking direction;
• a groove portion disposed between the bank portion and the membrane outer periphery end in the direction viewed in the stacking direction and having a groove surface opposite to the solid polymer electrolyte membrane in the stacking direction, the bank portion protruding beyond the groove portion toward the stepped membrane electrode assembly in the stacking direction, a roughness of the bank surface being smaller than a roughness of the groove surface;
• and
• a ledge portion disposed between the groove portion and the membrane outer periphery end in the direction viewed in the stacking direction so as to contact to the solid polymer electrolyte membrane in the stacking direction,
• wherein, in the inner protruding portion, a surface roughness of a tip of the ledge portion is larger than a surface roughness of the groove surface.