Membrane electrode assembly and fuel cell comprising core-shell catalyst

A membrane electrode assembly comprising

• an electrolyte membrane, and a pair of electrodes sandwiching the electrolyte membrane, wherein
• the pair of electrodes each include a catalyst layer, and a gas diffusion layer disposed on the catalyst layer on an opposite side to the electrolyte membrane,
• at least one of the catalyst layers of the pair of electrodes contains first catalyst particles, and second catalyst particles,
• the first catalyst particles are either platinum particles or platinum alloy particles, or both,
• the second catalyst particles are core-shell particles that have a core part and a shell part, the core part comprising at least one selected from the group consisting of transition metals other than platinum, the shell part covering the core part and comprising at least one of platinum and a platinum alloy, and
• in the catalyst layer of at least one of the electrodes, the second catalyst particles are present in a smaller percentage in an electrolyte membrane side than they are in a gas diffusion layer side.