ELECTRODE CATALYST, GAS DIFFUSION ELECTRODE-FORMING COMPOSITION, GAS DIFFUSION ELECTRODE, MEMBRANE ELECTRODE ASSEMBLY, AND FUEL CELL STACK

摘要

Provided is an electrode catalyst in which the content of chlorine (Cl) species and bromine (Br) species is reduced to a prescribed level or lower, said electrode catalyst being capable of exhibiting sufficient catalytic performance. The electrode catalyst is provided with a core/shell structure including: a carrier; a core part formed on the carrier; and a shell part formed so as to cover at least a portion of the surface of the core part. The electrode catalyst is characterized in that: the concentration of bromine (Br) species as measured by X-ray fluorescence (XRF) analysis is not more than 400 ppm; and the concentration of chlorine (Cl) species as measured by X-ray fluorescence (XRF) analysis is not more than 900 ppm.