ELECTRODE CATALYST, AND MEMBRANE ELECTRODE ASSEMBLY AND FUEL CELL USING ELECTRODE CATALYST

Provided is a catalyst that can exhibit high activity. The catalyst is an electrode catalyst having catalytic metals supported on a catalyst support, in which the catalytic metals include platinum and a metal component other than platinum; the electrode catalyst has mesopores having a mode radius of pore distribution of mesopores having a radius of 1 nm or more, of 1 nm or more and less than 2.5 nm; alloy microparticles of platinum and the metal component other than platinum are supported inside the mesopores; and a molar content ratio of platinum with respect to the metal component other than platinum in the alloy microparticles supported inside the mesopores is 1.0 to 10.0.