CATALYST, ELECTRODE, MEMBRANE ELECTRODE ASSEMBLY, AND AIR BATTERY

Provided is a catalyst that has excellent oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic activity and is useful as a catalyst for water electrolysis, an electrode catalyst for an air battery, or the like. The catalyst includes (A) either or both of Ni atoms and Fe atoms, (B) thiourea, and (C) fibrous carbon nanostructures. It is preferable that the catalyst includes (A) Ni atoms and Fe atoms, that the thiourea is coordinated with the Ni atoms and the Fe atoms, and that a mass ratio of the content of a Ni-thiourea coordination compound relative to the content of an Fe-thiourea coordination compound (Ni-thiourea coordination compound/Fe-thiourea coordination compound) is not less than 5/95 and not more than 70/30.