Method of forming catalyst layer

A method of forming a catalyst layer, comprising performing displacement plating using a displacement plating solution on a substrate comprising a surface that is made of a semiconductor and comprises a plurality of projections, thereby depositing a catalytic metal on each of the plurality of projections, wherein the displacement plating solution contains potassium tetrachloroaurate (III) and hydrofluoric acid, each projection of the plurality of projections having a needle shape extending in a direction intersecting with the surface, and the catalytic metal is deposited in particulate form extending in the direction so as to correspond to the needle shape of said each projection.