A catalyst-layer-supporting substrate comprising a substrate supporting a catalyst layer; wherein the catalyst layer comprises two or more porous catalyst metal particle layers that are superposed alternately with (i) two or more intersticed layers comprising at least one element selected from the group consisting of Mn, Fe, Co, Ni, Zn, Sn, Al, and Cu; or (ii) two or more fibrous carbon layers having interstices among fibers of the fibrous carbon. A method for forming a catalyst-layer-supporting structure that comprises porous catalyst metal particle by removing a pore-forming metal from a mixture layer containing a pore-forming metal and a catalyst metal.