Catalyst-supporting substrate, method of manufacturing the same, membrane electrode assembly, and fuel cell

A catalyst-supporting substrate, comprising:

• a substrate;
• and
• a catalyst layer which is supported by the substrate and which comprises a plurality of pores,
• wherein, in a section of the catalyst layer cut in a thickness direction, a section is observed by using a scanning electron microscope to obtain a sectional photograph, and five pores with boundaries being closed between the pore and the catalyst on the sectional photograph are selected, the pores have an average diameter of 5 nm to 400 nm and long-side to short-side ratios of 1:1 to 10:1 in average on the section in the thickness direction of the catalyst layer, and a ratio of the average diameter of the five pores to the thickness of the catalyst layer ranges from 85/1300 to 40/100, and
• wherein the catalyst layer comprises a single metal of an element selected from the group consisting of Pt, Ru, Rh, Os, Ir, Pd, Au, Zr, Ti, Ta, Si, Al, Sn, Hf, Ge, Ga, In, Ce, Nb, W, Mo, Cr, Ni, Co, Mn, Cu, Fe, Zn, B, and V, an alloy constituted of two or more of these elements, or an oxide containing at least one of these elements, and the entire catalyst layer comprises no carbon.