▎ 摘　　要

NOVELTY - A catalyst layer (10) comprises an ionomer-coated catalyst (20) and an ionomer-substrate composite (30). The ionomer-coated catalyst comprises an electrode catalyst in which catalyst particles are supported on the surfaces of conductive particles, and an ionomer (I1) which coats at least the surfaces of the conductive particles. The ionomer/substrate composite contains substrate particles and an ionomer (I2) which coats the surfaces of the substrate particles. The mass of the ionomer (I1), the mass of the conductive particles (C1), the mass of the ionomer (I2) and the mass of the substrate particles (C2) satisfy a preset relation. USE - Catalyst layer used for solid polymer fuel cell and water electrolysis device. ADVANTAGE - The catalyst layer has excellent proton conductivity and reduced catalyst poisoning by ionomer. DETAILED DESCRIPTION - A catalyst layer (10) comprises an ionomer-coated catalyst (20) and an ionomer-substrate composite (30). The ionomer-coated catalyst comprises an electrode catalyst in which catalyst particles are supported on the surfaces of conductive particles, and an ionomer (I1) which coats at least the surfaces of the conductive particles. The ionomer/substrate composite contains substrate particles and an ionomer (I2) which coats the surfaces of the substrate particles. The mass of the ionomer (I1), the mass of the conductive particles (C1), the mass of the ionomer (I2) and the mass of the substrate particles (C2) satisfy the relation: I2/C2/I1/C1 more than 1. DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the catalyst layer. (Drawing includes non-English language text) 10Catalyst layer 20Ionomer-coated catalyst 30Ionomer-substrate composite 40Electrolyte Film