CATALYST LAYER FOR POLYMER ELECTROLYTE FUEL CELLS, MEMBRANE-ELECTRODE ASSEMBLY, AND POLYMER ELECTROLYTE FUEL CELL

A catalyst layer for polymer electrolyte fuel cells that improves drainage or gas diffusion, reduces or prevents the occurrence of cracking in a catalyst layer, enhances catalyst utilization efficiency, exerts high output power and high energy conversion efficiency, and has high durability, and also provides a membrane-electrode assembly and a polymer electrolyte fuel cell using the catalyst layer. The catalyst layer for polymer electrolyte fuel cells contains a catalyst, carbon particles, a polymer electrolyte, and a fibrous material. In the catalyst layer, the carbon particles carry the catalyst. The catalyst layer for polymer electrolyte fuel cells has voids. The percentage of frequencies of the voids having a cross-sectional area of 10,000 nmor more is 13% or more and 20% or less among the voids observed in a thickness-direction cross section of the catalyst layer for polymer electrolyte fuel cells perpendicular to the surface thereof.