NOVELTY - Manufacture of membrane-electrode assembly comprises preparing an anode and a cathode, at least one of which comprises a catalyst layer comprising a catalyst (6) and a porous ionomer layer, where catalyst layer is formed by a process comprising coating a composition comprising the catalyst, ionomer (4), and plasticizer (2) and/or fumed silica onto an electrode substrate, and extracting the plasticizer when the plasticizer is used or firing the coated composition when the fumed silica is used, where electrode substrate enables a reactant to diffuse into the catalyst layer.    USE - Manufacture of membrane-electrode assembly for fuel cell.    ADVANTAGE - The catalyst layer has pores (8) and can maintain a high concentration of hydrogen and an oxidant on a surface of catalyst and realize a high-power fuel cell. The porous ion conductive ionomer allows the reactants to pass through the pores and be quickly transferred to the surface of the metal catalyst. The path between an electrode substrate and the surface of the catalyst is shorter compared to a catalyst layer without pores, and thus the reactant can be quickly transferred, and a limit for fuel cell performance due to a mass transfer limit can be overcome.    DETAILED DESCRIPTION - Manufacture of membrane-electrode assembly comprises preparing an anode and a cathode, at least one of which comprises a catalyst layer comprising a catalyst (6) and a porous ionomer layer, where catalyst layer is formed by a process comprising coating a composition comprising the catalyst, ionomer (4), and plasticizer (2) and/or fumed silica onto an electrode substrate, and extracting the plasticizer when the plasticizer is used or firing the coated composition when the fumed silica is used, where electrode substrate enables a reactant to diffuse into the catalyst layer; and preparing a polymer electrolyte membrane interposed between the anode and the cathode.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic diagram showing processes of forming a porous ionomer layer included in the catalyst layer.    Plasticizer (2)    Ionomer (4)    Catalyst (6)    Pores (8)