TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The zeolite includes hydrates of aluminosilicates containing an element selected from alkali metal and alkaline earth metal elements. The zeolite has a three-dimensional polyhedral structure including (Si,Al)O4 tetrahedrons as crystallographic basic units, linked to each other via chemical bonding. The zeolite has an acidity of pH 1-4. The zeolite is at least one selected from ZSM-5, zeolite A, zeolite X, zeolite Y, Mordenite, AlPO4, SAPO, MeAlPO, SAPO-5, XSM-5, AIPO-5, VPI-5, MCM-41, Chabazite, Clipptiolite, silica gel, zirconium-containing minerals, titanium-containing minerals and silicates. The zeolite has a size (particle diameter) of 0.1 nm to 1 mu m. The zeolite is used in an amount of 0.1-1000 parts by weight per 100 parts by weight of the sulfonated fluorine-free hydrocarbon-based polymer or a binder used in the catalyst layer. In the membrane electrode assembly, either or both of the first electrode and the second electrode are the electrode comprising a catalyst layer containing zeolite on either surface or both surfaces of a gas diffusion layer.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The sulfonated fluorine-free hydrocarbon-based polymer includes at least one polymer selected from sulfonated polyaryleneether (PAE), sulfonated polyaryleneetheretherketone (PAEEK), sulfonated polyaryleneetherethersulfone (PAEES), sulfonated polyazole, sulfonated polyvinylalcohol (PVA), sulfonated polyphenylene oxide, sulfonated polyphenylene sulfide, sulfonated polysulfone, sulfonated polycarbonate, sulfonated polystyrene, sulfonated polyimide, sulfonated polyamide, sulfonated polyquinoxaline, sulfonated (phosphated) polyphosphazene and sulfonated polybenzimidazole; or block copolymers, multiblock copolymers or their graft copolymers (preferably block copolymer having a block enriched with sulfonic acid groups). The sulfonated fluorine-free hydrocarbon-based polymer is a sulfonated multiblock copolymer having repeating units of formula (I).A, X and Y1=-(1,4-phenylene)-C(O)-(1,4-phenylene)-, -(1,4-phenylene)-SO2-(1,4-phenylene)-, -(1,4-phenylene)-Si(CH3)2-(1,4-phenylene)-, -(1,4-phenylene)-S-(1,4-phenylene)-, -(1,4-phenylene)-Si(Ph)2-(1,4-phenylene)-, or a group of formula (ia)-(ic);R=-NO2 or -CF3;Z=naphthalene-2,3-diyl (6-position substituted by Q), 1,4-phenylene (3-position substituted by Q), naphthalene-2,7-diyl (3,6-positions substituted by Q), naphthalene-1,7-diyl (3-position substituted by Q), or a group of formula (id)-(if);Q=-SO3H, -SO3-M+, -COOH, -COO-M+, -PO3H2, -PO3H-M+, or -PO32-2M+;M=Na or K;B1=group of formula (ig)-(ij);G=X;G1=Z;a-d=0-1; andm and n=1-100.The repeating unit (I)is obtained by polymerizing branched hydrophobic blocks with branched hydrophilic blocks, and has the hydrophobic blocks and hydrophilic blocks linked alternately with each other via chemical bonding. The catalyst layer comprises a polymer containing at least one hydrophilic functional group selected from sulfonic acid groups, phosphoric acid groups and carboxylic acid groups.