COMPOSITE ELECTROLYTE MEMBRANE, ELECTROLYTE MEMBRANE HAVING CATALYST LAYER ATTACHED THERETO, MEMBRANE-ELECTRODE COMPOSITE, SOLID POLYMER-TYPE FUEL CELL, AND METHOD FOR PRODUCING COMPOSITE ELECTROLYTE MEMBRANE

A composite electrolyte membrane having a composite layer that is a composite of a hydrocarbon polymer electrolyte and a fluorine-containing polymer porous substrate, wherein a fractal dimension D exhibiting the distribution of the hydrocarbon polymer electrolyte and the fluorine-containing polymer porous substrate in the composite layer is 1.7 or more. An object of the present invention is to enable a composite electrolyte membrane composed of a hydrocarbon polymer electrolyte and a fluorine-containing polymer porous substrate to achieve high proton conduction ability and high mechanical durability.