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 comprising a composite layer that is a composite of a hydrocarbon polymer electrolyte and a fluorine-containing polymer porous substrate, wherein

• the fluorine-containing polymer porous substrate has an oxygen atom content of 0 mass %,
• the fluorine-containing polymer porous substrate has a fluorine atom content of 70 mass % or more,
• the fluorine-containing polymer contained in the porous substrate includes polytetrafluoroethylene (PTFE), polyhexafluoropropylene, a tetrafluoroethylene-hexafluoropropylene copolymer (FEP), an ethylene-tetrafluoroethylene copolymer (ETFE) polyvinylidene difluoride (PVDF), polychlorotrifluoroethylene (PCTFE), a perfluoroalkoxy fluororesin (PFA), or an ethylene-chlorotrifluoroethylene copolymer (ECTFE),
• a porosity YI of the porous substrate defined as a value calculated by the following mathematical formula is 50 to 98 volume %
• Y1=(1−Db/Da)×100
• wherein Da is the specific gravity of the polymer that constitutes the fluorine-containing polymer porous substrate, and
• Db is the specific gravity of the entire fluorine-containing polymer porous substrate, and
• a fractal dimension D exhibiting the distribution of the hydrocarbon polymer electrolyte and the fluorine-containing polymer porous substrate in the composite layer is 1.70 or more.