Reinforced electrolyte membrane for fuel cell, membrane-electrode assembly for fuel cell, and polymer electrolyte fuel cell comprising the same

A reinforced electrolyte membrane for a fuel cell in which a porous substrate and a dispersion liquid of polyelectrolyte are made into a composite, wherein:

• the electrolyte membrane is obtained by impregnating a porous substrate with a dispersion liquid of polyelectrolyte containing a radical scavenger, wherein the porous substrate is a polytetrafluoroethylene (PTFE) membrane made porous by a stretching method;
• the electrolyte membrane contains a radical scavenger;
• a maximum tensile strength of the electrolyte membrane is 35 N/mm2 or more at 80° C. and at a relative humidity of 90% in either one of the machine direction (MD) and the transverse direction (TD;
• vertical to the MD direction) at the time of sheet making;
• and
• a relative elongation value, which is obtained by designating either larger one of the elongation degrees in the machine direction (MD) and in the transverse direction (TD) at the maximum tensile strength of the electrolyte membrane in the machine direction (MD) and in the transverse direction (TD) as a denominator, is 0.4 to 1.0 at 80° C. at a relative humidity of 90%.