Polymer electrolyte membrane and method for producing the same

A polymer electrolyte membrane, having an ion cluster diameter of 3.02 nm to 3.17 nm and a converted puncture strength of 300 gf/50 μm or more, comprising:

• a mixture of two or more fluorine-based electrolyte polymers, each of which has an ion-exchange group and has a monomer structure different from each other, wherein
• the fluorine-based electrolyte polymers are PFSA resins having structures represented by the following formula (5);
• and
• the PFSA resins are obtained by hydrolyzing a PFSA resin precursor composed of a copolymer of a fluorinated vinyl ether compound represented by the following formula (6) with a fluoroolefin monomer represented by the following formula (8),
• —[CF2CF2]a—[CF2—CF(—O—(CF2)m—SO3H)]g— (5)
• wherein 0 a≤1, 0<g≤1, and a+g=1;
• and m is an integer of 1 to 6,
• CF2═CF—O—(CF2CFXO)n-A (6)
• wherein X is F or a perfluoroalkyl group having 1 to 3 carbon atoms;
• n is an integer of 0 to 5;
• and A is (CF2)m-W, wherein m is an integer of 0 to 6, n and m are not 0 at the same time, and W is a functional group convertible to SO3H by hydrolysis,
• CF2=CFZ (8)
• wherein Z is H, Cl, F, a perfluoroalkyl group having 1 to 3 carbon atoms, or a cyclic perfluoroalkyl group which may contain oxygen, and
• wherein the polymer electrolyte membrane has an equivalent weight, EW, of 700 to 950 (g/eq);
• wherein the ion cluster diameter is measured after immersion for 24 hours in water at 25° C. by small angle X-ray scattering.