This disclosure provides polymer electrolytes, polymer electrolyte membranes (PEM's) and membrane electrode assemblies (MEA's) such as may be useful in fuel cells which contain or comprise polyoxometalates (POM's) or heteropolyacids (HPA's). In some embodiments the polyoxometalate, it's counterions or both may comprise Mn and/or Ce. In some embodiments the polymer electrolyte is fluorinated. In some embodiments the polymer electrolyte comprises a second acidic functional group other than a polyoxometalate. In another aspect, the present disclosure provides methods of making polymer electrolytes including methods which comprising a step of copolymerizing monomers comprising a covalently bound polyoxometalates and methods which comprise a step of covalently attaching a polyoxometalate to the polymer.