Abstract: An anhydrous, proton-conductive medium comprises a poly(amic acid)-based polyimide and at least one phosphorus compound from the group consisting of phosphorus oxides and phosphoric acids. The precursor solution for the polyimide is a mixture of a phosphorus oxide and a poly(amic acid). A suitable phosphorus oxide has the formula P4O10. A process for forming an anhydrous, proton-conductive membrane comprises mixing a phosphorus oxide in a poly(amic acid) solution to form a mixture, dispensing the mixture upon a support structure, and substantially drying the mixture. The mixture may then be cured.