A new class of proton conducting membranes for hydrogen fuel cell applications are being developed using thio-acids. These membranes are being designed to yield high proton conductivities (10-6 to 10-3 S/cm), to be anhydrous, thermally stable, chemically stable to H2O and O2 in a typical fuel cell setup, and have minimal fuel cross-over capability. New thio-acids are being synthesized to fulfill these goals. Thus far, conductivity values of 10-5 S/cm are achievable at ∼500o C, along with excellent thermal and chemical stability in contact with H2O and O2. Conductivities of 10-5 S/cm are also achievable from thio-acids intercalated with H2S at room temperature; however, these compounds decompose above room temperature to form the crystalline thio-acid counterparts.