Polypeptide for anhydrous proton conductor

The anhydrous proton conductor consisting of a polypeptide was prepared by the mixing of polyglutamic acid (poly(Glu)) and polyhistidine (poly(His)), which were synthesized by the polymerization of an amino acid with diphenylphosphoryl azide (DPPA). These polypeptide hybrid materials interacted between the carboxyl group of poly(Glu) and the imidazole group of poly(His) and produced the acid-base structure. As a result, these polypeptide hybrid materials showed a thermal stability at intermediate temperatures (≤ 200 °C). Additionally, these hybrid materials indicated the proton conductivity of 1.4 × 10−4 S cm−1 at 180 °C under anhydrous conditions. Furthermore, an activation energy of the proton conduction under anhydrous condition was 0.52-0.63 eV, one order higher than that of the customary humidified perfluorinated membranes. These results suggested that the proton transfer of hybrid material occurred by the anhydrous proton conductive mechanism. Therefore, the polypeptide hybrid material may have the potential to be utilized as a novel proton conductor under anhydrous condition.