Enhancement of Proton Transport by in an Oriented Secondary Structure in Polypeptide Thin Film

Proton transport properties of a partially protonated poly(aspartic acid)/sodium polyaspartate (PAsp) were investigated. A remarkable enhancement of proton conductivity has been achieved by a highly oriented structure in the thin film. Proton conductivity of 60-nm-thick thin film prepared on MgO(100) substrate was 3.4  10 S cm at 298K. The electrical conductivity of the oriented thin film was one order of magnitude higher than the bulk specimen and the activation energies for the proton conductivity were, respectively, 0.34 eV for the oriented thin film and 0.65 eV for the pelletized sample. This enhancement of the proton transport is attributable to the highly oriented structure on MgO(100) substrate. This result demonstrates proposes great potential for a new strategy to produce a highly proton-conductive material using the concept of an oriented thin film structure without strong acid groups.