Proton-conductive polymer thin films by molecular orientation and organized structure

Abstract

Highly proton-conductive polymers have attracted the attention of many researchers to be used in energy conversion devices, sensors, catalysts, actuators and others. From the viewpoint of the scientific history for developing highly proton-conductive polymers, one fundamental approach is based on the strategy of phase-segregated structures of polymers with strong acid groups. Understanding the relation between the structure and proton transport property is fundamentally important, but this attempt has often been hampered in many highly proton-conductive polymers like Nafion because of the lack of structural information derived from such amorphous or amorphous-like polymers. In this article, a new approach to enhance the proton conductivity of polymer thin films by an interface is reviewed. The author introduces suppressed proton conductivity in the Nafion thin films and then specifically examines the proton conductivity enhancement by orienting the polymers. As a related topic, highly proton-conductive organized polyimide thin films with a lyotropic liquid-crystal phase is demonstrated. The proton conductivity is enhanced by improved molecular ordering and the in-plane molecular orientation.