Proton-Conductivity Enhancement in Polymer Thin Films

Highly proton-conductive polymers have long attracted the attention of researchers for use in energy conversion, sensors, catalysts, and other applications. From the viewpoint of scientific history of creation of highly proton-conductive polymers, one fundamental approach is based on the strategy of phase-segregated structures with strong acid groups. This Feature Article presents a new approach to enhance the proton conductivity of the polymer thin films using an interface that can modify the degrees of freedom for a polymer structure through interaction between the substrate surface and polymers. The author introduces suppressed proton conductivity in Nafion thin films and then specifically examines the enhancement of proton conductivity by the molecular orientation in the polymers. As the last topic, the highly proton-conductive organized polyimide thin film is demonstrated using the lyotropic liquid-crystal property. Both molecular ordering and the in-plane oriented structure can enhance proton conductivity. Moreover, the optical domain and degree of the molecular ordering derived from the molecular weight can contribute strongly to the proton transport property