Gyroid-nanostructured polymer films that show highly activated surface proton hopping conduction

Abstract

Proton-conductive polymer membranes are key materials for creating various energy devices and sensors. We have developed a new class of proton-conductive materials using the liquid-crystalline self-assembly of specifically designed amphiphilic zwitterions. The combination of amphiphilic zwitterions and certain acids leads to the formation of bicontinuous cubic liquid-crystalline phases with gyroid nanostructures. These materials form a specific gyroid minimal surface where sulfonate groups are densely aligned. High proton conductivity is found for these liquid-crystalline materials under humidified conditions. The surface proton hopping conduction (SPHC) mechanism, which involves protons hopping between neighboring sulfonate groups via bound water molecules, acts as the principal proton conduction mechanism in the liquid-crystalline materials with the specific surface, whereas the Grotthuss mechanism is the dominant proton conduction mechanism in conventional proton-conductive polymer membranes. In this Focus Review, we summarize our molecular design for creating SPHC-dependent proton-conductive materials and the potential utility and functions of these materials. Our recent studies on the polymerization of amphiphilic zwitterions to afford gyroid nanostructured polymer films s are reviewed. In the first part of this article, our molecular design of self-organizing amphiphilic zwitterions is described. The second part of this article summarizes the proton conduction mechanism in the gyroid nanostructured polymer films. We have found that the surface proton hopping conduction mechanism is highly activated on the gyroid minimal surface where the sulfonate groups are densely aligned.