Nanostructured Polymer Composite Electrolytes with Self-Assembled Polyoxometalate Networks for Proton Conduction

The key challenge for the use of polymer electrolytes is to realize a high ionic conductivity without scarifying their mechanical performance. Herein, we re- port a facile strategy to prepare a nanostructured polymer electrolyte with both high proton conductivity and high modulus, based on the electrostatic self-assembly of polyoxometalate cluster H3PW12O40 (PW) and comb copolymer poly(ether-ether-ketone)-grafted-poly(vinyl pyrrolidone) (PEEK-g-PVP). The incorporation of protonic acid PW can enable the PEEK-g-PVP to be highly proton conductive and create flexible composite electrolyte membranes. Moreover, nanoscale phase separation between PEEK domains and PVP/PW domains spontaneously occurs in these membranes, forming a bicontinuous structure with three-dimensional (3D)-connected PW networks. Due to the dual role of PW networks as both proton transport pathways and mechanical enhancers, these membranes exhibit proton conductivities higher than 30 mS cm(-1) and modulus over 4 GPa. Notably, the direct methanol fuel cells equipped with these membranes show good cell performance. Given the wide tunability of comb copolymers and polyoxometalates, this system can be extended to develop a variety of functional electrolyte materials, for example, the lithium-ion conductive electrolytes by using polyoxometalate- based lithium salts, which provides a promising plat- form to explore versatile electrolyte materials for energy and electronic applications.