Intermolecular Acid–Base-Pairs Containing Poly (p-Terphenyl-co-Isatin Piperidinium) for High Temperature Proton Exchange Membrane Fuel Cells

How to optimize and regulate the distribution of phosphoric acid in matrix, and pursuing the improved electrochemical performance and service lifetime of high temperature proton exchange membrane (HT-PEMs) fuel cell are significant challenges. Herein, bifunctional poly (p-terphenyl-co-isatin piperidinium) copolymer with tethered phosphonic acid (t-PA) and intrinsic tertiary amine base groups are firstly prepared and investigated as HT-PEMs. The distinctive architecture of the copolymer provides a well-designed platform for rapid proton transport. Protons not only transports through the hydrogen bond network formed by the adsorbed free phosphoric acid (f-PA) anchored by the tertiary amine base groups, but also rely upon the proton channel constructed by the ionic cluster formed by the t-PA aggregation. Thorough the design of the structure, the bifunctional copolymers with lower PA uptake level (<100%) display prominent proton conductivities and peak power densities (99 mS cm⁻¹, 812 mW cm⁻² at 160 °C), along with lower PA leaching and higher voltage stability, which is a top leading result in disclosed literature. The results demonstrate that the design of intermolecular acid–base-pairs can improve the proton conductivity without sacrificing the intrinsic chemical stability or mechanical property of the thin membrane, realizing win-win demands between the mechanical robustness and electrochemical properties of HT-PEMs.