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High temperature proton exchange membrane is a key component of high temperature proton exchange fuel cells. However, its development has been impeded by problems such as mechanical stability and free...

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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.

Novel bifunctional polyhedral oligomeric silsesquioxane (Vi-POSS-SO3Na) and a surface densification method to fabricate the composite membrane based on sulfonated poly (fluorenyl etherketone) (SPFEK) is reported for application in direct methanol fuel cells (DMFCs). First, the synthetic Vi-POSS-SO3Na implants on the SPFEK surface by swelling-filling process. Then, the vinyl groups on POSS are cross-linked to form a dense X-POSS layer on the membrane surface by a simple thermal treatment called surface densification. The crosslinked dense X-POSS with sulfonated groups on the composite membrane surface can effectively prevent the permeation of methanol and enhance the oxidative stability without sacrificing proton conductivity. The SPFEK/POSS-0.09 membrane with an area loading of 0.09 mg cm-2 POSS exhibits enhanced oxidative stability and the lowest methanol permeability (2.12×10-8 cm2 s-1). A direct methanol fuel cell was assembled and its performance was evaluated. The peak power density using SPFEK/POSS-0.03 membrane reaches 65.1 mW cm-2 that is much higher than the one (24.8 mW cm-2) using pristine SPFEK membrane at 80°C. The results demonstrate that the surface densification is an effective method for suppressing methanol crossover and surface-densified SPFEK/POSS proton exchange membrane with X-POSS layer has improved the comprehensive performance of composite membrane.