Polyoxometalate-Cross-Linked Proton Exchange Membranes with Post-Assembled Nanostructures for High-Temperature Proton Conduction

High-temperature proton exchange membranes (HT-PEMs) are key components in high-temperature energy storage and conversion technologies, which require excellent proton conductivity and mechanical strength. However, it is difficult for HT-PEMs to balance their mechanical and conductive properties. Here, we present a strategy to prepare HT-PEMs based on the combination of polyoxometalate (POM)-dominated noncovalent cross-linking and H3PO4 (PA)-induced post-assembly. Hybrid membranes containing polyvinylpyrrolidone (PVP), poly(terphenyl piperidine) (PTP), and H3PW12O40 (PW) are prepared, where the polymers are electrostatically cross-linked by PW and maintain certain mobility. When the membranes adsorb PA, the polarity difference between the PVP–PW–PA moieties and the PTP–PW–PA moieties increases, causing the chains to rearrange into bicontinuous structures via a post-assembly process. The resultant membranes show a break strength over 7 MPa and a proton conductivity of ∼55 mS cm–1 at 160 °C. The high-temperature supercapacitors based on such membranes exhibit a specific capacitance of 145.4 F g–1 and a capacitance retention of 80% after 3000 charge–discharge cycles at 150 °C. Their H2/air fuel cells display a peak power of 273.6 mW cm–2 at 160 °C. This work provides a paradigm for using POMs as dynamic cross-linkers to fabricate nanostructured PEMs, which paves a feasible route to developing high-performance electrolyte materials.