Cross-linked Ion-Pair Microporous Polymers Enabling Durable High-Temperature Proton Exchange Membrane Fuel Cells.

Abstract

Phosphoric acid (PA)-doped ion-pair polymers have emerged as promising proton exchange membranes (PEMs) for high-temperature fuel cells, enabling operation from 80°C-160°C while effectively anchoring and retaining PA. However, conventional ion-pair-based PEM fuel cells suffer from performance degradation and unstable proton transport at temperatures above 160°C. In this study, a cross-linked ion-pair microporous polymer, poly(spirobisindane-co-terphenyl piperidinium) (C50-PSTP-x), is simultaneously used as both the PEM and catalyst-layer ionomer, achieving a strong acid anchoring effect across the entire membrane electrode assembly. The polymer integrates ion-pair-coordinated PA-cyclic quaternary ammonium groups, a spirobisindane backbone with intrinsic microporosity, and a highly roughened cross-linked structure. These structural features collectively promote efficient proton transport, well-defined triple-phase interfaces, and strong PA anchoring, enabling stable fuel cell operation at temperatures up to 220°C. C50-PSTP-x membrane and ionomer deliver high peak power densities of 0.680-0.778 W cm^-2 with a Pt loading of 0.5 mg_Pt cm^-2, along with excellent durability, exhibiting low voltage decay rate of 57.8 µV h^-1 over 800 h at 160°C and 33.3 µV h^-1 over 500 h at 180°C. This work establishes a robust ion-pair polymer platform for ultra-high-temperature PEM fuel cells (HT-PEMFCs), expanding both the operational temperature window and long-term stability of next-generation HT-PEMFCs.