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.