Ion-Pair Membrane Based on Imidazolium-Functionalized Poly(pentafluorostyrene) for High-Temperature Proton Exchange Membrane Fuel Cell Application

Abstract

Herein, an ion-pair membrane based on imidazolium-functionalized poly(pentafluorostyrene) (Me-PPFSt-Im) for high-temperature fuel cell (HT-PEMFC) application is reported for the first time. The polyelectrolyte Me-PPFSt-Im was obtained via a two-step synthesis and characterized with respect to its electrochemical application. A mechanically stable membrane was prepared by blending Me-PPFSt-Im with polybenzimidazole (F6PBI) followed by doping with phosphoric acid (PA). Ex situ impedance tests revealed stable conductivity for at least 160 h. Heat resistance tests showed extended stability of the polymers and membranes in the presence of PA. The ion-pair membrane displayed superior performance, exhibiting 1.54 W cm −2 of peak power density at 180 °C in a H 2 /O 2 fuel cell (FC). Accelerated stress test was carried out by thermal cycling from 80 to 160 °C, and the ion-pair membrane showed no significant performance decay for 100 cycles. The membrane exhibited operational stability without any loss of performance for about 400 h in the FC. Postmortem analysis showed membrane thinning from 45 μm down to 10 μm without noticeable changes in the catalyst layer. KEYWORDS: high-temperature proton exchange membrane fuel cell (HT-PEMFC), ion-pair membrane, polymer ionic liquids, anion exchange membrane (AEM), imidazolium-functionalized poly(pentafluorostyrene) (PPFSt), phosphoric acid (PA) doping