Bipyridine polybenzimidazole ionomer with optimized electrochemical boundaries enhanced power density of high-temperature proton exchange membrane fuel cells by 2.5 times

Abstract

The poor electrochemical boundaries involving pathways for gases, proton, and electron lead to low high-temperature proton exchange membrane fuel cells (HT-PEMFCs) performance. The ionomers within catalyst layers (CLs) are one of the vital factors for electrochemical boundaries. In this study, we design bipyridine polybenzimidazole (Py-PBI) copolymer as ionomers, which can construct highly efficient electrochemical reaction boundaries within whole CLs. First, the Py-PBI ionomer has a uniform coverage on the platinum carbon (Pt/C) catalyst in the absence of traditional solvents. Second, its good compatibility with PBI membrane reduces the interfacial contact impedance for proton transfer between CLs and proton exchange membranes (PEMs). More importantly, the Coulomb interaction between the bipyridine group of ionomers and free PA molecules builds stable and efficient proton transport channel within CLs, which increased the electrochemical reaction boundaries and accelerated the electrochemical reaction speed. Consequently, the ionomer exhibits ultra-high-power densities over 2.5-fold that of HT-PEMFCs widely employed in commercial polytetrafluoroethylene (PTFE). The design promises a viable route for synthesizing highly efficient ionomers for practical HT-PEMFC applications.