The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/mame.201700347.
Proton Conducting MembranesPolybenzimidazole membranes imbibed with phosphoric acid can support high proton conductivity at 120-200 °C, and have therefore emerged as the state-of-the-art electrolytes for fuel cells operating in this temperature range. This work presents a novel and operationally simple methodology for preparing mechanically robust covalent network polybenzimidazole membranes containing up to 95 wt% phosphoric acid. Diamino-terminal pre-polymers of different chain lengths are first prepared, followed by addition of a trifunctional carboxylic acid. The crude solutions are cast and subsequently heat treated at up to 230 °C, yielding free-standing membranes of networked polybenzimidazole with high proton conductivity at up to 180 °C and encouraging fuel cell performance.
Cross‐linking of phosphoric acid doped polybenzimidazole membranes as fuel cell electrolytes represents an attractive approach to improving the mechanical robustness at a high acid loading. Numerous cross‐linking concepts have been reported in the literature, but a deeper understanding of how the cross‐linking chemistry affects the physicochemical properties of the membrane and its fuel cell performance and durability remains to be assessed. In this work, a series of cross‐linked membranes are prepared using cross‐linking agents of different regio‐chemistry and steric nature. It is shown, that the nature of the cross‐linking agent has a large impact on the effective degree of cross‐linking, which in turn determines the acid doping characteristics and ultimately the fuel cell performance and acid retention during long‐term operation.
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