High free volume crosslinked membranes constructed by stereocrosslinker for high-temperature proton-exchange membrane fuel cells

The development of high-temperature proton-exchange membranes (HT-PEMs) with high phosphoric acid uptake (PU) and adequate mechanical strength presents a significant challenge. Researchers widely recognize crosslinking as an effective approach to address the conflict between mechanical strength and PU in phosphoric acid-doped membranes. Generally, crosslinked networks are constructed in an alkaline environment, limiting the scope of crosslinked membranes. Based on the Friedel–Crafts reaction, which occurs between carbocation ions and electron-rich skeletons or groups under acidic conditions, this study utilized a novel bifunctional 1,3-adamantanediol as a stereocrosslinker to construct a crosslinked network. The unique three-dimensional structure of the crosslinker resulted in a large free volume within the polymer networks during crosslinking, facilitating the formation of a continuous proton transfer network. Notably, compared with linear polybenzimidazole polymer (PBI), the crosslinked membranes exhibited significantly higher PA retention due to the presence of ultra-microporous structures. Additionally, the number of imidazole units remained unchanged due to the crosslinking site on the aromatic ring. As anticipated, the PA-doped crosslinked membranes exhibited a high conductivity of 167 mS cm⁻¹ and an excellent peak power density of 865 mW cm⁻² at 200 °C. Based on the generality of the crosslinking reaction with stereocrosslinkers and the expansion of the range of reaction media, this study proves a new insight into the fabrication of the high-performance HT-PEMs.