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 ultramicroporous 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 degrees 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.