Self-crosslinked alkaline polyelectrolyte membranes with exceptional stability under dry-wet alternating conditions

The emergence of alkaline polyelectrolytes (APEs) with high stability and high ionic conductivity has greatly improved the power density of alkaline polyelectrolyte fuel cells (APEFCs), now the cell stability has become an urgent problem to be addressed. The uneven distribution of humidity and hydration state inside large-scale electrodes will cause the membrane to swell and shrink repeatedly, resulting in the membrane rupture and/or the peeling off of catalyst layers, which is a fatal problem affecting the stability of APEFCs. In the present work, we report a new APE, self-crosslinked quaternary ammonia poly (N-methyl-piperidine-terphenyl and 7-bromotri-fluoro-heptanone), denoted as xQAPTF. The crosslinking network inside the membrane can be formed without introducing additional crosslinking agents, and can effectively limit the membrane swelling degree in water (only 4% at 80oC). More importantly, the xQAPTF membranes exhibit excellent mechanical strength and flexibility even after multiple all-wet-all-dry cycles. Under the dry-wet alternating condition (RH repeatedly switched between 100% and 50%), the APEFC using xQAPTF membrane run stably, with the cell voltage switching accordingly and steadily. Such a unique quality of APE membranes has so far not been reported in the literature, which strongly enhances the practicality of APEs, as well as the APEFC and relevant technologies.