Confined Nano‐Channels Incorporated with Multi‐Quaternized Cations for Highly Phosphoric Acid Retention HT‐PEMs

Abstract Developing a new strategy to retain phosphoric acid (PA) to improve the performance and durability of high‐temperature proton exchange membrane fuel cell (HT‐PEMFC) remains a challenge. Here, a strategy for ion‐restricted catcher microstructure that incorporates PA‐doped multi‐quaternized poly(fluorene alkylene‐ co ‐biphenyl alkylene) (PFBA) bearing confined nanochannels is reported. Dynamic analysis reveals strong interaction between side chains and PA molecules, confirming that the microstructure can improve PA retention. The PFBA linked with triquaternary ammonium side chain (PFBA‐tQA) shows the highest PA retention rate of 95%. Its H 2 /O 2 fuel cell operates within 0.6% voltage decay at 160 °C/0% RH, and it also runs over 100 h at 100 °C/49% RH under external humidification. This combination of high PA retention, and chemical and dimensional stability fills a gap in the HT‐PEMFC field, which requires strict moisture control at 90–120 °C to prevent acid leaching, simplifying the start‐up procedure of HT‐PEMFC without preheating.