Kaolin-phosphoric acid-PBI membrane for wide-temperature-range proton exchange membrane fuel cells

High-temperature proton exchange membranes (HT-PEMs) are crucial to widen the working temperature window of proton exchange membrane fuel cells (PEMFCs). In this study, we propose doping clays, including kaolin, bentonite, and sepiolite, into polybenzimidazole (PBI) to regulate phosphoric acid (PA) uptake and retention. We report that the interaction between PA and surface -OH groups of the clays governs both PA uptake and electrochemical performance. Kaolin, with its rigid lamellar structure and abundant Si–OH/Al–OH groups, forms hydrogen bonding and interfacial coordination with PA, enabling uniform distribution and effective confinement of acid molecules. Consequently, the PA-kaolin/PBI composite PEM exhibits superior electrical and electrochemical properties. 145% enhancement of peak power density is achieved as compared to that of the pristine one at 200°C. Concurrently, the PA retention improves ~23%. This work paves a new way to tune the thermal and electrochemical performance of HT-PEMFCs.