Achieving High and Stable Proton Conductivity in PBI Membranes at Elevated Temperatures via Starch-Induced Phosphoric Acid Retention

Phosphoric acid (PA) doped polybenzimidazole (PBI) membranes are among the most promising high-temperature proton exchange membranes (HT-PEMs) due to their excellent mechanical properties and high conductivities at high PA doping levels. However, PA leaching leads to reduced conductivity at high temperatures. To solve this problem, this study successfully prepared a series of novel starch-PBI composite membranes (St-OPBI-GO). FT-IR and XRD results indicate that starch constructs dense hydrogen bond networks within the membranes. The membranes exhibit excellent proton conductivity at a comparatively low PA doping level (3.04 mol H 3 PO 4 ), reaching up to 0.19 S/cm. PA retention results show that the membranes maintain nearly unchanged high proton conductivity at 200 °C despite PA leaching. Starch should facilitate and stabilize proton conduction by forming extensive hydrogen bonds with PA molecules and PBI chains through its abundant hydroxyl groups, which is confirmed by Molecular dynamics (MD) simulation results. Moreover, the St-OPBI-GO membranes exhibit outstanding oxidative stability (remaining unbroken after 120 h of Fenton’s test) and mechanical strength. Further, in the single cell test, the power density reaches up to 557.45 mW cm -2 at 220 °C, meeting the requirements for HT-PEMs use. This study provides an effective approach to solve the conductivity decline problem caused by PA leaching.