Montmorillonite Nanosheet-Laminated Proton Exchange Membranes for Efficient Water Vapor Electrolysis

Water vapor electrolysis is a promising route for green hydrogen production; however, its progress has been constrained by the lack of fluorine-free proton exchange membranes (PEMs) that simultaneously offer high proton conductivity and thermal robustness. Herein, we demonstrate that a montmorillonite nanosheet-laminated membrane serves as a fluorine-free PEM for water vapor electrolysis. The membrane, composed entirely of inorganic nanosheets without any binders, exhibited high proton conductivity (3.1 × 10–2 S cm–1 at 80 °C), enabling stable operation across a wide temperature range of 25–100 °C. The current–voltage characteristics show a low overpotential, with the onset of current at approximately 1.3 V, and current densities of 174 mA cm–2 at 1.5 V and 605 mA cm–2 at 2.0 V were achieved at 80 °C. This performance is among the highest reported for fully inorganic fluorine-free PEMs.