Solid polymer electrolyte water electrolysis systems for hydrogen production based on our newly developed membranes, Part I: Analysis of voltage–current characteristics

A new solid polymer electrolyte water electrolysis system was constructed using an original proton exchange membrane (PEM). The highly proton-conductive PEM was prepared by the γ-ray-induced post-grafting of styrene into a crosslinked-polytetrafluoroethylene (PTFE) film and subsequent sulfonation. The water vapor to be electrolyzed was controlled at a constant relative humidity and introduced into the cell at different temperatures up to 80 °C. As the cell voltage was increased, the current became higher; the maximum current was 50 mA/cm² at 2.5 V at a temperature of 80 °C, corresponding to a hydrogen production rate of 0.38 mL/min cm² in the normal state (25 °C, 1 atm). The voltage–current characteristics were analyzed with a theoretical model based on Butler–Volmer kinetics for electrodes and transport resistance through the PEM. This analysis revealed that the anode exchange current density and interfacial resistance determined the electrolysis performance.