Polysulfone-polyvinylpyrrolidone blend membranes as electrolytes in alkaline water electrolysis

Development of thin, dense and robust alkaline polymer membranes with high hydroxide ion conductivity is key to advanced alkaline electrolysis as it can enable operation at higher current density and/or efficiency, while improving the dynamic response of the electrolyzer. In this work, a homogeneous blend membrane system based on poly(arylene ether sulfone) (PSU) and poly(vinylpyrrolidone) (PVP) is explored as an alkaline ion-solvating polymer matrix. Increasing PVP content in the blend drastically increases electrolyte uptake, and at PVP contents higher than 45 wt%, the membrane can support ion conductivity in a technologically relevant range of 10–100 mS cm-1 or even higher when equilibrated in 20 wt% aqueous KOH. The membrane system is extensively characterized throughout the full composition range and the down-selected composition composed of 25% PSU and 75% PVP is employed in a single cell lab-scale water electrolyzer, showing excellent performance and stability during the course of one week at 500 mA cm-2 at 60 °C in 20 wt% KOH. Good performance stability was demonstrated for more than 700 h at 80 °C, but the gradually increasing KOH concentration due to evaporative loss of water resulted in membrane degradation.