Ion-solvating membranes as a new approach towards high rate alkaline electrolyzers

Abstract

Energy efficient and cost efficient water electrolysis is essential for the large scale implementation of renewable energy. The two commercial low temperature electrolyzer technologies each suffer from serious drawbacks. The proton exchange membrane (PEM) electrolyzers remain expensive and depend strongly on the scarce metal iridium. The alkaline electrolyzers suffer from a large footprint due to low rate capability. Here we present an approach to make an alkaline electrolyzer perform like a PEM electrolyzer by means of an ion-solvating membrane. A long lasting effort to replace the state-of-the-art thick porous diaphragm by an anion exchange membrane has not proven successful. The ion-solvating membrane represents a third way. Demonstration cells based on KOH doped polybenzimidazole membranes and nickel based electrodes exhibited 1700 mA cm⁻² at 1.8 V. This is far exceeding what has previously been achieved with membranes in alkaline environments without platinum group metal catalysts, and is comparable to state-of-the-art PEM electrolyzers.