Materials descriptors for advanced water dissociation catalysts in bipolar membranes

Abstract

The voltage penalty driving water dissociation (WD) at high current density is a major obstacle in the commercialization of bipolar membrane (BPM) technology for energy devices. Here we show that three materials descriptors, that is, electrical conductivity, microscopic surface area and (nominal) surface-hydroxyl coverage, effectively control the kinetics of WD in BPMs. Using these descriptors and optimizing mass loading, we design new earth-abundant WD catalysts based on nanoparticle SnO2 synthesized at low temperature with high conductivity and hydroxyl coverage. These catalysts exhibit exceptional performance in a BPM electrolyser with low WD overvoltage (ηwd) of 100 ± 20 mV at 1.0 A cm−2. The new catalyst works equivalently well with hydrocarbon proton-exchange layers as it does with fluorocarbon-based Nafion, thus providing pathways to commercializing advanced BPMs for a broad array of electrolysis, fuel-cell and electrodialysis applications. The voltage penalty driving water dissociation at high current density is a challenge for bipolar-membrane-based energy devices. Materials descriptors such as electrical conductivity, microscopic surface area and surface-hydroxyl coverage are now shown to control water dissociation kinetics in these membranes.