Reversible ternary nickel-cobalt-iron catalysts for intermittent water electrolysis

Global-scale application of water splitting technology for hydrogen fuel production and storage of intermittent renewable energy sources such as solar and wind has called for the development of oxygen evolution catalysts and hydrogen evolution catalysts that are inexpensive, efficient, robust, and can withstand frequent power interruptions and shutdowns. Current water electrolyzers must operate with a protective current in stand-by/idle modes to avoid a substantial catalyst degradation. Here, we show a hierarchically structured porous ternary composite catalyst of nickel, cobalt and iron (NiCoFe) hydroxides prepared via electrodeposition on three-dimensional (3D) nickel foam (NF) substrates as reversible bifunctional electrodes for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The NiCoFe/NF electrode exhibits exceptionally high catalytic activity, requiring overpotentials as low as 220 and 50 mV, respectively, for OER and HER to occur. In a water electrolysis cell comprising of two NiCoFe/NF electrodes, an overall cell overpotential of merely 300 mV is required to deliver a stabilized current density of 3 mA cm⁻². The ternary electrocatalyst also exhibits prolonged stability under both continuous and intermittent electrolysis and can be used for oxygen evolution and hydrogen evolution reversibly without degradation. (Figure presented.).