Design of the Low-Loading NiFe Hydroxide Alkaline Oxygen Evolution Catalyst Layers Based on Inverse Opal Supports

Anion exchange membrane water electrolyzers are designed to combine the advantages of high efficiency provided by polymer electrolyte membrane-electrode assemblies and low cost of non-noble-metal-based electrodes and catalysts, including NiFe-layered double hydroxides (LDH) used to catalyze the oxygen evolution reaction (OER). While NiFe LDH exhibit high intrinsic activity for the OER, the practical performance is limited by low electrical conductivity and inaccessibility of active sites. These limitations can be effectively resolved using high-surface-area inverse-opal (IO) metallic supports modified with thin (≪100 nm) NiFe LDH coatings to enable high areal and mass-normalized OER current densities. Herein, we investigate the effects of void size and chemical nature of the IO metal (Ni, Fe, Co) on the activity and stability of the NiFe LDH/IO catalyst layers. The optimized NiFe LDH/Ni IO composite with a thickness of only 900 nm and a void size of 320 ± 10 nm enables an OER rate of 100 mA cm_geom.^-2 (per geometric surface area) and 1000 A g_{NiFe LDH}^-1 at an overpotential of 0.307 ± 0.004 V at 23 ± 2 °C. The catalyst layers enable stable operation at 100 mA cm_geom.^-2 for at least 120 h.