Optimal Coatings of Co₃O₄ Anodes for Acidic Water Electrooxidation

Abstract

Implementation of proton‐exchange membrane water electrolyzers for large‐scale sustainable hydrogen production requires the replacement of scarce noble‐metal anode electrocatalysts with low‐cost alternatives. However, such earth‐abundant materials often exhibit inadequate stability and/or catalytic activity at low pH, especially at high rates of the anodic oxygen evolution reaction (OER). Here, the authors explore the influence of a dielectric nanoscale‐thin oxide layer, namely Al2O3, SiO2, TiO2, SnO2, and HfO2, prepared by atomic layer deposition, on the stability and catalytic activity of low‐cost and active but insufficiently stable Co3O4 anodes. It is demonstrated that the ALD layers improve both the stability and activity of Co3O4 following the order of HfO2 > SnO2 > TiO2 > Al2O3, SiO2. An optimal HfO2 layer thickness of 12 nm enhances the Co3O4 anode durability by more than threefold, achieving over 42 h of continuous electrolysis at 10 mA cm−2 in 1 m H2SO4 electrolyte. Density functional theory is used to investigate the superior performance of HfO2, revealing a major role of the HfO2|Co3O4 interlayer forces in the stabilization mechanism. These insights offer a potential strategy to engineer earth‐abundant materials for low‐pH OER catalysts with improved performance from earth‐abundant materials for efficient hydrogen production.