Optimal Coatings of Co₃O₄ Anodes for Acidic Water Electrooxidation

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 Al 2 O 3 , SiO 2 , TiO 2 , SnO 2 , and HfO 2 , prepared by atomic layer deposition, on the stability and catalytic activity of low‐cost and active but insufficiently stable Co 3 O 4 anodes. It is demonstrated that the ALD layers improve both the stability and activity of Co 3 O 4 following the order of HfO 2 > SnO 2 > TiO 2 > Al 2 O 3 , SiO 2 . An optimal HfO 2 layer thickness of 12 nm enhances the Co 3 O 4 anode durability by more than threefold, achieving over 42 h of continuous electrolysis at 10 mA cm −2 in 1 m H 2 SO 4 electrolyte. Density functional theory is used to investigate the superior performance of HfO 2 , revealing a major role of the HfO 2 |Co 3 O 4 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.