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