Optimal Coatings of Co 3 O 4 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.