Nanoscale TiO Coatings Improve the Stability of an Earth-Abundant Cobalt Oxide Catalyst during Acidic Water Oxidation.

The large-scale deployment of proton-exchange membrane water electrolyzers for high-throughput sustainable hydrogen production requires transition from precious noble metal anode electrocatalysts to low-cost earth-abundant materials. However, such materials are commonly insufficiently stable and/or catalytically inactive at low pH, and positive potentials required to maintain high rates of the anodic oxygen evolution reaction (OER). To address this, we explore the effects of a dielectric nanoscale-thin layer, constituted of amorphous TiO, on the stability and electrocatalytic activity of nanostructured OER anodes based on low-cost CoO. We demonstrate a direct correlation between the OER performance and the thickness of the atomic layer deposited TiO layers. An optimal TiO layer thickness of 4.4 nm enhances the anode lifetime by a factor of ca. 3, achieving 80 h of continuous electrolysis at pH near zero, while preserving high OER catalytic activity of the bare CoO surface. Thinner and thicker TiO layers decrease the stability and activity, respectively. This is attributed to the pitting of the TiO layer at the optimal thickness, which allows for access to the catalytically active CoO surface while stabilizing it against corrosion. These insights provide directions for the engineering of active and stable composite earth-abundant materials for acidic water splitting for high-throughput hydrogen production.