Nanoscale TiO 2 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 2 , on the stability and electrocatalytic activity of nanostructured OER anodes based on low-cost Co 3 O 4 . We demonstrate a direct correlation between the OER performance and the thickness of the atomic layer deposited TiO 2 layers. An optimal TiO 2 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 Co 3 O 4 surface. Thinner and thicker TiO 2 layers decrease the stability and activity, respectively. This is attributed to the pitting of the TiO 2 layer at the optimal thickness, which allows for access to the catalytically active Co 3 O 4 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.