Mechanistic insights into the oxygen evolution reaction of transition metal-based electrocatalysts enabled by atomic layer deposition

The production of green hydrogen heavily depends on the development of cost-effective and efficient electrolyzers for water splitting that are compatible with the intermittent nature of solar and wind energy. Due to the sluggish kinetics of the oxygen evolution reaction (OER), research in the field of earth-abundant OER electrocatalysts is flourishing. In particular, first-row transition metal-based electrocatalysts, such as oxides, phosphates, and sulfides, are promising, and efforts are focused on understanding and enhancing their OER performance by tailoring the electrocatalysts' bulk and surface properties. Atomic layer deposition (ALD) is already an established technology for the deposition of (electro-)catalytically active metal nanoparticles for OER, and it is also gaining traction for the deposition of thin film transition metal-based electrocatalysts. In this review, we showcase how the merits of ALD—such as film conformality, accurate control over film bulk properties (including thickness, chemical composition, and crystallographic phase), and film surface/interface engineering—have accelerated the synthesis of these electrocatalysts and enabled insights into their OER activation mechanisms. While this review focuses on transition metal-based thin films for the OER in mild alkaline environment, it can be anticipated that the highlighted ALD merits will permeate toward other electrocatalytic reactions.