Trends and Prospects of Bulk and Single-Atom Catalysts for the Oxygen Evolution Reaction

Electrolytic hydrogen is expected to play a key role in the production of green fuels and chemicals, while contributing to balancing consumption and supply in the future electricity grid relying largely on intermittent renewable sources for energy production. However, the oxygen evolution reaction (OER) is a major bottleneck in boosting conversion efficiency due to the sluggish kinetics of the four-electron transfer process. Intensive research efforts are thus directed toward the development of advanced OER electrocatalysts. This review aims at bringing together recent advances in bulk and single-atom electrocatalysts (SACs) for the OER. Starting from the established understanding of the OER mechanism, it offers an overview of state-of-the-art materials for the OER, highlighting the current research directions and shortcomings of bulk electrocatalysts. The final part addresses the novel development of SACs, covering their OER performance as well as the established synthetic routes and advances in characterization techniques that shine light on the geometric and electronic configuration of SACs. The review of experimental findings is complimented with theoretical insights from density functional theory (DFT). The article concludes with a summary along with future opportunities to further improve the activity of SACs for the OER.