Recent advances in noble-metal-free bifunctional oxygen electrode catalysts

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial reactions in energy storage. However, the sluggish rate of these oxidation electrode reactions and the strong dependence of these technologies on precious metal-based electrocatalysts has greatly restricted further progress. In response to this challenge, researchers have widely investigated the preparation of high-performance ORR and OER electrocatalysts using non-precious metals, reporting substantial advancements in the last ten years. This article provides a concise overview of the latest advancements in oxygen electrocatalysts that are not based on precious metals. The review focuses on the benefits and drawbacks of carbon materials, transition metal compounds, and their composite structures. Moreover, the inherent sources of activity in these materials, techniques for enhancing the density and usage of active sites, and novel design approaches and regulation methods rooted in response mechanisms are examined. Then, a statistical examination of documented bifunctional electrocatalysts is carried out to reveal the correlation between composition, structure, and performance. This report provides a comprehensive analysis of catalyst preparation, element selection, and future directions, delivering significant insights to guide future research endeavors.