Regulating the Catalytically Active Sites in Low-Cost and Earth-Abundant 3d Transition-Metal-Based Electrode Materials for High-Performance Zinc–Air Batteries

The rapidly increasing demand for clean and efficient energy devices is a critical issue for the sustainable development of human society. The green and low-cost aqueous zinc–air batteries (ZABs) with high theoretical energy density are therefore drawing increasing attention. As the key materials in the air cathode, electrocatalysts that catalyze the oxygen evolution/reaction reactions (OER and ORR) significantly determine the performance of ZABs. Therefore, exploring economic and efficient oxygen catalysts is of great importance for the practical application of ZABs. Among the numerous electrocatalysts, the earth-abundant 3d transition-metal-based nanomaterials have been widely explored as a result of their low cost and high activities. This review introduces some typical and recent progresses in 3d metal-based oxygen catalysts (i.e., metals, metal compounds, and carbon-supported hybrids) for ZABs. Especially, the active sites for catalyzing OER/ORR of different catalysts are classified, and the strategies for regulating the catalytic sites and their reaction mechanism are also introduced. In the end, the challenges and perspectives for further developing 3d metal-based oxygen catalysts are briefly discussed. This review aims to provide inspirations for the exploration of low-cost and efficient electrocatalysts as cathodes for ZABs.