Recent advances of transition metal based bifunctional electrocatalysts for rechargeable zinc-air batteries

Due to high energy density, abundant resource and eco-friendly efficiency, rechargeable zinc air batteries (ZABs) have been recognized as promising alternative energy storage systems for conventional lithium-ion batteries for powering vehicles. However, the sluggish reaction kinetics of oxygen reduction and oxygen evolution on the air electrodes of ZABs require to developing cost-effective and high-efficiency bifunctional electrocatalysts for commercialization ZABs. Currently, transition metal-based materials have been explored as potential bifunctional electrocatalysts for ZABs with the advantages of highly activity, cost-effective and excellent stability. Therefore, this review intends to give a comprehensive overview on developments of transition metal-based catalysts (TMCAs) in most recently. According to different constitutions of TMCAs, catalysts of single atom, nanoalloys, oxides, hydroxides, chalcogenides, nitrides and phosphides are systematically introduced in the review. The structural modulations of TMCAs via nanosizing, heteroatom doping and their interface effect are also discussed since they play vital roles in exposing sufficient intrinsic active sites for enhancing the catalytic performance. Finally, the existing challenges of TMCAs and feasible strategies for enhancing the bifunctional catalytic performance and promoting the performance of ZABs are also explored detailly. Based on this review, we hope to provide reference values for building effective bifunctional electrocatalysts for commercial rechargeable ZABs.