Electrocatalysts are one of the essential components for the devices of high-efficiency green energy stor-age and conversion,such as metal-air cells,fuel cells,and water electrolysis systems.While catalysts made from noble metals possess high catalytic performance in both oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),their scarcity and expensiveness significantly limit large-scale applications.In this regard,metal-free/non-noble metal carbon-based catalysts have become competitive alternatives to replace catalysts made of noble metals.Nevertheless,low catalytic ORR/OER performance is the challenge of carbon-based catalysts for the commercial applications of metal-air batteries.To solve the problem of poor catalytic performance,two strategies have been proposed:(1)controlling the microstructure of the catalysts to expose more active sites as the channels of rapid mass and electron transfer;and(2)reducing the reaction energy barrier by optimizing the electronic structures of the cat-alysts via surface engineering.Here,we review different types of bifunctional ORR/OER electrocatalysts with the activated surface sites.We focus on how the challenge can be overcome with different methods of material synthesis,structural and surface characterization,performance validation/optimization,to outline the principles of surface modifications behind catalyst designs.In particular,we provide critical analysis in the challenges that we are facing in structural design and surface engineering of bifunctional ORR/OER catalysts and indicate the possible solution for these problems,providing the society with clearer ideas on the practical prospects of noble-metal-free electrocatalysts for their future applications.

Institute of Materials,Shanghai University,Shanghai 200072,China;School of Materials Science and Engineering,UNSW Materials and Manufacturing Futures Institute,University of New South Wales,Sydney,NSW 2052,Australia;Institute for Sustainable Energy,Shanghai University,Shanghai 200444,China;School of Chemical Engineering,University of New South Wales,Sydney,NSW 2052,Australia;Shanghai Key Laboratory of High Temperature Superconductors,Shanghai 200444,China

[1]Huidong X;Jack Yan;Riyue Gee;Jiujun Zhang;Ying Li;Mingyuan Zhu;Liming Dai;Sean Li;Wenxian Li-.Carbon-based bifunctional electrocatalysts for oxygen reduction and oxygen evolution reactions:Optimization strategies and mechanistic analysis)[J].能源化学,2022(08):234-265

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