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sisyphus effects in hydrogen electrochemistry on metal silicides enabled by silicene subunit edge

Science Bulletin 2019年第9期64卷 617-624页

作者： Zechao Zhuang Yong Li Jiazhao Huang Zilan Li Kangning Zhao Yunlong Zhao Lin Xu Liang Zhou Lyudmila V. Moskaleva Liqiang Mai State Key Laboratory of Advanced Technology for Materials Synthesis and Processing International School of Materials Science and EngineeringWuhan University of Technology Institute of Applied and Physical Chemistry and Center for Environmental Research and Sustainable Technology University of Bremen Advanced Technology Institute University of Surrey Department of Chemistry University of the Free State

Nonmetal elements strictly govern the electrochemical performance of molybdenum compounds.Yet,the exact role played by nonmetals during electrocatalysis remains largely obscure.With intermetallic MoSi_2comprising silicene subunits,we present an unprecedented hydrogen evolution reaction(HER)behavior in aqueous alkaline solution.Under continuous operation,the HER activity of MoSi_2shows a more than one order of magnitude improvement in current density from 1.1 to 21.5 mA cm^(à2)at 0.4 V overpotential.Meanwhile,this activation behavior is highly reversible,such that voltage withdrawal leads to catalyst inactivation but another operation causes reactivation.Thus,the system shows dynamics strikingly analogous to the legendary sisyphus’labor,which drops and recovers in a stepwise manner repeatedly,but never succeeds in reaching the top of the mountain.Isomorphic WSi_2behaves almost the same as MoSi_2,whereas other metal silicides with silicyne subunits,including CrSi_2and TaSi_2,do not exhibit any anomalous behavior.A thin amorphous shell of MoSi_2is observed after reaction,within which the Si remains partially oxidized while the oxidation state of Mo is basically unchanged.First-principles calculations further reveal that the adsorption of hydroxide ions on silicene subunit edges and the subsequent Si vacancy formation in MoSi_2jointly lead to the anomalous HER kinetics of the adjacent Mo active centers.This work demonstrates that the role of nonmetal varies dramatically with the electronic and crystallographic structures of silicides and that silicene structural subunit may serve as a promoter for boosting HER in alkaline media.

关键词： sisyphus effect Electrochemistry Metal silicides Silicene subunit Hydrogen evolution reaction

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