Preparation And Investigation Of NiFe-based Chalcogenides Electrocatalysts For Oxygen Evolution Reaction

Hydrogen energy relies on its high energy density and zero pollution has been regarded as the most potential new energy carrier.Water splitting in alkaline electrolyte to produce hydrogen has the merits such as cleanliness and high safety,which attracted extensive research interest.Water splitting includes two half-reactions,i.e.oxygen evolution reaction（OER）for the anode and hydrogen evolution reaction（HER）for the cathode.The OER reaction is a four-electron process,and the slow reaction kinetics of OER has been regarded as the bottleneck of electrolytic water to produce hydrogen.Therefore,it is urgent to develop highly catalysts for OER reaction.At present,noble metal electrocatalysts（such as Ru O₂,Ir O₂）are recognized as the ideal electrocatalysts for OER in alkaline electrolytes.However,the high price and scarcity of those noble metals electrocatalysts are hindered their commercial and large-scale applications.Transition metal-based electrocatalysts（Ni,Fe and Co etc.）have been regarded as one of the most potential electrocatalysts due to their abundant reserves,low cost and high electrochemical performance.Herein,this paper first focused on the structural design of the electrocatalyst,combining carbon nanotubes with Ni Fe-based sulfide nanosheets to develop an OER electrocatalyst with high performance.At the same time,to reveal the catalytic mechanism of Ni Fe-based chalcogenides（sulfides,selenides）during the OER process,the real active components and dynamic evolution process of Ni Fe-based chalcogenides in OER reaction were systematically studied.And the density functional theory（DFT）calculations were used to explore the kinetics of its catalytic OER reaction.The main research contents are as follows:（1）Preparation and investigation of Fe-Ni S₂/NCNT electrocatalysts with high performance for OER reaction.Take a layer of nitrogen-doped carbon nanotubes（Ni/NCNT）grown on the surface of carbon cloth by vapor conversion methods.Then,the Fe-Ni S₂/NCNT electrocatalysts were constructed by hydrothermal reaction and vapor deposition method.The electrocatalytic performance and catalytic mechanism for Fe-Ni S₂/NCNT were also investigated.The Ni/NCNT grown on the surface of carbon cloth can enrich OH^-from the alkaline electrolyte to the near of Fe-Ni S₂,which provides sufficient conditions for the transform of Fe-Ni S₂into S,Fe co-doped Ni OOH（S,Fe-Ni OOH）,to further improve the electrocatalytic performance.The result showed that when the current density reached 100 m A cm^-2,the overpotential is only 190 m V.In addition,compared with Ni Fe LDH/NCNT,the presence of the S element can effectively reduce the dissolution of Fe in the electrolyte during the OER process,resulting in the electrocatalysts exhibiting excellent stability.Moreover,the DFT calculation also confirmed that the electrons in S,Fe-Ni OOH are more active,which can effectively promote the occurrence of OER reactions.（2）Preparation and investigation of Ni_xFe_1-xS and Ni_xFe_1-xSe electrocatalysts with high performance for OER reaction.To further compare the OER performance of Ni Fe-based chalcogenides,the Ni_xFe_1-xS and Ni_xFe_1-xSe were prepared by electrodeposition and vapor deposition methods.The OER electrochemical performance test and catalytic mechanism exploration of Ni_xFe_1-xS and Ni_xFe_1-xSe were also conducted.According to the result,Ni_xFe_1-xSe exhibited the best OER performance.The overpotential of Ni_xFe_1-xSe was only 272 m V at the current density of 100 m A cm^-2.After 80 h stability tested,the current density retention rate was still up to 90%.In addition,during OER process,Ni_xFe_1-xS and Ni_xFe_1-xSe can be oxidized to Ni O/α-Fe OOH and Se/γ-Ni OOH,respectively,which is the main active species in OER reaction.The DFT calculation results proved that the Se/γ-Ni OOH has the largest electron localization function（ELF）value of Ni-O bond,which makes Se/γ-Ni OOH more easily to combine with the intermediates of OER reaction and further effectively promote the occurrence of OER process.To sum up,both Ni Fe-based sulfides and selenides exhibited an excellent OER performance.During OER process,the electrocatalysts will undergo an oxidation process and converted to oxides or oxyhydroxides,which are the real active components in the OER reaction.This work provided theoretical guidance for the development of high performance OER electrocatalysts.