Construction Of Ni/Fe Atomic Single Layer On Au Single Crystal Surface And Its In Situ Scanning Tunneling Microscopic Studies Under Oxygen Evolution Reaction

Hydrogen production by water electrolysis technology to promote the development of hydrogen energy has important practical significance for alleviating energy crisis and improving environmental pollution.Electrolysis of water includes two processes: cathodic hydrogen evolution and anodic oxygen evolution.However,oxygen evolution reaction involves a multi-electron reaction process,resulting in slow reaction kinetics,which greatly limits the reaction efficiency of hydrogen production by electrolysis of water and becomes an urgent problem to be solved at present.Recent studies have shown that the oxides/hydroxides of cheap metals have high catalytic oxygen evolution performance,especially the Ni-Fe-based hydroxide nano-catalyst has the best oxygen evolution activity.However,the attribution of active sites for oxygen evolution of Ni-Fe-based hydroxides is controversial,and there is no direct evidence of active sites for Fe or Ni hydroxides.The reason is that most studies have adopted relatively complex nanometer Ni-Fe-based hydroxide catalysts,which leads to unclear exact structural information of the active site for OER catalysis,and it is impossible to construct effective structure-efficiency relationship.In particular,the in-situ structural information of the active site in the OER process is seriously missing.Therefore,Ni mono-atomic layer,Fe mono-atomic layer and Ni/Fe composite mono-atomic were constructed on the surface of Au single crystal with clear structure as model electrocatalysts for OER research,and to establish an effective structure-activity relationship.Furthermore,their real-time structural morphological changes under OER reaction conditions were investigated by electrochemical scanning tunneling microscopy in situ characterization technique,and the adsorption morphology and behavior of oxygen species(OH*,O*)were determined.The main work is as follows:(1)Ni mono-atomic layer model catalysts with different coverage were successfully prepared on Au(111)surface.The non-in-situ STM and electrochemical tests showed that the OER activity increased with the increase of the Ni monatom layer coverage,and a linear relationship between the edge length of the Ni monatom layer and the OER activity was preliminarily proved.In situ EC-STM results showed that with the positive potential shift,the edge of the Ni monatom layer was oxidized first and the edge was rough.Combined with the linear relationship between the edge length of the Ni monatom layer and the OER activity,the active site was located at the edge.(2)Fe mono-atomic layer model catalysts with different coverage were successfully prepared on Au(111)surface.Non-in-situ STM and electrochemical tests showed that the activity of OER increased with the increase of Fe mono-atomic layer coverage.It was initially proved that there was a linear relationship between the edge length of Fe mono-atomic layer and the OER activity.In situ EC-STM results showed that with the change of potential,the edge of the Fe monatomic layer was oxidized first.Combined with the linear relationship between the edge length of the Fe monatomic layer and the OER activity,the active site of the Fe monatomic layer was located at the edge.(3)Ni/Fe composite single atomic layers model structure was successfully prepared on Au(111)surface.The nucleation center of Ni is mainly Fe island,and it grows along the edge of the Fe island,which is impossible to achieve in the traditional nanometer complex materials.The real-time morphological changes of Ni/Fe composite mono-atomic layers during OER were observed in situ EC-STM.With the positive potential shift,the Ni/Fe composite mono-atomic layers were gradually oxidized.When the potential returned to the initial potential,the composite structure of Ni/Fe remained unchanged.The electrochemical deposition method was used to prepare Ni and Fe single atomic layers on the surface of single crystal,and then the in-situ EC-STM was used to characterize the real-time morphological changes of Ni and Fe single atomic layers under the condition of OER.It is helpful to study the catalytic active sites,and thus to further understand the catalytic mechanism of Ni and Fe based OER catalysts.To provide theoretical guidance and technical support for rational design of practical forms of nano catalysts.