Regulation Mechanism And Electrocatalytic Performance Of Transition Metal/Graphene Composite Catalyst

Since the industrial revolution,the massive use of fossil fuels has resulted in the annual increase of CO₂ content in the atmosphere,and caused a series of environmental problems.In recent years,the emission reduction and utilization of CO₂ has become a hot and difficult issue in the world.Electrocatalytic carbon dioxide reduction reaction（CO₂RR）can be driven by intermittent clean energy sources such as solar,wind and tidal power to achieve directional conversion of CO₂ under normal temperature and pressure conditions.This reaction has many advantages such as mild reaction,simple device and controllable selectivity.It has been obtained more and more attention in the field of environment and energy.The development of high efficiency electrocatalyst is a great challenge for CO₂RR,and the exploration of catalyst action mechanism is the premise of the development of high efficiency catalyst.In recent years,N doped carbon coated Ni（Ni@N-C）catalyst has shown excellent catalytic performance in the preparation of CO from CO₂RR.However,the determination of the active center of these catalysts and the interaction mechanism between the metal and carbon layer are still unclear,which greatly limits the development and utilization of these catalysts.To solve this problem,this work focuses on the development of transition metal/graphene-based catalyst and CO₂RR.The research mainly includes the following two parts:1.Ni-L-GO precursors were synthesized by using different N ligands(L=4,4’-bipyridine（4,4’-bipy）and 2,2’-bipyridine（2,2’-bipy）as"binder".Ni@N-C/r GO（2,2’-bipy）,Ni@N-C/r GO（4,4’-bipy）and Ni@C/r GO catalysts were prepared by high temperature treatment.The influence of ligands on the structure of catalyst was studied by different characterization methods.It was found that Ni@N-C/r GO（4,4’-bipy）catalyst had the best catalytic performance by electrochemical test.Under the condition of-0.97 V（vs.RHE）,the current density can reach 20 m A cm^-2,the Faraday efficiency of CO is as high as 88%,and the catalytic performance is not significantly reduced within 10 h.Poisoning experiments and acid treatments showed that the active site of the catalyst originated from N element in the N doped carbon coating.Density functional theory calculations showed that pyrrole-N is the optimal active site for the adsorption and activation of CO₂ molecules,and Ni3d electron transfer to theπorbital of N-C skeleton,thus improving the electronic structure of N species,promoting the desorption of the active species of^*CO,and thus enhancing the activity of CO₂RR.2.The coordination reaction of Ni ions with dimethylglyoxime（DMG）is a classic method for qualitative and quantitative determination of Ni ions in inorganic chemistry.Inspired by this reaction,GO was modified with the complexes of Ni ions and DMG as precursors,and r GO,N-C-r GO,Ni-r GO,Ni-N-C and Ni-N-C-r GO catalysts were obtained by high temperature treatment.The effects of N-C,Ni and Ni-N-C on the modification of graphene and the CO₂RR properties of different catalysts were investigated.Ni-N-C-r GO showed the best catalytic activity and selectivity,and the current density reached 10 m A cm^-2 at-0.87 V（vs.RHE）,and the CO Faraday efficiency was 85%.At the same time,it was found that there are no delay in catalytic performance of the catalyst within 10 h after a long cycle test.Therefore,Ni-N-C-r GO is an excellent electrocatalyst for CO production from CO₂.