Preparation And Properties Of Electrochemical Catalyst For CO₂ Reduction

In recent years,the "greenhouse effect" caused by excessive release of CO2 gas cause global warming,which causes a great threat to the global environment and human survival.Therefore,it is particularly important to control and reduce the atmospheric CO2 content.The method of electrochemical CO2 reduction can well fix carbon dioxide and switch it into CO,HCOOH,CH4,C2H4,C2H5OH and other chemicals under mild conditions.Among them,CO and C2H4,as the main raw materials for hydrocarbon fuel and polyethylene synthesis in actual production and life,have high application value and have been widely studied.However,the slow reaction rate and the hydrogen evolution are the key problems faced by this technology.Therefore,improving the selectivity in electrochemical CO2 reduction has practical application value and significance.Giving the problems in the process of carbon dioxide reduction,in this paper,the structure of nickel-nitrogen-carbon(M-N-C)was regulated by adding heteroatom S,and the Ni-N3S-C catalyst was obtained by heating.At the same time,Cu-based catalyst was prepared by fixing metal site pyrolysis through strong coordination of the coordination agent.The catalysts showed excellent activity in the electrochemical CO2 reduction process.The experimental process is as follows:Cu2+ was derived from copper nitrate,and disodium ethylenediamine tetraacetic acid was used as the coordination agent.Cu-based catalyst with high catalytic activity was prepared by heating strategy.The effect of calcination temperature on the electric reduction of CO2 was investigated.The results show that Cu-based catalyst exhibits excellent electrochemical carbon dioxide reduction performance when calcination temperature is 800℃.At-0.6 V(vs.RHE)potential,the ethylene production efficiency of FE(C2H4)=60.0%,FE(CO)=23%,FE(CH4)=3.35%,FE(H2)=16.9%.After nuclear magnetic detection,no liquid products were produced.In addition,the electrochemical performance of the electrolyte was tested with flow cell,and the results showed that hydrogen production was inhibited to a large extent.Using cheap available glucose as C source,urea and thiourea as N source and S source,respectively,Ni-N3S-C doped with S atom was prepared by simple pyrolysis strategy.The effects of metal loading,the addition of heteroatom S and calcination temperature on the electrochemical CO2 reduction performance of Ni-N3S-C catalyst were investigated,and the optimum conditions for the preparation of Ni-N3S-C catalyst were determined.The results showed that when the ratio of S to N was 1/4,the Ni content was 1%and the calcination temperature was 1000℃,the catalyst Ni-N3SC showed excellent electrochemical CO2 reduction performance.At-0.9 V(vs.RHE)voltage in KHCO3 electrolyte of 0.5 mol/L,the total current density of 27 mA/cm2 and FEco reached 98.4%,and the catalyst exhibited stability for nearly 12 h,its catalytic performance exceeds that of most nickel catalysts reported.In addition,DFT calculation showed that Ni-N3S was the active site of Ni-N3S-C catalyst,and a small amount of S doping played an important role in stabilizing the active site,electron transfer and accumulation during the reaction,and configuration regulation.