Metal Loading On Nitrogen Doped Carbon For Efficient CO₂ Electroreduction

Since the industrial revolution,fossil fuel has become the main part of the global energy supply.The increasing demand of energy for human beings has resulted in excessive emissions of carbon dioxide,which seriously threatens the sustainable development of human society.Tryingng to transform this cheap carbon dioxide into high-value chemicals with high selectivity and low cost has become a research hotspot in the world.Electrocatalysis has attracted much attention due to its high energy efficiency,mild reaction conditions and controllable selectivity.At present,researching on this kind of reaction is mainly from the design of catalysts,the design of reaction device and reaction conditions.In the aspect of catalyst design,noble metal catalysts are high cost and difficult to obtain,while non noble metal catalyst has poor selectivity and durability for carbon dioxide electrochemical reduction,which limit its large-scale application.This paper focuses on the chemical modification of non noble metal catalysts supported on carbon materials.The catalysts are designed in two ways:carbon-supported nickel particles and single Sb sites anchored on N-doped porous carbon to restrain the severe hydrogen evolution reaction of metallic nickel and antimony.The composition,morphology,size and structure of the catalysts are characterized.In the H-type electrolytic cell,the CO2-saturated KHCO3 solution is used for electrochemical test.The products in the gas phase and liquid phase are tested at last.The research mainly includes the following two parts:(1)Firstly,Ni-MOFs(metal organic frameworks)were synthesized and adsorbed on carbon black.Then calcining the MOFs to form N-doped carbon supported Ni nanoparticles(Ni-NC_X@C).The existence of nickel particles are proved by XRD,XPS,STEM and EXAFS.It is first reported that Ni nanoparticles enable efficient electroreduction of CO2 to CO by modifying Ni NPs with wrapped carbon layers.By changing ligand X,the catalytic performance of Ni particles can be controlled.Through electrochemical test,Ni-NC_ATPA@C(X:2-aminoterephthalic acid)presents an unprecedented CO faradaic efficiency of approximately 94%at-0.7 V(vs.RHE).The catalyst also affords a high CO partial current density and a large CO turnover frequency(TOF),reaching 22.7 mA cm-2 and 697 h-1 at-1.1 V(vs.RHE).Experiments combined with density functional theory calculations(DFT)showed that the enfolded carbon layers on Ni NPs and doped N in carbon material both play important parts in enhancing catalytic activity for electrochemical CO2 reduction to CO by stabilizing*COOH and improving*CO desorption.(2)Single Sb sites dispersed on N-doped carbon(Sb_NC)was synthesized by well-mixed SbCl3,urea and carbon black activated by concentrated nitric acid.The presence of single Sb sites are confirmed by XRD,XPS,Raman and STEM.The synthesis of single Sb catalyst has been first reported and applied to electrochemical reduction of CO2.In contrast to bulk Sb,Sb2O3,and bulk Sb which exclusively cause HER side reaction,Sb_NC perform high selectivity on electroreduction of CO2 to CO,enabling a CO turnover frequency(TOF)of about 16600 h-1 and a CO partial current is as high as 8.1 A mgsb-1 at-0.9 V(vs.RHE),even exceeding many other reported single site electrocatalysts.