Nonmetal Modification And Catalytic Performance Of Catalysts For CO₂ Electroreduction

Electrochemical CO₂ reduction（CO₂RR）could be powered with renewable electricity,and produce value-added commodity chemicals under ambient conditions.Among of various products,carbon monoxide（CO）and formic acid（HCOOH）are the most feasible products for practical application via the two-electron reduction.Thus far,many catalysts with high catalytic activity have been reported,and yet the catalytic activity and product selectivity are far from satisfactory using single-component catalyst.It is shown that the introduction of heteroatoms,such as fluorine（F）,nitrogen（N）,phosphorus（P）and sulfur（S）,could effectively alter the electronic structure of the catalyst and improve the catalytic performonce.In this paper,P and F were introduced into carbon-based catalysts and metals/metal oxides catalysts,respectively.Low overpotential,high selectivity and activity for CO₂RR could be achieved by modification using nonmetal elements.The main contents are as follows:1.Synthesis of P-modified carbon-based catalysts and their CO₂RR performance.In the typical process,the triphenylphosphine（PPh₃）was added during preparation of metal–organic framework（ZIF-8）.Then,the sodium tellurite（Na₂TeO₃）was introduced into ZIF-8 by impregnation method.Finally,the P-modified carbon-based materials（P/Te-CN）were prepared by pyrolysis.The X-ray diffraction（XRD）pattern showed only the broad peak of carbon,and no other diffraction peaks were observed.For CO₂RR,after P modification,the Faraday efficiency for CO(FE_CO)is above 90%from-0.4～-0.7 V vs.Reversible Hydrogen Electrode（RHE）,and reached 97.3%at-0.5 V vs.RHE.The Tafel slope is only 50.5 mV dec^-1,indicating a fast reaction kinetics during CO₂RR.The electronic structure of the catalyst could be regulated by P modification,which is helpful to improve catalytic performance of CO₂RR.2.Synthesis of F-modified Sn-based catalysts and their CO₂RR performance.F-modified Sn-based heterogeneous catalysts（F-Sn/SnO₂）were prepared by pyrolysis.XRD confirmed its crystal structure of catalyst.The nanoparticels with about 20 nm can be seen from Scanning Electron Microscope（SEM）.The element distribution shows that F is evenly distributed in the catalyst.For CO₂RR,the Faraday efficiency of the F-Sn/SnO₂ catalyst modified by F was up to 92.3%,while the Sn/SnO₂ catalyst without F modification was less than 80%.Tafel and electrochemical impedance tests showed that the material features a superior electron transfer process.The F modification significantly improves the performance of the catalyst.The research work provides a new method for the preparation of efficient CO₂RR catalysts.