Preparation Of Mxene Composite And Their Electrochemical CO₂ Reduction Properties

In recent years,with the rapid increase of carbon dioxide concentration in the atmosphere,the resulting environmental problems are becoming more and more serious.Carbon dioxide conversion technology has gradually received more and more attention.Fixing and and utilizing carbon dioxide through chemical methods is a possible solution to this problem.It can not only reduce the concentration of carbon dioxide in the atmosphere,but also convert it into products with added value.Among the methods for converting carbon dioxide,electroreduction of carbon dioxide is one of the most promising solutions.Electroreduction of carbon dioxide can be carried out at normal temperature and pressure,which has the advantages of mild reaction conditions,less equipment investment and controllable product distribution.Thus,it has a good application prospect.However,there are still some problems in the current using carbon dioxide electroreduction catalysts,such as low catalytic activity,uncontrollable side reactions and poor continuous catalytic stability.In order to solve the above problems,in this paper,a series of new carbon dioxide reduction electrocatalysts with controllable structure and rich surface active sites were prepared by supporting active ingredients on the highly conductive new two-dimensional substrate MXene.The research contents are as follows:1.MXene and melamine of different quality are mixed,frozen by liquid nitrogen,and calcined under inert gas to obtain MXene/C₃N₄ with foam-like structure.Ag NO₃was reduced by Na BH₄ to obtain Ag nanoparticles,which were loaded on C₃N₄ in the composite material MXene/C₃N₄ to prepare a series of catalysts Ag CN@MF1,Ag CN@MF2,Ag CN@MF3.Through the electrochemical performance test of each catalyst,the Ag CN@MF2 sample showed the best electrocatalytic performance.Specifically,when the electrolysis voltage is-1.0 V（v RHE）,the Faraday efficiency（FE）of the product CO is as high as 92%.The calculated Tafel slope is 177 m V dec^-1,indicating that the material has good electrocatalytic kinetics.Ag CN@MF2 can stabilize the reaction for more than 8 h,the current density can be maintained at 6m A.cm^-2,and the FE of CO can be maintained at more than 90%,indicating the outstanding stability of this electrocatalyst.2.Using Ti₃C₂ MXene as the substrate,Cd S/Ti₃C₂ was prepared by hydrothermal combination with cadmium acetate and thioacetamide,and then the compound Cd S/Ti₃C₂ was placed in a tube furnace and calcined in H₂/Ar mixture gas,the S vacancies containing composite catalysts were obtained.The effect of Cd S loading on the electrocatalytic performance of the material caused by the difference in the amount of cadmium acetate was experimentally studied.By characterizing the catalysts HV_S-Cd S/Ti₃C₂,V_S-Cd S/Ti₃C₂,LV_S-Cd S/Ti₃C₂,it was found that V_S-Cd S/Ti₃C₂ had appropriate Cd S loading and less Ti exposure.The electrochemical performance of the catalyst was tested separately.The results show that the catalyst V_S-Cd S/Ti₃C₂ has the best catalytic performance.The specific performance is that when the electrolysis voltage is-1.0 V（vs RHE）,the FE of the product CO is as high as 94%.The Tafel slope is 124 m V dec^-1,which has the advantage of optimal reaction kinetics,and the Faraday efficiency of CO can be maintained above 90%for 8 hours of cyclic electrolysis.