Surface Regulation Of Catalysts For Electroreduction Of Carbon Dioxide And Nitrogen And Their Catalytic Mechanisms

Based on the carbon neutral vision of human society and sustainable development goals,it is urgent to realize the artificial carbon cycle and use non-carbon-based fuels.In recent years,electrochemical synthesis methods using renewable energy sources such as solar energy and wind energy as power sources have attracted extensive attention from researchers at home and abroad due to their environmental protection,simplicity and controllability.Electrochemical reduction of CO2 and N2 can not only reduce CO2 emissions in the air,but also make use of N2 and H2O,the most extensive resources on earth,to produce high value-added chemicals,which has become one of the hot research directions.However,there are many problems in electrochemical reduction reaction of CO2 or N2(ECRR or ENRR),such as high overpotential,low Faradaic efficiency and energy efficiency,serious hydrogen evolution reaction(HER),and low product yield.The fundamental reason is that the selectivity and stability of the electrocatalyst used in the reaction are poor,which cannot meet the requirements of industrial application.Therefore,the preparation of high activity,high selectivity,high stability and high economic efficiency of ECRR and ENRR catalysts is the main research objective.In this paper,the surface regulation of ECRR and ENRR electrocatalysts and their catalytic mechanisms were predicted by using the method of experiment and density functional theory(DFT)calculation.The main contents and results are as follows:(1)The Cd S/carbon nanotube complex(Cd S-CNTs)catalyst was prepared by a simple solvo-thermal method.Faradaic efficiency of CO2 electrochemical reduction to CO by Cd S-CNTs was more than 95%.The results showed that vacancy type sulfur defects were produced on the surface of Cd S-CNTs in situ during the ECRR process.With the increase of sulfur vacancy,the yield of CO increased by 22.2%.The functional groups on the surface of the catalyst during the ECRR process were studied by in situ infrared technology,and the catalytic mechanism of Cd S-CNTs was revealed.DFT calculation shows that the formation of sulfur vacancy changes the electron density on the surface of the catalyst,reduces the energy required for the conversion of the intermediate*COOH to*CO,and promotes the electrochemical reduction of CO2 to CO.(2)Lattice-dislocated zinc oxide(LD-Zn O)with abundant defects was obtained on metal zinc foil by simple anodic oxidation method.Compared with the lattice-perfection zinc oxide(LP-Zn O),LD-Zn O has higher ECRR syngas activity and Faraday efficiency(90%),and the CO/H2 ratio can be adjusted in the range of 0.28 to 2.11,the syngas is applicable to the synthesis of various chemicals.Electrochemical noise technique(ECN)was innovatively used to evaluate the performance of the catalyst during the ECRR process.It was found that LD-Zn O could effectively prevent the corrosion of the electrode during the reaction process and had excellent stability.The lattice dislocation in LD-Zn O was analyzed by DFT calculation,and it was revealed that the lattice dislocation in LD-Zn O can enhance the catalytic activity of ECRR on CO and inhibit HER to some extent,so that the CO/H2 ratio can be adjusted in a large range by changing the potential.(3)A series of Mo-Fe carbides were prepared by the combination of hydrothermal method and high temperature pyrolysis method,and used in ENRR.The results show that the highest NH₃ yield is 72.5?mol h^-1 gcat.^-1,the Faraday efficiency is 27%,and the catalyst has good stability and almost no decay after 10 hours of reaction.Fourier-transformed alternating current voltammetry(FTACV)was innovatively used to explore the electron transfer in ENRR process.It was found that Mo Fe C-1 catalyst with main component of Mo3Fe3C was the most active in electron transfer in ENRR.The DFT calculation shows that the interaction between Mo-Fe bimetallic sites is more conducive to the activation and hydrogenation of N2,and the generation of intermediate*N2H is the decisive step of the electrode reaction in the ENRR process.The Mo3Fe3C with Mo-Fe bimetallic sites requires less energy to generate*N2H,which is more favorable to ENRR.(4)By calculating the formation energy(Ef)and dissolution potential(Udiss)of 96two-dimensional catalysts derived from different defect sites of monoclinic boron nitride,the catalysts with thermodynamic and electrochemical stability were selected,and the performance of ECRR and ENRR was predicted.Several catalysts suitable for the production of HCOOH(Ga/In@N-BN),CO(Sn@BN)and CH3OH(Co@N-BN)were selected through the comprehensive evaluation of the adsorption mode of carbon end or oxygen end of CO2,the binding energy of the intermediate*COOH and*CO,the hydrogen evolution ability of the catalyst,and the energy and potential required for the reaction.Through the investigation of adsorption and activation capacity of the catalyst for N2,the hydrogenation mode and required energy of N2,and the inhibition of HER,it is concluded that Fe@BN has a good activity and selectivity for NH3 production.In this study,selective calculation method is used to predict the key steps of the reaction process,which greatly saves computational resources.Meanwhile,the results obtained can provide guidance for the design and development of new catalysts for ECRR and ENRR.