Study On Activity Regulation And Catalytic Mechanism Of High Performance Catalysts For Electroreduction Of CO₂

The excessive consumption of fossil fuels and industrial production by human beings have caused a drastic increase in atmospheric CO₂ levels,becoming a severe threat to the environment and energy safety.China has set the goal of realizing carbon peak emssion by 2030,carbon neutral by 2060,and reducing carbon dioxide emissions of unit GDP by more than 65 percent comparing with emission levels in 2005 by 2030.The electrochemical reduction of carbon dioxide（CO₂RR）using renewable energy sources is a promising solution toward carbon neutral.A recent techno-economic analysis suggests that HCOOH and CO are the most commercially profitable targets for CO₂RR.Tremendous efforts have been dedicated to the production of CO and formic acid while the study on reaction mechanism and descriptors of CO₂RR were lacked which are essential for screening and predicting efficient catalysts.This thesis mainly focuses on using combined characterizations such as in-situ FTIR and XAS with DFT calculations to study the reaction mechanism and descriptors of CO₂RR toward CO and HCOOH.The main research contents are as follows:1.The influence of a series of secondary elements（Co,Ni,Cu,Ag,Zn,Ga,Bi）on the CO₂RR performance of Sn has been investigated.The addition of a secondary element could influence the CO₂RR performance,and transition metals and main group elements showed different effects on the selectivity and partial current density of HCOOH.Combined in-situ characterization and DFT calculations reveal that the Gibbs free energy differences of key intermediates（ΔG（HCOO*）-ΔG（*H））can be used as descriptors for predicting the CO₂RR performance to produce formic acid.2.To further disclose the interaction between main group metals（Bi,Sn,In）and transition metals,the CO₂RR performance of Cu modified Bi,Sn and In-based catalysts have been studied.The optial selectivity and partial current density of HCOOH are obtained on the MCu（M=Bi,Sn,In）catalysts with molar ratio of 2:1.The anions in electrolyte play a more important role than cations in controlling the HCOOH selectivity.The interaction between Cu and main group metal are through Cu O and main group metal oxides.The optimal Bi2Cu1 obtains a FE（HCOOH）above 90%during 20 h stability tests.3.Two dimentional transition metal carbides（MXenes）,which possess better electrochemical properties,are selected as the supports to further fabricate efficient CO production catalysts.Based on the DFT calculations and conclusions obtained in last charpter,we propose that the prerequest for a good MXenes based CO₂RR catalysts is the M₃C₂O₂ structure should have a higherΔG（*H）,meaning that HER should be inhibited.Ta₃C₂O₂is promising due to the highestΔG（*H）.Pd,Ag and Au confined in Ta₃C₂O₂ show good CO activity and Au clusters confined in Ta₃C₂O₂ can stably catalyze CO₂RR.The effect of O vacancy and Ta vacancy are also studied which are important for further designing and synthesizing efficient CO₂RR catalysts.4.A series of transition metal carbides（TMCs）and nitrides（TMNs）of Group VB elements（V,Nb and Ta）are used as supports to tune the CO₂RR activity and CO/H₂ratios over Ag-and Au-based electrocatalysts.The electronic modification is found to be the key controlling factor in the interactions between TMC/TMN and supported Ag/Au.Combined electrochemical measurements and density functional theory（DFT）calculations identify that the Gibbs free energy for adsorption of the*COOH intermediate（ΔG（*COOH））as a potential descriptor for CO₂RR,which can be adjusted by using different TMCs and TMNs supports.The obtained trends and descriptors are helpful for designing efficient CO production catalysts.