Density Functional Theory Investigation Of Structure-performance Relationships Of Metal And Metal Oxide Catalysts For CO₂ Reduction

The excessive utilization of fossil fuels and the large amounts of anthropogenic CO₂ emissions have led to global energy crisis and adverse environmental changes.Electrochemical and photoelectrochemical reduction of CO₂ into chemicals and fuels,such as CO,CH₄ and CH₃OH,have been considered as a promising approach to address the above problems.However,the poor conversion efficiency of CO₂ and selectivity for carbonaceous products hamper practical applications of CO₂ reduction.The design of high-performance catalysts for CO₂ reduction has become a hot topic in energy and environmental researches.The investigation of the structure-performance relationship of catalysts is critical to develop new types of catalysts.Thus,based on density functional theory（DFT）studies,this thesis aims to develop advanced catalysts with high selectivity for CO₂ reduction through exploring the size effect of metal nanoparticle catalysts and the crucial role of functional groups on metal oxide catalysts,revealing the relationship between catalyst structures and CO₂ reduction performances.The first section of this thesis investigates the selectivity for CO product on different reaction sites over Au and Pd nanoparticle models which overcome the limitations of periodic surface models.Based on those more realistic models,it is found that terrace sites exhibit higher selectivity for CO than edge sites on Au NPs,which is opposite to the results on corresponding Au periodic surfaces.For Pd catalysts,the coverage effect is more significant.On bare Pd NPs and periodic surfaces,the selectivity for CO at edge sites is nearly identical to that at terrace sites,whereas edge sites display higher selectivity for CO than terrace sites in the case of high CO coverages.Through calculating faradaic efficiency of CO,we successfully describe the size effect of Au and Pd NPs on CO selectivity.Though noble metal catalysts exhibit high CO selectiviy,the expensive cost limits their applications.Some non-noble catalysts,such as Cu₂O,can not only suppress the side H₂ evolution reaction（HER）but also convert CO₂ into more valuable hydrocarbons.However,the complexity of Cu₂O surface structure under reducing conditions leads to the limited guidance in designing the improved Cu₂O catalysts.The second section of this thesis focuses on the development of Cu₂O（111）with different coverages of surface bounded hydroxyls and their application in CO₂ reduction by DFT calculations.It is found that high coverage of hydroxyls could suppress HER but has low CO₂ conversion efficiency.Low coverage of hydroxyls could lead to serious HER with low selectivity for CO₂ reduction.The surface hydroxyls play a crucial role in these reactions,and a moderate coverage of hydroxyls is optimal to promote CO₂reduction and suppress HER simultaneously.