Theoretical Study Of Photoelectroreduction Reactions Of Carbon Dioxide Adsorbed On Noble Metal Surfaces

Carbon dioxide(C02)photoelectric reduction reaction is an important research field,because it can be used to solve environmental and energy problems.CO2 is an extremely thermodynamically stable linear molecule with a very negative reduction potential.The re-duction of C02 by capturing electrons and protons to CO or organic compounds has become a big challenge in electrochemistry and photochemistry.Previous studies show that CO is the major product on silver and gold electrode in electrochemical reaction,and silver and gold nanoparticles can induce C02 to reduce to methanol and methane in photochemical reaction.The difference of products and undefined mechanism of CO2 reduction limited the practical application of silver and gold electrode.In order to solve this problem,the density functional theory is used to simulate the electrochemical and photochemical reac-tion of C02.According to the geometrical morphology,electronic structure,orbital energy level and reaction energy to study this reduction reaction,and illuminate structure-property relationship and reaction mechanism.This thesis includes my major works which I have finished during my PhD study.It will provide the research details,computational methods,model construction,and results and discussion in detail.The main findings of this thesis are outlined as follows:(1),C02 electrochemical reduction on metal electrode,which divides into three part-s.First,the single-crystal surfaces of Ag(111),Ag(100),Ag(110),and Ag(211)are mim-icked to study the CO2 reduction reaction(C02RR)on silver electrodes.The geometric and electronic structures,adsorption energies,and reaction activation energies of all species are calculated and analyzed.The monodentate HCOOM*is firstly formed in HCOOH path.In addition,the water can assist in promoting CO formation.This finding shows that the C02RR selectivity for CO over HCOOH is a synergetic effect of thermodynamic and ki-netic control,which strongly depends on the geometric and electronic structure of silver electrode surface.Second,electrocatalytic C02 reduction on boron-doping palladium elec-trode surface is studied,and a suitable model of boron doping Pd lattice is built.From the reaction Gibbs free energies,adsorption energies,and geometric and electronic structures,we can know that HCOOH is major product rather than CO.It is different from CO2 reduc-tion on Pd surface.Previous studies show that B/Pd catalyst can promote HCOOH oxidation to C02,we can know it is a unique dual functional catalyst for the carbon cycle.Third,the catalytic properties of Cu/Au bimetallic catalyst are studied.Cu deposits on single crystal Au surface,and the Cu atoms are broadened to commensurate with substrate of Au atoms.The value of d band center up shifts toward to Fermi level,and the surface activity of in-creases.C02 reduce to C1 compounds on Cu/Au surface has a lower barrier than that case on Cu surface.(2),Au and Ag nanoparticles display strongly visible absorption due to the surface plasmon resonances(SPR),which can generate hot electrons and promote catalytic reac-tions of adsorbates at the metal surfaces.We adopt density functional theory calculations combining the metallic cluster model and low-index single crystal surfaces of Au and Ag to investigate the SPR photocatalytic C02RR.Firstly,our calculation results show that on low-index single crystal surfaces,the C02 formation needs a highly negative electrode po-tential accompanied with H+transfer to CO or directly to the CO bond dissociation with high activation barriers.Secondly,the energy of SPR induced hot electrons well matches to the LUMO level of CO2 on Ag and Au nanoparticles,and then the hot electrons can easily transfer to the LUMO of C02 because of the strong orbital coupling interaction.The charge transfer state,corresponding to chemisorb state,greatly decreases the energy barriers of the CO bond cleavage to CO.Furthermore,our theoretical results also elucidate that the prod-ucts of CO2RR can further transform to methanol and methane on Ag and Au nanoparticles under the SPR.This is different from CO on low-index single crystal surfaces.(3),The Oxygen reduction on metal electrode is studied.In this section,the geometric structure of water adsorption on metal surface and the relationship between electric field and vibration frequency are first considered.Next,the geometric structure,vibration frequency,and Gibbs free energy of oxygen reduction on Pt(hkl)and bimetallic surface are calculated.The more effective catalytic performance is found in bimetallic surface.