Preparation And Structural Relationship Investigation Of Transition Metal Nanomaterials In Photocatalytic And Electrocatalytic CO₂ Reduction

CO₂ reduction is a green,environmentally friendly energy conversion method to realize the carbon cycle of ecosystem,which is widely concerned by researchers.CO₂reduction reaction process is also complex with the amount kinds of products.It is important to find effective catalysts to improve the selectivity and yield of CO₂reduction.In this thesis,we explore the structural relationship between metal compounds and CO₂ reduction,according to reasonable material design,material preparation and DFT theoretical calculation.The essential relationship between atomic configuration and CO₂ performance is investigated,significantly improving the photocatalytic and electrocatalytic CO₂ reduction performance.1.The Z-type photocatalyst C₃N₄/bismuthene/Bi OCl with two-dimensional metal electronic media is synthesized by in-situ solvothermal method.This catalyst performs high CO₂ reduction activity and stability.The theoretical calculation and ultra-fast spectroscopy show that bismuthene,as a two-dimensional electronic mediator,plays the role of the electronic collector in heterogeneous junction,accelerating the interface electronic transmission rate.The two-dimensional electron mediator also processes a large interface contact area and balances the residual charge in C₃N₄ and Bi OCl,inhibiting the photo-corrosion of Bi OCl.CNBB showed excellent photocatalytic CO₂ reduction activity,with CH₄ and CO yields of 61?mol·g^-1 and 71?mol·g^-1 after 3 h light irradiation,respectively.It also maintained good stability in 5cycle reactions.This work provides a new direction for the selection,design and synthesis of metal electron mediator for Z-scheme photocatalysts.2.This work synthesized four morphology Cu₂O of cube,octahedron,icosahedron and polyhedron fifty-facet for electrocatalytic CO₂ reduction.This work explored the crystal lattice dependency between Cu₂O and electrocatalytic CO₂reduction performance.Experimental and DFT calculations show that(311)high-index lattice plane is beneficial to reduce CO₂ adsorption energy and improve C₂H₄ faradaic efficiency.The polyhedron fifty-facet Cu₂O achieves 33%C₂H₄faradaic efficiency at the-1.0 V vs.RHE potential and room temperature,in 0.1 M KHCO₃ electrolyte.This work discusses the relationship between Cu₂O lattice plane and CO₂ reduction performance,providing a new idea for the further design and mechanism investigation of Cu₂O-based catalysts in CO₂ reduction area.3.The Cu₂O derived cubic Cu and octahedron Cu crystals containing surface oxide layer were synthesized.The influence of the Cu₂O thin layer in oxide-derived Cu was explored by using the density functional theory.Cu₂O layer change the charge transfer ability between Cu atom and adsorption H atom,Cu atom and adsorption CO₂molecule.The oxide layer enhanced the surface CO₂ adsorption ability and decreased the competitive H₂ production.CO₂ reduction performance of cubic Cu₂O@Cu is more excellent than that of octahedron Cu₂O@Cu,processing the appropriate H₂/CO yield ratio from 0.8 to 4,in the range of-0.6 V to-1.0 V.The product meet the industrial demand for different H₂/CO proportions of syngas.This work provides a new way for the design and preparation of Cu-based catalysts,and a new direction for the study of the structural and performance relationship in CO₂ reduction.4.The Cu single atom in N-dope CNT(Cu@N-CNT)electrocatalyst is synthesized by thermal polymerization method for electrocatalytic CO₂ reduction reaction at room temperature and pressure.Cu@N-CNT samples processes enhanced electrocatalytic CO₂ reduction activity and selectivity,because of the porous structure,large electrochemical active area and the strong adsorption capacity of CO₂.The theory calculation show that the introduction of Cu atom as an active site can effectively reduce surface CO₂ adsorption energy.The Cu nanoparticle on the surface of N-CNT increases the H₂competitive production.Cu@N-CNT-20 achieves 84%CO faradaic efficiency at the-0.9 V vs.RHE potential and room temperature,in 0.1 M KHCO₃ electrolyte,better than the control catalyst N-CNT and other Cu proportions of samples.This work provides ideas for further designing the C-N based material for electrocatalytic CO₂ reduction.