Precise Construction Of Two-dimentional Layered Composite Materials And Exploration Of Their Photo/electrocatalytic CO₂ Reduction

With the rapid consumption of fossil fuels and the significant emissions of greenhouse gases,utilizing clean and environmentally friendly energy sources（solar,wind,etc.）to obtain syngas,hydrocarbons,alcohols from CO₂ reduction is one of the exploration strategies with large development potential.Compared to bulk materials,two-dimensional materials have advantage with super active surface area,high exposure of active sites,and adjustable rich defect structures,which can effectively promote the catalytic activity.However,due to low catalytic efficiency,poor material stability and product selectivity,unclear structure-activity relationships and reaction mechanisms,a variety of strategies have been explored and applied to the contruction of morphology and electronic structure for the further improvement of catalytic performance.Based on the above analysis,this thesis focused on the design and construction of two-dimensional layered materials via the regulation of defects and electronic structure,energy bands,heterojunctions for the efficient photo/electrocatalytic CO₂ reduction into highly-valued products（CO,C₂H₄,HCOOH）,furthermore,a paired reaction system of anodic small molecules oxidation coupled with cathodic CO₂ reduction was constructed via optimizing the reaction electrolysis cell to achieve the improvement of total electrolysis efficiency.And the structure-activity relationship and reaction mechanism were deeply explorated by various in/ex situ characterizations along with DFT calculation.The main contents are shown as follows:1.By utilizing the properties of laminate composition elements that can be adjusted and highly dispersed,a series of layered double hydroxides（LDHs）,including Co Al-LDH,Co Mg Al-LDH,and Mg Al-LDH were synthesized for photocatalytic CO₂ reduction reaction.Under irradiation of visible light,the TOF value(11.57 h^-1)of Co atom in Co Mg Al-LDH was more than three times that of Co Al-LDH,and Co Mg Al-LDH exhibited good catalytic activity under650 nm monochromatic light with a quantum efficiency of 0.86%.The results of XAFS,PDF,DFT,etc.indicated that moderate dispersion of Co in Co Mg Al LDH can promote the regulation of band structure and the generation of defects,effectively improving the photocatalytic efficiency of CO₂ reduction and solar energy utilization.This work provides a design idea for constructing efficient photocatalysts for CO₂ reduction driven by long wavelengths light.2.Based on the adjustable property of interlayer anions in LDHs,the supramolecular assembly structure of Ni Al-Fe-TCPP was constructed via introducing biomimetic porphyrin molecule（Fe-TCPP）.When using Ni Al-Fe-TCPP as a photocatalyst for CO₂ reduction,the selectivity of C₂H₄ in carbon containing products was achieved as high as 93.35%,with a yield of 24.7μmol?h^-1 underλ>400 nm irradiation.Comprehensive studies have shown that the supramolecular assembly structure of Ni Al-Fe-TCPP was conducive to the transfer of photo generated carriers from Ni Al-LDH to Fe-TCPP and the activation of Fe sites in Fe-TCPP,thereby promoting CO*hydrogenation and coupling with CHO*to COCHO*.According to theoretical calculations,it was speculated that the process of CO₂ reduction to C₂H₄ on Ni Al-Fe-TCPP was that CO₂ was reduced to CO on Ni Al-LDH laminates,and the resulting CO diffused to Fe-TCPP and coupled with the CHO*intermediate to generate COCHO*,thus facilitating the production of C₂H₄ along with the inhibition of HER.This work paves an avenue for achieving CO₂ photocatalytic reduction to high carbon products under visible light.3.To further improve the CO₂ reduction efficiency,the Bi/Ni doped-Bi₂O₂CO₃（Bi/Ni-BOC）heterostructures were prepared by facile electroreduction and used as electrocatalyst for CO₂ reduction.Within the voltage range of-1.7 V to-2.2 V（reference electrode Ag/Ag Cl）,the Faraday efficiency of HCOOH(FE_HCOOH)in Bi/Ni BOC can reach over 90%,and the highest FE_HCOOH in the flow cell was 97%.It also exhibited excellent stability for 15 hours at a current density of approximately 220 m A?cm^-2 in flow cell.In/ex situ XAFS and DFT results demonstrated that Ni doping was beneficial for the enhancement of electronic metal-support interaction between Bi nanoparticles and BOC nanosheets to promote the generation and stable existence of electron rich Bi species,thereby improving CO₂ activation and*OHCO hydrogenation,thereby promoting HCOOH production while effectively suppressing competitive HER.This work provides an exploration approach for constructing bismuth based composite materials with high catalytic activity for CO₂ reduction.4.Based on the exploration of cathodic CO₂ reduction,in order to further utilize the efficiency of the electrocatalytic anode and improve the overall electrocatalytic activity,Bi OCl-Cu O composite materials were prepared via the loading of Cu O for electrocatalytic CO₂ reduction to HCOOH and anode-cathode pairing by coupling oxidation of 5-HMF at the oxidation.The HCOOH Faraday efficiency(FE_HCOOH)over Bi OCl-Cu O was achieved to above 90%in the voltage range of-1.7 V to-2.2 V vs.Ag/Ag Cl in flow cell.And the current density could be kept for 15 h at>200 m A?cm^-2 along with FE_HCOOH over 90%during the stability test,further,by optimizing the electrolytic cell,the reaction current density can be significantly increased to 700 m A?cm^-2 with FE_HCOOHgreater than 80%.In/ex situ XAFS characterization indicated that the loading of Cu O was beneficial for the structure transformation of Bi OCl to Bi and the construction of Bi Cu/Bi OCl heterojunction structures,thereby effectively enhancing the promotion of FE_HCOOH.In addition,the theoretical calculation proved that the introduction of Cu could promote electron transfer from Cu to Bi,which is beneficial for the activation of CO₂ molecules and the effective decrease of Gibbs free energy barriers,leading to efficient conversion of CO₂reduction to HCOOH.Furthermore,by replacing OER with HMF oxidation,a total FE could be successfully achieved up to 190%with high current of 140m A?cm^-2 in the CO₂ER-HMFOR pairing system.This work offers a strategy for the exploration and construction of highly-efficient cathode anode pairing reaction system to further promote the overall electrocatalytic activity and efficiency.This thesis achieved the construction of two-dimensional LDHs,regarding photocatalytic CO₂ reduction,the expansion of catalysts response to visible light long wavelengths could pave a way for the effective utilization of solar energy.The preparation of high carbon products under visible light provides effective strategies for the construction of photocatalysts for CO₂ reduction under mild conditions;to further improve the CO₂ conversion efficiency,bismuth based composite materials were constructed for highly efficient electrocatalytic CO₂ reduction,the efficient production of HCOOH under high current provides a green and efficient strategy for the promising industrial production and application of formic acid,furthermore,the successful pairing of anode and cathode reaction systems effectively promotes the overall electrolysis efficiency and lays the foundation for the preparation of high-value chemicals from electrocatalytic system in future industrial exploration.