Synthesis Of Cerium Oxide Facilitated Copper-Based Materials And Their Applicatio N In Electrocatalytic Carbon Dioxide Reduction

The Industrial Revolution greatly increased social productivity and drove human progress and development,but it also led to a heavy reliance on fossil fuels.Unrestrained use of fossil fuels caused a rapid increase in greenhouse gas concentrations,especially carbon dioxide（CO₂）,which seriously affects the ecological environment of the earth and poses significant challenges for sustainable development of civilization.The 20th National Congress of the Communist Party of China highlighted the importance of actively and prudently promoting carbon peaking and achieving carbon neutrality,making adjustments to industrial structure and vigorously developing a low-carbon economy an important direction for China’s future economic and social development.Artificially fixing atmospheric CO₂is an important way to reduce its concentration,and electrochemical reduction of CO₂is considered an effective method for achieving carbon cycle.With the decrease of the cost of electricity,the research on the electrocatalytic carbon dioxide reduction of other high value-added chemicals is getting more and more attention.Copper-based materials are one of the most widely used electrocatalysts for CO₂reduction due to their ability to convert CO₂into high-value-added multiple carbon products and hydrocarbons under mild conditions.However,the multi-step CO₂electroreduction process of copper-based catalysts produces gas-liquid mixtures,leading to low Faradic efficiency of target products.Rare earth elements（except scandium and yttrium）have unfilled 4f orbitals,rich electronic structure,and good catalytic properties for many reactions.This paper aims to investigate the impact of rare earth modification on copper-based electrocatalysts for CO₂reduction,study the structure-performance relationship through controllable synthesis of materials favorable to catalytic performance,and provide guidance for catalyst design and structure optimization.Additionally,incorporation of in situ characterization techniques monitors structural dynamics during the reaction,delving deep into the reaction mechanism and providing new ideas for designing stable and efficient new catalytic materials.Specific works are as follows:Ⅰ:Copper-based catalysts undergo structural evolution and surface reconstruction during electrocatalysis,resulting in excellent catalytic performance.Cu_2-xS was selected as the original material to study the performance of CeO₂on its electrocatalytic carbon dioxide reduction reaction and the influence of evolution path in the electrocatalytic process on catalyst performance.We designed CeO₂-modified Cu S catalysts with high current density and selectivity of C₂₊products in CO₂RR.CeO₂/Cu S catalyst can achieve a total current density of 160 m A cm^-2and a Faraday efficiency（FE）of 75.2%of C₂₊product in a flow cell system.Experiments and density functional theory（DFT）calculations show that,compared with Cu S catalyst,the modification of Cu S catalyst by CeO₂reduces the formation energy of*CHO thermodynamically,and the rapid activation of water around CeO₂accelerates the formation of*COCHO kinetics.Therefore,the CeO₂/Cu S catalyst promotes the C-C coupling step through the*CHO pathway,and thus has excellent catalytic properties for C₂₊products.Ⅱ:Copper sulfide is known for its crystalline phase diversity and tunable plasma properties.Therefore,we designed and constructed the composite material of CeO₂and different crystal phases Cu_2-xS,including CeO₂/Cu S,CeO₂/Cu₉S₈,CeO₂/Cu₇S₄,CeO₂/Cu_1.81S and CeO₂/Cu_1.96S,respectively.CeO₂/Cu_2-xS could generate ethanol in CO₂RR at-0.5 V vs.RHE,and the FE_C2+of CeO₂/Cu_1.96S at-0.3V vs.RHE is 72%.We focused on the structural evolution,interaction and activity sources of catalysts during theCO₂RR process.Comprehensive in situ characterization showed that the presence of CeO₂inhibited the entire self-reduction process of Cu_2-xS,resulting in stable active Cu⁰/Cu⁺.The remaining S is adsorbed on the surface of Cu as an electronic regulator and promotes the conversion of CO₂to CO.In different crystal phases Cu_2-xS,CeO₂/Cu_1.96S presents an appropriate Cu-Cu distance and an initial high proportion of Cu⁺,which benefits from the adaptive structural evolution of this dual regulatory effect and improves the selectivity of C₂₊.Our results show that adjusting the composition of copper valence states in the initial material and the distance between Cu-Cu sites can enhance the selectivity of C₂₊in CO₂RR in electrochemical reactions.Ⅲ:Metal-organic frameworks（MOFs）combine Metal ions with Organic ligands to form an ordered network.The controllable aperture/shape,high surface area,chemical tunability,Lewis acidity and open metal sites of MOFs provide a way to optimize selectivity,activity and efficiency.Therefore,we modified HKUST-1 with CeO₂to obtain CeO₂/HKUST-1 catalyst,and achieved high current density and selectivity for C₂₊products in CO₂RR.The grain size of Cu is negatively CO₂RR related with the selectivity of C₂₊,and its smaller grain size（～10 nm）and more exposed grain boundaries and high index surface are favorable for C-C coupling reaction.Therefore,decreasing grain size is an effective way to improve the performance of copper catalyst CO₂RR.Ⅳ:CeO₂/CuO_x@C with carbon layer was prepared by pyrolyzing CeO₂-modified copper organic skeleton（CeO₂/HKUST-1）.High resolution transmission electron microscopy（HRTEM）images show that the surface of CeO₂/CuO_x@C is covered with a uniform carbon layer（～2 nm）.In situ Raman spectroscopy and X-ray photoelectron spectroscopy（XPS）results show that CeO₂and the carbon layer stabilize the Cu⁺during theCO₂RR process and promote the C-C coupling.In situ Raman and in situ infrared spectroscopy also indicate that stable Cu⁺is conducive to CO formation at low current density and promotes C-C coupling at high current density.The Faraday efficiency of CeO₂/CuO_x@C in the electrocatalytic carbon dioxide reduction was 55%,higher than that of unmodified CuO_x@C（～10%）.