Rational Design Of Inorganic Nanomaterials And Their Applications For Electrocatalytic Carbon Dioxide Reduction Reaction

Since the industrial revolution of the 19th century,fossil fuels such as coal,oil,and natural gas have played an important role in the global energy supply.However,the large amount of carbon dioxide gas produced by the burning of fossil fuels can cause climate problems such as global warming and ocen acidification.How to reduce the atmospheric carbon dioxide level and effectively utilize it has become an urgent problem to be solved.Among many solutions,the electrochemical carbon dioxide reduction reaction teconology has been widely concerned by researchers.It enables atmospheric carbon dioxide conversion into carbon-based fuels such as carbon monoxide,formic acid,acetic acid,methane,etc.utilizing renewable energy(such as solar energy,wind energy and tidal energy),however,the key of carbon dioxide reduction reaction technology lies in the development of electrocatalysts.After lots of exploration by researchers worldwide,the study of carbon dioxide reduction catalysts has made some progress.However,there still exists many disadvantages of carbon dioxide reduction catalysts,such as low current density,low Faradaic efficiency and poor stability.Therefore,we need to further optimize carbon dioxide reduction catalysts to meet the needs of practical application.In this dissertation,we designed and prepared novel inorganic nanomaterials and studied their electrocatalytic carbon dioxide reduction performance.We have fabricated a series of carbon dioxide reduction catalysts using high-temperature annealing,liquid phase exfoliation and solvothermal synthesis method,etc.We investigated their crystal structure,morphology,and phase characteristics through various characterization techniques.Additionally,we also systematically studied carbon dioxide reduction performance of all catalysts,and rationally clarified the structure-activity relationship between the structure of the nanomaterials and carbon dioxide reduction performance.The main content of this dissertation is in the following:1.The carbon dioxide reduction product(carbon monoxide)of a single nitrogen-doped carbon material is limited by low current density(<2 mA cm-2)and undesirable selectivity(<90%).Therefore,we propose a nitrogrn,phosphorus co-doping strategy to further improve carbon dioxide reduction reaction performance of carbon materials.Nitrogen,phosphorus co-doped mesoporous carbon was prepared by high-temperature annealing phytic acid-modified zeolitic imidazolate framework-8.Nitrogrn,phosphorus co-doped mesoporous carbon material displays concave dodecahedron shape,and features large specific surface area and abundant mesoporosity.Electrochemical measurements suggested that nitrogrn,phosphorus co-doped mesoporous carbon catalyst enabled the selective carbon dioxide reduction to carbon monoxide with excellent carbon monoxide selectivity close to unity,and the maximum partial current density of?8 mA cm-2.Its selectivity and carbon monoxide partial current density are superior to existing singly doped carbon free of metal.The synergy between nitrogen and phosphorus significantly enhanced the adsorption of both*COOH and*CO intermediates,thereby promotes carbon dioxide reduction performance.2.Sn-based carbon dioxide reduction catalysts reported up to now cannot achieve high formate Faradaic efficiency until at very large overpotential.Therefore,we synthesized mesoporous tin dioxide nanosheet through a self-template method and utilized it for electrocatalytic carbon dioxide reduction reaction.Mesoporous tin dioxide nanosheet featured large specific surface area,abundant mesoporosity and three-dimensional hierarchical structure.When acted as the carbon dioxide reduction catalyst,it delivered small onset potential,large cathode current density,high formate formate Faradaic efficiency,and decent stability.Impressively,the Faradaic efficiency of formate can be as high as 83%at ?=710 mV,which is 150-300 mV lower than that reported in previous literatures.In addition,we coupled mesoporous tin dioxide nanosheet cathode with commercially available anode to achieve battery-driven carbon dioxide/water full-cell with the overall electricity-to-formate conversion efficiency of 22%.3.Hexagonal metallic bismuth has a layered structure similar to that of black phosphorus,hence metallic bismuth can be exfoliated by a top-down method of liquid-phase exfoliation to obtain two-dimensional ultrathin nanosheets.Bismuth nanosheets present thin lamellar morphology with lateral dimensions ranging from several hundred nanometers to several microns.It can selectively reduce carbon dioxide to formate with the Faradaic efficiency of?90%in a wide potential range,whose carbon dioxide reduction reaction performance is better than that of commercial bismuth powder.The large number of exposed active sites on bismuth nanosheets result in superior carbon dioxide reduction performance than that of commercial bismuth powder.4.In-based carbon dioxide reduction catalysts still fall short of the undesirable current density and Faradaic efficiency.Octahedral indium oxide was synthesized by high-temperature calcination of indium-based metal-organic framework precursor.The final product displayed octahedral morphology that is significantly different from the indium-based metal-organic framework precursor,the size is also greatly reduced.Oxygen defect structure in octahedral indium oxide material increases the number of electrochemical active sites,thus promotes carbon dioxide reduction reaction performance.Compared with that of commercial indium powder,the catalyst exhibits a smaller onset overpotential(230 mV),higher formate Faradaic efficiency(88%)and a larger formate partial current density(23.1 mA cm-2).Furthermore,the catalyst can achieve a formate Faradaic efficiency of?90%,the maximum current density of formate can reach?80.4 mA cm-2 in a flow cell.5.At present,the research on carbon dioxide reduction mainly focuses on the morphology and structure design of the catalyst,while less attention is paid to the design of the gas diffusion electrode.Here,the concept of self-standing electrode is introduced into carbon dioxide reduction reaction.We designed and optimized the gas diffusion electrode,and constructed a self-standing carbon electrode with one-dimensional pore canals,which was convenient for the transport of ions,water and gas involved in the electrocatalytic reaction.Additionally,we deposited bismuth on the wood-derived carbon self-standing electrode by magnetron sputtering to obtain a bismuth-supported self-standing carbon electrode.The carbon electrode features multichannel structure and flat surface.Bismuth is deposited on the surface of the carbon electrode in the form of metal nanoparticles.Electrochemical carbon dioxide reduction reaction measurements showed that bismuth-supported self-standing carbon electrode can selectively reduce carbon dioxide to formate,the maximum partial current density of formate can reach?20 mA cm-2.