Preparation Of Copper Bismuthate-based Thin Films And Study On The Kinetics Of Photocatalytic Carbon Dioxide Reduction

Organisms in nature rely on unique and complex biochemical processes,such as natural photosynthesis,to drive CO₂ conversion with solar energy,enabling most organisms to survive and reproduce.However,with the population drastically increasing,it is being difficult for natural photosynthesis to meet the tremendous demands of energy and food.Because natural photosynthesis is composed of dozens of biochemical reactions,which is too complex to control,the solar conversion efficiency of CO₂ reduction is commonly mediocre.Inspired by nature photosynthesis,the artificial photosynthesis is proposed,which can benefit from materials design,fabrication and performance optimization,for highly efficient conversion of CO₂ reduction.In this thesis,we mimic the nature photosynthesis of CO₂ reduction by the photoelectrochemical cell system.We aimed to study the kinetics of CO₂ reduction reaction on CuBi₂O₄ photocathode,and the charge transfer reaction rate in the CO₂ reduction process was studied throughoutly.The results could be summarized as follows:（1）The aminopropyl-modified amorphous SiO_x layer was used to improve the charge separation efficiency of CuBi₂O₄,where we found that the positive surface layer had little effect on the catalytic CO₂ reduction reaction.First,the Cu-Bi alloy was deposited through electrochemical deposition,which was converted to CuBi₂O₄ film after the spin coating and thermal annealing treatment.Second,the hydrolysis of siloxane APTES,an amorphous SiO_x layer with aminopropyl groups was obtained,as CuBi₂O₄/APTES film.The SEM morphology,XRD structure,XPS surface composition,energy band structure and transient photovoltage curves of the CuBi₂O₄ film materials were investigated.The films were fabricated into photoelectrode,which were used for the analysis of the photoelectric CO₂reduction performance and electrochemical stability.Moreover,the other photoelectrochemical tests such as light intensity coupled photocurrent（IMPS）spectroscopy,chopped transient photocurrent（TPC）spectroscopy,photoelectrochemical impedance spectroscopy（PEIS）,and photoelectric efficiency conversion（IPCE）spectroscopy were used for PEC reaction kinetics and efficiencies.（2）The stability of the CuBi₂O₄ photocathode was drastically improved by using a metal-organic framework（MOF）structure.It is shown that the MOF can form an ordered structure on oxide surface,which is used to catalyze the CO₂ reduction with enhanced reaction kinetics.The MOF-modified CuBi₂O₄ film electrodes were prepared by in-situ growth from the precursors.We also compared different metal ions in the MOF structure,so that the separation and transfer efficiencies of modified charges were compared.The photocurrent spectroscopy,photoelectrochemical impedance spectroscopy and light intensity coupled photocurrent spectroscopy were used to study the charge transfer kinetics of the photocatalytic CO₂ reduction reaction.Based on the density functional theory（DFT）calculations,we suggested that the rate-limiting step of the reaction could be a vital factor for the charge transfer mechanism.In summary,by applying the amorphous silicon dioxide layer or crystalline metal-organic framework structure layer on the CuBi₂O₄ photocathode,the stability and kinetics of the surface modification for CO₂ reduction were significantly improved.We found that the main bottleneck of the photocatalytic CO₂ reduction reaction on CuBi₂O₄ is possibly due to the poorer charge separation efficiency or the lower charge concentration at surface.The quick and efficient charge transport to the electrode surface for a high-concentration is particularly important for the CO₂ reduction reaction.