The Study Of Photoelectrochemical Conversion Of Carbon Dioxide And Cathode Nanocatalysts

Considering the inevitable use of fossil fuels and the continued increase in global energy consumption,it is imperative to face the challenges of climate change induced by anthropogenic CO₂ emissions,and to seek the economical and environmental--friendly alternatives to replace the fossil fuel energy.The photoelectrochemical?PEC?reduction of CO₂ is a kind of potential technology,which use renewable solar energy and CO₂ to produce fuels and chemicals?e.g.carbon monoxide?.This way can decrease the amount of released CO₂ into the atmosphere,and achieve sustainable production process.In this paper,on the basis of construction of photoelectrode,the nanocatalyst of cathode was studied,and then the photoelectrocatalytic reduction of CO₂ was evaluated.The main contents are as follows:Chapter 1.The significance and current progress of CO₂ utilization and photocatalytic reduction of CO₂ are reviewed.Then,the progress of metal electrocatalysts for reduction of CO₂ is described.At last,the main contents of this thesis was presented.Chapter 2.Firstly,WO₃ and BiVO₄ semiconductor films were prepared by polymer-assisted deposition method and metal-organic decomposition method,respectively.Then,the band structures of the prepared WO₃ and BiVO₄ films were characterized by solid-state UV-Vis diffuse reflectance spectroscopy,electrochemical impedance spectroscopy and linear sweep voltammetry.Based on the study of their band structures,the WO₃/BiVO₄ heterojunction composite photoelectrodes were prepared,and their cross-section morphology,crystal structure and elemental composition were analyzed by scanning electron microscopy,X-ray diffraction and X-ray photoelectron spectroscopy,respectively.Finally,the photoelectric conversion performance of WO₃/BiVO₄ composite photoelectrode was also studied.The results showed that the monoclinic WO₃ and BiVO₄ formed type II heterojunction with the film thickness of about 450 nm.At the applied potential of 1.23V versus the reversible hydrogen electrode,the photocurrent density of WO₃/BiVO₄ composite photoelectrode was 1.926 mA·cm^-2,indicating its better photoelectric conversion performance.Chapter 3.The traditional conversion of CO₂ in aqueous solution have serious drawbacks,such as low solubility,slow diffusion and complicated existing form of CO₂in water,and the competitive H₂ evolution from reduction of H₂O,which lead to the unsatisfactory conversion efficiency and the poor product selectivity.To overcome these problems,gas CO₂ has been directly introduced,in this work,to a flow cell in which a membrane cathode assembly with Ag nanocubes is used as an electrocatalyst.It is surprised to find that with this PEC reduction strategy,the competitive H₂ evolution has been completely suppressed.At the applied voltage of 1.4 V,Faradaic efficiency of this system is as high as 96.5%with the CO production rate of 1.11 mmol·min^-1·g^-1 and electro-to-chemical energy efficiency of 92.1%.In addition,when the applied voltage is below 1.4 V,the solar energy could fully compensate the related energy losses,and begins to be stored in the chemical bond of CO.Chapter 4.The main research results of this paper are summarized,and the development of photoelectrocatalytic reduction of CO₂ is prospected.At last the problems faced by future research are analyzed.