Researches On Bismuth Based Catalysts For Electrocatalytic Reduction Of Carbon Dioxide

With the progress and development of social industrialization,the increasingly prominent problems of energy shortage and environmental pollution have made people pay more attention to the sustainable development of resources.In recent years,the concentration of CO₂ in the atmosphere increases sharply,the global greenhouse effect has become a nonnegligible environmental problem,the research and application of CO₂ pollution control technology has great significance.CO₂ electrocatalytic reduction technology is considered as the most promising method for the resource utilization of CO₂ due to the advantages of moderate and controllable reaction condition,recyclable raw material,effortless modularization and so on.The method uses renewable energy such as solar energy and wind energy to generate electricity,and conversion of CO₂ to fuels with high energy density?such as formic acid?to cyclic utilization,which reduces the CO₂ concentration and relieve the pressure of energy shortage to some extent.At present,the main problems of CO₂electrocatalytic reduction technology are listed as follows:?1?high overpotential and energy consumption;?2?low current density and reaction rate;?3?low selectivity of target product.Therefore,the development of efficient novel catalytic materials is the key to solve the above technical problems.Based on the existing research,the Bi based catalytic material with high activity,lowcost and non-poisonous as the main research object in this work,and the synthesis of catalysts employed a sixpenny and convenient method to increase the selectivity and current density,and lower the overpotential.The main research contents and conclusions are as follows:?1?BiOX_0.5Y_0.5(BiOCl_0.5Br_0.5,BiOBr_0.5I_0.5 and BiOCl_0.5I_0.5)catalysts were prepared by hydrothermal method,and the catalytic performance of electroreduction of CO₂ was studied.Investigated the effect of loading amount on the performance of electrocatalytic reduction of CO₂,contrastively analyzed the electrochemical catalytic behavior of BiOCl_0.5Br_0.5,BiOBr_0.5I_0.5 and BiOCl_0.5I_0.5,discover that the halogen combination has a regulating effect on the size of nanometer Bi particles after electroreduction,the smaller the nanosize of Bi,the larger the electrochemical activity area and the current density,consquently the higher the faradaic efficiency and the generation rate of the product,achieving faradaic efficiency of 98.4%for electroreduction of CO₂ to formate at-1.6 V vs.SCE.?2?Nanorod Bi₂O₃ catalyst?Bi₂O₃-R?was prepared using oil-melt method,and modified the smooth surface via corrosion to obtain Bi₂O₃-E with rough surface.Contrastively sdudied the performance of electrocatalytic reduction of CO₂ over Bi₂O₃-R,Bi₂O₃-E and commercial Bi₂O₃?Bi₂O₃-C?,analyzed the morphology and structure by physical characterization technology,discovered that corrosion treatment enriched the internal channel structure of Bi₂O₃ catalyst,and increased the BET surface area and active sites,facilitated the adsorption and reaction of CO₂ on catalyst surface,accordingly enhanced the catalytic activity for electroreduction of CO₂.The faradaic efficiency of formate on Bi₂O₃-E electrode was 99.2%at-1.5 V,and kept stable at least for 20 h.?3?Tafel slope was evaluated on BiOX_0.5Y_0.5 and Bi₂O₃ electrode to speculate the possible mechanism for electrocatalytic reduction of CO₂,that is BiOX_0.5Y_0.5 or Bi₂O₃was firstly reduced to Bi nano particles,then CO₂ was adsorbed on electrode surface and transformed into adsorption state CO₂^?-,which further combined with hydrogen ion in electrolyte after acquiring an electron,ultimately generated formate ion.?4?Cu-Bi bimetallic catalysts were synthesized via hydrothermal method,the effects of the synthesis conditions of catalysts on the catalytic performance of CO₂reduction were investigated.The structure of catalysts was analyzed by physical characterization technology,and the results showed that the performance of electrocatalytic reduction CO₂ of Cu-Bi bimetallic catalysts was superior Bi metal catalyst due to the abundant pore structure which is beneficial to CO₂ adsorption and reaction.Besides,Cu/Bi ratio is an important factor of affecting the catalytic activity,and highest activity was showed on Cu-Bi catalyst with Cu/Bi ratio of 1/1 due to the special heterogeneous structure,with faradaic efficiency of 84.7%at-1.45 V.?5?Bi₂O₃-CuO?x,x=0,0.25,0.5,0.75,1.0,1.25?composite catalysts were prepared using amorphous complexometry method.By comparison,the catalytic activity of Bi₂O₃-CuO?x?catalyst for electroreduction of CO₂ was exceeded Bi₂O₃catalyst due to its relatively larger current density and electrochemical surface area.The effect of CuO/Bi₂O₃ ratio on electrochemical activity of catalyst was investigated,and found that the regulation of CuO/Bi₂O₃ ratio can effectively improve the morphology,enrich the pore structure and increase the surface area of Bi₂O₃-CuO?x?composite catalyst.The best catalytic performance achieves at CuO/Bi₂O₃ ratio of 0.75,with faradaic efficiency of 89.3%at-1.4 V,and kept stable for 10 h.