Preparation Of Bismuth-based And Cobalt-based Nano-electrocatalysts And Their Reduction Performance Of Carbon Dioxide

With the increasing progress of human society,the use of fossil fuels is increasing day by day.At present,with the decrease of fossil fuel storage,human development is facing enormous challenges.At the same time,a large number of combustion of fossil fuels has brought negative impacts on the natural environment,such as NO_x,SO_x and so on,which will cause acid rain,and a large number of CO₂ enrichment in the air causing“greenhouse effect”.In order to mitigate these adverse effects,CO₂ will be converted into fuel or chemicals in order to realize the transformation of energy from today's“fossil fuel economy”to the“carbon dioxide economy”of sustainable development.Compared with other conversion methods,electrochemical reduction of CO₂ has plenty of advantages,such as:?1?the use of carbon-free renewable energy,which has good environmental compatibility and none secondary carbon emissions;?2?it can operate at ambient temperature and pressure;?3?it can control the reaction by adjusting external parameters?such as electrolyte and applied potential?;?4?it is easy to expand its application.In this paper,Bi-based and Co-based electrocatalysts were prepared by simple methods,and their performance of the electrochemical reduction of CO₂ in aqueous solution were investigated.The details are as follows:?1?The spherical precursor BOC was synthesized by the method of hydrothermal synthesis,and then calcined at 300,400 and 500°C to form Bi₂O₃-1,Bi₂O₃-2 and Bi₂O₃-3 samples,respectively.The prepared BOC and Bi₂O₃ materials were modified on the glassy carbon electrode and reduced in situ to metal,then the performance of the CO₂ electrocatalytic reduction of Bi-based catalysts was studied.The results showed that the crystal structure of Bi₂O₃ obtained at different calcination temperatures gradually changes from hexagonal?-Bi₂O₃ to monoclinic?-Bi₂O₃ along with increasing temperature.With the increase of calcination temperature,the performance of electrocatalytic reduction of CO₂ by the reduced catalysts is improved.The r-Bi₂O₃-3 calcined at 500°C has the best performance for electroreduction of CO₂ to formate.At the potential of-1.6 V?vs.Ag/AgCl?,the maximum faradaic efficiency of electrochemical reduction of CO₂ to formate on r-Bi₂O₃-3 is 95%.The overpotential and the current density were 0.99 V and 17 mA cm^-2,respectively.Therefore,by regulating the crystal structure of Bi-based catalyst,it may be a new way to improve the activity of the electrocatalyst.?2?The relationship between the cell potential and energy efficiency was studied in different cathodic catalysts?Sn foil or r-Bi₂O₃-3?,anodic catalyst?Pt or Ir/C?and anolytes?0.1 M KHCO₃,0.1 M KOH and 1 M KOH?.The catholyte?0.1 M KHCO₃?of the system remains unchanged throughout the experimrnt.The results showed that the energy efficiency of the r-Bi₂O₃-3 electrode with higher activity of CO₂electrocatalytic reduction is higher than that of the traditional Sn electrode.The energy efficiency of the Ir/C anodic electrode with better electrocatalytic oxygen evolution performance is higher than that of the Pt electrode.It is indicated that the application of highly active cathodic catalyst and anodic catalyst can improve energy efficiency in the system.The cell potential with r-Bi₂O₃-3 cathodic catalyst and Ir/C anodic catalyst is 2.83 V when the catholyte and anolyte are both 0.1 M KHCO₃ solution.In the r-Bi₂O₃-3?Ir/C system,when 0.1 M KOH was used to replace 0.1 M KHCO₃ as the anolyte,the cell potential was further reduced.Moreover,the cell potential decreases with the enlargement of KOH concentration.In 1 M KOH anodic electrolyte,the lowest cell potential of electrochemical reduction of CO₂ to formate is 2.06 V,and the energy efficiency is 65.9%.The increase of energy efficiency can provide an application for electrochemical reduction of CO₂.?3?Co?CO₃?_0.5?OH??0.11H₂O nanowires containing CO₃^2-groups were synthesized by solvothermal method.Then the performance of this catalyst for electrochemical reduction of CO₂ was studied.It was found that the the liquid product obtained by electrochemical reduction of CO₂ with Co?CO₃?_0.5?OH??0.11H₂O in 0.1 M NaHCO₃electrolyte was methanol.The maximum faradaic efficiency of electrochemical reduction of CO₂ with Co?CO₃?_0.5?OH??0.11H₂O was 68%,the current density was 0.3mA cm^-2 and the overpotential was 260 mV at the potential of-0.85 V?vs.Ag/AgCl?.For the catalytic mechanism of this new catalyst,we suspect that CO₃^2-may participate in the reaction as a reaction intermediate,and the holes generated after the product formation can be used to stably adsorb the CO₂ molecule,thereby promoting the reaction and reducing the reaction overpotential.The study of Co?CO₃?_0.5?OH??0.11H₂O provides a new idea for electrochemical reduction of CO₂ by catalysts containing CO₃^2-groups.