Preparation Of Sn And Bi Based Catalysts Supported On Carbon Materials And Electrocatalytic Properties For Carbon Dioxide Reduction

The increasing CO₂ emission has led to a series of environmental problems with the progress and development of the society.Conversion of carbon dioxide into useful chemicals can not only effectively solve environmental problems such as the greenhouse effect,but also realize the cycling utilization of energy,which has attracted widespread attention.The electrochemical CO₂ reduction reaction（CO₂RR）is considered to be an effective method for CO₂reduction due to its advantages such as controllable conditions,recyclable electrolyte and simple operation.Formic acid（HCOOH）,one of the products of CO₂RR,is an important raw material of basic organic chemicals and is widely used in printing and dyeing,food additives,medicine and other industries.It is a good hydrogen storage material and can be used in fuel cells.More and more attention has been paid to the selection of a cheap,non-toxic and easily available catalyst for the efficient preparation of formic acid.In this paper,cheap tin and bismuth salts were used as metal precursors and carbon nanotubes and conductive carbon black were used as catalyst carriers to prepare supported tin and bismuth based catalysts for the electrocatalytic reduction of CO₂.The main contents are as follows:（1）The supported SnO₂ catalyst SnO₂/CNTs was prepared by the method of adsorption and oxidation using stannous chloride as precursor and carbon nanotubes as support.The influence of the loading amount of SnO₂ and the post-treatment temperatureon on the electroreduction of carbon dioxide was investigated.The results show that the catalyst with 12wt%loading of SnO₂ and no post-annealing treatment exhibits the best catalytic performance for CO₂RR with the faraday efficiency of HCOOH of 74%and the total current density of 10.4mA cm^-2 at-1.2 V.The SnO₂ particle size of SnO₂/CNTs-E catalyst can be controlled with colloid method by changing the heating rate.The results show that the catalytic performance of small SnO₂ particles is better.At the potential of-1.3 V,the faraday efficiency of HCOOH is80%,the current density of HCOOH is 11 mA cm^-2 and the average current density is 14 mA cm^-2.（2）SnO₂-BiOCl/C composites were synthesized in one step with stannous chloride and bismuth nitrate as precursors and conductive carbon black as carriers without the additional add of chlorine.The ratio of stannous chloride to bismuth nitrate precursor was changed to explore the effect of Sn:Biratio on the CO₂RR performance of SnO₂-BiOCl/C catalyst.The results show that the addition of BiOCl can improve the selectivity of formic acid.When Sn:Bi=1:4（mol）,the catalyst has the highest selectivity to produce formic acid in CO₂RR.The Faraday efficiency of formic acid is 86%and the average current density is 12.7 mA cm^-2 at a potential of-1.3 V.Compared with the CO₂RR performance of Bi₂O₃/C,it was found that the formic acid selectivity of SnO₂-BiOCl/C catalysts was less than that of Bi₂O₃/C catalysts.Therefore,it is necessary to further explore the mono-metal bismuth-based catalysts for CO₂RR.Bi₂O₃/C and BiOCl/C catalysts were synthesized,potimized characterized and evaluated their electrocatalytic CO₂RR.LSV,XPS,TEM and other characterization methods were adopted to explore the active species of Bi₂O₃/C catalyst and BiOCl/C catalyst for CO₂electroreduction reaction.It is found that the catalytic performance of the two catalysts is similar.Bi₂O₃/C and BiOCl/C themselves can be reduced in the process of catalytic CO₂electroreduction,and are reduced to the same substance Bi.So they actually have the same active substance when catalyzing the CO₂RR reaction.