Bi-based Catalyst For Electrochemical Carbon Dioxide Reduction Reaction

CO₂ electrochemical reduction reaction（CO₂RR）has been considered as an effective way to solve the energy crisis and achieve carbon neutrality due to its advantages such as mild reaction conditions,compact device and easy modularization.As one of the 2 electronic products of CO₂RR,formic acid（HCOOH）is a kind of chemical products with high added value.As one of the main metal catalysts for formic acid production,Bi-based material has the advantages of low cost,low toxicity,high selectivity and activity for formic acid production,and is a potential CO₂RR catalyst.In this thesis,starting from the metal Bi,a series of Bi-based catalysts were synthesized and their catalytic performance in CO₂RR was explored.The specific work contents are as follows:（1）Bi₂O₃,Bi₂S₃,Bi₂Se₃ and Bi were prepared using simple hydrothermal method and bismuth nitrate pentahydrate（Bi（NO₃）₃﹒5H₂O）as bismuth source.The morphology,crystal structure and surface chemical composition of the catalysts were characterized by SEM,TEM,XRD and XPS.The four catalysts were tested for the CO₂RR and showed good formic acid selectivity.The faraday efficiency of the metal Bi catalyst was the highest,reaching 94%～98%in the wide potential range of-0.9 V to-1.15 V.Compared with metallic Bi,Bi compounds showed higher formic acid partial current density and yield,among which Bi₂S₃ was the highest.Taking Bi₂Se₃ catalyst as the research object,the changes of the catalyst in the process of electrocatalytic reduction reaction were analyzed.It was found that Bi compound catalysts experienced the process of Bi³⁺→Bi⁰,and then Bi⁰ as the catalytic active site catalyzed the CO₂ electroreduction to selectively generate formic acid.（2）Using ammonium bismuth citrate as bismuth source and sodium borohydride（Na BH₄）as reducing agent,a series of carbon supported Bi nanoparticles were designed and synthesized by water solution reduction method.The effects of the amount of Bi and the type of carbon supports on the CO₂RR performance of the catalysts were investigated.According to TEM,XRD,XPS and Raman characterization results,it can be seen that Bi nanoparticles can be uniformly loaded onto the supports.With the increase of the loading of Bi,the agglomeration of Bi nanoparticles on the supports increased.The results of CO₂RR showed that 5%Bi@CNTs catalyst could obtain high formic acid selectivity（88.6%）,the corresponding current density was-18.84 m A cm^-2,and the yield of formic acid reached351.41μ mol h^-1.Through the investigation on the stability attenuation of CO₂RR,it was found that during the process of CO₂ electroreduction,the cathode electrolyte concentration increased continuously,while the anode electrolyte continued to consume,resulting in the increase of the internal resistance of the anode solution.Therefore,the electrode reaction was blocked,and the current density of CO₂RR decreased rapidly.Through the analysis of anode and cathode electrode reactions in the CO₂RR,the reason of stability degradation of this electrocatalytic system was explained well.