Study On Electrochemical Reduction Of CO₂ To Formic Acid With Bi/Sn Bimetallic Alloy Catalysts

With the continuous development of economy and society,excessive CO₂ gas is emitted into the atmosphere,which has caused greenhouse effect to become increasingly prominent.At the same time,the over-exploitation of resources has caused the global energy crisis to become increasingly severe.The conversion of CO₂ into clean fuel has important practical significance for improving the human living environment and alleviating the problem of energy shortage.The electrochemical reduction of CO₂ technology has the advantages of good environmental compatibility,mild reaction conditions,simple operation,and easy modularization.The CO₂ resource utilization approach that uses electricity output from renewable energy sources such as wind energy and solar energy to convert CO₂ into high-energy-density formic acid and other value-added chemicals has shown broad application prospects.However,the current technology has problems such as high electrocatalytic reaction overpotential,low catalytic activity,selectivity and current density.Therefore,the development of high-performance electrocatalytic materials is the key to solving the problem.In this article,low-cost,non-toxic,environmentally friendly,and highly active formic acid-producing Sn and Bi catalytic materials were used as the research object.A safe and simple electrodeposition method was used to synthesize Sn single metal and two kinds of Bi/Sn bimetal electrodes with 60 mesh copper mesh as the substrate in order to improve the catalytic performance and provide a certain theoretical basis for the development of this technology.Sn single metal electrodes with different deposition times were successfully synthesized by electrodeposition.Among them,the branch-like morphology structure of the Sn₄₀ electrode was the most uniform and regular,and the CO₂ reduction performance was the highest.Under the applied potential of-1.6 V vs Ag/Ag Cl,the maximum formate Faraday efficiency of 85.1%was reached,the current density was14.3 m A cm^-2,and the formate yield was 447.3μmol cm^-2 h^-1.The Bi/Sn bimetal electrodes with different deposition time were successfully synthesized by two-step electrodeposition method.Compared with the single metal electrode,its performance was significantly improved.Among them,the Bi₅Sn₆₀electrode surface had a uniform and compact pine needle-shaped dendritic structure.Due to the abundant Sn（200）and Sn（211）active crystal faces,metal oxide/metal interface and optimized electronic structure,Bi₅Sn₆₀ bimetal electrode showed the highest catalytic activity.The initial potential of formate production was the most positive,and the reaction overpotential was the lowest.Under the applied potential of-1.6 V vs Ag/Ag Cl,the maximum formate Faraday efficiency of 94.8%was reached,the current density was 34.0 m A cm^-2,and the formate yield increased to 634.3μmol cm^-2 h^-1.By optimizing the electrodeposition method,the co-electrodeposition method was used to successfully synthesize Bi/Sn bimetal electrodes with different deposition times.Among them,the Bi Sn₆₀ bimetal electrode had a uniform porous honeycomb structure.Bi Sn₆₀ bimetal electrode exhibited the most excellent performance of electrochemical reduction of CO₂ due to the existence of metal oxide/metal interface and proper electronic structure.The initial potential of formate production was the most positive,and the reaction overpotential was the lowest.Under the applied potential of-1.6 V vs Ag/Ag Cl,the Faraday efficiency of formate reached the maximum,which was 96.2%.Moreover,it maintained a level higher than 90%in a wide potential range,the current density was 14.3 m A cm^-2,and the formate yield was 266.5μmol cm^-2 h^-1.Therefore,the Bi/Sn alloy catalyst was beneficial to improve the CO₂ reduction performance.