Preparation And Catalytic Performances Of In-Sn Nanoalloy/Mesoporous Sn-based Electrodes For The Electrochemical Reduction Of CO₂

The conversion and utilization of carbon dioxide have received an extensive attention around the world.The electrochemical method is a green,simple and efficient approach for the CO₂ utilization.By use of electrochemical method,CO₂ could be transformed into value-added chemical products,such as CO,formic acid/formate or alcohols.Among the numerous reduction products,formic acid is one of the important chemicals.The electrochemical reduction of CO₂ to formic acid/formate has a potential industrial application.In the previous studies,metal electrodes with high hydrogen evolution potential,such as indium and Sn,have shown a good selectivity for formic acid/formate formation in the process of CO₂ electroreduction.However,it should be noted that some key issues have not yet been solved,such as the easy deactivation of catalysts and low electrolytic current density.Therefore,the key to the electrochemical reduction of CO₂ is to modify or optimize the electrode,to improve the catalytic performance.In this paper,indium and Sn electrode materials were studied.In-Sn alloy nanocatalysts and mesoporous Sn electrodes were prepared by electrochemical deposition and anodic oxidation,respectively,and successfully applied to catalyze CO₂ to form formate in aqueous solution.In this paper,the microstructure,morphology and chemical composition of the prepared electrode catalysts were characterized by XRD,SEM,XPS and ICP-AES,respectively.And their electrochemical performances were analyzed by LSV,i-t Curve and EIS.The aqueous products of CO₂ electroreduction were qualitatively and quantitatively determined by nuclear magnetic resonance spectroscopy and ion chromatography,respectively.The main conclusions obtained in this paper are as follows:?1?GDE-In_xSn_1-x-x nanoalloy electrodes were prepared on the pretreated carbon paper electrode?GDE?by an electrodeposition method.The experimental results show that various GDE-In_xSn_1-x electrodes have the similar micromorphology,but different crystal phase structures and electrochemical active surface areas.Among the prepared GDE-In_xSn_1-x-x nanoalloy electrodes,GDE-In_0.90Sn_0.10 electrode has better catalytic activity than indium,Sn foil and other In-Sn alloy electrodes(such as GDE-In_0.22Sn_0.78,GDE-In_0.47Sn_0.53),and could catalyze CO₂ to form formate with Faradaic efficiency of 92.7%at-1.2 V vs.RHE.More importantly,the catalytic activity of GDE-In_0.90Sn_0.10 electrode remained reasonably stable over a 22-hour period of electrolysis,with a relatively high electrolytic current density(15 m A cm^-2),and Faradic efficiency of formate without obvious decay?>90%?.The experimental results have indicated that the excellent catalytic activity of GDE-In_0.90Sn_0.10 alloy is due to its composition,unique crystal phase and nanostructure.?2?Sn-based electrode with mesoporous structure was successfully prepared by using anodic oxidation.The SEM result showed that the surface of anodized electrode was densely packed with nanopores,with the diameter about⁵0 nm,and the surface oxide layer was amorphous SnO_x.In the process of catalyzing CO₂ reduction,the mesoporous Sn-based electrode has exhibited better catalytic activity than bulk Sn metal foil.With the mesoporous Sn-based as the electrode catalyst,the Faradaic efficiency of formate formation could reach89.6%at-1.2 V vs.RHE,with the reduction current density of 11.2 m A cm^-2,and good catalytic stability during 12 h electrolysis process.The anodized Sn-based electrode with mesoporous structure has a high catalytic activity,which is due to the fact that the mesoporous Sn-based electrode has a higher specific surface area and smaller electrochemical impedance.