Research On Organic Systems And Gallium-based Catalysts For Electrolysis Of CO₂ To C

Electrochemical reduction CO₂to the value-added products utilizing surplus renewable electricity provides a method for alleviating environmental pollution and renewable electrical energy storage.Ga has attracted much attention in CO2 electro-reduction due to its simultaneous metallic and liquid natures.However,Ga electrode facilitate hydrogen evolution reaction in aqueous electrolytes,resulting in low CO selectivity and inability to meet the practical application of CO2 reduction.To improve the CO selectivity on Ga catalysts,an organic solvent was chosen as the most suitable electrolyte for converting CO₂to CO on the Ga electrode.Then the Ga–Cl adlayer,the oxide-derived active gallium sites,oxygen vacancies and composite catalysts was constructed for CO2 adsorption and activation in organic electrolytes.The main research and conclusions are as follows:（1）Tetrabutylammonium chloride（Bu4NCl/AN）was chosen as the most suitable organic solvent for converting CO2 to CO on the gallium electrode.The weakly solvated Cl^-ion in organic solutions could form a Ga-Cl adlayer on the Ga electrode surface through a covalent bond.The electrons flowed from Cl^-to the carbon atom of CO₂,which is beneficial to stabilize CO2 in the vicinity of the Ga surface.Specifically adsorbed Cl^-can effectively hinder proton adsorption and production.The current density measured in Bu₄NCl/AN remained stable at 10 m A/cm²at-2.4 V and the CO faradic efficiency reached 83%.（2）The carbon supported gallium microspheres catalyst was synthesized by ultrasonic oxidation of liquid metal gallium.Potentiostatic electrolysis test shows current density increased gradually in the beginning of electrolysis and then became stable at 14.5 m A/cm²on Ga/C-CP electrode.XPS results reveal that this is because a portion of surface Ga2O3 was reduced to Ga⁰during the CO₂reduction.The oxide-derived active gallium sites efficiently enhance the reaction rate of CO2 conversion on the electrode.In addition to the effect of the oxide-derived active gallium sites,we found that the adsorbed chloride adlayer significantly favor the protonation of CO₂and suppress the proton reduction.During the electrolysis process,the CO Faradic efficiency measured on the oxide-derived gallium in Bu4NCl/AN achieved 84%.（3）We discovered that stirring oxidized the eutectic gallium indium（EGa In）and the reduction pretreatment are beneficial for introducing oxygen vacancies.The XPS results showed that the OV concentration in the oxide-derived EGa In（OD-EGa In）is much larger than that in the EGa In samples.Electrokinetic studies indicated that the introduction of OV facilitates electron transfer to CO2.Density functional theory（DFT）calculations further revealed that the electrons tend to accumulate around the OV,resulting in the enhancement of CO2 adsorption and activation.The CO Faradaic efficiency measured on the OD-EGa In achieved a maximum of 86%.（4）A porous Ga-Ag9In4 catalyst was prepared by an electrochemical assisted particle-internalization method.The electrochemical performance showed that the prepared porous Ga-Ag9In4 catalyst could convert CO2 into CO with high catalytic activity and selectivity.The CO faradic efficiency reached 88%at-2.3 V and current density remained stable at 30.2m A/cm².The XPS results show that the corresponding peaks of Ga 3d and In 3d of Ga-Ag9In4shift to higher binding energy after EGa In alloying with Ag,indicating that a depletion of electron density around Ga and In atoms.Ga-Ag9In4 electrode with a higher amount of oxidation state has higher activity for the formation of CO.