Synthesis Of Supported Bi-based Catalysts And Study On Electrocatalytic Performance Of CO₂ Reduction

The continuous use of fossil fuels has caused a sharp rise in the concentration of carbon dioxide（CO₂）in the atmosphere,leading to severe climate problems and threatening the ecological environment on which human beings depend.Electrochemical reduction CO₂ into high value-added chemicals is an effective way to promote the anthropogenic carbon cycle.As an important liquid-phase product in the electrocatalytic CO₂ reduction reaction,formate is widely used in the fields of pharmaceutical synthesis,hydrogen storage materials and proton fuel cells.However,the efficiency of electrocatalytic CO₂ reduction to formate is limited by electrocatalytic materials.Some metals including Pb,Hg,In,Cd and Tl are effective catalysts for converting CO₂ into formate.However,the disadvantages of high toxicity or high cost limit their large-scale applications.Therefore,there is an urgent need to develop efficient,inexpensive and stable electrocatalysts.Two highly active catalysts were prepared by adjusting the surface electronic structure of Bi-based catalysts and enhancing the interaction between metal oxides and supports,which can effectively inhibit the hydrogen evolution reaction and improve the catalytic stability.（1）The oxygen-vacancy-rich ultrasmall bismuth subcarbonate supported on reduced graphene oxide composite（Vo-BOC/G）is synthesized for electrochemical CO₂-to-formate conversion.Electrochemical test results show that the Vo-BOC/G exhibits an outstanding formate selectivity up to 100%at-1.2 V vs.RHE and corresponding an impressive formate partial current density of 38 m A cm^-2 in CO₂-saturated 0.1 M KHCO₃ solution,superior to the bismuth subcarbonate composite（BOC/G）without oxygen vacancies under the same conditions.More importantly,the considerable formate selectivity（>80%）was obtained over an impressively wide potential range of 600 m V.Theoretical results show the abundant Vo defects significantly lower energy difference for*CO₂ formation and*HCOOH desorption,suppress the hydrogen evolution reaction,resulting in high formate selectivity over a wider potential window.（2）The Bi₂O₃ nanoparticles（Bi₂O₃/NV-C₃N₄）supported on carbon nitride（NV-C₃N₄）with nitrogen vacancies was prepared by a hydrothermal method.The results show that Bi₂O₃/NV-C₃N₄ exhibits excellent activity and stability for electrocatalytic CO₂ reduction to formate.The Bi₂O₃/NV-C₃N₄ can achieve 95%formate faradaic efficiency and 25 h long-term stability in 0.1 M KHCO₃ solution.More importantly,Bi₂O₃/NV-C₃N₄ exhibits high formate selectivity（>80%）over a wide potential range of 600 m V,outperforming most of reported CO₂ reduction electrocatalysts in the literature.The excellent performance can be attributed to the efficient electron transfer between NV-C₃N₄ and Bi₂O₃,which facilitates the generation of reaction intermediates.Theoretical results show that nitrogen vacancies in NV-C₃N₄ can effectively lower the energy difference for*CO₂ formation and*HCOOH desorption,turning the reaction into a spontaneous reaction,resulting in high formate selectivity.