Synthesis And Catalytic Mechanism Of Copper-modulated Bismuth-based Electrocatalytic CO₂ Reduction Materials

With clean energy generation as the main energy supply,the reduction conversion of carbon dioxide（CO₂）into stable,storable,high energy density fuels or chemicals such as low carbon alcohols（acids）or low carbon hydrocarbons through electrochemical processes is an effective way to achieve efficient and green cycle conversion and utilization of carbon resources.Bismuth metal（Bi）-based materials are one of the effective catalysts for the electrocatalytic targeted conversion of CO₂ to formic acid（salt）（HCOOH or HCOO^-）.However,due to their insufficient intrinsic catalytic ability,Bi-based materials need to activate CO₂ at lower potentials,and the reported catalytic performance is still not up to industrial application specifications.Therefore,based on the mechanism of electrocatalytic CO₂ reduction reaction（CO₂RR）,it is important to develop new Bi-based materials to reduce the overpotential of the reaction and improve the conversion efficiency and stability of the reaction for the practicalization of CO₂RR.In this thesis,aiming to improve the performance indexes of Bi-based materials towards CO₂RR,perturbation of the p-state electronic structure of Bi by the unique d-band electronic properties of transition metal copper（Cu）,we have constructed bismuth/copper oxide（Bi/Cu₂O）composites and self-supporting bismuth-copper（BiCu）bimetallic electrodes.The electron structure of Bi-based materials is modulated by the transition metal Cu,which improves the intrinsic catalytic activity of the materials.（1）Synthesis of bismuth-copper oxide composites and CO₂RR mechanism.In this part of work,Bi/Cu₂O composites have been prepared by combining simple solvothermal synthesis,pyrolytic treatment and electrochemical conversion processes.In-situ Raman spectroscopy combined with off-site XRD tests verifies the transformation and catalytic active sites of Bi species under the effect of negative voltage,and demonstrates the competition between surface adsorbed species and reaction intermediates during the reaction process.Experimental and theoretical calculations show that the p-state electrons of metal Bi at the Bi/Cu₂O interface are transferred to Cu₂O due to the modulation effect of Cu₂O,which optimizes the adsorption of*OCHO intermediates on Bi and enhances the intrinsic catalytic activity of the material,which can catalyse the conversion of CO₂ to HCOOH at lower potentials.These results highlight the modulation effect of transition metal d-state electrons on Bi p-state electrons.（2）Supported BiCu bimetallic electrode for high throughput catalytic conversion of CO₂ to HCOOH.In this part,a controlled thickness BiCu bimetallic film have been constructed on the surface of copper foam using copper foam as the copper source and collector,combining with in-situ desolvation and redeposition,and electrochemical conversion processes.In CO₂RR,the BiCu bimetallic electrode can obtain a high current density of 1000 m A cm^-2,and the HCOOH Faraday efficiency is higher than 85%in a wide electrochemical window range,and these performance indicators meet the requirements of industrial applications.Experimental and theoretical results demonstrate that metallic Cu promotes the metal Bi p-electron delocalization,which in turn changes the decisive step of the reaction,lowers the reaction energy barrier from CO₂ to HCOOH,and optimizes the process of CO₂RR reaction kinetically and thermodynamically.In addition,copper foam facilitates the exposure of abundant active sites and promotes electron transport.This study shows that high throughput CO₂RR electrodes can be constructed by orbital delocalization strategy,which provides a potential pathway for carbon resource recycling and utilization.