Preparation And Electrocatalytic Performance Of Nano-porous Alloy Materials For CO₂ Reduction

The electrocatalytic reduction of CO₂ from renewable energy to produce valuable carbonnaceous fuels is a potential technological approach to realize carbon cycling and carbon neutralization.In the past few decades,researchers have made encouraging progress in the exploration and development of cost-efficient CO₂reduction catalysts,which can regulate products from C₁ to C₃,such as carbon monoxide（CO）,formic acid（HCOOH）,ethanol（C₂H₅OH）,and n-propanol（C₃H₇OH）.Among the CO₂ reduction products,CO and HCOOH are considered as the most important 2-electron reduction products,which have advantages in terms of process cost,safety and economic benefits.However,due to the limitation of CO₂ solubility in neutral aqueous solution and the inevitable competitive reaction of hydrogen evolution,there are still some problems in the field of electrochemical CO₂ reduction,such as low selectivity,high overpotential and low current density,which hinder the industrialization process of CO₂ resource utilization.Therefore,in terms of improving performance and reducing cost,it is of great practical significance to develop new CO₂ reduction catalysts.Aiming at the above key problems,with the help of metallurgical phase diagram theory and metal alloy material design,Cu Au,In Sn,Bi Sn and Ir Ni Co alloy catalysts with three-dimensional macro porous structure were developed and successfully applied to electrocatalytic CO₂ reduction reaction.Combined with in-situ spectroscopy and density functional theory（DFT）calculation,the relationship between catalyst material structure and catalytic performance of electrocatalytic CO₂reduction was explored,and the corresponding structure-activity relationship was established to reveal the microscopic mechanism of electrocatalytic CO₂ reduction at atomic/molecular level.The main research contents and results are as follows:1.Nanoporous Cu₁Au single atom alloy（SAA）was successfully prepared by combining chemical dealloying and electrochemical etching.Benefiting from the hierarchically porous architectures with abundant vacancies as well as three-dimensional（3D）accessible active sites,the as-prepared nanoporous Cu₁Au SAA catalyst shows remarkable CO₂ reduction performance with nearly 100%CO Faraday efficiency（FE）in a wide potential range（-0.4～-0.9 V vs.RHE）and 40 h stability.In-situ XAS and theoretical analysis showed that the synergistic effect of single atom alloy effect and defect site strengthens CO₂ adsorption and activation,stabilizes*COOH intermediate,and then promotes the formation of final product CO.2.Based on the principle of alloy phase separation and selective phase corrosion,np-In₃Sn and np-In Sn₄ intermetallic compounds with large specific surface area,good catalytic activity and stability of CO₂ were successfully developed.In the H-type electrolytic cell test,it is found that np-In₁Sn₄ has excellent CO₂ reduction performance.The FE of HCOOH is more than 90%in the wide voltage range of-0.8V～1.1 V vs.RHE,and reaches a maximum of 96%±1 at-0.8 V vs.RHE.Moreover,in the alkaline flow-cell,the initial potential is-0.4 V,and the partial current density of HCCOH is as high as 230 m A cm^-2 at-1.0 V vs.RHE.The density function theory（DFT）results show that the excellent catalytic activity is attributed to the orbital interaction of In/Sn elements in In Sn₄ intermetallic compounds,which accelerates the charge transfer between Sn atoms and*OCHO intermediates,promotes the formation and stability of*OCHO intermediates,and then improves the selectivity of formic acid.3.A novel nanowire（NWs）catalyst with high conductivity Bi metal core and amorphous Sn-doped Bi O_x shell was prepared by one-step electrochemical dealloying method.The Bi/Bi（Sn）O_x NWs exhibit impressive formate selectivity over 92%from-0.5 to-0.9 V versus reversible hydrogen electrode（RHE）and achieve a current density of 301.4 m A cm^–2 at-1.0 V vs RHE in flow cell.In-situ Raman spectroscopy and theoretical calculations reveal that the introduction of Sn atoms into BiO_x species can promote the stabilization of the*OCHO intermediate and suppress the competitive H₂/CO production,resulting in excellent formic acid selectivity.4.Nanoporous Ir-based ternary alloy micron wire(np-Ir₇₀Ni₁₅Co₁₅ MWs)was successfully synthesised by electrochemical dealloying for electrocatalytic oxygen evolution reaction（OER）and coupled CO₂ reduction reaction.The catalyst exhibited excellent oxygen evolution performance at wide p H（0<p H<14）.The surface oxidation reconstruction during OER,and the low coordination Ir Ox surface doped with transition metal Ni and CO is its real catalytic active site,which promotes OER activity and stability.In addition,it is coupled with neutral electrocatalytic CO₂reduction to improve the overall energy efficiency of the full reaction electrolytic cell.To sum up,in this paper,single atom alloy catalysts,intermetallic compound catalysts and multi-alloy system catalysts with nanoporous structure were accurately constructed on the atomic scale,and applied in the field of electrocatalytic CO₂reduction.This paper not only opens up a new direction for the application of nanoporous metals in the field of CO₂ reduction,but also provides insights into the structure-activity relationship between the structure and performance of CO₂reduction catalysts.