Surface And Interface Engineering And Investigation Of Mechanism Of Non-noble Electrocatalysts Towards Electroreduction Of Carbon Dioxide

Using renewable energy to produce high value-added chemicals by electrocatalytic reduction of CO₂(CO2RR)can realize the closed-loop cycle of carbon,which has attracted wide attention.However,in the actual reduction process,due to the stability of the CO₂ molecule,a larger negative potential is often required to promote its conversion.Under a relatively negative potential,a serious hydrogen evolution reaction will occur,resulting in the decrease in activity,meanwhile,most catalysts are unstable at negative potential.Therefore,it is very important to design catalysts with high selectivity and stability.This paper mainly focuses on the design and preparation of Sn,Cu based catalysts with abundant resources and good catalytic performance.The specific research content includes the following three aspects:(1)We report a simple strategy for the preparation of heterostructured intermetallic Cu Sn electrocatalysts(Cu₃Sn/Cu₆Sn₅)supported on porous copper foam through an electrodeposition-calcination process.Compared with the performance of pre-calcination and pure phase alloy,it is found that the formation of heterojunctions was the main reason for the performance improvement.The obtained Cu Sn intermetallic catalysts demonstrate a faradaic efficiency of 82%and a current density of 18.9 mA cm^-2 at-1.0 V vs the reversible hydrogen electrode(RHE)for formate production in 0.1 M NaHCO₃ electrolyte for as long as 42 h.By using a gas diffusion electrode and 1 M KOH electrolyte,the current density of this catalyst for formic acid production can reach up to 148 mA cm^-2.Results from theoretical calculation results show that,compared with pure Cu₃Sn and Cu₆Sn₅ alloys,the adsorption of formate intermediates is stronger than that of CO intermediates at the interface of Cu₃Sn/Cu₆Sn₅ and the moderate hydrogen adsorption on the interface,which not only suppresses hydrogen evolution,but also favors the production of formic acid.This study explores the relationship between catalytic activity and structure by preparing heterojunction catalysts,and demonstrates a straightforward approach to the preparation of high-performance electrocatalysts towards the selective electroreduction of CO₂ to formate.(2)The active centers of some metal oxides are often unstable under the reduction potential.For instance,pure phase SnO₂ will be quickly reduced to metallic Sn,and some previous experiments and theoretical calculations indicate that the reactivity of SnO₂ is higher than that of metal Sn.Therefore,in order to maintain a higher activity of SnO₂ at the CO2RR reduction potential,metals of strong oxyphilicity are doped to stabilize metal oxides.For instance,a core-shell catalyst with metal oxide In-SnOx as the shell and metal alloy InSn₄ as the core is prepared by a one-step reduction method at low temperature.Electrochemical studies show that the catalyst exhibits efficient selective reduction of CO₂ to formate(>80%)in a wide potential window(0.7?1.2 V vs RHE,0.1 M KHCO₃),and the partial current density of formate can reach the maximum value of 34.15 mA cm^-2 at-1.1 V vs RHE,and have a high energy efficiency(61.2%),and remain stable for 58 h.Flow cell test showed that the selectivity of the catalyst to formate is above 90% under alkaline conditions,and the partial current density of formate can reach 236 mA cm^-2 at-0.98 V.Measurements based on operando X-ray absorption near edge structure spectroscopy(XANES),Raman spectroscopy and DFT theoretical calculations show that the introduction of metal In stabilizs oxygen in the catalyst,thereby making the oxide stable under the reduction condition,and it also reduces the Gibbs free energy of formate formation.Therefore,this work achieved the purpose of stabilizing the metal oxide catalyst by doping,thereby improving the activity of the catalyst,and can provide some ideas on how to retain some active centers of metal oxides at reduction potential.(3)In the CO2RR process,CO₂ is reduced to methane,formic acid,etc.,requiring hydrogen protons.However,in alkaline electrolyte,hydrogen protons mainly come from water decomposition.Therefore,the kinetics of water decomposition may limit CO2RR kinetics and selectivity of products.Thus,activatation of water molecules is an important step.In this study,copper nanowires are prepared by the oil bath method,and then modified by different organic molecules.Electrochemical studies show the selectivity of the modified catalyst for CH₄ can be significantly improved,especially when modified with4-dimethylaminopyridine,the selectivity of CH₄ can reach 56%at-0.88 V and its partial current density was 134 mA cm^-2.By the hydrogen production rate and hydrophilicity test,it is found that the high selectivity of CH₄ production may be due to the difference in the electron donating ability of the substituents on different organic molecules,which will change the binding strength between the nitrogen atom on the pyridine ring and the hydrogen atom in the water molecule,which facilitates the breaking of the H-O bonds in water molecule and hence water splitting.This leads to the production of a large number of adsorbed H^* on the catalyst surface,which promotes the CO^* hydrogenation,thereby increasing the selectivity of CH₄ formation.Therefore,in this work,the catalyst modified by organic molecules can promote the activation of water molecules,thereby improving the selectivity to deeper C1 products.This paper focuses on non-toxic,non-noble metal catalysts,and explores the relationship between catalyst structure and CO₂ reduction activity;the stability of catalyst structure and how to promote the performance improvement by activating water molecules,which realizes the conversion of CO₂ to a single product.It provides ideas for the preparation of efficient and stable catalysts in the future.