Preparation Of Ag₂S-Au Heterogeneous Nanocomposites For Electrocatalytic CO₂ Reduction

Growing concerns on carbon dioxide（CO₂）emissions leading to global warming have prompted the search for environmentally friendly technologies.Electrochemical carbon dioxide reduction reaction（CO₂RR）converting excess CO₂ into value-added chemicals or fuels is considered as an effective strategy to store abundant intermittent renewable energy and build a carbon neutral society,which provides a practical solution to the current environmental issues.However,this reaction still faces many challenges such as high reaction overpotential and low product selectivity due to the proton coupling-electron transfer process and the inevitable hydrogen evolution reaction（HER）.Therefore,the rapid development of an efficient and stable CO₂ reduction catalyst with high selectivity,large current density,and low overpotential has become an urgent problem in the field of energy storage and conversion.Over the past few decades,noble metal-based nanomaterials have been regarded as effective catalysts for CO₂RR because of their high catalytic activity,long-term stability,and excellent selectivity to target products.For example,gold（Au）-based nanocatalysts have been shown to be promising candidates for selectively reducing CO₂ to carbon monoxide（CO）due to their low reaction overpotential,good product selectivity,high Faradaic efficiency,and inhibition of HER.However,due to its high price and limited reserves,reducing the Au content in electrocatalysts while improving the catalytic activity is the key to the industrial application of electrocatalytic CO₂ reduction.Recent studies have found that preparing noble metal-semiconductor nanocomposites for electrocatalytic CO₂reduction can not only effectively improve its catalytic activity,but also reduce the content of Au and save the cost.The main content of this paper is the fabrication of silver sulfide-gold heterostructure nanocomposites（Ag₂S-Au HNs）and their application and theoretical study in electrocatalytic CO₂RR.The specific research content and results are as follows:（1）First,gold nanoparticles（Au NPs）with an average diameter of 10 nm were successfully prepared by a simple wet-chemical method using chloroauric acid as a precursor.Then,it was supported on activated carbon to prepare a powder catalyst,and its electrocatalytic performance for CO₂ reduction was investigated.The experimental results show that Faradaic efficiency of Au NPs for electrocatalytic reduction of CO₂ to CO at a potential of-0.8 V vs.RHE is as high as 74.84%.In addition,silver sulfide nanoparticles（Ag₂S NPs）with an average diameter of 7 nm were successfully prepared using silver nitrate and sulfur powder as the precursors and oleylamine as the reducing agent,and the electrocatalytic CO₂ reduction performance was also tested.It was found that the CO Faradaic efficiency of Ag₂S NPs was as high as 67.35%at-0.8 V vs.RHE.In order to reduce the amount of Au and improve the electrocatalytic activity,Ag₂S-Au HNs were synthesized by a generalized metal ion phase transfer method.To explore the optimal electrocatalytic CO₂ reduction performance of Ag₂S-Au HNs,the amounts of precursor Ag₂S organosol and Au3+solution in n-hexane phase were adjusted.The experimental results show that the molar ratio of Ag₂S and Au is 1:1,Faradaic efficiency of Ag₂S-Au HNs for electrocatalytic reduction of CO₂to CO is as high as 94.5%,which also greatly reduces the amount of Au.（2）Density functional theory（DFT）calculations show that compared with Au NPs and Ag₂S NPs,the Ag₂S-Au heterostructure catalyst can further improve the adsorption strength of intermediate COOH*and reduce the energy barrier of product CO desorption,improving the selectivity of the electrocatalytic CO₂reduction reaction.Furthermore,it can be seen from the differential charge density map that electrons in the Ag₂S-Au heterostructure are concentrated at the interface of Ag₂S and Au,indicating that the interface is enriched with charges,which improves the performance of Ag₂S-Au nanocomposites for electrocatalytic CO₂reduction.