Surface Engineering Of Two-dimensional Transition Metal Nanosheets For Efficient CO₂ Electroreduction

With the development of modern chemical manufacturing,the excessive emmision of CO2 molecules leads to their ever-increasing contents in the atmosphere,as well as the unbanlanced carbon cycle in nature.The high concentrations of CO2 brings about a series of environmental problems like greenhouse effect,which seriously endangers the living environments of human beings.Recently,there are growing interests in reusing the renewable energy such as solar and wind to convert CO2 into value-added carbonaceous products.With the assistances of these technologies,we anticipate to build up the "chemical metabolism" that contributes to the goal of carbon neutrality.To this end,various techiques have been reported for CO2 conversion,including electrochemical,photochemical,biochemical and thermochemical methods.Among these methods,the electroreduction of CO2 attracts large attention due to its high efficiency,controllable selectivity,simple operation condition,and available renewable energy.Due to the inertness of CO2 molecules,CO2 electroreduction reaction relies on highly active catalysts.Two-dimensional transition metal nanosheets are regarded as promising electrocatalysts because of their unique structural composition and excellent electrochemical activity.In addition,considering the pivotal roles of electron-transfer from catalysts surface to reactants in CO2 electroreduction,which are closely associated with the surface electronic structures of catalysts,it is required to finely tuning the surface structures of nanosheets for modulating their catalytic performance towards CO2 electroreduction.Herein,we reported several strategies of surface engineering in two-dimensional transition metal nanosheets towards CO2 electroreduction.These modified nanomaterials,including Ni-doped SnS2 nanosheets,hydrogen-incorporated SnS2 nanosheets,and reconstructed InN nanosheets,showed superior performances in CO2 electroreduction.We also investigated the relation between atomic surface regulation and their performance of CO2 electroreduction.These related projects are concluded as follows:1.We firstly reported a facile solvothermal method for the synthesis of Ni-doped SnS2 nanosheets towards CO2 electroreduction.Experimental tests show that Ni doping significantly enhanced the current density and Faraday efficiency for carbonaceous products of SnS2 nanosheets.At-0.9 V vs.RHE,5%Ni-doped SnS2 nanosheets achieved the FE of 93%for carbonaceous product with a current density of 19.6 mA cm-2.Mechanism studies revealed that Ni doping induced the formation of a defect level near the conduction band bottom of SnS2 and reduced its work function,which benefited the electron transfer process between catalysts and reactants.As such,the adsorption and activation abilities of CO2 molecules on catalysts were strenghtened,thus improving their activities of CO2 electroreduction.2.We further discussed the utilization of surface hydrogen incorporation to engineer the surface structures of SnS2 nanosheets,and systematically analyzed the impacts of surface hydrogen injection process on the performances of SnS2 nanosheets towards CO2 electroreduction.With the assiatances of surface hydrogen incorporation,HySnS2 nanosheets exhibited enhanced current density and Faraday efficiency for carbonaceous products.Density functional theory(DFT)calculations further show that the incorporation of hydrogen in HySnS2 nanosheets contributed to the activation of CO2 molecules into HCOO*intermediates,which finally promoted the production of formate in CO2 electroreduction reaction.3.We finally illustrated the electrochemical reconstruction of InN nanosheets for efficient CO2 electroreduction into formate.A series of in-situ measurements indicate that the catalytic performances of InN nanosheets were closely related to the structural evolution during CO2 electroreduction.InN nanosheets were reconstructed into an In-rich surface during CO2 electroreduction.DFT calculation further shows that the electron-transfer process between In surface and InN led to the redistribution of surface charges,which directly altered the adsorption of HCOO*intermediates and ultimately improved the performances of CO2 electroreduction into formate product.