Investigation Of Their Performance Of Cu Overlayers On Pd Nanocrystals For CO₂ Electroreduction

Extensive depletion of fossil fuels and the amount of CO2 emission lead to a series of environmental problems.Electrochemical conversion of CO2 holds promise for utilization of CO2 as a carbon feedstock and for storage of intermittent renewable energy.Metal electrodes as catalysts of CO2 electroreduction have attracted increasing attention.Intensive research efforts,Cu is the only catalyst known to electrochemically convert CO2 to hydrocarbons and/or oxygenates.The high-index planes of Cu have been studied extensively because of their remarkable enhancement of activity and stability.Nevertheless,the synthesis of Cu nanocrystals(NCs)with high-index facets is quite challenging.In addition,there are still several fundamental problems for Cu electrodes for CO2 reduction,such as a high overpotential,wide product distribution,and a severe competing reaction of hydrogen evolution.In comparison with Cu,Pt-group metals have a low overpotential for CO2 electroreduction.High-index planes of Pt-group metals,having a high density of low coordinated step atoms,also favor CO2 electroreduction.However,strong CO adsorption hinders the deep reduction of CO2 to hydrocarbons.Surface modification can effectively regulate the activity and selectivity of catalyst through ligand and strain effects,which alter the adsorption energy of the reaction intermediates.Therefore,it is a new way to study the electrocatalytic performance of Cu overlayers on Pt-group metal nanocrystals with high-index facets for CO2 electroreduction.In this paper,tetrahexahedral Pd nanocrystals(THH Pd NCs)with open structure and high step atom density are prepared by square wave potential method.A foreign metal of different layers were modified on THH Pd NCs,to explore the effect of coverage for CO2 reduction.Cu overlayers on Pd NCs with different lattice planes were prepared,which were used to investigate the relationship between crystal structure effect and performance of clectrocatalytic CO2 reduction.The main results are as follows:1)Cu overlayers were prepared by electrochemical deposition of Cu on the Pd NCs.The electrocatalytic CO2 reduction was performed by constant potential electrolysis method.The result demonstrated the selectivity for CO2 electroreduction was readily tuned by varying the coverage of Cu on THH Pd NCs.The Cu0.8mL/THH Pd NCs exhibit a high selectivity for methanol(FEmethanol=19.5%,FEethanol/FEmethanol ＝0.3),while the Cu1 ML/THH Pd NCs show a high selectivity for ethanol(FEethanol =20.4%,FEethanol/FEmethanol = 6.6).The Cu1.2mL/THH Pd NCs show a low FE for both methanol and ethanol.Therefore,the liquid products of CO2 reduction can be controlled by tuning the coverage of Cu on THH Pd NCs.2)The different surface structures of Pd nanocrystals can be tuned finely through regulating Eu.Monolayer Cu modified on Pd NCs with different surface structures was prepared by underpotential deposition(UPD).The relationship between selectivity of CO2 reduction and surface structure was investigated by constant potential electrolysis method.The result shows that,with the increasing of EU,we can prepare Pd nanocrystals with increase crystal surface index.The FE of ethanol enhances with the increase of atomic density of surface steps of catalysts.Therefore,we can infer that Cu modified Pd NCs with high-index facets has higher selectivity for CO2 reduction.The FE of ethanol was enhanced with the increase crystal surface index of Pd NCs.Electroreduction of CO2 is a surface-structure-sensitive reaction,the selectivity can be varied by tuning the surface structure of catalysts.