Carbon Dioxide Reduction To Formic Acid,methane,and Methanol On Pd₃M?M=Au,Fe? Alloy:A Theoretical Investigation

Carbon dioxide?CO₂?capture and sequestration,and conversion of it to useful products has attracted intensive attention,since carbon dioxide is one main kind of greenhouse gas.Electrochemical conversion of carbon dioxide is a promising alternative for its moderate requirements during reaction process.Meanwhile if this technology is supplied with electricity from sustainable resources such as solar or thermal power,which could further achieve carbon recycling.Among all sorts of electro-catalysis in carbon dioxide reduction reaction,copper is one of the unique materials that can catalyze carbon dioxide into appreciable quantities of hydrocarbon products.But copper turns out with high over-potential and poor selectivity,which limits its further applications.To our delight,it has been reported that alloy made of transition metals as electro-catalyst has made much progress with respect to product selectivity and reducing over-potential.However,simply applying traditional“synthesis-test”model to select highly efficient catalysis requires time and sources.Therefore in this paper,we have applied density functional theory calculations to probe into possible carbon dioxide reaction mechanism on binary metal systems as Pd-Au and Pd-Fe.Major results are summarized as follow:There were two possible pathways for carbon dioxide reduction to formic acid on Pd-Au alloy.The Gibbs free energy for total reaction was 0.46 eV.The potential determining step for the reaction was CO₂?COOH*?*denotes intermediates?,the standard electrode potential for it was 0.89 V.There were three possible thermodynamic pathways for carbon dioxide reduction to methane on Pd-Au alloy.The Gibbs free energy for total reaction was-0.98 eV.The potential determining step for the reaction was CO₂?COOH*,and the standard electrode potential for it was 0.89 V.There were two possible thermodynamic pathways for carbon dioxide reduction to methanol on Pd-Au alloy.The Gibbs free energy for total reaction was 0.44 eV.The potential determining step for the reaction was CO*?CHO*,and the standard electrode potential for it was1.21 V.There were two possible thermodynamic pathways for carbon dioxide reduction on Pd-Fe alloy.The Gibbs free energy for total reaction was 0.71 eV.The potential determining step for the reaction was CO₂?OCHO*,and the standard electrode potential for it was 0.46 V.There were three possible thermodynamic pathways for carbon dioxide reduction to methane on Pd-Fe alloy.The Gibbs free energy for total reaction was-1.87eV.The potential determining step for the reaction was CO*?CHO*,and the standard electrode potential for it was 0.81 V.There were two possible thermodynamic pathways for carbon dioxide reduction to methanol on Pd-Fe alloy.The Gibbs free energy for total reaction was-0.15 eV.The potential determining step for the reaction was CO*?CHO*,and the standard electrode potential for it was 0.81 V.The results above revealed possible and relatively favored pathways for carbon dioxide reduction on Pd-Au and Pd-Fe alloy,which may provide guidance for designing alloy catalyst based on Pd metal.