A Dft Study Of CO₂ Reduction Reaction Electrocatalyzed By Co₃O₄ And Doped Nanosheet

Electroreduction of CO2 is a way to reduce the content of CO2 in atmosphere and produce the fules that could replace fossil fuels.Thus,it is an potential way to solve the problems in environment and resource.Co3O4 nanosheet has exhibited advantages on catalytic activity,selectivity,and stability in catalystic electroredution of C02.On the other hand,the ideal for designing Co3O4 nanosheet provides an example for CO2 reduction catalysts.However,the way to improve performance of Co3O4 nanosheet was not clear because of the unsystematic reaction mechanism study..In this thesis,a systematic DFT calculation of CO2 reduction on Co3O4(001)surface was performed to find a minimum energy pathway to HCOOH.Meantime,the influences of electric field and oxygen vacancy were studied;these provide the data for explaining the current density change with potential,and relation between oxygen vacancy and Tafel slop.Detailed contents are summarized as follows:1.The HCO3-was treated as a reactant in this thesis,and a most likely reaction pathway was confirmed by transition state energy.Both the intermediate CO2-and adsorbed H were the reaction products of HCO3-on C03O4(001)surface.Then,a reaction between adsorbed CO2-and H atom produces HCOO-.The reaction pathway proved the effect of HCO3-concentration on the reaction rate.2.An external electric-field with direction vertical to surface was used to simulate the actual electric-field influence on reaction because the interaction between CO2 and the surface is greatly affected by it.Obviously,the reaction barrier of hydrogenation increases with increasing electric field,and the hydrogen reduction and hydrogenation are rate-limiting steps,which correspond to a Tafel slop about 39 mV·dec-1.However,the reaction barrier of hydrogenation change with increasing electric-field and actual capacity of CO2-on surface would lead to a greater Tafel slop.3.The reaction pathway on the surface with oxygen vacancy was also calculated.As a result,the oxygen vacancy would reduce the reaction barrier of hydrogen reduction,and turn the hydrogenation to the only rate-limiting step,which means the Tafel slop should be greater than 30 mV dec-14.A calculation on the surface of Ni-doped C03O4 nanosheet was performed,and the affection of Ni replace the CoTet could be forecasted by result.Nanosheet would have a lower catalytic activity if Ni atoms replace CoTet at surface,but another replace would lead a higher catalytic lower.Besides,the experiments proved that a little Ni doping could improve the catalytic activity of Co3O4 nanosheet,and the doping amount continued to increase to a certain extent,which in turn reduced the catalytic activity.The calculation and experimental results consistently show that Ni doping may be an effective way to improve the catalytic activity of C03O4 nanosheets for C02 reduction.