First-principles Study On Catalytic Activity Of Noble Metals Supported On Tantalum Carbide For Oxygen Dissociation And Carbon Monoxide Oxidation

Energy crisis and environmental pollution are increasing serious.In recent years,the problems of PM2.5 and haze endanger human body and heart,bring much inconvenience to people.The proton exchange membrane fuel cell?PEMFC?as a green energy device could transfer the chemical energy of the fuel into electricity with conducting water.The Pt/C catalyst is traditional electrode catalyst of PEMFC.But the carbon black is corroded in the harsh electrochemical reaction environment,and the Pt catalytyst is poor stability and resistence to the carbon monoxide?CO?poisoning,meanwhile the Pt is expensive and scarce,which limit the application of PEMFCs.So it is expected that the catalysts with well activity,low cost and high corrosion-resistance replace the Pt/C.The nanosystems with less noble metal loading on transition metal carbides?TMCs?are supposed to achieve the goal by optimizating the supported and the supported metal,the catalytic activity of tantalum carbide?TaC?as the research object was systematically investagated.The oxygen reduction reaction and CO oxidation are research hotspots,and based on density functional theory,the adsorption of Pd and Pt on the Pure TaC?100?was investgated firstly,meanwhile the stability of the composite system was verified.And we analyzed the electronic structure to understand the interplay between the metal and the surface of substrate.Finally,we calculated the adsorption and dissocation of oxygen molecule on the four different configurations,combined with data of clean TaC?100?surface and pure Pt?111?surface,implying the high catalytic activity to oxygen dissociation and stablity of Pd_ML/TaC.The oxygen dissociation is the first step of CO oxidation,so we further explored the mechanism of Pd _ML/Ta C to CO oxidation and the resistance strengh of Pd_ML/TaC to CO poisoning.The main work performed and results are follows:1.The catalytic activity of oxygen on the TaC?100?modified by the four and monolayer M?M=Pd,or Pt?was investigated.Charge difference density and Mullken charge showed that the electron transfer between noble metal and TaC?100?surface was obvious,indicating the interaction between them.The cohesive energy of Pd bulk was smaller than the binding energy of Pd atoms and Ta C?100?surface,confirming that Pd atoms preferred to form two-dimension configuration on the TaC?100?.Compared to bare TaC?100?and the other three supported systems,the DOS peak of Pd_ML/TaC is the highest in the vicinity of the Fermi energy,demonstrating the probable high activity of Pd_ML/TaC.Meanwhile,combined the results we calculated of adsorption energies and dissociation adsorption energies of oxygen on the Ta C?100?with the four supported systems,we could conclude that deposition of Pd_ML on TaC?100?enhance the oxidation resistance of TaC?100?with stable structure.In the end,we could find by the results of transition state?TS?:Compared to the bare Pt?111?and the other three supported systems,the dissociation barrier of oxygen on the Pd_ML/TaC is most small.Above results indicated that Pd_ML/TaC has the high catalytic property to the oxygen dissociation and the oxidation resistance.2.The mechanism of carbon monoxide?CO?oxidation on the TaC?100?with monolayer Pd(Pd_ML)modified was investigated.Firstly,we calculated and contrasted the adsorption of small molecule involving CO oxidation on the substrate surface,insuring the most stable configuration.The adsorption energy of carbon dioxide?CO₂?on the Pd _ML/Ta C was high-low,indicationg that the CO₂ on the substrate surface was easily desorbed.In addition,the computational data showed that the adsorption energies of O₂ and CO was so close,and the coadsorption energy of O₂ and CO was nearly eauql to the sum of their separate adsorption energies.So we next considered the three reaction mechanisms:Langmuir-Hinshelwood?LH?,Eley-Rideal?ER?and termolecular Eley Rideal?TER?,we found that the CO oxidation is preferable to ER mechanism than the other mechanisms by searching transition state,and activation of the rate-determining step?RDS?,heat of reaction and activation energy were 0.48 eV,-4.62 eV and 0.13 eV respectively.Analysis results showed that the ability of Pd_ML/TaC to catalyze CO oxidation and resistant to CO poisoning were high.In conclusion,we speculate that Pd_ML/TaC may be a substitute for the Pt-based catalysts in PEMFC.