DFT Study For Oxgen Reduction Reaction On Titanium Nitride And Cu-doped Titanium Nitride@Pt Core-shell Electrocatalysts

Oxygen reduction reaction?ORR?is an ideal reaction of cathode of fuel cell,which greatly determines the efficiency of electricity production of the fuel cell.Currently,commercial Pt/C is the most widely used catalyst for ORR,however,the large overpotential of oxygen reduction reaction and the loss of Pt by dissolution limits the comprehensive popularization of fuel cell.Core-shell catalyst Ti N@Pt with titanium nitride as core and Pt as shell is a promising catalyst that has higher onset potential of oxygen reduction reaction and higher electrochemical stability than traditional Pt/C catalyst.Relevant studies also found that core-shell catalyst Ti_0.9Cu_0.1N@Pt,which using copper-doped titanium nitride as core and Pt as shell,has even higher ORR performance than Ti N@Pt.However,the mechanism of how the Ti N and copper-doped Ti N carrier improve the ORR activity of Pt is not clear yet.The Density Functional Theory?DFT?calculation studies may help us to understand how Ti N and copper-doped Ti N affect the electron structure of Pt.This paper build a Ti N/Pt model and a Cu-d-Ti N/Pt modle,which represents Ti N@Pt and Ti_0.9Cu_0.1N@Pt respectively,and carried out series of DFT studies.The result shows that the d-band center of a Pt?111?monolayer anchored on Ti N?111?or Cu-doped Ti N?111?by Ti-Pt bonds is lower than that of the topmost Pt layer of natural Pt?111?surface,which indicated weakened surface reactivity and better ORR performance.Free enegy diagram of ORR species on Ti N/Pt,Cu-d-Ti N/Pt,Pt?111?was obtained by series of DFT calculations.Compared with Pt?111?,the highest*OOH formation potential of Ti N/Pt and Cu-d-Ti N/Pt are both higher than Pt?111?,indicated that ORR on Ti N/Pt and Cu-d-Ti N/Pt can take place under higher potential.*O can strip from the surface of Ti N/Pt under higher potential than Pt?111?,the surface of Ti N/Pt keeps lower coverage of*O under higher potenical so that O₂ absorption and*OOH formation can take place on Ti N/Pt surface under higher potential,which can bring improvement on the ORR perfromance.Copper doping of the Ti N/Pt can enhance the*O stripping potential and bring more improvement on ORR performance.Relative stronger*OH absorption of Ti N/Pt than Pt?111?is the only shortage for Ti N/Pt,but copper doping can improve this shortage by weakening*OH absorption.In general,the ORR perfromance of Ti N/Pt is better than Pt?111?,which is consistent with the LSV results.Although the results of the simplified Cu-d-Ti N/Pt are slightly different from the experimental results,the effect of Cu-doping is consistent with the characteristics of high ORR performance catalysts.Activation energies of each ORR element step on Pt?111?and Ti N/Pt is calculated.Except of the activation energies of reaction*O₂+*H?*OOH on Pt?111?is slightly lower than that on Ti N/Pt,the activation energies of other all reaction on Ti N/Pt is lower than that on Pt?111?.The ORR on Ti N/Pt and Pt?111?has the same rate limiting step,*O+*H?*OH,but the activation energy on Ti N/Pt is much lower than Pt?111?.All this result indicated that the overall ORR rate on Ti N/Pt surface is higher than that on Pt?111?surface,which is consistent with the tafel slope results in the experiment.