The Performance And Characterization Of PtFeN/C And PtNiMoN/C Oxygen Reduction Electrocatalyst

The high cost and poor stability of catalysts are the main obstacles for the commercialization of proton exchange membrane（PEM） fuel cells, particularly, the electrocatalysts for the oxygen reduction reaction（ORR）. In order to reduce costs, improve the stability of the electrocatalyst, we prepared two different kinds of the new type of fuel cell electric catalysts with the method of impregnation-chemical reduction. Using a range of physico-chemical properties and electrochemical performances to characterize the two kinds of electrocatalysts, and analyse their mechanism in detail.（1）Here, PtFe nanocatalysts with different Pt to Fe atomic ratios were prepared by the impregnation reduction method and subsequently thermal annealing in NH₃ at ambient pressure. XRD, STEM, XPS and ICP were employed to investigate the corresponding physico-chemical properties of the as-prepared catalysts, which demonstrated that the samples were Pt-rich core-shell nanostructures. The results of cyclic voltammetry showed that these catalysts display high ORR activity in O2-saturated 0.1 mol·L-1 HCl O4 aqueous solutions, and PtFe3N/C presented the highest mass activity of 369.32 m A·mg-1 Pt in 0.90 V vs. RHE, which was about 3 times higher than that of a commercial Pt/C catalyst（129.15 m A·mg-1 Pt） at the same potential. Moreover, it was also found that the PtFe3N/C catalysts were almost 2 times more stable than the commercial Pt/C after 30 K cycles in O2-saturated 0.1 mol·L-1 HCl O4 aqueous solutions, and the mass activity of PtFe3N/C was 209.68 m A·mg-1, was reduced by 37.68%, whereas the corresponding activity of commercial Pt/C catalyst was 38.68 m A·mg-1and it was reduced by 71.44%. The possible reason was the formed iron nitrides under the condition of high temperature, which has excellent stability. On the other hand, Fe atom modified Pt effectively, shortened the atomic spacing between Pt and Pt, changed the adsorption/stripping state of oxygen on the surface of the catalyst, which finally improved the electro-catalytic activity.（2）PtNi Mo alloy electrocatalysts with different Pt-Ni-Mo atomic ratios were prepared by the same progress with the precursor of（NH4）6Mo7O24·4H2O and C4H6 Ni O4·4H2O. But the amount of reducing agent and the temperature of thermal annealing in NH₃ atmosphere were different from PtFe system. XRD and XPS demonstrated that Pt, Ni, Mo, N does contain in these alloy catalysts. By cyclic voltammetry and CO adsorption experiments, it can reveal that the ESAs of Pt3Ni3 Mo N/C catalyst was the largest one and its CO tolerance performance was more brilliant than that of commercial Pt/C catalyst. After the testing of ORR, it was easy to see that the mass activity of Pt3Ni3 Mo N/C was 539.41 m A·mg-1（0.90 V vs. RHE）, which was surprior than that of commercial Pt/C catalyst, which only reached to 154.46 m A·mg-1. Pt3Ni3 Mo N/C catalyst′s mass activity decreased to 463.15 m A·mg-1 after 5K cycles in O2-saturated 0.1 mol·L-1 HCl O4 aqueous solutions, whereas the corresponding activity of commercial Pt/C catalyst was 98.65 m A·mg-1 and its rate of descent was 2 times than that of Pt3Ni3 Mo N/C. So we can take it for granted that Pt3Ni3 Mo N/C electrocatalyst is more stable than commercial Pt/C catalyst. This mechanism is similar to that of a PtFe series electric catalyst, also due to structural effect the electronic effects, rainie effect and anchor effect, which caused by Ni, Mo element.