The Simulation Of The PtNi Catalyst And Carbon Carrier

Proton Exchange Membrane Fuel Cells may be used in electric vehicles and distributed power plants, due to their advantages of environment friendly, efficient energy conversion and high specific power. However, before large-scale commercial production of PEMFCs the problems of high cost, poor stability and complex water management should be resolved, among which the cost and stability of the catalyst are the key problems.Because of its relatively high stability and catalytic activity of oxygen reduction in strong acidic electrolyte, Pt is still one major component of catalysts used in the PEMFCs both in the practical application and in the basic research. Platinum is a costly substance, and the catalyst platinum can not reach the practical requirement of stability. To solve the problems mentioned above, the alloy catalysts have been developed by mixing transition metal Ni with Pt, which improves the activity of oxygen reduction reaction and stability and reduces the amount of Pt. But the mechanism of its high activity and stability needs further research.Two periodic slab models of Pt₃Ni surface have been proposed in this paper, and Density function theory (DFT) is adopted to calculate the properties of the two models. Results obtained after Ni doped to Pt are as follows: First, micro-roughness of the two models increases, which improves the catalyst's utilization. Second, lattice contracting effect can be observed, which is helpful to oxygen desorption. Third, combination of Pt surface atoms and sublayer atoms becomes closer, which makes catalysts harder to migrate or drain. Fourth, d state density of surface atoms expands along low energy axis, causing the d band center far away from Fermi level in a certain degree, which reduces the adsorption of intermediates in ORR. Finally, the energy difference between the HOMO of model D and the LUMO of oxygen is only 0.91eV, 20% lower than that between the HOMO of pure Pt and the LUMO of oxygen.Besides, Pt/C and Pt₃Ni/C catalyst systems, in which C carrier is modeled as period slab while Pt and Pt₃Ni catalysts are modeled as clusters, have been simulated with DFT, and the effect of C carrier on catalyst is studied. For the Pt₃Ni/C catalyst system, it is found that the interaction between the C carrier and Pt₃Ni catalyst reinforces in some degree and the Pt₃Ni catalyst cluster anchores on the carrier surface, thereby, the Pt₃Ni catalyst is hard to migrate or drain. For the Pt/C catalyst system, delocalizedÏ€-bond of graphene providing electrons to Pt catalyst leads to the surface atoms of Pt catalyst negatively charged. Thus, the charged atoms act as electron donners, making electron transfer from Pt to oxygen easier in ORR.