Synthesis And Improvement Of Pd-V/C And Pd-Co-Cu/Cc Series Electrocatalysts For ORR

At present, Pt-based material is commonly recognized as cathode electrocatalysts for the oxygen reduction reaction. However, the reservation of Pt on the earth is scarcity, and the cost of Pt is very high. Furthermore, Pt endures a high overpotential and poor methanol tolerances performance for the oxygen reduction reaction. Based on the advantages of the similar electronic structure, physical and chemical properties between Pd and Pt, as well as the cost of Pd is lower and the reservation is more abundant, it is of great importance to explore Pd-based catalysts for fuel cell application. In this paper, by introducing 3d-transition metals?M=V, Co and Cu? in Pd catalyst to enhance the activity for the oxygen reduction reaction. However, Pd-based catalysts suffer from serious degradation during cycling. A strategy of introducing a trace amount of Pt or Au is used to optimize the performance and durability. The main results are summarized as follows:?1?Pd-V series bimetallic electrocatalysts for oxygen reduction reaction have been successfully obtained by using a simple impregnation reduction method. The electrocatalytic activity of Pd₃V/C series catalysts is better than that of Pd V/C and Pd V3/C. The Pd₃V/C nanoparticles after heat-treated at 500 oC exhibit the highest electrocatalytic activity than 300 oC and 700 oC. Based on the poor stability of Pd₃V/C-500 catalyst, a spontaneous displacement reaction and a co-reduction method are adopted to obtain Pt decoration Pd₃V/C-500 catalysts. The electrochemical results show that the activity of Pd₃V@Pt/C and Pt-Pd₃V/C is far more than that of Pd₃V/C-500 catalyst. And after 10,000 cycles, the electrocatalytic activity of Pd₃V@Pt/C and Pt-Pd₃V/C catalysts do not decay and still remain relatively intact nanostructures, since a Pt-rich shell on particle surface form with cycling, which plays a key role in providing more active sites and stabilizing the catalytic activity.?2?Pd₃Co/C, Pd₃Cu/C bimetallic and Pd₆ Co Cu/C ternary electrocatalysts are obtained by impregnation reduction method and the electrocatalytic activity of Pd₆ Co Cu/C is better than that of Pd₃Co/C and Pd₃Cu/C. Based on the poor stability of Pd₆ Co Cu/C catalyst, a trace amount of Pt or Au is introduced to improve its cycling stability. The results show that the electrocatalytic activity of Pt decoration Pd₆ Co Cu/C after 10,000 cycles suffers from no attenuations, the half-wave potential is more 17 m V than that of Pt/C and the thickness of the Pt overlayer is slight increase, which plays a key role in providing more active sites and stabilizing the catalytic activity. Although the activity of Au decoration Pd₆ Co Cu/C is not enhanced, the cycling stability of Pd₆ Co Cu@Au/C in N2 atmosphere, O2 atmosphere and the actual fuel cell test have been significantly improved. Pt or Au decoration Pd₆ Co Cu/C nanoparticles can not only optimize the durability but also improve the utilization of noble metal.