| Electro-catalyst is one of the key materials in direct methanol fuel cells and strongly affect the performance, stability and durability of DMFC. Exploring cathodic electro-catalysts with low cost and methanol tolerant has important value both in theory and application for DMFCs.In this dissertation, Pd/C and PdCo/C electro-catalysts were prepared by ethylene glycol (EG) reduction and H2 aftertreatment. X-ray diffusion (XRD) and rotating disk electrode (RDE) technique were carried out to characterize these electrocatalysts. The results show that EG as reducing agent can not reduce transition metal Co well, however, the activity of PdCo/C electro-catalyst is better than that of Pd/C electro-catalyst calculating from Pd mass specific activity.A series of PdCo/C electro-catalysts were prepared by sodium borohydride reduction method with varying synthetic parameters, such as reducing atmosphere, complexing agents and Pd/Co atomic ratio. The results show that the PdCo/C electro-catalyst synthesized under N2 atmosphere, using NH3 as a complexing agent and with Pd/Co atomic ratio of 3:1 achieve the highest ORR activity.PdCo/C electrocatalyst was synthesized by sodium borohydride successive-reduction method (denoted as PdCo/C-S) and compared to the co-reduction PdCo/C electro-catalyst (denoted as PdCo/C-C). The results show that the successive-reduction PdCo/C-S nanoparticle has smaller size and better dispersion. The PdCo/C-S electrocatalyst not only has higher oxygen reduction reaction (ORR) activity but also shows good methanol tolerant capabilities. This may attribute to Pd rich surface structure of the PdCo/C-S electrocatalyst, which takes the advantage of the lattice-strain effect and reduces disadvantage of the surface-ligand effect between Co and Pd. The DMFC single cell test results show that the single cell with PdCo/C-S electrocatalyst as cathode catalyst shows a peak power density of 96 mW/cm2, which is a little lower than that of Pt/C of 102 mW/cm2 and exhibits good stability.
|
PDF Full Text Request