Palladium/Cobalt Coated on Multi-Walled Carbon Nanotubes as an Electrocatalyst for Oxygen Reduction Reaction in Passive Direct Methanol Fuel Cells

摘要

This work reports the synthesis of Pd-based alloy electrocatalysts of Co supported on multi-walled carbon nanotubes (MWCNTs) and their evaluation as cathode materials in a passive direct methanol fuel cell (PDMFC). The X-ray diffraction (XRD) analysis showed well-defined reflections corresponding to a face centered cubic phase of palladium. As compared to the Pd/MWCNT electrocatalyst, the bimetallic alloy electrocatalysts with the different PdxCo atomic ratios showed highly enhanced mass activity (MA) for the oxygen reduction reaction (ORR); however, the significant enhancement in the specific activity (SA) by a factor of about 1.2-5.6 for the ORR was found on the PdxCo alloy electrocatalysts in the presence and absence of methanol electrolyte solution. This enhancement SA in of the Pd-based electrocatalysts was correlated to the changes in the lattice parameter and PdxCo surface composition. Surface area changes of Pd-based electrocatalysts supported on MWCNT were evaluated using an accelerated durability test (ADT). The results obtained using the ADT were correlated to the performance of the Pd-based electrocatalysts in the PDMFC. A better performance was obtained for the cell using Pd3Co/MWCNT (2.53 mW cm~(-2)) compared to Pd/MWCNT (1.64 mW cm~(-2)) and Pt/C-Electrochem (1.20 mW cm~(-2)) as cathode in the PDMFC. In the presence and absence of methanol the impedance Bode spectra showed one time constant that associated to follow a four electron pathway.