(273g) Carboxyl Multi-Walled Carbon Nanotubes Stabilized Palladium Nanocatalysts for Fuel Cell Application

Carboxyl Multi-walled carbon nanotubes (MWNTs-COOH) supported palladium (Pd) nanoparticles (NPs) catalysts (Pd/MWNTs-COOH) were prepared by a one-pot solution-based method, i.e., direct decomposing palladium acetylacetonate (Pd(acac)₂) in a refluxing xylene solution in the presence of MWNTs-COOH without any additives. Pd/MWNTs-COOH with different Pd loadings were prepared by altering the amount of Pd(acac)₂. Different annealing temperature effect was also investigated on Pd/MWNTs-COOH in a reducing atmosphere. X-ray diffraction (XRD) results indicate a successful deposition of Pd NPs on MWNTs-COOH. Transmission electron microscope (TEM) micrographs revealed that Pd NPs with increasing size were uniformly grown onto MWNTs surface with the increase of Pd loadings, and varying Pd particle sizes were also observed implying varying steps of Pd NPs as diffusing, contacting and coercing on tube wall surface with the increase of annealing temperature. The loading of Pd was calculated from the thermal gravimetric analysis (TGA), the variation of –COOH was investigated by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The electrocatalytic activities of the Pd/MWNTs-COOH catalysts were evaluated for methanol oxidation and ethanol oxidation in KOH solutions. For methanol oxidation, bare Pd NPs and Pd/MWNTs (MWNTs without -COOH) was also synthesized and compared, parameters including the concentration of methanol and KOH were investigated, showing that the best catalyst performance was achieved by the balance between the adsorption of hydroxyl and methanol. A pronounced influence of temperature on methanol oxidation has been manifested, which indicates the positive role of increasing temperature. For ethanol oxidation, Cyclic voltammetry (CV), chronoamperometry (CA), electrochemical impedance spectroscopy (EIS) and Tafel were introduced to characterize the electro-performances, Pd/MWNTs-COOH with initial precursor ratio of 2:1 gave the best performance, 100 °C annealed Pd/MWNTs-COOH also gave best performance compared with other temperature annealed ones