Multiwalled Carbon Nanotubes Composited with Palladium Nanocatalysts for Highly Efficient Ethanol Oxidation

Carboxyl multi-walled carbon nanotubes (MWNTs-COOH) decorated with different palladium (Pd) nanoparticle loadings were synthesized by thermally decomposing different amounts of palladium acetylacetonate (Pd(acac) 2 ) in a refluxing xylene solution with a fixed amount of dispersed MWNTs-COOH. The increased ratio of D band/G band and the decreased area ratio of oxygen containing groups (COOH, C–O and C=O) to C–C group suggested an increased occupation of defects on MWNTs. Transmission electron microscope (TEM) revealed different distributions of Pd NPs on the MWNTs with the variation of Pd(acac) 2 amount and the particle size increased with increasing the Pd loading. A relatively higher conversion of Pd(acac) 2 to Pd (76.21%) was achieved when the initial precursor ratio of Pd(acac) 2 to MWNTs was 2 : 1 (product denotes as Pd/MWNTs-(2:1)). The Pd/MWNTs-2:1 catalysts were demonstrated to exhibit the most efficient performance toward ethanol oxidation reaction (EOR) among all the precursor ratios, which is evaluated by the highest Pd mass-based peak current density (1.23 A/mg Pd ) and stable current density (0.175 A/mg Pd ) in cyclic voltammetry (CV) and chronoamperometry (CA). In addition, both reduced charge-transfer resistance and increased reaction kinetics with increasing the Pd loading were obtained from electrochemical impedance spectroscopy (EIS) and Tafel characterization.