Carboxyl Multiwalled Carbon-Nanotube-Stabilized Palladium Nanocatalysts toward Improved Methanol Oxidation Reaction.

Carboxyl-functionalized multiwalled carbon nanotubes (MWNT-COOH) decorated with palladium (Pd) nanoparticles (NPs, Pd-MWNT-COOH) are prepared by using a one-pot thermal decomposition method without addition of reductant or surfactant. An increased ratio of the D band to G band in Raman spectra and a decreased ratio of oxygen-containing groups measured using X-ray photoelectron spectroscopy suggest the interaction between Pd NPs and carboxyl groups in Pd-MWNT-COOH. TEM studies reveal improved dispersion of Pd NPs after introducing MWNT-COOH or MWNTs; the carboxyl groups act as anchors to perfectly disperse Pd NPs in Pd-MWNT-COOH, which is responsible for the highest peak current of Pd-MWNT-COOH for the methanol oxidation reaction. The best catalytic performance is observed in conditions that afford a balanced adsorption between hydroxide and methanol through varying the concentrations of methanol and KOH. Increasing temperature can also improve the catalyst performance due to enhanced reaction kinetics. [ABSTRACT FROM AUTHOR]