Pd nanoparticles-embedded carbon nanotube interface for electrocatalytic oxidation of methanol toward DMFC applications

Abstract

Pd nanoparticles-embedded multiwalled carbon nanotubes (Pd–MWCNTs) were synthesized via in situ chemical reduction method, which provided promising results for preparing finely divided and uniform sized Pd nanoparticles supported on MWCNTs. The Pd–MWCNT catalysts were synthesized in three different weight (wt) ratios of Pd and MWCNT (1:5, 2:5 and 3:5). Morphology and crystallinity of the catalysts were studied by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Electrocatalytic activity of these catalysts toward methanol oxidation was analyzed with two different dispersing agents, such as chitosan (CS, 0.1% w/v) and Nafion (Nf, 0.05% w/v), for the preparation of catalytic inks. Dramatic increases in the electrocatalytic activity of Pd–MWCNT–CS catalysts compared to Pd–MWCNT–Nf catalysts toward methanol oxidation were revealed from cyclic voltammetric, chronoamperometric and CO stripping analysis studies. The anodic peak current densities of the Pd–MWCNT (2:5 wt ratio) interface prepared with chitosan and Nafion inks in alkaline 1 M CH3OH were 2541 and $$1 0 4 1\,\,{\text{A}}\,\,\mathop {{\text{g}}^{ - 1} }\nolimits_{\text{Pd}}$$ , respectively. High CO tolerance of the Pd–MWCNT catalysts was ascertained from the ratio of peak currents and coulombic charges of forward and reverse scans (I f/I b and Q f/Q b) of CV studies and from the less positive potentials for CO stripping, as low as − 0.2 V versus Ag|AgCl. The steady-state current density for methanol oxidation at Pd–MWCNT–CS electrode is nearly five times higher than that of Pd–MWCNT–Nf electrode.