Expanded graphite and carbon nanotube supported palladium nanoparticles for electrocatalytic oxidation of liquid fuels

Abstract

Catalyst supporters with large areas and highly active catalysts play key roles in the electrocatalytic oxidation of liquid fuels. The nanocomposite of expanded graphite and multi-walled carbon nanotubes (EG-MWCNT) was employed as the catalyst supporter due to its large electrode area. Palladium nanoparticles (Pd NPs) electrodeposited on the EG-MWCNT were utilized as the electrocatalysts. The synthesized Pd-NP/EG-MWCNT electrocatalysts were characterized with scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and electrochemical techniques. Electrochemical activity and double-layer capacitances of the Pd-NP/EG-MWCNT electrocatalysts with different EG-to-MWCNT mass ratios were investigated to optimize their compositions. Electrocatalytic oxidation of alcohols (methanol, ethanol, ethylene glycol), carboxylic acids (formic acid), and aldehydes (formaldehyde) was studied in alkaline media. On these electrocatalysts, their oxidation currents are stable and in the order of formaldehyde > formic acid > glycol > methanol > ethanol. The oxidation occurs in two steps: the oxidation of freshly chemisorbed species in the forward scan and then in the reverse scan the oxidation of the incompletely oxidized carbonaceous species formed during the course of the forward scan. These electrocatalysts are thus useful for the fabrication of direct methanol fuel cells.