Gold nanoparticles dispersed polyaniline grafted multiwall carbon nanotubes as newer electrocatalysts: Preparation and performances for methanol oxidation

Newer electrocatalysts were prepared by dispersing gold nanoparticles onto a polyaniline (PANI) grafted multiwall carbon nanotube (MWNT-g-PANI) matrix through a two-step electrochemical process. In the first step, PANI chains were grafted onto amine-functionalized MWNT (MWNT-NH2) by electropolymerizing a mixture of aniline and MWNT-NH2 (dispersed in cetyltrimethyl ammonium bromide) using cyclic voltammetry. In the second step, Au nanoparticles were dispersed into the film of MWNT-g-PANI by electrochemical reduction of HAuCl4. MWNT-g-PANI-modified electrodes with varying amounts of Au nanoparticles were prepared. Films of MWNT-g-PANI-Au were analyzed by field emission transmission electron microscopy (FETEM). The FETEM images indicate that Au particles of 8–10 nm in size are uniformly distributed into MWNT-g-PANI. X-Ray diffraction patterns provide support for the existence of Au nanoparticles. The electrocatalytic properties of the MWNT-g-PANI-Au electrode toward oxidation of methanol and adsorbed carbon monoxide (COads) were investigated by chronoamperometry and COads stripping voltammetry and compared with the properties of MWNT-Au and pristine Au electrodes. MWNT-g-PANI-Au catalysts exhibit excellent electrocatalytic activity toward the oxidation of methanol and COads. Oxidation of methanol occurs at a much lower oxidation potential (780 mV) at the MWNT-g-PANI-Au electrode with high current densities compared with the MWNT-Au electrode (890 mV) and pristine Au electrode (930 mV), due to the dispersion of Au nanoparticles into the three-dimensional network of MWNT-g-PANI. Further, our results suggest that the MWNT-g-PANI-Au electrode has better oxidation kinetics for the oxidation of COads to CO2 than the MWNT-Au and pristine Au electrodes. Our results indicate that the MWNT-g-PANI-Au catalyst can have potential applications in direct methanol fuel cells.