Aqueous Deposition of Metals on Multiwalled Carbon Nanotubes to be Used as Electrocatalyst for Polymer Exchange Membrane Fuel Cells

The polymer exchange membrane fuel cell (PEMFC) is considered the new power source technology for portable applications. Pt and Pt–alloy nanoparticles supported on carbon black have been used traditionally to make electrodes due to their high activity for $H2$ oxidation and $O2$ reduction under PEMFC conditions. Recently, ammonium hexachloroplatinate (IV) $((NH4)2PtCl6)$ has been shown to be a good precursor of metallic Pt by thermal decomposition. In addition, multi-walled carbon nanotubes (MWCNTs) present convenient physical and chemical properties to be employed as a support for electrocatalysts. MWCNTs were synthesized by spray pyrolysis using a precursor solution of ferrocene dissolved in benzene or toluene. Ammonium hexachloroplatinate, ammonium hexachlororhutenate, and ammonium hexachloropaladate were used as the Pt, Ru, and Pd precursors, respectively. Aqueous solution reaction, followed by a two stage thermal process, was utilized to support separately Pt, Ru, and Pd nanoparticles on the MWCNT. The results suggest that the deposition takes place on anchored sites formed during the aqueous reaction, due to the in situ oxidation of the external wall of the nanotube. Very good dispersion and particle size between $3nm$ and $12nm$ were obtained for each metal. Such characteristics are advantageous for the use of CNT supported electrocatalyst in PEMFC and direct methanol fuel cell (DMFC) electrodes.