Carbon-supported Pd catalysts: Influences of nanostructure on their catalytic performances for borohydride electrochemical oxidation

In the present work, a Pd catalyst supported on multiwalled carbon nanotubes (MWCNTs) is successfully synthesized and its property as the anode material for borohydride oxidation is investigated. Compared with other carbon-supported Pd catalysts, the Pd/MWCNT catalyst exhibits improved polarization properties due to its smaller Pd particles dispersing homogeneously on carbon nanotubes. The hydrogen evolution behavior on the Pd/activated carbon sample is found to be very sensitive to the concentrations of NaOH and NaBH4 in the solution. On the other hand, borohydride oxidation on Pd/carbon black and Pd/MWCNT displays reaction mechanisms near the 4e stoichiometry. It is thus supposed that the primary direct borohydride oxidation on Pd may be a 4e reaction. The simultaneous electro-oxidation of adsorbed hydrogen occurs conditionally, depending on its relative activity with the direct oxidation of BH4−.