Pd-Ni-B/C Nanocatalysts for Electrochemical Oxidation of Ethanol in Alkaline Media

Abstract

This paper describes the synthesis of Pd<sub>0.70</sub>-Ni<sub>x</sub>-B<sub>y</sub> nanoparticles (x:y = 0.30:0, 0:0.30, 0.25:0.05, 0.20:0.10, 0.15:0.15, and 0.10:0.20) supported on carbon Vulcan XC-72 R by the chemical reduction method using ethylene glycol as a reducing agent for the study of the electrochemical oxidation of ethanol in alkaline media. Neither surfactants nor templates were used during the syntheses. The catalysts were physically characterized by transmission electron microscopy that showed the formation of nanoparticles with diameters of approximately 3 nm. Analyses of X-ray dispersive energy spectroscopy coupled with scanning electron microscopy identified the presence of the synthesized metals in concentrations close to the nominal ones. The electrochemical study was performed by CO-stripping, cyclic voltammetry, chronoamperometry, and steady-state polarization curves. The catalytic efficiency was also evaluated against the oxidation of CO, which is the principal intermediate adsorbed on the surface of catalysts during ethanol oxidation. The Pd<sub>0.70</sub>Ni<sub>0.15</sub>B<sub>0.15</sub>/C catalyst showed the lowest oxidation onset potentials for both CO (0.37 V) and ethanol oxidation (0.51 V) compared with the Pd/C catalyst (0.63 V and 0.64 V). Chronoamperometric tests also revealed that the Pd<sub>0.70</sub>Ni<sub>0.15</sub>B<sub>0.15</sub>/C catalyst displayed current densities four times higher than those of the Pd/C catalyst, probably because of the electronic and geometric effect that favors the removal of intermediate species from the catalyst surface. The synthesized ternary catalysts were more efficient toward the electrochemical oxidation of ethanol in alkaline media than Pd<sub>0.7</sub>Ni<sub>0.3</sub>/C and Pd/C catalysts. Thus, the synergistic effect of boron on the structure of binary nanoparticle catalysts supported on carbon for use in direct alcohol fuel cells was demonstrated for the first time.