Effect of AuM (M: Ag, Pt & Pd) bimetallic nanoparticles on the sorbitol electro-oxidation in alkaline medium

In this work, the effect of the second metal of AuM (M: Ag, Pd & Pt) materials on the sorbitol electro-oxidation reaction (SOR) in alkaline medium was evaluated. For this purpose, AuM nanoparticles were synthesized following the Brust's method. The obtained nanoparticles presented similar average particle size (similar to 7 nm), while the gold content ranged between 53 and 77 atomic %, the Vulcan carbon support loading was found to be close to 80 +/- 5 wt%. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical analyses confirmed the formation of the bimetallic catalysts and revealed close electronic interactions between the noble metals. Cyclic voltammograms performed using 0.1 M sorbitol in 0.3 M KOH indicated that AuPt/C displayed the lowest onset potential (-0.36 V vs. NHE), which is 120 mV lower to that determined for Au/C as the reference material. Furthermore, AuPd/C catalyst presented the highest current density (43.65 [mA mg(Aupd)(-1)] at a fixed potential of 0.14 V vs. NHE). Further experiments varying the sorbitol and KOH concentrations, the scan rate and the operating temperature were performed as well as electrochemical impedance spectroscopy (EIS) experi- ments. These results shown that the SOR followed the typical trend for the electro-oxidation of polyol fuels (such as glycerol), where Pt promotes lower onset potentials, but the adsorption of intermediates limits the maximum current density in comparison with Pd-based catalysts. As summary, this study found that AuPd and Pd-containing materials could be excellent candidates for sorbitol oxidation in alkaline medium.