Enhancement of catalytic properties for glycerol electrooxidation on Pt and Pd nanoparticles induced by Bi surface modification

Effects toward electrocatalytic activity for glycerol oxidation of the modification of carbon supported Pd and Pt-based nanomaterials by bismuth were evaluated in alkaline medium. Pd/C, Pd(0.9)Bi(0.1)/C, Pt/C, Pt(0.9)Bi(0.1)/C and Pd(0.45)Pt(0.45)Bi(0.1)/C catalysts were synthesized by a colloidal route, and physical and electrochemical methods were used to characterize the structure and the surface of the catalysts (TEM, HRTEM, EDX, XRD, ICP-OES and XPS). It was shown that only a few amount of bismuth was deposited on the Pt and/or Pd surface, and that no alloy was formed between bismuth and the other metals. The onset potential of glycerol oxidation is ca. 0.15 V lower on Pt/C than on Pd/C. However, Pt-free Pd(0.9)Bi(0.1)/C catalyst presented the same catalytic activity than platinum catalyst. The Pt(0.9)Bi(0.1)/C led reaching a higher catalytic activity by shifting the oxidation onset potential by ca. 0.2V toward lower potentials compared with the Pt/C catalyst. But, the replacing of half of the platinum atoms by palladium atoms in the Pd(0.45)Pt(0.45)Bi(0.1)/C material allowed achieving the same catalytic activity as with Pt(0.9)Bi(0.1)/C. Electrochemical experiments combined with in situ infrared spectroscopy measurements have shown that glycerol electrooxidation mechanism is independent on the catalyst, but dependent on the electrode potential. Chronoamperometry experiments combined with HPLC measurements showed that the main reaction products were glycerate, dihydroxyacetone and tartronate at low potentials, and that the increase of the electrode potential led to the formation of mesoxalate. For potential higher than 0.8 V vs RHE, the C-C bond cleavage occurred and oxalate and formiate were detected. (C) 2011 Elsevier B.V. All rights reserved.