ADSORPTION OF GLYCEROL ON PLATINUM IN ALKALINE-MEDIUM - EFFECT OF THEELECTRODE STRUCTURE

The electro-oxidation of glycerol on platinum in alkaline medium shows structural effects, Pt(111) appearing to be the most active orientati on. This results from different adsorption interactions of the glycero l molecule with the single-crystal plane. The number of electrons per platinum site, N(eps) associated with the oxidation of the adsorbed gl ycerolic residues was thus determined. For each single-crystal plane c onsidered, N(eps) has a value of around 2 at long adsorption times. At short adsorption times differences are observed according to the orie ntation, with values of N(eps) which can be greater than 2. The case o f polycrystalline platinum is different, with a constant value of N(ep s) of around 1.5 for the whole range of adsorption times studied. The value of N(eps) almost-equal-to 2 determined for long adsorption times is in agreement with the first conclusions drawn from electromodulate d IR reflectance spectroscopy experiments, which confirm the presence of linearly adsorbed CO. Other values of N(eps) can be explained eithe r as a consequence of the breaking of C-C bonds for N(eps) > 2 or by t he formation of aldehyde functions for N(eps) < 2.