ADSORPTION OF GLYCEROL ON PLATINUM IN ALKALINE-MEDIUM - EFFECT OF THE ELECTRODE STRUCTURE

The electro-oxidation of glycerol on platinum in alkaline medium shows structural effects, Pt(111) appearing to be the most active orientation. This results from different adsorption interactions of the glycerol molecule with the single-crystal plane. The number of electrons per platinum site, N(eps) associated with the oxidation of the adsorbed glycerolic residues was thus determined. For each single-crystal plane considered, N(eps) has a value of around 2 at long adsorption times. At short adsorption times differences are observed according to the orientation, with values of N(eps) which can be greater than 2. The case of polycrystalline platinum is different, with a constant value of N(eps) 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 electromodulated IR reflectance spectroscopy experiments, which confirm the presence of linearly adsorbed CO. Other values of N(eps) can be explained either as a consequence of the breaking of C-C bonds for N(eps) > 2 or by the formation of aldehyde functions for N(eps) < 2.