Electrosorption of D-sorbitol on Pt(110) and Pt(111) electrodes in acid medium: A study by programmed potential voltammetry

The adsorption and electro-oxidation of D-sorbitol on Pt(110) and Pt(111) single-crystal surfaces in acid medium was studied using programmed potential voltammetry (PPV). The coverage (θ_org) of the surface and the number of electrons per site (N_eps) involved in the electro-oxidation of the adsorbed species coming from the D-sorbitol electrosorption was estimated for both electrodes. Limiting values for θ_org of 0.90 and 0.85, were obtained for Pt(111) and Pt(110), respectively, although the limit is reached at shorter adsorption times (100 s) in the case of Pt(111). For Pt(111), N_eps was found to increase with increasing adsorption times reaching a value around 2 for long adsorption times, related to the formation of linearly-bonded CO, while for Pt(110) its value is near 1 in the range 0.5-300 s, corresponding to a mixture of different species, including multibonded and bridge-bonded CO, as confirmed by EMIRS. A very fast oxidation process occurs at Pt(111), in contrast to Pt(110), where the strongly adsorbed species formed upon adsorption remain attached to the surface, blocking it almost completely. The reoxidation process taking place at Pt(111) prevails over the reduction of the oxygenated species formed on the platinum surface when a sufficiently high coverage of the electrode surface (θ_org ≥ 0.8) is attained.