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(1 11) single-crystal surfaces in acid medium was studied using programme d potential voltammetry (PPV). The coverage (theta(org)) of the surfac e and the number of electrons per site (N-eps) involved in the electro -oxidation of the adsorbed species coming from the D-sorbitol electros orption was estimated for both electrodes. Limiting values for theta(o rg) of 0.90 and 0.85, were obtained for Pt(111) and Pt(110), respectiv ely, 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 adsorp tion 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 for med upon adsorption remain attached to the surface, blocking it almost completely. The reoxidation process taking place at Pt(lll) prevails over the reduction of the oxygenated species formed on the platinum su rface when a sufficiently high coverage of the electrode surface (thet a(org) greater than or equal to 0.8) is attained. (C) 1997 Elsevier Sc ience S.A.