Fourier transform infrared reflectance spectroscopic investigation of the electrocatalytic oxidation of D-glucose: Identification of reactive intermediates and reaction products

In situ reflectance infrared spectroscopic techniques (under the SPAIRS and SNIFTIRS variants) have been applied to the investigation of the electrooxidation process of D-glucose at platinum electrodes in alkaline medium. Various reactive or poisoning intermediates were identified and their potential dependence monitored. The following mechanism was postulated. At low potentials, the first step leads to an adsorbed intermediate (A) formed by dehydrogenation of the anomeric carbon of glucose. Oxidation of (A) at higher potentials follows two possible routes. At E < 0.6 V vs. the, species (A) is oxidised as weakly adsorbed gluconate, either linked by two oxygens (species I, at E < 0.3 V), or by only one oxygen at 0.3 < E < 0.6 V (species II). The second route is observed at 0.6 < E < 1.6 V. In this potential range, ie, all over the range where the surface is covered by oxygenated species, species (A) is oxidised as weakly adsorbed delta-gluconolactone (B). Desorption of (I) (II) and (B) gives the corresponding solution species, ie gluconate (C) and delta-gluconolactone (D). In solution, slow hydrolysis of(D) leads to (C), so that gluconate is the only final product accumulating in solution.