FOURIER-TRANSFORM INFRARED REFLECTANCE SPECTROSCOPIC INVESTIGATION OFTHE ELECTROCATALYTIC OXIDATION OF D-GLUCOSE - IDENTIFICATION OF REACTIVE INTERMEDIATES AND REACTION-PRODUCTS

In situ reflectance infrared spectroscopic techniques (under the SPAIR S and SNIFTIRS variants) have been applied to the investigation of the electrooxidation process of D-glucose at platinum electrodes in alkal ine medium. Various reactive or poisoning intermediates were identifie d and their potential dependence monitored. The following mechanism wa s postulated. At low potentials, the first step leads to an adsorbed i ntermediate (A) formed by dehydrogenation of the anomeric carbon of gl ucose. Oxidation of (A) at higher potentials follows two possible rout es. At E < 0.6 V vs. the, species (A) is oxidised as weakly adsorbed g luconate, either linked by two oxygens (species I, at E < 0.3 V), or b y 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 th e 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 gluco nate (C) and delta-gluconolactone (D). In solution, slow hydrolysis of (D) leads to (C), so that gluconate is the only final product accumula ting in solution.