Voltammetric Studies of Glycerol Electrooxidation at Boron-Doped Diamond Electrodes: Effects of Solution pH, Concentration, and Scan Rate

High Resolution Image Download MS PowerPoint Slide The electrochemical oxidation of glycerol was investigated at polycrystalline boron-doped diamond (BDD) thin-film electrodes using cyclic and linear sweep voltammetry. The films were deposited on conducting Si substrates by microwave-assisted chemical vapor deposition using a 1% CH 4 /H 2 source gas (v/v) mixture with B 2 H 6 added for boron-doping. The highly conducting films possessed a nanocrystalline morphology. The effects of electrolyte solution pH, analyte concentration, and scan rate on the oxidation peak potential and current were systematically examined. Cyclic voltammetric curves revealed an optimum response for 10 mmol L –1 glycerol in 0.1 mol L –1 carbonate buffer, pH 12, characterized by E p o x of ca. 0.81 V vs. Ag/AgCl and an onset potential of 0.6 V. A well-defined irreversible oxidation peak was seen for glycerol oxidation. An oxidation peak was observed on the forward, positive-going scan, and a near-equivalent magnitude oxidation peak current at the same potential was seen on the reverse, negative-going scan. E p o x shifted negatively, and j p o x increased with increasing solution pH from 7 to 12. The peak current density for 10 mmol L –1 glycerol in 0.1 mol L –1 carbonate buffer, pH 12, was 292 ± 35 μA cm –2 . The glycerol electrooxidation mechanism is proposed to involve anodic oxygen transfer mediated by electrogenerated hydroxyl radicals generated at localized sp 2 carbon sites on the electrode surface that then react with glycerol molecules adsorbed on the nearby BDD surface. Comparison measurements performed with boron-doped tetrahedral amorphous carbon thin-film and glassy carbon electrodes showed no faradaic current for glycerol oxidation. The results indicate that BDD electrodes are unique in the carbon electrode family in terms of their ability to support the electrooxidation of glycerol.