MORPHOLOGICAL AND MICROSTRUCTURAL STABILITY OF BORON-DOPED DIAMOND THIN-FILM ELECTRODES IN AN ACIDIC CHLORIDE MEDIUM AT HIGH ANODIC CURRENTDENSITIES

Boron-doped diamond thin films have been examined before and after hig h-current-density electrolysis to investigate the morphological and mi crostructural stability of this new electrode material. The diamond th in films were used to generate chlorine from a solution of 1.0 M HNO3 + 2.0 M NaCl at current densities of 0.05 and 0.5 A/cm(2) for times up to 20 h. Comparative studies were made using common ''graphitic'' ele ctrodes including highly oriented pyrolytic graphite, glassy carbon, a nd Grafoil (R). The electrodes were characterized using four-point pro be resistivity measurements, atomic force microscopy, scanning electro n microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, an d cyclic voltammetry. In all cases, no severe morphological or microst ructural damage (i.e., corrosion) was observed on films exposed to the highest current density. There were surface compositional changes in the forms of oxygenation and nondiamond carbon impurity etching that p roduced an increase in the reaction overpotential. Specifically, the o verpotential was supposed to result from a combination of decreased su rface conductivity due to the formation of carbon-oxygen functional gr oups and loss of kinetically active redox sites due to the oxidative e tching of nondiamond carbon impurities.