Electrochemistry of homoepitaxial CVD diamond: energetics and electrode kinetics in aqueous electrolytes

The electrochemical properties of highly doped p-type single crystalline di amond electrodes (100 and 110 oriented) in aqueous electrolytes were invest igated. The interfacial capacitance obeys the Mott-Schottky relationship in a considerable potential range and can be assigned to a depletion layer in the diamond. The energetic position of the valence band edge is about 4 an d 2 V versus SHE for (100) and (110) oriented diamond respectively. Oxygen and hydrogen evolution occur at large overpotentials (1 V) in agreement wit h previous results reported for polycrystalline diamond. Interestingly, wit h reversible redox systems, metal-type redox kinetics around the equilibriu m potential are observed. The mechanism of electron exchange between the va lence band of diamond and simple redox systems was investigated in detail u sing electrochemical impedance spectroscopy. A quantitative model is propos ed, that assumes that electron exchange is mediated by bandgap states. (C) 1999 Elsevier Science S.A. All rights reserved.