Modulation of Electron Transfer Activity at Diamond Films by Dissolved Oxygen in Aqueous Solution

Abstract

The electron transfer activities of conductive undoped, boron-doped, and sulfur-doped chemical vapor-deposited diamond films were observed in terms of increases or decreases in both hydrogen and oxygen evolution, i.e., over a wide potential range, as modulated by the presence or the absence of dissolved oxygen as a typical oxidant in an aqueous acid solution. The electrochemical behavior of n-type sulfur-doped nanocrystalline chemical-vapor-deposited diamond films was such that the current corresponding to the electrochemical hydrogen evolution decreased reversibly in the presence of dissolved oxygen in the solution, in contrast to the behavior of the p-type materials, boron-doped (microcrystalline) and undoped (nanocrystalline) diamonds. For the sulfur-doped film, we propose that the presence of oxygen at the interface may cause a decrease in the number of majority carrier electrons near the surface. The influence of the doping levels of sulfur in the diamond films on the films’ oxygen sensitivities was examined in detail. We propose that the electron transfer activity, modulated by the concentration of oxygen dissolved in an aqueous solution, necessitates the development of a model for the electrochemical behavior of the types of diamond films examined in the present work.