Photoelectrochemical characterization of p- and n-doped single crystalline silicon carbide and photoinduced reductive dehalogenation of organic pollutants at p-doped silicon carbide

Abstract

In this work, the photoelectrochemical properties of single crystalline p- and n-SiC, now available from Cree Research, Inc., will be presented. 4H- and 6H-SiC were investigated by electrochemical impedance spectroscopy and cyclic voltammetry. Flatband potentials of p-SiC determined by application of the Mott–Schottky-relation varied from 1.8 to 2.5 V versus NHE depending on the C or Si face and the doping concentration of the single crystalline samples. The flatband potential of n-SiC was found to be −1.3 V vs. NHE. A nearly Nernstian dependence on the pH was found for both the n-SiC and the p-SiC-types. The onset of the cathodic photocurrent at p-SiC occurred with a large overpotential in aqueous solution. P-SiC was used as photocathode for the reductive dehalogenation of halogenated acetic acids due to its chemical stability, its highly energetic conduction band and the overvoltage for the hydrogen evolution. It was especially suitable for the reduction of less reducible chlorinated acetic acids in the aqueous phase. The dehalogenation of brominated acetic acids resulted in the complete release of bromine in form of bromide. The bromide yields were about 98%. In case of chlorinated acetic acids, the dehalogenation stopped at the level of monochloroacetic acid, since this halide was very slowly reduced.