Influence of some solvents and solutes on illuminated red mercury(II) sulphide electrodes

Abstract

A study has been made of the irradiation of red mercury(II) sulphide electrodes in water, acetonitrile, pyridine and methanol containing dissolved tetra-alkylammonium salts. Photocurrents were found to be due to solvent oxidation, iodide oxidation and lattice decomposition, but which of these processes actually operates is determined by the individual solvent, solvation of the iodide ion and adsorption of the tetra-alkylammonium cation on the semiconductor surface. The length of the alkyl chain of the substituted ammonium ion was critical.

Instability of the sulphide resulted from adsorption of tetra-alkylammonium cations in methanol and acetonitrile. In the case of pyridine, cation adsorption was not significant, but the presence of iodide induced a negative shift of the sulphide band edges.