Some reactions at a mercury(II) sulphide photoanode

Abstract

The photoelectrochemical reactions of pigmentary mercury(II) sulphide have been investigated using electrochemical cells having a platinum electrode coated with the sulphide. E.m.f. and current measurements show that the sulphide behaves as an n-type semiconductor and when sodium nitrate is used as electrolyte the photoanode is stable. Use of other electrolytes can lead to solubilisation and a change of colour of the sulphide. The darkened form of the sulphide so produced is more photoreactive than the red form. The sulphide photoassists the electrolysis of water and this is rationalised on the basis of an energy level diagram drawn up from experimental data.