First evidence of the oxidation and regeneration of polysulfides at a GaAs electrode, under anodic conditions. A study by in situ UV-visible spectroelectrochemistry

We report on the oxidation and regeneration, at a GaAs electrode, of polysulfides present in (NH4)(2)S-n aqueous solutions. The concentration of the polysulfide ions can be monitored by optical absorption spectroscopy. Thus, the variation of their concentration at a GaAs/(NH4)(2)S-n solution interface, under anodic potential, was followed by in situ UV-visible spectroelectrochernistry performed in thin layer conditions and in g-alvanostatic mode. Under these conditions, the variation of the solution absorption at the interface allowed us, on one hand, to confirm that the polysulfides are oxidized at a GaAs electrode, leading to the release of Sdegrees, and, on the other hand, to underscore that Sdegrees reacts with HS- ions to restore polysulfides. Moreover, it was shown that the main polysulfide species present in a 1% (NH4)(2)S-n aqueous solution is the pentasulfide ion, S-5(2-). Finally, this work shows that under definite conditions of anodic current and electrolyte composition, the surface of the GaAs anode is neither oxidized nor passivated.