The Electrochemical Behavior of Selenium and Selenium Compounds in Sodium Tetrachloroaluminate Melts

The electrochemistry of selenium and various selenium compounds in melts has been investigated by a variety of techniques including pulse and cyclic voltammetry, coulometry, and the rotating‐disk electrode. It was found that selenium can be reduced, in both acid and basic melts, by a single two‐electron step to selenide which exists in the melt as either or (or their analogous solvated species and ) depending upon the acidity. The mechanism for the oxidation of selenium to Se(IV) was found to be dependent upon the melt acidity. In basic melts, selenium was first oxidized by a two‐electron step to an Se(II) species and then by a further two‐electron step to Se(IV). In acid melts the oxidation was a single quasireversible four‐electron step. The reduction of Se (IV) to selenium was a single four‐electron step at all melt acidities. The kinetics of these oxidation and reduction processes were investigated extensively. From studying solutions, it was found that there were two Se(IV) species in the melt, and , linked by the acidity‐dependent equilibrium for which the equilibrium constant was calculated to be on the mole fraction scale.