Spectro-Electrochemical Investigations in Molten Salt and Aqueous Media

摘要

The electroreduction of the manganese oxyanions in alkaline solutions and the electrooxidation of elemental sulfur and electroreduction of Nb(V) in molten AlCl sub 3 -NaCl mixtures has been investigated in situ by means of spectroelectrochemical tecniques and thin-layer coulometry at optically transparent electrodes. The reduction of the manganese oxyanions in alkaline solutions has been found to consist of simple reversible one electron transfers when carried out in solutions in which the reduction product is stable. One or more soluble intermediate species, probably containing Mn(IV) and possibly Mn(V), are formed when reduction is carried out in solutions where the product is unstable and undergoes disproportionation. The effect of varying the pH of the solution on the overall reduction process is discussed. Spectral data on the reduction products are presented. The oxidation of elemental sulfur in AlCl sub 3 -NaCl (63 to 37 mole %) melt was investigated by means of uv-visible absorption and electron spin resonance spectroelectrochemical techniques. The initial oxidation step produces several lower oxidation state sulfur species such as S sub 162+ , S sub 82+ , and possibly S sub 192+ . Two radical cations are also involved, S sub 5+ and possibly S sub 8+ . The interactions of these species as a function of temperature and concentration are discussed. Reactions are proposed describing chemical equilibria between these species. Further oxidation produces S(I), as S sub 22+ , and S(IV), as SCl sub 3+ . Spectroelectrochemical evidence for the formation of S sub 42+ and S(II) as intermediate products during the oxidaton is discussed. Spectral data on the oxidation products are presented. An overall reaction sequence for the oxidation of S(0) to S(IV) is proposed. (ERA citation 07:015241)