ANODIC-OXIDATION OF DIMETHYL-SULFOXIDE BASED ELECTROLYTE-SOLUTIONS - AN IN-SITU FTIR STUDY

Anodic oxidation of dimethyl sulfoxide (DMSO) based electrolyte soluti ons, containing LiClO4, LiBF4 and KPF6, on platinum (Pt), glassy carbo n (GC) and n-TiO2 (anatase), electrodes was studied using in situ Four ier transform infrared spectroscopy (FTIR). All solutions contained sm all amounts of H2O. Regardless of the supporting electrolyte all syste ms were unstable at potentials above 1.0 V vs SCE. The major oxidation product is dimethyl sulfone, formation of which is initiated by the t race water breakdown. In contrast to acetonitrile based solutions ther e is no evidence of electrolyte involvement in the breakdown process. Photoanodic decomposition of dimethyl sulfoxide based solutions procee ds in the same way as the anodic oxidation in the dark. In the presenc e of nucleophilic agent (iodides) the prevailing redox process is iodi de oxidation. Small amounts of, probably, methylsulfinyliodide are als o formed. The irreversible consumption of charge mediator significantl y restricts the possible practical use of DMSO in photoelectrochemical devices.