INSITU SPECTROELECTROCHEMICAL STUDIES ON THE REDUCTION OF SULFUR IN DIMETHYL-SULFOXIDE SOLUTIONS

The electrochemical reduction of sulfur has been studied employing in situ spectroelectrochemical techniques. Previously unreported absorption bands in the UV region observed during the electrochemical reduction are assigned to the reduced sulfur species with high electron-to-atom ratios. The spectroelectrochemical studies indicate that reduction products generated at the first reduction step are essentially identical to those formed at the second with S(3)2- and S(4)2- as ultimate reduction products. This suggests that chemical reactions following the first electron transfer to produce S(8)2- are important. The derivative cyclic voltabsorptometric (DCVA) results indicate that all the reduced sulfur species, i.e., S(8)2-, S(6)2-, S(4)2-, S(3)2-, and S3-. are generated at the first cathodic wave and three of these, i.e., S(8)2-, S(6)2- and S3-. are reduced at the second reduction wave, while other species show a delayed generation. A mechanism consistent with these observations is proposed.