Time-resolved in situ spectroelectrochemical study on reduction of sulfur in N,N′-dimethylformamide

Real-time in situ spectroelectrochemical studies have been carried out in N,N'-dimethyl formamide containing lithium trifluoromethane sulfonate as an electrolyte and the results are reported. The results indicate that the primary reduction product of the cyclic form of sulfur, S-8c(2-), undergoes an equilibrium reaction to its linear chain counterpart, S-81(2-), which then dissociates into various products. These two dianions and S-3(-.) were produced along with a minor product, S-4(2-), at the potential corresponding to the first electron transfer. These products were further reduced or dissociated to species including S-7(2-), S-6(2)-, S-5(2-), S-4(2-), S-3(2-), S-2(2-), and S2- at the second electron-transfer step as evidenced by the spectral shifts observed during electrolysis. The reduction reactions are generally chemically reversible, making it possible to use sulfur reduction as a cathode reaction for Li/S batteries. (C) 2004 The Electrochemical Society.