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 2- 8c , undergoes an equilibrium reaction to its linear chain counterpart, S 2- 8l , which then dissociates into various products. These two dianions and S - 3 were produced along with a minor product, S 2- 4 , at the potential corresponding to the first electron transfer. These products were further reduced or dissociated to species including S 2- 7 , S 2- 6 , S 2- 5 , S 2- 4 , S 2- 3 , S 2- 2 , and S 2- 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.