Thermodynamic analysis for a new process of electrochemical decomposition of aqueous hydrogen sulfide solution into sulfur and hydrogen gas

The difficulty for electrochemical decomposition of aqueous hydrogen sulfide solution into elemental sulfur and hydrogen gas is the anode passivation caused by deposition of solid sulfur on the anode surface.Thermodynamic analyses for a novel approach to get rid of the anode passivation are presented in this paper. Pourbaix diagrams for the simplified sulfur-H_2O system show that polysulfide ions in alkaline solution are stable species and dominant regions of higher polysulfide ions become bigger with the increase of total sulfur concentration T(s) of all dissolved species.When the anolyte is reacted with H_2S gas,solid sulfur phase is stable if both pH of the solution and partial pressure of H_2S gas are lower.Thermodynamic calculations show that the appropriate H_2S gas partial pressure is chosen to be 1 atm,and that,when the solution pH is less than 8,most of the polysulfide ions are decomposed into elemental sulfur and S~(2-),HS~- or H_2S(aq.).The result is useful both for determining optimum electrolytic conditions in electrochemical formation of the polysulfide ions and for decomposition of the polysulfide ions by H_2S gas into elemental sulfur.6figs.,1tab.,10refs.