The Directional Oxidation Studies Of Sulfur Compounds In Air Cathode Fuel Cell

As an odorous gas ubiquitously present in industrial and domestic waste streams, hydrogen sulfide (H2S) is of special concern due to its toxicity and corrosivity.The air-cathode fuel cell has great potential for simultaneous elemental sulfur (So) and electricity recovery from aqueous sulfide. In this work, we demonstrate the electrochemical oxidation of sulfide in the air-cathode fuel cell can be manipulated by controlling solution pH. Below pH 7.0 the sulfide oxidation produces So as the main product, while in alkaline solution another product thiosulfate is formed together with So. Elevating solution pH improves the fraction of sulfide converted to thiosulfate by moving the equilibrium shift from H2S(aq) to polysulfide. In addition, the electron transfer from aqueous sulfide to the carbon electrode is facilitated at high pH values. However, the passivation of electrode surface by So deposition is aggravated at increased pH, thus slowing down the electrochemical oxidation rate of sulfide. The operation of air-cathode fuel cell at pH 7.0 obtains the highest sulfur recovery efficiency of 71.3%, meanwhile the coulombic efficiency achieving as high as 55.0%.In order to further improve the oxidation rate of air-cathode fuel cell to sulfide, the air cathode fuel cell conditions were adjusted, and Mn3O4/GF composites were prepared with high catalytic activity. When Mn3O4/GF composites were as the anode with the solvent thermal time of 12h, and under different pH conditions, the complete oxidation time of sulfides shortened. And under the condition of pH=8 and pH=9, the mass of thiosulfate decreased, when increasing the solvent thermal time, under the condition of pH=7, as the increase of solvent thermal time, complete oxidation time of sulfide decreased. Complete oxidation time of Mn3O4/GF composite materials with solvent thermal time of 36h was 20h shorter than that solvent thermal time of 12h, which was 30h shorter than the blank activated carbon felt. Under the condition of pH=8, with the increase of solvent thermal time, complete oxidation time of sulfide reduced and the mass of thiosulfate reduced in the process of sulfide oxidation loading Mn3O4/GF composites, promoting the sulfide turned into elemental sulfur (So) directly.In the fuel cell, under the conditions of pH=7, sulfide concentration of lOmM/L, external resistor for 100, and Mn3O4/GF composite as anode with solvent thermal time of 36h, the complete sulfide oxidation time was 90h and coulombic efficiency was up to 65%.