Solution pH Manipulates Sulfur and Electricity Recovery From Aqueous Sulfide in an Air‐Cathode Fuel Cell

Abstract

The air‐cathode fuel cell has great potential for simultaneous elemental sulfur (S0) and electricity recovery from aqueous sulfide. This work demonstrates the electrochemical oxidation of sulfide in the air‐cathode fuel cell can be manipulated by controlling solution pH. Below pH 7 the sulfide oxidation produces S0 as the main product, while in alkaline solution another product thiosulfate is formed together with S0. Elevating solution pH improves the fraction of sulfide converted to thiosulfate by moving the equilibrium shift from H2S(aq) to polysulfide. In addition, electron transfer from aqueous sulfide to the carbon electrode is facilitated at high pH values. However, the passivation of electrode surface by S0 deposition is aggravated at increased pH values, thus slowing down the electrochemical oxidation rate of sulfide. The operation of the air‐cathode fuel cell at pH 7 obtained the highest sulfur recovery efficiency of 71.3%, meanwhile the coulombic efficiency achieving as high as 55%.