Electrochemical oxidation of H₂S on polycrystalline Ni electrodes

Abstract: We have evaluated the applicability of Ni anodes in electrochemical conversion of H₂S to form sulfur (polysulfides) and H₂. Two different electrolytes containing sulfide were evaluated: a buffered solution of Na₂HPO₄ at pH 9.2, and a NaOH solution at pH 13. At pH 9.2, deposition of sulfur on the Ni anode was observed, resulting in a significant decrease in electrochemical performance. The composition, morphology, and thickness of the sulfur deposit, as determined by Raman spectroscopy and SEM, was found to strongly depend on the applied potential, and ranged from dense S₈ films to highly porous spherical sulfur structures. Oxidation of the anode was also observed by conversion of Ni to NiS₂. The formation of the sulfur film was prevented by performing the reaction at pH 13 in NaOH in the range of − 1.0 V to + 0.6 V versus Hg/HgO. It is proposed that at these highly basic pH values, sulfur is dissolved in the electrolyte in the form of polysulfides, such as S₂ ²⁻ or S₈ ²⁻. When using Ni anodes some oxygen evolution was observed at the anode, in particular at pH 13, resulting in a Faradaic efficiency for sulfur removal of ~ 90%. Graphic Abstract: [Figure not available: see fulltext.].