Coupling Fe(II)/Fe(III) Redox Mediated SO₂ Conversion with Hydrogen Production

Abstract Water electrolysis is recognized as a green hydrogen production technology, but the high voltage required for anodic oxygen evolution reaction restricts the practical application. In this work, a Fe(II)/Fe(III) redox mediated SO₂ conversion is proposed to couple the cathodic hydrogen evolution reaction to achieve sulfur dioxide conversion and hydrogen production at low voltage. The onset potential of Fe(II) electrooxidation to Fe(III) is as low as 0.75 V_RHE (vs reversible hydrogen electrode). Ex situ ultraviolet spectroscopy (UV) spectrum and ion chromatography indicate that SO₂ in electrolyte can reduce Fe(III) to Fe(II), completing the Fe(II)/Fe(III) redox cycle as well as the conversion of SO₂ to sulfuric acid. The assembled flow cell electrolyzer requires a low operating voltage of 0.97 V at 10 mA cm⁻² and shows good performance under both acidic and neutral conditions. This study proposes an innovative energy saving and environment friendly strategy for simultaneous hydrogen production and sulfur dioxide capture based on low‐cost catalyst materials.