Boosting SO2-depolarized electrolysis with anodic HI for efficient and energy-saving hydrogen production.

The SO 2 -depolarized electrolysis (SDE) is a promising method for SO 2 capture and hydrogen production. But the SDE is limited by the high overpotential and slow kinetics of anodic SO 2 oxidation reaction (SOR). Herein, to boost SDE process, we add hydroiodic acid (HI) to the anolyte and form HI-assisted SO 2 -depolarized electrolysis (HASDE). The mechanism of HI assisted SOR is explored, the existence of HI reduces the onset potential and impedance, but increases current density and reaction rate of SOR. HI is supposed to change the single-step SOR into three-step reactions, without changing the overall anodic reaction. A HI concentration of less than or equal to 0.02 mol/L and an operating temperature of 50 °C or less are recommendable. The comparison of SDE and HASDE processes indicates that HASDE delivers a lower cell voltage than SDE during continuous constant-current electrolysis, and has negligible effect on cathodic H 2 evolution, while it achieves 27.03–48.65% reduction in electric energy consumption compared with SDE. The present work provides an innovative strategy for improving SDE and energy-saving production of value-added chemicals like H 2 SO 4 and H 2. Image 1 • HI-assisted SO 2 -depolarized electrolysis (HASDE) was proposed. • Anodic HI assisted SO 2 oxidation reaction (SOR) was more favorable than SOR. • Mechanism of anodic oxidation reaction in HASDE was elucidated. • HASDE was more efficient and energy-saving than SDE. [ABSTRACT FROM AUTHOR]