Sustainable and Energy Efficient Sulfion-Sulfite Reaction Coupled Electrocatalytic H₂ Evolution from Water

Energy-efficient alternatives for oxygen evolution reaction (OER) is desirable to promote the viability and energy efficiency of H₂ production via electrocatalytic water splitting. Herewith, sulfion-sulfite reaction (SSR) (thermodynamic potential = -0.66 V_SHE) is introduced as an anode half-cell reaction for the O₂-free H₂ generation in a sustainable and energy-efficient manner. The SSR utilizes industrial wastes such as S^2- and SO₃ ^2- and produces value-added S₂O₃ ^2-. Furthermore, the process doesn't necessitate the use of any additional base/acid and membrane, like conventional OER and SOR-based processes. The SSR coupled process realizes an overall current density value of 100 mA/cm² at 0.70 V under ambient conditions, which is much superior to that of the OER (1.97 V) and SOR (0.89 V) coupled processes. The ultra-low energy consumption value (1.67 kWh/m³ of H₂) and system simplicity further support the viability of the SSR-based process over that of the conventional OER (4.71 kWh/m³ of H₂) and SOR (2.12 kWh/m³ of H₂) based technologies. The energy efficiency is anticipated to improve further with suitable catalyst development targeting the SSR process in the future. Overall, the SSR offers new energetically favourable and economically viable opportunities for low-cost H₂ production via a hybrid water electrolysis process.