Energy-Saving Cathodic Hydrogen Production Enabled by Anodic Oxidation of Aqueous Sodium Sulfite Solutions

The potential energy of SO2 is wasted in the process of converting Na2SO3 to Na2SO4 via air oxidation during conventional treatment of SO2-contaminated air. Considering that the oxidation of Na2SO3 is thermodynamically and kinetically much easier than the oxygen evolution reaction (OER), this study proposes replacing the OER with Na2SO3 oxidation to recover the potential energy of SO2 and simultaneously reduce the energy consumption of water electrolysis. First, the influences of the reaction temperature and Na2SO3 concentration on Na2SO3-assisted water electrolysis (SAWE) were studied. Then, the difference between Na2SO3 electrolysis and water electrolysis was compared under optimum conditions. Furthermore, the long-term stability of SAWE was assessed. The results of this study suggest that the onset potential of water electrolysis decreases from 0.73 V vs saturated calomel electrode (SCE) to 0.28 V vs SCE by replacing the OER with Na2SO3 oxidation. The energy consumption of producing hydrogen by water electrolysis is reduced with the use of the potential energy of SO2. For SAWE, the Na2SO3 oxidation kinetics and hydrogen production rate are improved as the reaction temperature and Na2SO3 concentration increase.