Chlorine-Suppressed Direct Brine Electrolysis with a Multifunctional Cobalt–MnO ₂ /Sn–IrO ₂ Catalyst for Sustainable Co-generation of Hydrogen, Oxygen, Sodium Hydroxide, and Hydrochloric Acid

The valorization of industrial and natural brines for co-producing commodity chemicals (e.g., inorganic acids such as hydrochloric acid (HCl) and bases such as sodium hydroxide (NaOH)) and sustainable energy carriers (e.g., hydrogen (H 2 ) and oxygen (O 2 )) while producing less saline solutions for reuse or environmentally benign disposal is an underexplored approach with high transformative impact. One of the key scientific challenges in advancing direct electrolysis (DE) technologies lies in tuning the competitive evolution of chlorine gas (Cl 2 ) vs oxygen gas (O 2 ). Suppressing Cl 2 gas evolution is associated with enhanced O 2 gas evolution and production of HCl. To this end, stable multifunctional electrodes that suppress Cl 2 evolution reaction (CER) and enhance O 2 evolution reaction (OER) are architected using layered Co-modified MnO 2 (in which Cobalt composition is varied from 3 to 10 mol %) supported on Sn–IrO 2 -coated Ti foil. The catalyst with 5% Co achieves high yields of 13.89 mol of HCl/kWh, 22.22 mol of NaOH/kWh, and 5.18 mmol of H 2 /kWh, while decreasing Cl 2 generation by 60% compared to a platinum anode. Life cycle assessment reveals that our approach lowers net CO 2 emissions to 0.56 g CO 2 eq/g NaOH, 34% lower than the 0.85 g CO 2 eq/g NaOH from the conventional diaphragm chlor-alkali process. These results demonstrate that multifunctional co-modified MnO 2 /Tin–IrO 2 catalyst on Titanium foil electrodes are effective in enhancing the co-production of NaOH, HCl, H 2, and O 2 from brine while suppressing Cl 2 gas evolution.