Electrochemical Coproduction of Hydrogen, Oxygen, Sodium Hydroxide, and Hydrochloric Acid from Brines via Direct Electrosynthesis with Chlorine Suppression

Hydrogen production is of growing interest as a low-carbon energy carrier. While technologies to produce H2 via steam methane reforming and water electrolysis remain well developed, the use of brine electrolysis is gaining increasing attention due to the feasibility of producing multiple high-value coproducts, including acids, bases, and O2. However, the conventional method for producing acid and base simultaneously using bipolar membrane electrodialysis (BMED) consumes significant energy and has a complex process configuration. Additionally, it is important to suppress Cl2 gas evolution and produce HCl instead during brine electrolysis. This study investigates the performance and economic viability of three different brine electrolysis systems: direct electrosynthesis (DE) without a bipolar membrane, anion exchange membrane (AEM), and cation exchange membrane (CEM) systems, using a new manganese–molybdenum-coated titanium (MnMo/Ti) electrode that suppresses Cl2 gas evolution. Results demonstrate that the DE-MnMo/Ti electrode system produced 0.005 mol of H2, 0.0041 mol of O2, 0.37 M NaOH, and 0.2 M HCl (∼98% purity). Compared to pure water electrolysis, brine electrolysis offers higher economic potential due to the production of value-added products, such as O2, NaOH, and HCl. The revenue generated per year using the proposed approach is 4 times higher than that of alkaline electrolysis using pure water, even though H2 yields are lower compared to those of water electrolysis. By unlocking the feasibility of harnessing low value brines for brine electrolysis, the energy needs associated with producing fresh water via energy-intensive desalination processes are circumvented. Therefore, this study highlights the potential for brine electrolysis with the DE-MnMo/Ti electrode system as an economically viable and environmentally sustainable route for producing H2, NaOH, HCl, and O2.