Integrated Membrane Distillation-solid Electrolyte-based Alkaline Water Electrolysis for Enhancing Green Hydrogen Production

This paper investigates the circularity of green hydrogen and resource recovery from brine using an integrated approach based on alkaline water electrolysis (AWE). Traditional AWE employs highly alkaline electrolytes, which can lead to electrode corrosion, undesirable side reactions, and gas cross-over issues. Conversely, indirect brine electrolysis requires pre-treatment steps, which negatively impact both techno-economics and environmental sustainability. In response, this study proposes an innovative brine electrolysis process utilizing solid electrolytes (SELs). The process includes an on-site brine treatment facility leveraging a self-driven phase transition technique and incorporates a hydrophobic membrane as part of a membrane distillation (MD) system to facilitate the gas pathway. Polyvinyl alcohol (PVA) and tetraethylammonium hydroxide (TEAOH)-based electrolytes, combined with potassium hydroxide (KOH) at various concentrations, function as a self-wetted electrolyte (SWE). This design partially disperses water vapor while effectively preventing the intrusion of contaminated ions into the SWE and electrode-catalyst interfaces. PVA-TEAOH-KOH-30 wt% SWE demonstrated the highest ion conductivity (112.4 mScm−1) and excellent performance with a current density of 375 mAcm−2. Long-term electrolysis confirmed with a nine-fold brine in volume concentration factor (VCF) demonstrated stable performance without MD membrane wetting. The Cl−/ClO− and Br− concentrations in the SWE were reduced by five orders of magnitude compared to the original brine. This electrolyzer supports the circular use of resources, with hydrogen as an energy carrier and concentrated brine and oxygen as valuable by-products, aligning with the sustainable development goals (SDGs) and net-zero emissions by 2050.