Design and control of atmospheric water electrolysis systems for green hydrogen in arid environments.

Freshwater scarcity limits green hydrogen production in arid regions like the Middle East and North Africa (MENA), despite high solar potential. This study compares two atmospheric-moisture-based systems: a Direct Air Electrolyzer (DAE) using a hygroscopic H₂SO₄ electrolyte in a porous sponge, and a hybrid dehumidifier-alkaline electrolyzer (DH-AE) that condenses ambient moisture via vapor-compression refrigeration. Both are designed for Cairo's worst-case relative humidity (RH = 38.19%). The four-module DAE sizing is anchored to a platinum-referenced electrochemical ceiling (1.686 V per module, 87.8% energy efficiency, 97.3% electrolysis efficiency). For the SS‑904 L stainless-steel prototype employed herein, an electrode-material correction (80-140 mV penalty) yields a realistic operating band of 1.766-1.826 V and an energy efficiency of 81.1-83.9%, which brackets the measured prototype range of 1.82-1.95 V. The DH‑AE achieves equivalent output at 68.5% overall efficiency. Thermal simulations (ANSYS) confirm safe operation of SS‑904 L electrodes within the iso-corrosion envelope. A closed-loop control framework (humidity/temperature sensing, PID current regulation, SCADA) is proposed and validated in simulation, enabling autonomous operation. Techno-economic analysis for 50-1,000 kg·day⁻¹ shows a benchmark levelized cost of hydrogen (LCOH) of 4.7 USD·kg⁻¹ for the DAE at 1,000 kg·day⁻¹. When full maintenance, electrolyte replenishment, and long-term degradation are included, the fully loaded LCOH rises to approximately 5.8 USD·kg⁻¹-yet this remains roughly 15% lower than the comparable DH‑AE estimate. Prototype implementations are presented. Overall, atmospheric-moisture-based electrolysis offers a viable, decentralized, water-independent pathway for green hydrogen in arid environments.