A gel electrolyte-based direct seawater electrolysis†

In situ direct seawater electrolysis driven by renewable energy on floating platforms in deep and far oceans has become an attractive option for green hydrogen generation. By introducing a waterproof and breathable interface between seawater and an electrolyte and utilizing the interfacial vapour pressure difference, impurity ions from seawater can be isolated, and pure water for hydrogen production can be attained. However, liquid electrolytic systems may have certain drawbacks, such as leakage and pressure fluctuations in oceans with uncontrollable waves. Here, a flexible gel electrolyte with favourable ion conductivity and water capture performance was prepared and used in direct seawater electrolysis. Simulations were conducted to reveal the process of water migration in the gel electrolyte, and they indicated that the migration of the water molecules in the gel was driven mainly by the concentration gradient and depended on the bonding and dissociation of the hydrogen bonds between the water molecules and OH⁻. The system operated stably for more than 400 hours using untreated real seawater at a current density of 250 mA cm⁻². In addition, a gel electrolyte-based hydrogen production system with a scale of 1045 mL H₂ h⁻¹ was constructed and operated stably for 20 hours with sunlight as the source of power in a flowing and fluctuating river. Additionally, this gel electrolyte was extremely easy to scale up (dimensions of 45 × 35 cm²). Moreover, the potential of the gel electrolyte to operate at 1 A cm⁻² or lower temperatures (7.1 °C) and its applicability for hydrogen production directly from a humidified gas atmosphere (N₂@99 RH, 25 °C, stable operation for 220 h) were investigated. These results provide an efficient pathway for achieving scalable hydrogen production under fluctuating ocean conditions.