Membrane‐Free Direct Seawater Electrolysis via Redox Mediator for H ₂ Production

Acidic seawater electrolysis offers a promising strategy for sustainable hydrogen production. However, its practical application still faces critical challenges including membrane dependency, complex seawater pretreatment, and limited compatibility with intermittent renewable energy. Herein, we construct a decoupled seawater direct electrolysis (DSDE) system employing TQBQ-COF (Covalent Organic Framework) as a solid-state redox mediator, enabling membrane- and desalination-free operation. TQBQ-COF exhibits excellent electrochemical performances in both acidic deionized water and acidic seawater, demonstrating that common seawater ions do not interfere with its redox activity. When coupled with a Ru-modified TQBQ-COF catalyst (COF-Ru), the DSDE system decouples anode and cathode reactions, allowing flexible integration with intermittent renewable energy for high-purity H₂ and Cl₂ production. This system achieves a hydrogen production cost of US$2.5 per kg H₂, offering a simplified, robust, and scalable solution for practical seawater electrolysis.