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

Abstract 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 H 2 and Cl 2 production. This system achieves a hydrogen production cost of US$2.5 per kg H 2 , offering a simplified, robust, and scalable solution for practical seawater electrolysis.