Membrane-Free Two-Step Water Electrolysis Enable by A Stable Organic Redox Mediator

Abstract

Electrochemical decoupled water splitting utilizes a solid-state redox mediator (SSRM) to reversibly store proton-electron pairs, thereby separating hydrogen and oxygen evolution without the use of membrane and promoting the conversion of sustainable energy sources into hydrogen. However, the widespread appalication of this apporach is currently limited by issue such as instabilty and discontinuty of SSRM. Herein, a novel and membrane-free system is designed for decoupled hydrogen production in acidic medium, based on the highly reversible SSRM of sustainable quinone-based organic polymer (P-ACD). Due to intramolecular hydrogen bonds, the P-ACD-electrode with low loading (1-2 mg cm-2) exhibits high discharged specific capability (215.32 mAh g-1 at 0.2 A g-1), ultrafast chargeability (86.90 mAh g-1 at 100 A g-1, just 3.12 s), and exceptional cyclability over 30,000 cycles. More importantly, Two-step water electrolysis under high loading achieves a remarkable coulombic efficiency of nearly 100% even after 600 consecutive cycles, concurrently exhibiting favorable cycle stability surpassing 184 h for hydrogen production. Consequently, this system provides a new avernue for achieving operational flexibility and membrane -free hydrogen production.