Abstract Electrocatalytic water splitting powered by renewable energy is a sustainable approach for hydrogen production. However, conventional water electrolysis may suffer from gas mixing, and the different kinetics between hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) will limit the direct use of unstable renewable energies, leading to increased cost of H2 production. Herein, a novel phenazine‐based compound is synthesized to develop the solid‐state redox mediator associated water splititng process, and thus decoupling the H2 and O2 production in acid solution without the use of membrane. Excitingly, this organic redox mediator exhibits high specific capacity (290 mAh g−1 at 0.5 A g−1), excellent rate performance (186 mAh g−1 at 30 A g−1) and long cycle life (3000 cycles) due to its π‐conjugated aromatic structure and the fast kinetics of H+ storage/release process. Furthermore, a membrane‐free decoupled water electrolysis architecture driven by solar energy is achieved, demonstrating high‐purity H2 production at different times.
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