Anchoring Redox Mediator on COFs for Efficient Solar to Hydrogen Conversion

To address severe carrier recombination in Z-scheme heterojunctions, redox mediators such as IO₃ ^-/^I- or Fe³⁺/Fe²⁺ are often introduced, yet their dispersion in solution causes instability, low electron transport efficiency and side reactions. Herein, an innovative Fe-coordinated 2D Z-scheme heterojunction composed of TpPa-1-COF (TP1C) and Bi₂WO₆ (BWO) is developed for efficient photocatalytic H₂ production. Unlike traditional indirect Z-scheme heterojunctions, the Fe³⁺/Fe²⁺ mediator is firmly anchored on the skeleton of COFs, thus enhancing recyclability, charge migration and long-lasting stability, which is supported by extended X-ray absorption fine structure (EXAFS) and a range of electrochemical tests. In addition, the formation of 2D Z-scheme heterojunctions not only retains high redox properties but also provides abundant active sites for photocatalytic reactions. Consequently, the photocatalytic H₂ production rate of 25% BWO/Fe/TP1C reaches up to 6.31 mmol·g^-1·h^-1 without the addition of co-catalysts, being about 28.68 times as high as that of pure COFs and 2.3 folds over that of 25% BWO/TP1C, exceeding a host of COF-based photocatalysts. The findings of this research highlight the potential of novel indirect Z-scheme heterojunctions for advanced photocatalytic applications, offering a new pathway to overcome the limitations of traditional COF-based systems in hydrogen production.