pH‐Switchable Recoverable Quasi‐Homogeneous Hydrophilic Polymeric Photocatalysts for Efficient Hydrogen Production

Conjugated polymer (CP) photocatalysts for hydrogen evolution often face a critical trade‐off between high activity achieved through nano‐structuring and practical recyclability. To address this challenge, we design a series of CPs incorporating pH‐responsive carboxyl (−COOH) groups, enabling a reversible transition between a quasi‐homogeneous state for reaction and an aggregated state for recovery. The optimal material, EDBT(OH) 0.25 , forms stable nano‐colloids in alkaline solution and exhibits photocatalytic hydrogen evolution rates up to 114.54 and 107.66 mmol g −1 h −1 in deionized water and natural seawater, respectively, under visible light without the need for cosolvents or Pt co‐catalysts. Experimental and theoretical analyses suggest that the dissociated −COO − groups enhance hydrophilicity, modulate electron distribution, and help prolong the lifetime of photogenerated carriers. Importantly, these nano‐catalysts can be recovered (95% yield) via acid‐triggered aggregation, retaining over 93% initial activity across four consecutive cycles. This work establishes a proof‐of‐concept strategy for designing recyclable quasi‐homogeneous photocatalytic systems for solar hydrogen production, including operation in complex aqueous environments such as seawater.