The Redox Cycle of Viologen-Based Porous Organic Polymers for High-Performance Hydrogen Peroxide Photosynthesis

Harnessing solar energy to produce hydrogen peroxide (H₂O₂) is an important strategy to address the current energy shortage. Among various materials, porous organic polymers (POPs) stand out as promising candidates for photocatalytic H₂O₂ generation due to their versatile structures and extended π-conjugation; however, their efficiency in H₂O₂ synthesis is often constrained by poor charge separation and high reaction energy barriers. To address these challenges, we drew inspiration from the redox reactions of coenzyme NADPH in natural photosynthesis, the redox-active methyl viologen (MV²⁺) moiety was rationally incorporated into two polymer frameworks (TPE-MV and TPB-MV) as pivotal active sites for photocatalytic oxygen (O₂) reduction to H₂O₂ via the reversible redox cycle of MV²⁺ and zerovalent methyl viologen (MV⁰). Through this redox cycle, MV²⁺ accepts two photogenerated electrons, reducing it to MV⁰. MV⁰ sequentially reduces O₂ to H₂O₂ while regenerating MV²⁺. Mechanistic studies show that this approach effectively suppresses charge recombination and lowers the reaction energy barriers. Consequently, the photocatalytic H₂O₂ generation rates of TPE-MV and TPB-MV reached 6068 and 2015 µmol g⁻¹ h⁻¹, respectively. This work offers a new strategy for designing efficient photocatalysts by incorporating biomimetic redox-active moieties to enhance solar energy utilization for H₂O₂ production.