Long-term photocatalytic hydrogen peroxide production by hydroquinone-buffered covalent organic frameworks

Abstract

Photocatalytic hydrogen peroxide (H₂O₂) production offers a sustainable route to convert water and oxygen into H₂O₂ using solar energy. However, achieving long-term stability in photocatalysts remains a critical challenge due to mismatched kinetics between oxygen reduction (ORR) and water oxidation (WOR), which leads to hole accumulation and oxidative degradation. Here, we report a redox-mediated strategy to address this bottleneck by designing a hydroquinone-embedded covalent organic framework (Tz-QH-COF) that enables reversible hole buffering and kinetic balance. The hydroquinone (QH) units act as dynamic hole reservoirs, capturing excess holes during ORR and converting to benzoquinone (Q), which is regenerated to QH via WOR, thereby preventing oxidative decomposition. This reversible QH/Q cycle, directly visualized through in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy, ensures unmatched stability, achieving continuous H₂O₂ production for 528 h (22 d) with an accumulated yield of 18.6 mmol L^–1—the highest reported duration for organic photocatalysts. Density functional theory calculations reveal that the QH units exhibit a strong oxygen adsorption energy and favorable two-electron ORR/WOR pathways with low energy barriers. The synergy between experimental and theoretical insights elucidates a redox-mediated charge-balance mechanism, advancing the design of robust photocatalysts for solar-driven H₂O₂ synthesis.