Chloromethylation Modified Pyranonitrile-Based Conjugated Microporous Polymers for Selective One-Step Two-Electron O2 Reduction to H2O2

Abstract

Hydrogen peroxide (H₂O₂) production utilizing conjugated microporous polymers (CMPs)-based photocatalysts represents a crucial green technology for achieving solar-to-chemical energy conversion. Proper material design is paramount to improve the dispersity and charge transfer of CMPs for enhanced H₂O₂ production performance. Herein, a post-modification strategy employing chloromethylation reaction was proposed to enhance H₂O₂ production. The simple one-step chloromethylation reaction simultaneously achieved two objectives: One is enhanced hydrophilicity through the hydrolysis of cyanogen groups in the pyranonitrile unit to carboxyl groups, the other is the improved O₂ adsorption and charge transfer by incorporating chloromethyl groups. The two objectives synergistically enhanced the H₂O₂ production rate of the chloromethylated CMP named DCM-TPA-Cl, reaching 5.01 mmol g⁻¹ h⁻¹ in air, 6.7-fold of the unmodified photocatalyst. Moreover, the rate achieved at an O₂ atmosphere increased by only 1.8%, highlighting its superior O₂ utilization efficiency in air. An exceptional 38.02 mmol g⁻¹ h⁻¹ rate was further achieved in water/benzyl alcohol mixtures, exceeding most reported polymer photocatalysts. Experimental and theoretical results corroborated the predominant role of the one-step two-electron O₂ reduction pathway in the H₂O₂ generation. This work demonstrates the potential of a post-modification method to significantly enhance H₂O₂ production performance directly from water and air.