# Constructing dual charge-transfer tunnels within highly charge-confined COFs for efficient photosynthesis of hydrogen peroxide from water and air

## TL;DR

Researchers designed a new type of covalent organic framework (COF) with improved charge transfer to efficiently produce hydrogen peroxide from water and air using sunlight.

## Contribution

A new strategy for COF design using bipyrimidine to create dual charge-transfer tunnels, enhancing H2O2 photosynthesis.

## Key findings

- COF-BPM achieves a high H2O2 production rate of 5521 μmol g−1 h−1 without sacrificial reagents.
- Dual charge-transfer tunnels in COF-BPM significantly accelerate charge transfer and reduce energy barriers for water oxidation.
- COF-BPM efficiently produces H2O2 under various pH conditions and in real-world water using solar light.

## Abstract

Insufficient charge separation and sluggish two-electron water-oxidation reaction are two critical factors restricting the photosynthesis performance of metal-free covalent organic frameworks (COFs) for hydrogen peroxide (H2O2) generation from naturally abundant water and air. Herein, we develop a facile strategy to simultaneously boost the charge-separation efficiency and water-oxidation capability through constructing short and rapid charge-transfer tunnels within highly charge-confined COFs via replacing the phenyl with pyrimidine. Compared with a single charge-transfer tunnel within a lowly charge-confined COF-5-(4-aminophenyl)pyrimidin-2-amine (APM) with pyrimidine, dual charge-transfer tunnels are constructed within a highly charge-confined COF-5,5′-bipyrimidine-2,2′-diamine (BPM) with bipyrimidine due to the ground-state charge transfer between para-carbon and meta-nitrogen, which significantly accelerates the intermolecular charge-transfer process and prevents charge recombination. This strategy also decreases the energy barrier of rate-determining water oxidation in H2O2 photosynthesis and thus promotes the effective generation of the key *OH intermediates, facilitating the generation of H2O2 at a production rate of 5521 μmol g−1 h−1 from water, oxygen and light without sacrificial reagents or additional energy consumption by COF-BPM. Furthermore, COF-BPM can also efficiently produce H2O2 under broad pH conditions, in widely available real water, on a floatable foam sheet, in a continuous-flow reactor and in a scaled-up reactor by using natural solar light for water decontamination.

This work provides new insights into the design of covalent organic frameworks (COFs) by constructing charge transfer tunnels to boost hydrogen peroxide photosynthesis, and paves the way for practical application of COFs in solar-driven synthesis.