Amide-Linked Donor–Acceptor Covalent Organic Polymer Photocatalysts for Visible-Light-Driven Water Oxidation Without Metal Cocatalysts

Abstract

A critical challenge in solar-driven water splitting is developing efficient photocatalysts for the oxygen evolution reaction without relying on metal cocatalysts. Herein, we address this challenge by employing amide linkage engineering in donor–acceptor covalent organic polymers (COPs). Two such polymers, COP-M and COP-I, were synthesized via straightforward sol–gel condensation of acyl chlorides (donor) and melamine (acceptor). The inherent donor–acceptor structure of these COPs imparts an appropriate bandgap (~ 2.9 eV), facilitating effective intramolecular charge separation. Remarkably, these metal-free COPs exhibit intrinsic visible-light-driven oxygen evolution activity without any metal cocatalysts. Their performance can be enhanced approximately fivefold by introducing Co²⁺, with COP-M achieving an optimal O₂ evolution rate of 106 μmol/h. Both experimental and theoretical analyses suggest that the polar amide bond enhances surface hydrophilicity and modulates the thermodynamic barrier for initial water activation. Additionally, enhanced charge separation and transfer kinetics within the symmetrical donor–acceptor architecture of COP-M underscore its enhanced performance. This study emphasizes the collaborative role of amide linkages and donor–acceptor motifs in designing metal-free polymer photocatalysts, offering a strategy for artificial photosynthesis.

Keywords

Covalent organic polymers / Donor–acceptor structure / Amide linkage / Charge transfer / Metal-free photocatalysis / Oxygen evolution reaction

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