A post-modified donor–acceptor covalent organic framework for enhanced photocatalytic H2 production and high proton transport†

The production of fuel and membranes for proton exchange membrane fuel cells (PEMFCs) typically involves disparate materials, highlighting the need for a bifunctional material capable of integrating hydrogen supply and proton conduction. Herein, we modified a donor–acceptor covalent organic framework (PyBT-COF) by converting its cyano groups into carboxyl groups, resulting in PyBT-COF-COOH. The modification significantly enhances the photocatalytic hydrogen production activity, achieving a rate of 8.15 mmol g⁻¹ h⁻¹ with Pt as the cocatalyst, over 2.8 times higher than that of the original PyBT-COF. It also demonstrates an impressive quantum efficiency of 5.10% at 420 nm due to the improved hydrophilicity and carrier separation. Additionally, the rich proton carriers and exchange binding sites within PyBT-COF-COOH also give it a notable proton conductivity of 4.91 × 10⁻³ S cm⁻¹ at 353 K and 98% RH. Upon visible light irradiation, the proton conductivity of PyBT-COF-COOH can be further increased to three times compared to that under normal conditions (1.5 × 10⁻² S cm⁻¹ at 353 K and 98% RH). This study suggests an inspiration for developing and utilizing such bifunctional COF materials in terms of solar energy conversion.