A Post-modified Donor-Acceptor Covalent Organic Framework for Enhanced Photocatalytic H2 Production and High Proton Transport

The production of both the fuel and membrane for proton exchange membrane fuel cells (PEMFCs) often involves disparate materials, therefore, exploring a bifunctional material that can integrate hydrogen source supply and proton conduction is of significant application value in terms of PEMFCs. Herein, we perform a simple post-modification on a donor-acceptor (D-A) COF (PyBT-COF) through converting the abundant cyano group in its pores into carboxyl group (named PyBT-COF-COOH). The minor alteration yields remarkable improvement for PyBT-COF-COOH in photocatalytic hydrogen production activity and endows it with high proton conductivity. With Pt serving as a cocatalyst, PyBT-COF-COOH exhibits significantly improved photocatalytic hydrogen production rate of 8.15 mmol g-1 h-1, over 2.8-fold higher than that of PyBT-COF (2.88 mmol g-1 h-1), and reaches an apparent quantum efficiency of 5.10 % at 420 nm, owing to its enhanced hydrophilicity, dispersion, and carrier separation. 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. This study will provide inspiration for developing and utilizing such bifunctional COF materials with both excellent photocatalytic and proton conduction properties in terms of solar-energy conversion.