Electron-donor engineering of heptazine-based donor–acceptor conjugated microporous polymers for efficient metal-free photocatalytic hydrogen evolution

Abstract

Heptazine-based conjugated microporous polymers (CMPs) constructed by s-heptazine and designable linkers are considered promising materials for photocatalytic hydrogen evolution (PHE). However, there is a lack of systematic research concerning the influence of linker regulation on the structure–property–performance relationship of heptazine-based CMPs, the detailed mechanism of which remains largely elusive and is usually ignored. Herein, we propose an electron-donor engineering strategy that introduces the electron donors TAPB and TAPPy at different feed ratios to construct a series of novel heptazine-based donor–acceptor CMPs (Y1–Y4). The substantial experimental and theoretical evidence support that linker replacement of TAPB with the stronger electron donor TAPPy can facilitate the formation of more powerful local built-in electric fields, which thereby significantly reduces exciton binding energy, accelerates charge separation and enhances PHE performance. At the optimized conditions, the hydrogen evolution rate of Y4 is up to 27 mmol g⁻¹ h⁻¹, which is 57 and 1928 times that of Y1 and g-C₃N₄, respectively. Without a cocatalyst, the AQY of Y4 can reach 8.5% at 420 nm, superior to most catalysts currently reported. This work uncovers the key role of the electron-donating linker and provides new ideas for the design of high-performance heptazine-based CMPs.