The activation of bridged N atoms based on the structure engineering of PCN to boosts the release of visible-light photocatalytic hydrogen

The inherent electronic structure of the bridged N atoms of polymeric carbon nitride (PCN) weakens the carriers transport process, which seriously reduced the activity of PCN. How to modulate the electronic structure of bridged N and break its limitation of charge transfer is a major challenge. Herein, PCN with bridged N atoms activated (PCNG) was designed and synthesized by the thermal copolymerization of glyoxal and melamine. Experimental and DFT calculation results show that the strong hydrogen evolution ability of PCNG is due to the wide visible absorption range, which is contributed by the mid-gap states. More importantly, the LUMO of PCNG shows great delocalization on the all-heptazine units and forms a polarized electric field between heptazine units. Therefore, the optimal PCNG-1 performs so far high H₂ evolution rate (261 umol·h⁻¹) and apparent quantum yield (AQY = 5.32%, λ = 420 nm), under the visible light.