π‐Conjugated In‐Plane Heterostructure Enables Long‐Lived Shallow Trapping in Graphitic Carbon Nitride for Increased Photocatalytic Hydrogen Generation

Abstract The relatively short‐lived excited states, such as the nascent electron–hole pairs (excitons) and the shallow trapping states, in semiconductor‐based photocatalysts produce an exceptionally high charge carrier recombination rate, dominating a low solar‐to‐fuel performance. Here, a π‐conjugated in‐plane heterostructure between graphitic carbon nitride (g‐CN) and carbon rings (C rings ) (labeling g‐CN/C rings ) is effectively synthesized from the thermolysis of melamine–citric acid aggregates via a microwave‐assisted heating process. The g‐CN/C rings in‐plane heterostructure shows remarkably suppressed excited‐state decay and increased charge carrier population in photocatalysis. Kinetics analysis from the femtosecond time‐resolved transient absorption spectroscopy illustrates that the g‐CN/C rings π‐conjugated heterostructure produces slower exciton annihilation (τ 1 = 7.9 ps) and longer shallow electron trapping (τ 2 = 407.1 ps) than pristine g‐CN (τ 1 = 3.6 ps, τ 2 = 264.1 ps) owing to C rings incorporation, both of which enable more photoinduced electrons to participate in the photocatalytic reactions, thereby realizing photoactivity enhancement. As a result, the photocatalytic activity exhibits an eightfold enhancement in visible‐light‐driven H 2 generation. This work provides a viable route of constructing π‐conjugated in‐plane heterostructures to suppress the excited‐state decay and improve the photocatalytic performance.