Asymmetric atomic-level engineering of phosphorus-modified Cu single-atom coordination centers on carbon nitride for enhanced photocatalytic hydrogen evolution.

Single-atom photocatalysts (SACs) have emerged as an effective strategy for enhancing solar energy conversion by improving light absorption and charge carrier dynamics; however, precise construction of isolated active sites remains challenging. Herein, we report atomically dispersed Cu single atoms uniformly anchored on phosphorus-doped graphitic carbon nitride (Cu-PCN). The optimized catalyst achieves an excellent hydrogen evolution rate of 3276 µmol g-1 h-1 with an apparent quantum yield (AQY) of 31% at 400 nm, surpassing most reported metal-N coordinated systems. X-ray absorption spectroscopy (XAS) confirms the atomic dispersion and defined coordination of Cu single atoms within the g-C3N4 framework. Combined experimental and theoretical studies reveal that the Cu sites extend light absorption, enhance charge separation and interfacial transfer, and promote H2O activation by guiding electron migration toward Cu centers with reduced energy barriers, thereby facilitating the formation of H* intermediates as the crucial step in hydrogen evolution. Overall, this work demonstrates an effective approach to engineer asymmetric active sites via coordination tuning, providing valuable insights for designing efficient photocatalysts for solar-driven hydrogen evolution reaction.