In situ protonated-phosphorus interstitial doping induces long-lived shallow charge trapping in porous C3−xN4 photocatalysts for highly efficient H2 generation

Abstract

Efficient photocatalytic solar-to-H₂ conversion is pivotal to zero-carbon energy supply. Graphitic carbon nitride (g-C₃N₄) is a promising visible-light photocatalyst but suffers from intrinsic electron–hole recombination and deep-charge trapping, limiting its efficiency. Here, we show a synergistic strategy of porosity, vacancy and shallow(trapping)-state engineering to enrich catalytic sites and promote the lifetime of active electrons by thermochemical treatment and phosphorus-interstitial-doping. The latter enhances the electron delocalization in the π-conjugate polymeric structure. The optimized photocatalyst shows a ∼800% increase in H₂ generation (6323 μmol h⁻¹ g⁻¹) and an about 5-fold increase in quantum efficiency (QE_{420 nm} = 5.08%). The superior performance is attributed to the long-lived shallow charge trapping, as a result of proton-feeding to the coordinated phosphorus site during the photocatalytic reaction, which enhances the photogenerated carrier lifetime and positively optimizes the band structure of the catalyst. Femtosecond transient absorption spectroscopy reveals a doubling lifetime of shallow-trapped charges (∼405.5 ps), favoring high mobility for electron-involved photocatalytic H₂ generation. This work provides a new mechanism for improving charge carrier dynamics and photocatalytic performance.