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

Abstract

<p>Efficient photocatalytic solar-to-H<small>₂</small> conversion is pivotal to zero-carbon energy supply. Graphitic carbon nitride (g-C<small>₃</small>N<small>₄</small>) 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 H<small>₂</small> generation (6323 μmol h<small>⁻¹</small> g<small>⁻¹</small>) and an about 5-fold increase in quantum efficiency (QE<small>_{420 nm}</small> = 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 H<small>₂</small> generation. This work provides a new mechanism for improving charge carrier dynamics and photocatalytic performance.<br></p>