Photocatalytic Hydrogen Evolution over Electron-Deficient Nitrogen Vacancy Engineered Graphitic Carbon Nitride Nanosheets

Abstract

Graphitic carbon nitride (g-C₃N₄) termed CN has gained significant attention as a potential candidate for photocatalytic H₂ evolution owing to its visible-light absorption and adjustable electronic characteristics. However, its performance is confined by the fast charge carrier recombination and limited active sites. Recently, vacancy engineering has been identified as an efficient strategy to alter the electronic structure, optical absorption, and charge carrier separation of CN, thereby boosting its photocatalytic performance. Herein, we employ N-(4-cyanophenyl)-glycine (referred to as NCyPG) as a precursor to derive electron-deficient nitrogen vacancy (N_v) and urea as a CN precursor to construct N_vCN-X (X = 1, 3, 5, and 7 mg of NCyPG) photocatalysts via a one-step pyrolysis. The experimental results show that N_v significantly expands optical absorption, enhances charge carrier separation and transport, and provides electron-trapping sites, thus augmenting H₂ evolution from water splitting. The best N_vCN-3 photocatalyst culminates in a maximum H₂ evolution rate of 1632.0 μmol h^–1 g^–1 upon visible light (λ ≥ 420 nm) irradiation, which surpasses that of pristine CN (327.5 μmol h^–1 g^–1) by nearly 5-fold. Additionally, stability and recycling tests show the outstanding stability of the N_vCN-3 photocatalyst over five cycles. This augmented performance is attributed to the small organic molecule-derived N_v engineering strategy, whereas N_v serves as electron-trapping sites that facilitate charge carrier separation, accelerate electron transport toward the platinum (Pt) cocatalyst, and ultimately boost the reduction of protons (H⁺) while hindering the charge recombination. This study introduces a simple and rational route for vacancy engineering to construct exceptionally effective CN-based photocatalysts for practical applications.