C/N Vacancy Co‐Enhanced Visible‐Light‐Driven Hydrogen Evolution of g‐C₃N₄ Nanosheets Through Controlled He⁺ Ion Irradiation

Graphitic carbon nitride (g‐C₃N₄) is reported to be a promising metal‐free semiconductor for photocatalytic water splitting. However, the performance of g‐C₃N₄ is substantially limited by its insufficient visible‐light absorption and low photogenerated charge carrier separation efficiency. In this work, an innovative method (ion irradiation) to efficiently introduce both defined C‐ and N‐vacancies (V_C and V_N) simultaneously into g‐C₃N₄ nanosheets are explored. Unlike traditional chemical methods, by controlling He⁺ ion fluence, tunable vacancy concentrations are able to be obtained in g‐C₃N₄. Defect‐engineered g‐C₃N₄ shows highly improved performance under optimized conditions, the defective g‐C₃N₄ exhibits a significantly higher (2.7‐fold) hydrogen evolution rate of 1271 µmol g⁻¹ h⁻¹ than that of the g‐C₃N₄ nanosheets under visible light (λ > 420 nm) illumination. Meanwhile, the defective g‐C₃N₄ exhibits a significantly enhanced (threefold) photocurrent density as photoanodes for photoelectrochemical (PEC) water splitting. Further characterizations show that the enhanced visible light absorption and an extended charge carrier lifetime, can be ascribed to the presence of C‐ and N‐ vacancies. These experimental results are in line with density functional theory (DFT) calculations. Therefore, the present work shows that defect‐engineering on g‐C₃N₄ using ion irradiation technique, is an effective, controllable, and defined approach to improve the photocatalytic and PEC water splitting performance of g‐C₃N₄.