Dual alkali metal modulation of g-C 3 N 4 for enhanced inter-/intralayer charge transfer and O 2 activation toward efficient photocatalytic H 2 O 2 production

Abstract

Photocatalytic oxygen reduction provides a sustainable method for on-site hydrogen peroxide (H₂O₂) synthesis. However, most photocatalysts suffer from moderate kinetics due to sluggish electron transfer and inefficient oxygen adsorption and activation. Herein, sodium (Na) and potassium (K) are co-incorporated into graphitic carbon nitride (g-C₃N₄) via a stepwise co-doping strategy combining sodium chloride-induced and molten salt-assisted polymerization. Experimental results and density functional theory calculations demonstrate that the synergistic interaction between intralayer Na⁺ ions and interlayer K⁺ ions facilitates charge carrier separation and migration both within and between g-C₃N₄ layers. Additionally, multiple heteroatom sites enhance surface charge polarization and introduce cyano groups, which synergistically promote oxygen molecule (O₂) adsorption and elevate local proton coverage. Simultaneously, the energy barrier for H₂O₂ desorption on the optimal photocatalyst (5Na/3.3K-CN) is lowered, thus improving H₂O₂ production efficiency. Eventually, 5Na/3.3K-CN exhibits an impressive H₂O₂ yield of 2541.6 μmol g⁻¹ h⁻¹ in an artificial reactor, which is 10.6 times higher than that of pure g-C₃N₄ (240.2 μmol g⁻¹ h⁻¹). Under natural sunlight outdoors, 5Na/3.3K-CN still maintains ultrahigh H₂O₂ photosynthesis efficiency, achieving an H₂O₂ photosynthesis rate of 2068.7 μmol g⁻¹ h⁻¹. This work introduces a straightforward method to simultaneously optimize charge transfer and O₂ activation for boosting H₂O₂ photosynthesis, offering valuable insights toward the real-world deployment of g-C₃N₄-based photocatalysts in environmental protection and energy conversion.