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

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.