Enhanced electron delocalization in potassium poly(heptazine imide) triggered by indium sites and nitrogen defects promotes highly efficient H2O2 photosynthesis
Polymeric carbon nitride (PCN) is a promising photocatalyst for H2O2 production due to its visible-light response, low cost, and high selectivity for the two-electron oxygen reduction reaction (ORR). However, its H2O2 yield is limited by narrow light absorption, low charge separation efficiency, and insufficient active sites. Here, crystalline poly(heptazine imide) (PHI)-based carbon nitride with highly dispersed In sites and N defects was prepared via an ionothermal method using LiCl/KCl molten salts. The large π-conjugated system and N defects enhance visible-light harvesting. Remaining K+ ions in nitrogen cavities act as interlayer electron channels, while N defects induce asymmetric charge distribution on the heptazine network, promoting interlayer and in-plane charge separation and transfer. In sites accelerate charge transfer dynamics and serve as active sites for ORR. The synergistic effect of metal modification and defect engineering boosts electron delocalization, significantly improving photocatalytic activity. The H2O2 production rate of 10InPHI reaches 15.3 mmol g−1 h−1 via a two-step single-electron ORR pathway, underscoring the potential of modified carbon nitride for efficient H2O2 photosynthesis.