Surface defect engineering and MOF derivatives regulate the electron transport pathway of polymeric carbon nitride for an efficient photocatalytic 2e− oxygen reduction reaction to form H2O2

Abstract

The photocatalytic two-electron oxygen reduction reaction (2e⁻ ORR) for H₂O₂ production remains a promising alternative to the industrial anthraquinone process, but it is limited by a high carrier recombination rate and a lack of reactive sites. Herein, surface defect sites (N vacancies) and electron bridges on graphite-phase carbon nitride (g-C₃N₄) are designed by regulating KCl and 2D Zn-MOF-NH₂ to overcome these limitations and enhance the separation and transfer of photogenerated carriers. The N vacancies also work as active sites, promote O₂ adsorption and activation, and thereby synergistically improve the activity and selectivity of H₂O₂ production. K-CZ-2 achieves an H₂O₂ yield of 7.8 mmol g⁻¹ h⁻¹ via a 2e⁻ ORR, with a 1.5-fold and 19.6-fold improvement compared to those of K-C₃N₄-like and g-C₃N₄, respectively, surpassing previously reported CN-based photocatalysts. K-CZ-2 also exhibits an apparent quantum yield (AQY) of 3.08% at 420 nm and a solar-to-chemical energy conversion (SCC) efficiency of 0.63%. Characterization and theoretical calculations reveal that the N vacancies and electron bridges optimize the photoelectronic response and the surface reaction process from O₂ to H₂O₂ in K-CZ-2, thereby accelerating H₂O₂ generation. This work provides a simple method that simultaneously increases photogenerated carrier transfer and active sites for high-performance H₂O₂ production.