Metal-free catalyst for photocatalytic production of H₂O₂ is highly desirable with the long-term vision of artificial photosynthesis of solar fuel. In particular, the specific chemical bonds for selective H₂O₂ photosynthesis via 2e^– oxygen reduction reactions (ORR) remain to be explored for understanding the forming mechanism of active sites. Herein, we report a facile doping method to introduce boron-nitrogen (B–N) bonds into the structure of graphitic carbon nitride (g-C₃N₄) nanosheets (denoted as BCNNS) to provide significant photocatalytic activity, selectivity and stability. The theoretical calculation and experimental results reveal that the electron-deficient B–N units serving as electron acceptors improve photogenerated charge separation and transfer. The units are also proved to be superior active sites for selective O₂ adsorption and activation, reducing the energy barrier for *OOH formation, and thereby enabling an efficient 2e^– ORR pathway to H₂O₂. Consequently, with only bare loss of activity during repeated cycles, the optimal H₂O₂ production rate by BCNNS photocatalysts reaches 1.16 mmol·L^–1·h^–1 under 365 nm-monochrome light emitting diode (LED_365nm) irradiation, increasing nearly 2–5 times as against the state-of-art metal-free photocatalysts. This work gives the first example of applying B–N bonds to enhance the photocatalytic H₂O₂ production as well as unveiling the underlying reaction pathway for efficient solar-energy transformations.