H₂O₂ Photosynthesis from H₂O and O₂ under Weak Light by Carbon Nitrides with the Piezoelectric Effect

Driven by the essential need of a green, safe, and low-cost approach to producing H₂O₂, a highly valuable multifunctional chemical, artificial photosynthesis emerges as a promising avenue. However, current catalyst systems remain challenging, due to the need of high-density sunlight, poor selectivity and activity, or/and unfavorable thermodynamics. Here, we reported that an indirect 2e^- water oxidation reaction (WOR) in photocatalytic H₂O₂ production was unusually activated by C₅N₂ with piezoelectric effects. Interestingly, under ultrasonication, C₅N₂ exhibited an overall H₂O₂ photosynthesis rate of 918.4 μM/h and an exceptionally high solar-to-chemical conversion efficiency of 2.6% after calibration under weak light (0.1 sun). Mechanism studies showed that the piezoelectric effect of carbon nitride overcame the high uphill thermodynamics of *OH intermediate generation, which enabled a new pathway for 2e^- WOR, the kinetic limiting step in the overall H₂O₂ production from H₂O and O₂. Benefiting from the outstanding sonication-assisted photocatalytic H₂O₂ generation under weak light, the concept was further successfully adapted to biomedical applications in efficient sono-photochemodynamic therapy for cancer treatment and water purification.