Unraveling the dipole field in ultrathin, porous, and defective carbon nitride nanosheets for record-high piezo-photocatalytic H2O2 production

Piezo-photocatalysis is capable of concerting mechanical vibration into chemical energy, portraying a promising alternative technology for H₂O₂ production. However, low mechanical energy conversion efficiency and constrained surface active sites hinder its practical application. Herein, ultrathin porous carbon nitride nanosheets with controlled carbon vacancies and oxygen doping (OCN-X, where X represents the calcination temperature) are synthesized by thermal oxidation etching to achieve unprecedented piezo-photocatalytic H₂O₂ production. The carbon vacancies and oxygen doping cause the formation of asymmetric structure of triazine unit with a strong dipole field, which creates spontaneous polarization field to speed up directional electron transfer to the nitrogen active sites for effective piezo-photocatalysis. Meanwhile, the ultrathin and porous structure formed by hot-oxygen etching enhances the mechanical energy conversion efficiency and collaboratively induces adsorbed oxygen via indirect two-electron oxygen reduction reaction (ORR) transfer pathway to effectively produce H₂O₂. Consequently, without any co-catalysts, the as-prepared OCN-460 displays record-high piezo-photocatalytic H₂O₂ production rate of 19.30 ​mmol ​g⁻¹ ​h⁻¹, far outdistancing those previously reported for piezo-photocatalysts. Furthermore, it also still maintains a notable piezo-photocatalytic activity of 2.87 ​mmol ​g⁻¹ ​h⁻¹ in the pure water system. This work offers some new insights for the future design of an effective piezo-photocatalytic H₂O₂ production system.