Boosting Piezoelectric Catalytic H ₂ O ₂ Production in Pure Water of Graphitic Carbon Nitride via Defect Engineering With Tunable Oxygen‐Doping

Piezocatalytic conversion of mechanical energy into chemical energy offers a sustainable route for hydrogen peroxide (H₂O₂) synthesis. However, its practical application is hampered by low polarization intensity, charge recombination, and the requirement of sacrificial agents. Herein, we report a one-step co-calcination strategy to introduce tunable oxygen defects into graphitic carbon nitride (g-C₃N₄), enabling efficient sacrificial-agent-free piezocatalysis in pure water. The optimized sample (CN-40) delivers a remarkable H₂O₂ yield of 671 µmol g^-1 h^-1, four times higher than pristine g-C₃N₄, surpassing most reported metal-free piezocatalysts. Structural analyses reveal that oxygen incorporation disrupts the tri-s-triazine symmetry, enhances lattice distortion, and strengthens piezoelectric polarization. Electrochemical and spectroscopic studies confirm the increased carrier density, reduced charge-transfer resistance, and generation of reactive oxygen species under ultrasonic excitation. Band structure analysis and COMSOL simulations further clarify the synergistic mechanism of single-electron water oxidation and oxygen reduction reactions. This work demonstrates a defect-engineering strategy to overcome intrinsic limitations of g-C₃N₄, providing both mechanistic insights and practical solutions for green chemical synthesis and environmental remediation.