Synergistic Defect-Piezoelectric Modulation of C₃N₅ for Scalable On-Site Hydrogen Production

We present a precursor-directed precision synthesis of defect-engineered carbon nitride (C₃N₅) for efficient piezo-photocatalytic hydrogen (H₂) production. By finely tuning the ratio of 3-amino-1,2,4-triazole (3AT) to thiourea, we achieve a selective triazine-ring reduction that introduces intrinsic nitrogen defects with atomic-level control. X-ray photoelectron spectroscopy confirms a systematic decrease in N₂C contributions, evidencing precisely regulated defect formation. These tailored defects expand the surface area and porosity, enhance charge separation, and disrupt lattice symmetry, thereby inducing a pronounced piezoelectric response. Under simultaneous solar and ultrasonic excitation, the optimized composition (3AT:thiourea = 4:1) achieves an exceptional hydrogen evolution rate of 4769 μmol g^-1 h^-1, outperforming most reported carbon nitride systems. This work establishes a precision defect-piezoelectric modulation framework that links molecular-level design to macroscopic catalytic efficiency, offering a scalable and metal-free strategy for decentralized hydrogen production in sustainable energy applications.