Piezoelectric Polarization Optimized Photocharge Separation and Surface Proton Cycling for Efficient Pure Water Splitting

The simultaneous production of hydrogen (H₂) and hydrogen peroxide (H₂O₂) from pure water represents an ideal solar-to-chemical pathway for sustainable fuel and oxidant generation. However, conventional photocatalysts face intrinsic limitations, including sluggish carrier dynamics and insufficient power for water oxidation. Herein, we unveil an intramolecular electron transfer pathway from cyano groups to hydroxyl groups in C₃N₅ that creates a high-performance piezo-photocatalyst for water splitting. The hydroxyl/cyano groups direct electron-hole flow, optimizing the surface potential and dipole moment (DM) for a stronger piezoelectric response. Interestingly, the piezoelectric polarization induced by mechanical strain in MCN-8 enhances its H⁺ desorption ability to facilitate a rapid adsorption-reaction-desorption process. In situ infrared spectroscopy results indicate that MCN-8 generates key substances such as ·O₂ ^- and ·OOH, clarifying the water oxidation process. Thus, the rates of H₂ and H₂O₂ release by its piezo-photocatalysis were 4.14 mmol g^-1 h^-1 and 1.39 mmol g^-1 h^-1, respectively. Under simulated outdoor sunlight and ultrasonic conditions, the as-fabricated MCN-8/PVDF-HFP composite film retains its ability to produce H₂ and H₂O₂. This strategy of enhancing the piezo-photocatalytic performance through surface group modulation provides a new idea for the development of highly efficient and multifunctional water decomposition catalysts.