Asymmetric Single-Unit-Cell Layer Enriching Polar Inherent Hydroxyls Eliminates Interlayer Electric Field Shielding Effect and In Situ Self-Polarize for Piezocatalytic Water Splitting

Piezocatalytic two-electron water splitting into spontaneously isolated H₂ and H₂O₂ shows huge prospects in meeting industrial requirements. Herein, asymmetric single-unit-cell Bi₂O₂(OH)(NO₃) monolayer (BON-M) with superb force-sensitivity are developed for pure water and seawater dissociation. The formation of a monolayer structure allows sufficient exposure of polar inherent hydroxyls and eliminates the interlayer electric field screening induced by hydrogen bonding between [Bi₂O₂OH] slices and [NO₃] layers, resulting in larger piezoelectricity and strengthened internal electric field. It also benefits surface charge carrier decoupling and renders more favorable H₂O molecules adsorption and H^* desorption. Particularly, the mechanical strain can induce the in situ self-polarization of BON-M, which further enhances electric field intensity and reduces energy barriers of H^* desorption and key intermediate ^*OH formation, facilitating water splitting to H₂ and H₂O₂ kinetically and thermodynamically. An exceptional piezocatalytic H₂ and H₂O₂ production rate up to 2071.05 and 970.27 µmol g^-1 h^-1 is delivered by BON-M from pure water. It also accumulates H₂ output of 12 429.68 µmol g^-1 within 8 h from seawater splitting, along with mechanical-to-hydrogen efficiency of 0.15%. This work develops an effective strategy for exploiting high-performance piezocatalyst by building ultrafine nanostructure enriched with inherent polar groups on the surface.