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 H and HO shows huge prospects in meeting industrial requirements. Herein, asymmetric single-unit-cell BiO(OH)(NO) 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 [BiOOH] slices and [NO] layers, resulting in larger piezoelectricity and strengthened internal electric field. It also benefits surface charge carrier decoupling and renders more favorable HO 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 H and HO kinetically and thermodynamically. An exceptional piezocatalytic H and HO production rate up to 2071.05 and 970.27 µmol g h is delivered by BON-M from pure water. It also accumulates H output of 12 429.68 µmol g 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.