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

Abstract Piezocatalytic two‐electron water splitting into spontaneously isolated H 2 and H 2 O 2 shows huge prospects in meeting industrial requirements. Herein, asymmetric single‐unit‐cell Bi 2 O 2 (OH)(NO 3 ) 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 [Bi 2 O 2 OH] slices and [NO 3 ] layers, resulting in larger piezoelectricity and strengthened internal electric field. It also benefits surface charge carrier decoupling and renders more favorable H 2 O 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 2 and H 2 O 2 kinetically and thermodynamically. An exceptional piezocatalytic H 2 and H 2 O 2 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 H 2 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.