Bi Off‐Centering in Centrosymmetric BiOBr Leading to Ultrahigh Bifunctional Piezocatalytic Fuel Generation Efficiencies in Seawater

Abstract Piezocatalytic water‐splitting to simultaneously produce H 2 and H 2 O 2 has many potential advantages. However, the necessity to utilize materials having polar structures limits the choice of piezocatalysts. Herein, it is demonstrated that centrosymmetric BiOBr with oxygen defects can simultaneously produce H 2 and H 2 O 2 with ultrahigh efficiencies from pure and seawater without needing assistance from noble metals or scavengers. High‐pressure studies confirm that there are no non‐polar‐to‐polar phase transitions in BiOBr, though a novel isostructural phase is discovered. Computational studies reveal that oxygen vacancy distorts the BiOBr structure to induce charge‐localization and polarization. Furthermore, high pressure (i) reduces carrier effective masses and (ii) increases relative O‐2 p contribution in the valence band maximum to assist catalysis and improve stability. The role of oxygen vacancy is confirmed by changing its concentration, which proportionally affects H 2 evolution. The work paves the way for defect engineering to develop piezocatalysts from a large pool of non‐polar materials.