A Macroscopic Polarizable Piezocatalyst of Bismuth Selenite Fluoride Derived from BiOIO <b>3</b> with Highly Efficient Hydrogen Evolution

Abstract Piezocatalytic water splitting presents an emerging route for producing “green hydrogen” that can overcome several limitations of photocatalytic and electrocatalytic systems. However, existing piezocatalysts are few, and the insufficient polarization efficiency of these piezocatalysts is a critical obstacle to practical applications. Rational design of a macroscopic polarizable piezocatalyst from the design point of crystal structure for highly efficient hydrogen evolution is promising but still challenging. In this study, we propose a chemical cosubstitution strategy using the classic BiOIO3 with an Aurivillius-related crystal structure as the parent structure, where synergistic substitution of O2–/IO3– with F–/SeO32– yields a macroscopic polarizable piezocatalyst, bismuth selenite fluoride BiFSeO3. Systematic morphological engineering tuned by mechanical ball milling (1–4 h) revealed a volcano-shaped structure–activity relationship between H2 evolution activity and milling duration, with the 3-h milled sample (e.g., BiFSeO3-3 nanosheets) achieving the maximum rate of 1.059 mmol·g–1 h–1. Furthermore, mechanistic investigations integrating PFM, EPR, and band theory confirm the enhanced piezoelectric properties (d33 = 196 pm V–1) and strain-driven charge separation pathways in BiFSeO3-3 nanosheets.