Sulfur‐Doping Tailors BiOI for High‐Efficiency Cocatalyst‐Free Piezocatalytic H ₂ Evolution

Piezocatalytic water splitting has emerged as a promising method for green hydrogen production, yet its efficiency typically relies on costly noble metal cocatalysts. Here, we hypothesize that tailoring the defect chemistry of a piezoelectric material can optimize its piezoelectric polarization, carrier transport, and intrinsic catalytic activity without relying on noble metals. As a proof of concept, we successfully synthesized sulfur‐substituted BiOI through a controlled anion exchange (O 2− → S 2− ) method. The optimized 10% sulfur‐substituted catalyst achieved a 2.8‐fold increase in piezocatalytic H 2 evolution activity, rising from 1.40 to 3.97 mmol·g −1 ·h −1 , matching or surpassing the performance of noble‐metal‐modified BiOI systems. Experimental and theoretical analyses confirm that this performance leap stems from enhanced piezoelectric polarization, a narrowed bandgap, accelerated charge migration, optimized H* adsorption Gibbs free energy, and enhanced water affinity. This structural engineering strategy offers an economical, noble‐metal‐free methodology for designing advanced micro/nanostructured piezocatalysts for sustainable energy conversion.