Facet‐guided Photocarrier Decoupling in SrTaO 2 N Photocatalyst: A 600 nm‐Responsive Platform Toward Efficient Solar‐Driven Overall Water Splitting

ABSTRACT A crystal facet‐guided photocarrier decoupling mechanism has been identified in strontium tantalum oxynitride (SrTaO 2 N), representing a critical determinant for unlocking its intrinsic photocatalytic overall water splitting (POWS) capability. Single‐crystalline SrTaO 2 N particles with low defect density and well‐defined {202} and {001}/{110} crystal facets were successfully synthesized via a charge‐compensated, molten salt‐assisted nitridation strategy. Combined experimental and theoretical investigations confirm that this distinctive facet architecture generates an intrinsic internal electric field within the crystals, which efficiently directs the separation and unidirectional migration of photocarriers toward spatially resolved crystal facets, laying a robust foundation for the POWS performance. Upon the selective deposition of RhCrO x (H 2 ‐evolution cocatalyst) and CoOOH (O 2 ‐evolution cocatalyst) onto the corresponding crystal facets, SrTaO 2 N can stably drive POWS under both visible‐light (λ ≥ 420 nm) and simulated sunlight (AM1.5G) illumination, achieving stoichiometric H 2 and O 2 evolution (2:1 molar ratio). This study provides fundamental mechanistic insights into the structure‐activity relationship governing POWS over SrTaO 2 N, offering a rational materials‐design framework for the development of high‐performance photocatalysts toward efficient solar‐to‐hydrogen conversion.