Interfacial d‐Band Center Modulation via Si–Ir Coupling Enables Efficient and Durable Acidic Solar Water Splitting

ABSTRACT The pursuit of efficient and stable photoelectrochemical water oxidation in acidic media is impeded by issues of severe photo‐corrosion and sluggish reaction kinetics. This study presents a novel dual‐modification approach for hematite (α‐Fe 2 O 3 ) photoanodes, incorporating an acid‐resistant silicon oxide (SiO x ) passivation layer and an interconnected iridium oxide (IrO x ) cocatalyst. The optimized Fe 2 O 3 ‐Si/Ir photoanode achieves a record photocurrent density of 2.32 mA cm −2 at 1.23 V RHE in acidic electrolyte, along with exceptional stability over 60 min, significantly surpassing all previously reported hematite‐based systems under acidic conditions. A key innovation lies in the multifunctional role of the SiO x overlayer, which not only passivates surface states to improve bulk charge separation but also promotes the formation of a uniform IrO x network and inhibits over‐oxidation of Ir to soluble high valent species (e.g., IrO 4 2– ). Combined experimental and theoretical evidence reveals strong electronic interaction at the Si–Ir interface, modulating the d‐band center of Ir, enhancing interfacial charge transfer, and reducing the Gibbs free energies of the rate‐determining step in water oxidation. This work establishes a synergistic materials design strategy for highly efficient and durable solar water splitting in acidic environments, offering a viable route toward practical solar hydrogen production.