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

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-Fe₂O₃) photoanodes, incorporating an acid-resistant silicon oxide (SiO_x) passivation layer and an interconnected iridium oxide (IrO_x) cocatalyst. The optimized Fe₂O₃-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., IrO₄ ^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.