Development of All‐Solid‐State Sputtered S‑Scheme Heterojunction Photoanode for Stable and Efficient Solar‐Driven Water Oxidation

Scalable, clean hydrogen production via photoelectrochemical (PEC) water splitting is limited by poor light absorption and rapid charge recombination. Here, we report a rationally designed, all‐solid‐state plasmon‐coupled S‐scheme heterojunction photoanode, MoSe 2 /Au/TiO 2 , fabricated entirely through a scalable magnetron sputtering technique. The Initial MoSe 2 /TiO 2 S‐scheme heterojunction enhances light harvesting and achieves a photocurrent density of ∼0.25 mA/cm 2 at 1.23 V rhe , supported by a surface photovoltage of 223 mV and a carrier lifetime of 0.2 s. The strategic introduction of an ultrathin Au interlayer profoundly modifies the interface. This Au mediator established a stronger built‐in electric field, a more favorable band alignment, maintained high redox potentials, enhanced light absorption, and improved photo‐charge separation with transfer. This engineered MoSe 2 /Au/TiO 2 heterojunction photoanode delivers a markedly superior performance, with a photocurrent density of ∼0.54 mA/cm 2 at 1.23 V rhe , a high surface photovoltage of 293.7 mV, and a prolonged carrier lifetime of 0.55 s, while maintaining stable operation over 6.5 h. Comprehensive experimental analysis, including in situ photoelectrochemical studies and spectroscopic characterization, systematically unveils the Au‐mediated S‐scheme mechanism, highlighting enhanced charge separation, reduced interfacial resistance, and preserved high redox potentials. This work establishes a scalable, robust S‐scheme architecture for efficient solar‐driven hydrogen generation.