Design of Z-scheme heterojunction integrated two-compartment plasmonic fabry–perot cavities array with high solar absorptivity for atmospheric pure water splitting

High charge combination and insufficient solar energy utilization are two main problems hindering the efficiency of photocatalytic hydrogen production. In this study, a two-compartment plasmonic moth-eye nanostructured Fabry-Perot (F-P) cavity integrating Z-scheme heterojunctions (TiO₂/Au-WO₃-Ag/nanohemisphere (NH)/Ag) is proposed to simultaneously reduce the charge recombination and achieve full-spectrum solar light utilization. The overall system comprises a large cavity structured from interconnected upper and under-layer F-P cavities, sharing a consistent nanostructure that facilitates plasmonic F-P enhanced Mie resonance. This design ensures the confinement of ultraviolet, visible, and infrared light within the upper cavity, broadening and intensifying light localization while exhibiting angle-insensitive characteristics. Since the Z-scheme heterojunction is positioned on the top half of the upper F-P cavity, the localized light interacts directly with the Z-scheme heterojunction (TiO₂/Au-WO₃), significantly boosting hydrogen production efficiency. As evidence, the TiO₂/Au-100 nm WO₃-Ag/NH/Ag configuration exhibits a solar absorptivity of 71.6 % and achieves H₂ production rate of 5.2 mmol·m⁻²·h⁻¹ for pure water splitting, which is 16.4 times higher than that of TiO₂/Au alone under atmospheric condition and without the use of a sacrificial agent. More noteworthy is the fact that no hydrogen peak is detected on the pristine P25 under such conditions.