Enhanced charge separation at coherent semiconductor/substrate Interface in oxygen vacancy-enriched ZnO Nanorods decorated SnO2 inverse opal skeletons Photoanode.

Efficient extraction of photogenerated electrons across the semiconductor/conductive-substrate interface is essential for photoelectrochemical (PEC) water oxidation, yet this interface is often less considered than bulk and surface charge-transfer processes. Herein, oxygen-vacancy-enriched ZnO nanorods (Ov-ZnO NRs) were grown on three-dimensionally ordered SnO2 inverse-opal skeletons to construct a hierarchical SnO2 IOs/Ov-ZnO photoanode. The interconnected SnO2 inverse opal simultaneously provides a conductive framework and enhances light harvesting through multiple scattering and slow-photon effects, while its crystallographic compatibility with the FTO substrate alleviates electron-transfer losses at the semiconductor/substrate interface. The one-dimensional Ov-ZnO NRs provide short carrier-transport pathways, a large electrode/electrolyte contact area, and defect-mediated active sites for water oxidation. The optimized photoanode delivered a photocurrent density of 1.13 mA cm-2 at 1.2 V vs. RHE, approximately 3.3 times that of the flat SnO2/ZnO NRs reference (0.34 mA cm-2), together with an applied-bias photon-to-current efficiency of 0.274% at 0.80 V vs. RHE. Its bulk charge-separation and surface charge-injection efficiencies reached 53.3% and 71%, respectively, at 1.2 V vs. RHE. Spectroscopic, electrochemical, and density functional theory analyses collectively indicate enhanced interfacial charge redistribution, lower charge-transfer resistance, and more favorable OER energetics. These results establish the coordinated engineering of the conductive substrate interface, photonic architecture, and oxygen-vacancy defects as an effective strategy for improving ZnO-based PEC photoanodes.