Controlling ZnO nanopagoda structure enhances photoelectrochemical water splitting

Hierarchically structured ZnO nanomaterials are attracting increasing attention as photoanodes for photoelectrochemical (PEC) water splitting owing to their favorable electronic properties and large surface areas. In this study, ZnO nanopagoda arrays (NPGs) with precisely controlled architectures were successfully fabricated on FTO substrates via a two-step aqueous solution process by systematically varying the secondary growth duration. The resulting ZnO NPGs consisted of multiple stacked hexagonal nanosheets grown on vertically aligned ZnO nanorods, exhibiting high crystallinity and strong c-axis orientation. PEC measurements revealed a strong dependence of photoelectrochemical performance on the nanopagoda morphology. Among the samples, the ZnO NPGs synthesized for 4 h exhibited the highest photocurrent density under AM 1.5G illumination at 1.23 V vs. RHE, which was attributed to an optimal balance among light absorption, charge separation efficiency, carrier density, and suppressed recombination. Furthermore, finite-difference time-domain simulations confirmed enhanced light trapping and electric field distribution within the nanopagoda structures. These results highlight the critical role of precise nanostructural control in optimizing ZnO-based photoanodes and provide valuable design guidelines for high-performance PEC water-splitting systems.