CeO2 quantum dots and stepwise band alignment enhance the photoelectrochemical water splitting performance of ZnO nanotube arrays structures

This study fabricated a type-II heterojunction photoanode system via a two-step synthesis strategy, constructing ZnO/CeO 2 nanotube arrays (NTAs) heterostructures by using zinc oxide NTAs as the substrate with surface-loaded cerium dioxide quantum dots (QDs). Firstly, one-dimensional ZnO nanorod arrays (NRAs) structures were prepared via electrochemical deposition, followed by etching in an alkaline solution to fabricate ZnO NTAs. Subsequently, CeO 2 QDs were synthesized using a precipitation method and loaded onto the surface of ZnO NTAs through spin-coating, successfully fabricating ZnO/CeO 2 heterostructures. The ZnO/CeO 2 heterojunction exhibits a photocurrent density of 35 μA cm −2 in neutral electrolyte under zero bias,1.75 times that of pristine ZnO NTAs. Its hydrogen evolution rate increases from 9.9 μmol h −1  cm −2 to 12.8 μmol h −1  cm −2 , demonstrating enhanced photoelectrochemical performance. The enhancement mechanism of photoelectrochemical performance was analyzed through Mott-Schottky ((MS) measurements, X-ray photoelectron spectroscopy (XPS), and bandgap characterization. Theoretical simulations, including finite-difference time-domain (FDTD) and first-principles calculations, were employed to model surface electric field variations and photoexcited carrier transfer pathways, further elucidating the charge transfer mechanism within the heterostructure. The improved photoelectronic properties and hydrogen evolution performance were attributed to the synergistic effects between ZnO and CeO 2 QDs, including enhanced light absorption capacity, increased exposure of surface active sites, and efficient separation of photogenerated carriers driven by the type-II band alignment of the two semiconductors.