We developed nanostructured photoanodes for photoelectrochemical (PEC) water splitting and hydrogen generation. They are based on ZnO nanorods electrodeposited on conductive ITO glass on which ZnO@ZnS heterojunctions were formed using two different approaches. In the first case, the ZnO nanorods were sulfided by a prolonged contact with Na2S aqueous solution, while in the second one, they were immersed in an alcoholic solution of 2 nm sized polyol-made ZnS quantum dots (QDs). Transmission electron microscopy showed that a continuous thin layer of ZnS is formed around ZnO leading to a core@shell structure in the first case, while discrete QD aggregates were grafted at the surface of these rods leading to a kind of tologyin, in the second case. PEC properties of both composite films were measured, using a home-made electrochemical cell and illuminating the anodes with a Xenon lamp. A net enhancement of the photocurrent was observed when the ZnS coating was processed, suggesting a low carrier recombination rate, a higher efficiency toward water oxidation, and then electron transfer to the used cathode (Pt wire) for H+ reduction and H2 generation. Interestingly, the performances of the two composite films were found to be comparable, suggesting that a discrete coating of the ZnO nanorods by a small amount of preformed ZnS QDs is enough to improve their properties for the desired application.
