Modulating light absorption and charge recombination in photoelectrochemical water oxidation with spin-coated MoS₂ co-catalyst on ZnO nanorods

Efficient oxygen evolution reaction (OER) on a photoanode is until today considered a major challenge. In the case of ZnO, one of the most investigated semiconductors, the limitation is due to its low visible light absorption and severe charge recombination. Combining ZnO with catalytically active 2D materials such as MoS₂ has been proven to increase its water oxidation performance, but they are still often produced using complex methods. Here, we present a simple and low-cost method of spin-coating to fabricate ZnO nanorods/MoS₂ nanosheets (ZRM) heterostructures for OER photoanode. Using this method, we successfully produce heterostructures with improved performance, that is, measured photocurrent density (J_ph) of 0.61 mA cm⁻² at 1.23 V vs. RHE, about threefold than that of pure ZnO, with excellent photostability, which is on par with similar heterostructures synthesized using more complex methods. Beyond benchmarking the performance, we also unravel the mechanism by which MoS₂ improves the water oxidation process, that is, through the efficient light-harvesting (η_LHE), charge separation (η_sep), and charge injection (η_inj). Our findings provide a straightforward route to produce metal oxide/2D materials heterostructure-based photoanodes for photoelectrochemical water splitting.