Vertically aligned MoS2 flakes were grown on indium tin oxide (ITO) and ITO/ZnO substrates using metalorganic chemical vapor deposition. The thickness of MoS2 flakes was manipulated at the few-layer level (5-10), which is desirable for energy-storage and energy-conversion applications. For photoelectrochemical (PEC) cells, a few-layer flake photoelectrode yielded a considerably higher photocurrent density (930 mu A/cm(2) at 0.2 V) than a MoS2 thin-film photoelectrode (360 mu A/cm(2) at 0.2 V) due to the former's high density of active sites, slow intraband relaxation rate from excitonic states, and low defect density. Furthermore, the heterostructure of ZnO/MoS2 flakes exhibited a remarkably high photocurrent density of 1.6 mA/cm(2) at 0.2 V and a long-term stability under the PEC operating conditions because of its enhanced photogenerated carrier separation and transfer. Thus, such a heterostructure is promising as an efficient, nontoxic, inexpensive, and earth-abundant PEC electrode. (c) 2017 Elsevier Ltd. All rights reserved.