Besides their application in photovoltaics, semiconductor solar-energy-materials can be directly employed as photocatalysts of hydrogen fuel production using sunlight and water feedstock. In this paper, through a facile hydrothermal route, we synthesized a CuO-ZnO pn junction nanocomposite in the absence and presence of carbon nanotube (CNT), and applied them in a water photosplitting setup to evolve hydrogen gas. The investigation revealed that in the presence of CNT, the photocatalyst performance increases significantly becomes approximately twice. The superior activity witnessed here for the ternary nanocomposite (CuO-ZnO/ CNT) was explained in terms of the ability of CNT to enlarge the photocatalyst surface area, enhance the absorption of photons, and prohibit the recombination of photogenerated e/h pairs. Finally, quantum yield and energy efficiency analyses were performed on both binary and ternary nanocomposite materials as well as on their semiconductor components, and the results were discussed in detail from physicochemical viewpoint.