Core-shell p-CuO/n-ZnO heterojunction nanocomposites were synthesized by microstructural refinement and solid-state reactions using a non-equilibrium technique. This nanocomposite was found to serve significantly as an electrode material for photoelectrochemical (PEC) energy conversion in 0.5 M polysulfide (Na2Sx) redox couple which showed an efficiency of about 6.12%. This might be due to the broadband absorption of incident irradiation and mutual transfer of electrons and holes in the p-CuO/n-ZnO heterojunction which also minimizes charge recombination, thereby improving the efficiency. N-2-sorption analyses showed mesoporous nature of the synthesized material. Energy Dispersive X-ray Spectroscopy (EDX) showed almost no change in the composition of the composite after milling. Cyclic voltammetry and electrochemical impedance spectroscopy of the photoanode in presence of the polysulphide solution were also carried out to understand the redox and interfacial properties of the PEC cell. (C) 2016 Elsevier Ltd. All rights reserved.