The flower-shaped ZnO was synthesized to form composite with the delafossite structure CuFeO2. The composite heterojunction formed for the ZnO-CuFeO2 composite material demonstrates a profound significance for exploring novel materials in solid oxide fuel cell (SOFC) field. At 550 degrees C, power outputs of 300 mW cm(-2) and 468 mW cm(-2) were achieved for SOFC devices using pure ZnO and composite with CuFeO2 as the electrolytes, respectively. The composite showed a good performance at low temperatures, for instance, it showed a power output of 148 mW cm(-2) at 430 degrees C. The studies on photocurrent-time curves with visible light on/off irradiation provided an evidence for electron-hole separation. The heterojunctions separate holes and electrons, preventing short-circuiting while used in the SOFC device. These results demonstrate that introducing the heterojunctions in the electrolyte is an innovative approach for advanced SOFCs. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.