Co-ionic (H+/O2-) electrolytes are fabricated by compositing both proton conductor (BaZr0.85Y0.15O3-delta, BZY) and oxygen-ion conductor (Nd0.1Ce0.9O2-delta, NDC) for intermediate temperature-solid oxide fuel cells (IT-SOFCs). This hybrid electrolyte decreases the electronic loss of NDC under reducing atmospheres and improves the poor sinterability of BZY. The electronic conduction caused by the NDC reduction is effectively blocked by the BZY in the composite electrolyte, thus offering both advantages of BZY with its high OCV and more rigid electro-chemo-mechanical property. In addition, the composite BZY-NDC electrolyte also exhibits great chemical stability against exposure to steam and CO2. Furthermore, the compositing of BZY and NDC improves the proton conductivity of the electrolytes, and the conductivity of composite electrolyte is higher than that of single BZY at temperatures >600 degrees C. (C) 2016 Elsevier B.V. All rights reserved.