Proton-conducting solid oxide fuel cells (SOFCs), consisting of BaCe0.7In0.3O3-�� (BCI30)-NiO anode substrates, BCI30 anode functional layers, BCI30 electrolyte membranes and BCI30-LaSr3Co1.5Fe1.5O10-�� (LSCF) composite cathode layers, were successfully fabricated at 1150 ��C, 1250 ��C and 1350 ��C respectively by a single step co-firing process. The fuel cells were tested with humidified hydrogen (���3%H2O) as the fuel and static air as the oxidant. The single cell co-fired at 1250 ��C showed the highest cell performance. The impedance studies revealed that the co-firing temperature affected the interfacial polarization resistance of a single cell as well as its overall electrolyte resistance. �� 2009 Elsevier B.V. All rights reserved.