Proton conducting ceramics based on acceptor doped perovskites are the subject of investigation as candidate electrolyte materials for Solid Oxide Electrolyser Cells (SOECs) that operate at intermediate temperatures. Initial work has focused on BaCe0.9Y0.1O3-delta (BCY10) and BaZr0.9Y0.1O3-delta (BZY10) as these materials have been proven to have high proton conductivities [K.H. Ryu, M. Haile, Solid State Ionics 125 (1999) 355]. Conductivity data from AC impedance spectroscopy measurements for BCY10 is in agreement with the literature. BZY10 doped with 1 wt.% ZnO was found to have a significantly lower conductivity between 200 and 600 degrees C than BCY10. BCY10 has been confirmed as a suitable electrolyte material for a reversible proton conducting solid oxide fuel cell. Large losses are observed at lower temperatures in electrolysis mode and are attributed to the slow progression of reactions at the electrodes. (c) 2008 Elsevier B.V. All rights reserved.