Yttrium-doped barium zirconate (BZY) perovskite structured materials are the first protonic electrolytes proven to be stable for use at intermediate temperatures (450-700C) in hydrogen containing 5000 ppm H2S. Structures of materials were characterized and stability was confirmed using XRD, SEMI and EDX methods. While BZY powders and membranes are stable proton conductors in H2S-containing atmosphere, in contrast Y-doped barium cerate has poor chemical stability. The resistance of BZY, measured by impedance spectroscopy, is strongly dependent on temperature and atmosphere. Total conductivity of BZY increased with temperature in both hydrogen and dilute H2S atmospheres. (c) 2007 Elsevier Ltd. All rights reserved.