Cermet (ceramic-metal composite) hydrogen separation membranes consisting of barium oxide, cerium oxide, yttrium oxide and palladium were characterized by utilizing X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy/ energy dispersive spectroscopy (SEM/EDS). Characterization was performed at room temperature and 650 degreesC, and after exposure to hydrogen. Changes in both elemental composition and oxidation states were observed at elevated temperatures and as a function of time. Permeation of hydrogen through the membranes also changed with time and temperature. (C) 2003 Elsevier Science B.V. All rights reserved.