The catalytic activity of metals (Ni and Cu) for CH4 decomposition was compared in the mixture of CH4, D2O (heavy water), and O-18(2) (stable isotope of oxygen) by image analysis of secondary ion mass spectrometry (SIMS). Annealing of samples was conducted in the stable isotopes of O-18(2) and D2O to label the movements of oxygen and hydrogen at high temperature (1073 K). Mesh-shaped electrode/Y2O3-stabilized ZrO2 samples were adopted to determine the gas/electrode/electrolyte interfaces in a submicrometer level. On the mesh electrode surfaces (Ni and Cu), thin oxide layers were formed, and the oxide layers were active for isotope oxygen exchange. On the Ni surface, diffusion of D and/or exchange of H/D occurred within 20 nm in depth. Carbon deposition occurred on the Ni surface, whereas no carbon deposition was observed on the Cu surface. (C) 2004 Elsevier B.V. All rights reserved.