The pairing of proton conducting electrolytes with chemically compatible electrode materials is key to their use in electrochemical devices. The reactivity of BaZrO3 with respect to the well known ceramic oxides LaMnO3, LaFeO3, LaCoO3 and La2NiO4 has been investigated with a view to the development of chemically inert cathode materials. Annealing of powder mixtures of the candidate electrode and BaZrO3 showed only formation of small quantities of La2Zr2O7 as a secondary phase. The low level of reaction and good chemical compatibility were further evidenced by diffusion couples of electrode I electrolyte. Only minor inter-diffusion of Ba and La was observed. However, the materials show considerable mismatch in thermal expansivity, resulting in detachment of the electrode from the electrolyte on cooling. These results have predictive relevance across a wider range of systems, and indicate that co-existence can be achieved with careful balancing of chemical activity via chemical substitution. (C) 2007 Elsevier B.V. All rights reserved.