Chemical compatibility of proton conducting LaNbO4 electrolyte with potential oxide cathodes

The chemical and physical compatibility of the proton conducting electrolyte material LaNbO4 with the potential partner materials LaMO3 (MMn, Fe, Co) and La2NiO4 is investigated via the reaction of fine-grained powders and solid-state diffusion couples. Results show generally good chemical compatibility for LaNbO4 with perovskite type compositions, particularly the LaFeO3 and LaMnO3 systems. In contrast, Ruddlesden–Popper type phases are predicted to be poor candidates for use with LaNbO4. Investigation of the La2O3–NiO–Nb2O5 and La2O3–CoO–Nb2O5 phase diagrams finds two new perovskite-related materials of stoichiometry LaNb1/3M2/3O3 (MNi, Co), and indicates coexistence of LaNbO4 with the binary oxides NiO and CoO. Additionally, reduction of a LaNbO4–NiO composite confirms coexistence of LaNbO4 with Ni, and so it is concluded that doped-LaMO3|LaNbO4|Ni-LaNbO4 type electrochemical cells may be manufactured via a direct co-firing route without the formation of secondary phases at inter-phase boundaries.