Chemical compatibility of proton conducting LaNbO 4 electrolyte with potential oxide cathodes

Abstract

The chemical and physical compatibility of the proton conducting electrolyte material LaNbO 4 with the potential partner materials LaMO 3 (M Mn, Fe, Co) and La 2NiO 4 is investigated via the reaction of fine-grained powders and solid-state diffusion couples. Results show generally good chemical compatibility for LaNbO 4 with perovskite type compositions, particularly the LaFeO 3 and LaMnO 3 systems. In contrast, Ruddlesden–Popper type phases are predicted to be poor candidates for use with LaNbO 4. Investigation of the La 2O 3–NiO–Nb 2O 5 and La 2O 3–CoO–Nb 2O 5 phase diagrams finds two new perovskite-related materials of stoichiometry LaNb 1/3M 2/3O 3 (M Ni, Co), and indicates coexistence of LaNbO 4 with the binary oxides NiO and CoO. Additionally, reduction of a LaNbO 4–NiO composite confirms coexistence of LaNbO 4 with Ni, and so it is concluded that doped-LaMO 3|LaNbO 4|Ni-LaNbO 4 type electrochemical cells may be manufactured via a direct co-firing route without the formation of secondary phases at inter-phase boundaries.