Transport and Electrochemical Properties of SrFe(Al,Mo)O3–δ

Abstract

In this work, effects of molybdenum doping on the crystal structure, stability, electrical conductivity, oxygen permeability and thermomechanical properties of Sr(Fe,Al)O_3–δ-based perovskites, were studied. The electrochemical performance of model anodes of solid oxide fuel cells (SOFCs), made of SrFe_0.7Mo_0.3O_3–δ, was assessed. Whilst the introduction of Mo cations improves structural stability with respect to the oxygen vacancy ordering processes, excessive molybdenum content leads to a worse phase and mechanical stability under oxidizing conditions. Mo-doping was shown to decrease the thermal and chemical expansivity, to reduce p-type electronic conductivity and to increase n-type electronic conduction. The oxygen permeation fluxes through gas-tight Sr_0.97Fe_0.75Al_0.2Mo_0.05O_3–δ membranes are determined by both the bulk oxygen diffusion and surface exchange kinetics. The role of the latter factor increases on decreasing temperature and reducing oxygen partial pressure. Due to a relatively high electrical conductivity and moderate thermal expansion coefficients in reducing conditions, SrFe_0.7Mo_0.3O_3–δ-based anodes show a substantially high electrochemical activity.