Ceramic‐based Anode Materials for Improved Redox Cycling of Solid Oxide Fuel Cells

Abstract

AbstractIn order to improve the reliability of anode‐supported solid oxide fuel cells (SOFCs) in terms of tolerance to redox cycles, and to minimise fuel preprocessing for the direct use of readily available hydrocarbons in SOFCs, alternative ceramic‐based anode substrate materials and functional anode materials were investigated, with the emphasis on perovskite oxides. Compared to (Sr,La)TiO3–δ and Nb2TiO7–δ, (Sr,Y)TiO3–δ ceramics (SYT, with a Y content of about 7 at.‐%) reduced at high temperatures are promising redox‐stable anode substrate materials due to their very small dimensional change upon redox cycling (0.14%). Correspondingly, the composite ceramic SYT/YSZ impregnated with ∼5 vol.‐% Ni has a good chance of being applied as a redox‐stable functional anode material due to its even smaller dimensional change upon redox cycling (<0.05%) and superior electrochemical performance for H2 oxidation (polarisation resistance ∼0.2 Ω cm2 at 800 °C). The small fraction of Ni homogeneously dispersed on the pore walls of the SYT/YSZ ceramic framework significantly enhances the electrocatalytic activity, and should not have a detrimental effect on the redox stability of the electrode. In addition, two mixed conductors with perovskite structure, (La0.8Sr0.2)0.94Al0.5Mn0.5O3–δ and La0.4Sr0.6Ti0.4Mn0.6O3–δ, were also investigated. They show promising electrochemical performance for the oxidation of H2. However, the high‐level Mn substitution which seems necessary to achieve a significant electrical conductivity and catalytic activity has a detrimental effect on the chemical stability of these two materials. Consequently, they show relatively large and irreversible chemical expansion and are thus not considered to be qualified functional anode materials.