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

Abstract

In 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.

Integration of Oxide Anodes into the Rolls‐Royce IP‐SOFC Concept

“…Of course, the fact that this layer also contains porosity is also helpful in this respect as this will provide some free volume in which this chemical volume change can also be accommodated. This is in agreement with recent studies which suggested that when the electrochemical function of the anode is separated from the requirements of current collection and support, higher volumetric changes can be tolerated in a thin, porous anode layer that would be allowed in a thicker combined anode support of similar material [18]. This review suggested that anode volume changes up to 1% could be tolerated in such a scenario and is exactly the situation described above for this development of the IP-SOFC.…”

Electrical Properties of Sr0.86Y0.08TiO3 Under Redox and Full Cell Fabrication Conditions

“…The changes of conductivities show noticeable parabolic time dependence features, which was also reported in Petric et al's study [9]. Two processes in series have been proposed for the reduction reactions, the gas solid interface reaction and bulk diffusion [9,15]. The behavior showed in Fig.…”

Synthesis, Structure and Electrical Properties of Mo‐doped CeO2–Materials for SOFCs

“…Among the various anode materials investigated, CeO 2 based materials are also being considered due to their excellent electro-catalytic activity on various fuels (e.g. H 2 , CH 4 ) as a result of mixed ionic and electronic conduction [16,20,23,30]. The excellent catalytic activity for fuel oxidation stems from the oxygen-vacancy formation and migration associated with reversible CeO 2 -Ce 2 O 3 transition [31][32][33][34].…”