B site doped strontium titanate as a potential SOFC substrate

Abstract

Abstract. Excellent thermal and mechanical stability coupled with low cost have attracted interest in the application of the cubic perovskite SrTiO~ as a substrate material in supported SOFC designs. For such designs increased substrate conductivity is beneficial. A method of improving conductivity is by cation substitution. Due to the constraint of electro-neutrality, oxygen ion vacancies can be generated in strontium titanate by successful substitution of tetra-valent titanium ions with divalent metal ions (M) to produce materials of stoichiometry SrTi~, ~,M~O,3~. By raising the intrinsic oxygen vacancy concentration in this manner there is an increase in available hopping sites. The increase in vacant sites facilitates oxygen transport through the crystal hence increases the potential for oxide ion conductivity. The synthesis of such materials was carried out by standard solid-state techniques using calcium and magnesium as dopants. B site solubility limits for both species were obtained by powder X-ray diffraction. The conductivity behaviour of successful phase pure compounds was investigated using AC impedancc spectroscopy and four point DC measurements across a range of pO., values. The B site solubility limit for magnesium was found to lie between 5 and 7 %. SrTi,~sMg~r,5029s exhibited increased conductivity and a~ducoJ activation energy for conduction as compared to undopcd strontium titanate. DC measurements lbr the same material confirmed the increased p-type behaviour of the system associated with magnesium doping at high oxygen partial pressures. IntroductionSolid oxide l~hcl cells (SOFCs) are currently at the forefront of research into new generations of energy conversion systems owing to their high efficiency, versatility and environmentally friendly nature. Considerable attention has been focused on these systems, particularly on the electrode front, where materials with improved propcrties are being sought. This study is part of a more general goal to develop new anode materials and designs which negate the problems associated with the current Ni/YSZ cermet anode; notably sintering of Ni at operating temperatures, and coking and sulphur poisoning when using natural gas as fuel [1 ].Perovskites oxide materials possess general stoichiomerry ABO~. Conventionally the A cation is larger than the B cation. In the archetype the A cation has an oxidation state of +2 and the B cation has oxidation state +4. These materials comprised of 3 different ionic species,

Chemical Environment-Induced Mixed Conductivity of Titanate as a Highly Stable Oxygen Transport Membrane

“…This value is approximately one order of magnitude higher than that of undoped SrTiO 3 membrane exposed to air/argon p O 2 gradient at 1000°C (Schulze-Küppers et al., 2015), indicating the positive influence of Mg and/or Zr doping on oxygen permeability of SrTiO 3 . This observation can be supported by the increased electrical conductivity and reduced activation energy for oxygen transport through Mg-doped SrTiO 3 as compared with undoped SrTiO 3 (Inoue et al., 1991, McColm and Irvine, 2001). However, the oxygen permeation flux of such titanate-based membrane is still too low under high p O 2 because of the presence of air.…”

Structure and properties of MgMxCr2−xO4 (M = Li, Mg, Ti, Fe, Cu, Ga) spinels for electrode supports in solid oxide fuel cells

“…Relative densities of measured pellets were 55-70 % dense, while the sample MnFeCrO 4 had a relative density of 80 %. The experimental setup is described in ref 40 . Table 1.…”

The role of defect chemistry in strontium titanates utilised for high temperature steam electrolysis

“…The electrical properties of the undoped parent perovskite SrTiO 3 were not determined as part of this study, however this material is a known n-type conductor under reducing conditions. 33 The observed n-type conductivity of both (La,Sr)TiO 3 perovskites confirmed the suitability of these materials for the highly reducing environment, both electrochemically and chemically, encountered at the electrolysis cell cathode during steam electrolysis.…”