Compromising Between Phase Stability and Electrical Performance: SrVO₃–SrTiO₃ Solid Solutions as Solid Oxide Fuel Cell Anode Components

Abstract

The applicability of perovskite‐type SrVO3−δ in high‐temperature electrochemical energy conversion technology is hampered by the limited stability domain of the perovskite phase. The aim of the present work was to find a compromise between the phase stability and electrical performance by designing solid solutions in the SrVO3–SrTiO3 system. Increasing titanium content in SrV1−yTiyO3−δ (y=0–0.9) perovskites is demonstrated to result in a gradual shift of the upper‐p(O2) phase stability boundary toward oxidizing conditions: from ≈10−15 bar at 900 °C for undoped SrVO3−δ to ≈10−11–10−5 bar for y=0.3–0.5. Although the improvement in the phase stability is accompanied by a decrease in electrical conductivity, the conductivities of SrV0.7Ti0.3O3−δ and SrV0.5Ti0.5O3−δ at 900 °C remain as high as 80 and 20 S cm−1, respectively, and is essentially independent of p(O2) within the phase‐stability domain. Combined XRD, thermogravimetric analysis, and electrical studies revealed very sluggish kinetics of oxidation of SrV0.5Ti0.5O3−δ ceramics under inert gas conditions and a nearly reversible behavior after exposure to an inert atmosphere at elevated temperatures. Substitution by titanium in the SrV1−yTiyO3−δ system results also in a decrease of oxygen deficiency in perovskite lattice and a favorable suppression of thermochemical expansion. Variations of oxygen nonstoichiometry and electrical properties in the SrV1−yTiyO3−δ series are discussed in combination with the simulated defect chemistry of solid solutions.

Development of Ni-Sr(V,Ti)O3-δ Fuel Electrodes for Solid Oxide Fuel Cells

“…XRD analysis confirmed that both as-synthesized STVN powders (1200 °C, 30 h) and sintered STVN ceramics (1450 °C, 10 h) comprised a Sr 1- a Ti 1- b V b O 3-δ solid solution with a cubic perovskite-type lattice (space group ) isostructural to the parent SrTiO 3 and SrVO 3 , and a fraction of metallic nickel phase. In agreement with the data on the Sr(Ti,V)O 3-δ system [ 34 , 48 ], the unit cell parameter of the perovskite phase shows a tendency to decrease with increasing vanadium content ( Table 1 ), which is consistent with the values of ionic radii for six-fold coordinated V 4+ and Ti 4+ (0.58 Å and 0.605 Å, respectively [ 49 ]). The only exception to this trend is S96V40N8, the sample with the highest nickel content.…”

“…The representative examples for the selected samples are depicted in Figure 4 . Similar to SrTi 1- y V y O 3-δ series [ 34 ] and other SrVO 3-δ -based materials [ 14 , 15 , 22 ], increasing deviation from the linear thermal expansion at higher temperatures can be partly attributed to a minor contribution of chemical expansion associated with the variable oxygen content in the perovskite lattice.…”

“…A reasonable compromise between high electrical conductivity and phase stability can be reached by balancing the fractions of vanadium and titanium cations in the B sublattice [ 11 , 34 ]. In particular, SrV 1- y Ti y O 3-δ solid solutions with moderate titanium content (0.3 ≤ y ≤ 0.5) showed electrical conductivity ≥ 20 S/cm at temperatures ≤ 900 °C, combined with a phase stability domain extended up to p(O 2 ) of at least 10 −11 atm at 900 °C [ 34 ]. In addition, increasing the titanium content was found to gradually suppress thermochemical expansion, thus improving the thermomechanical compatibility with solid electrolyte ceramics [ 34 ].…”

“…In particular, SrV 1- y Ti y O 3-δ solid solutions with moderate titanium content (0.3 ≤ y ≤ 0.5) showed electrical conductivity ≥ 20 S/cm at temperatures ≤ 900 °C, combined with a phase stability domain extended up to p(O 2 ) of at least 10 −11 atm at 900 °C [ 34 ]. In addition, increasing the titanium content was found to gradually suppress thermochemical expansion, thus improving the thermomechanical compatibility with solid electrolyte ceramics [ 34 ].…”

“…To this end, the general cation composition was formulated as Sr 1- α Ti 1- β (1+γ) V β Ni βγ O 3-δ (STVN) and particular compositions were selected employing Taguchi-type experimental planning [ 47 ]. Based on previous results [ 34 ], the vanadium content was kept at 20–40 at.%. The experimental procedure relied on the conventional solid-state reaction route in reducing atmospheres combined with mechanical activation.…”