Enhanced stability of perovskite-like SrVO3-based anode materials by donor-type substitutions

Abstract

Strontium vanadate-based perovskites are considered as promising anode materials for hydrocarbon-fueled solid oxide fuel cells due to high electronic conductivity, sulfur tolerance and resistance to coking, but possess a narrow phase stability domain precluding their use in practice. This study aimed at expanding the perovskite phase stability domain by donor-type substitutions focusing on Sr_0.8Ln_0.2V_1−yNb_yO_3−δ (Ln = La or Y, y = 0–0.10) solid solutions. The upper-p(O₂) stability boundary at 900 °C was found to shift from ∼10⁻¹⁵ atm for the parent strontium vanadate to ∼6 × 10⁻¹³ atm for Sr_0.8Y_0.2VO_3−δ, whereas oxidative decomposition of Sr_0.8La_0.2VO_3−δ occurs in the p(O₂) range between 10⁻¹⁰ and 10⁻⁵ atm. Co-substitution by niobium in the vanadium sublattice has rather minor (Y-containing series) or even negative (La-containing series) effects on the perovskite phase stability boundary, but results in a slower kinetics of oxidative decomposition in an inert atmosphere. Sluggish oxidation kinetics in inert gas environments, demonstrated by electrical, thermogravimetric, dilatometric and structural studies, results in a nearly reversible behavior of Sr_0.8Ln_0.2V_1−yNb_yO_3−δ after exposure to inert atmosphere, thus enabling the fabrication of solid-electrolyte cells with SrVO_3−δ-based anodes under these conditions. Donor-type substitution is demonstrated also to decrease the electronic conductivity, which still remains sufficiently high for electrode application (>100 S cm⁻¹ at temperatures ≤950 °C), and to suppress chemical expansion thus improving the thermomechanical compatibility with solid electrolytes.