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(0.8)Ln(0.2)V(1-y)Nb(y)O(3-delta) (Ln = La or Y, y = 0-0.10) solid solutions. The upper-p(O-2) stability boundary at 900 degrees C was found to shift from similar to 10(-15) atm for the parent strontium vanadate to similar to 6 x 10(-13) atm for Sr0.8Y0.2VO3-delta, whereas oxidative decomposition of Sr0.8La0.2VO3-delta occurs in the p(O-2) 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(0.8)Ln(0.2)V(1-y)Nb(y)O(3-delta) after exposure to inert atmosphere, thus enabling the fabrication of solid-electrolyte cells with SrVO3-delta-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 degrees C), and to suppress chemical expansion thus improving the thermomechanical compatibility with solid electrolytes.