Reversible electrodes based on B-site substituted Ba0.5Sr0.5Co0.8Fe0.2O3-δ for intermediate temperature solid-oxide cells

Abstract

The Ba0.5Sr0.5Co0.8Fe0.2O3-δ perovskite is a promising electrode material for solid-oxide electrochemical cells exhibiting excellent oxygen reduction reaction (ORR) activity and mixed ionic-electronic transport properties at intermediate temperatures but suffers from stability issues. In this work, the effect on stability and electrochemical performance of several B-site substituted cations (Sc, Zr, Y) are studied. The presence of these substituted cations improved stability by preventing (a) the formation of the detrimental hexagonal phase during long term air exposure experiments and (b) reducing the formation of carbonates in CO2-containing atmospheres. Symmetrical cell testing revealed that the Sc-substituted material mixed with an ionic gadolinium-doped ceria (GDC) phase has the lowest polarization resistance among the materials and thus was chosen as the cathode for the full cell construction. The composite electrode achieved encouraging power density values ~877 mW/cm2 at 700 °C. The material showed stable hydrogen generation during intermediate temperature electrolysis tests and its performance improved upon the introduction of CO2 to carry out co-electrolysis. Furthermore, methane was obtained during co-electrolysis and Sabatier reaction at temperatures below 450 °C. The superior stability and performance of the Sc-substituted Ba0.5Sr0.5Co0.8Fe0.2O3-δ make it an exciting candidate for application as a cathode in reduced temperature electrochemical cells.