BaCe0.7–xZr0.2Y0.1FexO3–δ derived from proton-conducting electrolytes: A way of designing chemically compatible cathodes for solid oxide fuel cells

Abstract

The present study describes the rational engineering, preparation and characterisation of new mixed ionic-electronic conductors (MIECs) having great potential for application in solid oxide fuel cells (SOFCs) based on proton-conducting electrolytes. The developed MIECs are derived from promising Ba(Ce,Zr)O 3 -materials doped with iron as a transition element: BaCe 0.7–x Zr 0.2 Y 0.1 Fe x O 3–δ (x = 0–0.7, Δx = 0.1). The comprehensive analysis of the functional properties (crystal structure, densification, microstructure, defect structure, thermal expansion behaviour, electrical conductivity) indicate that a moderate iron content is beneficial in order to achieve a certain compromise. In detail, the gradual Fe-doping results in an enhancement of transport properties (including, ionic-electronic conductivity level) and deterioration of mechanical characteristics (an increase of average thermal expansion coefficient values). The composition with x = 0.6, identified as more optimal, was used as a cathode for an intermediate-temperature SOFC; this cathode displays a satisfactory polarisation resistance level, 0.21 Ω cm 2 at 700 °C, without the use of any additional electroactivation technique. The obtained results indicate that BaCe 0.7–x Zr 0.2 Y 0.1 Fe x O 3–δ MIECs having one of the highest chemical compatibility with state-of-the-art proton-conducting electrolytes can be considered as advanced electrodes for designing new solid oxide electrochemical devices with prolonged and stable operation mode. • BaCe 0.7–x Zr 0.2 Y 0.1 Fe x O 3–δ (BCZYFx) materials were prepared for the first time. • The BCZYFx materials are single-phase across the entire x range (0 = x ≤ 0.7). • Fe-doping leads to an increase in both ionic and electronic conductivities (at x ≥ 0.4). • At the same time, TECs values increase and chemical strain becomes more pronounced. • BCZYF0.6 with an optimal combination of properties was utilised as a SOFC cathode.