A Layered Perovskite EuBaCo₂O_5+δ for Intermediate‐Temperature Solid Oxide Fuel Cell Cathode

Abstract

A layered perovskite EuBaCo2O5+δ (EBCO) has been prepared by a solid‐state reaction, and evaluated as potential cathode for intermediate‐temperature solid oxide fuel cells. Structural characterizations are determined at room temperature using powder X‐ray diffraction and transmission electron microscopy technique. The good fits to the XRD data by Rietveld refinement method are obtained in the orthorhombic space group (Pmmm). The lower average thermal expansion coefficient, 14.9 × 10–6 °C–1 between 100 and 800 °C, indicates its better thermal expansion compatibility with conventional electrolytes, compared with the other cobalt‐containing cathode materials. The high electrical conductivity and large oxygen nonstoichiometry at intermediate temperatures suggest the effective charge transfer reactions including electron conduction and oxide‐ion motion in cathode. As a result, a highly electrochemical activity towards the oxygen reduction reaction is achieved between 600 and 700 °C, as evidenced by low area‐specific resistances, e.g. 0.14–0.5 Ω cm2. In addition, cathodic overpotential and oxygen reduction kinetics of the EBCO cathode have also been studied.

EuBaCo2O5+δ-Ce0.9Gd0.1O2−δ composite cathodes for intermediate-temperature solid oxide fuel cells: high electrochemical performance and oxygen reduction kinetics

“…4 shows thermal expansion curves of EBCO and EBCO-xCGO (x = 5-40) samples in the temperature range of 100-800 C in air. A nearly linear thermal expansion behavior is observed in EBCO, which was reported by our group [26], suggesting that the chemical reduction factor on the cell dimension can be negligible. The average TEC value of EBCO is calculated to be 14.9Â10 À6 K À1 , which is lower than those of similar Co-containing double perovskite oxides, e. g. the TEC values of PrBaCo 2 O 6Àd is 21.5 Â 10 À6 K À1 in the temperature range of 30-1000 C [27] introduction of CGO into EBCO further reduces the TECs of the composite materials.…”

“…1 shows the room temperature XRD pattern of as-synthesized EBCO powder calcined at 1150 C for 24 h in air. This structural feature has been presented in our previous publication [26]. It can be seen that EBCO oxide crystallizes in a single-phase double perovskite without any additional diffraction peaks arising from impurities detected.…”

“…3 shows the electrical conductivity of EBCO and EBCO-xCGO (x = 5-40) samples as a function of temperature in air. The EBCO oxide possesses a semiconductor-metal transition behavior at elevated temperatures [26], with a maximum electrical conductivity value of 100 S cm À1 at 423 C. The similar transitions were also reported in the other double perovskite LnBaCo 2 O 6Àd oxides [17]. This metal metallic nature is the characteristic of Co-based perovskites, which is attributed to the energy band overlap between Co-3d and O-2p [29].…”

“…Rietveld refinement fitting results converge to a weight-profile R-factor (R wp ) of 6.71% and a profile-fitting R-factor (R p ) of 4.87%, which indicates the excellent fit for the XRD data. The detailed lattice and structure parameters obtained from Rietveld refinement have been reported elsewhere [26]. Fig.…”

“…Therefore, it is important to improve the thermal expansion compatibility between the LnBaCo 2 O 6Àd cathodes and the electrolytes. Our group recently reported that layered perovskite EuBaCo 2 O 5+d (EBCO) has a low TEC value of 14.9Â10 À6 K À1 in the temperature range of 100-800 C [26]. This indicates its good thermal expansion compatibility with the conventional electrolytes.…”