B Cation Ordered Double Perovskite Ba₂CoMo_0.5Nb_0.5O_6-δ As a Potential SOFC Cathode

Abstract

This paper reports the evaluation of the cubic B site cation-ordered double perovskite system Ba2Co2−x (Mo1/2Nb1/2) x O6, resulting in the single phase composition Ba2CoMo0.5Nb0.5O6−δ (BCMN) with a mixed Co charge state stabilized by a combination of Mo and Nb doping as a new mixed conductor with potential SOFC cathode applications. X-ray, neutron, and electron diffraction show that hexagonal intergrowths found in multiple phase samples at lower Mo/Nb contents are suppressed in BCMN, which has large domains of rock-salt ordered B site cations with separate Co and Mo/Nb sites. Conductivity measurement and impedance spectroscopy investigation shows that BCMN has a considerably reduced dc conductivity compared with materials such as BSCF but exhibits comparable electrochemical properties to some existing cathode materials in symmetrical cell measurements, and shows higher structural stability and reduced reactivity with the Ce0.8Sm0.2O2−δ (SDC) electrolyte. The role of Mo in dioxygen activation is proposed to offset the reduction that the d 0 Mo(VI) and Nb(V) cations on the B site produce in the electronic and ionic conductivity.

Evaluation of double perovskite Sr2FeTiO6−δ as potential cathode or anode materials for intermediate-temperature solid oxide fuel cells

“…The inflections on the electrical conductivity curves at 600 1C are attributed to the release of lattice oxygen and the thermal reduction of Fe 4 þ to Fe 3 þ and Fe 3 þ to Fe 2 þ on heating. The electrical conductivity values of the SFT sample are 2.83-2.33 S cm À 1 in the temperature range of 600-800 1C and reaches a maximum value of 2.83 S cm À 1 around 600 1C, which is much higher than that of Ba 2 CoMo 0.5 Nb 0.5 O 6 À δ cathode [42]. It agrees well with the previously reported in the literature [38].…”

Comparative Studies of SrCo1−xTaxO3−δ (x=0.05–0.4) Oxides as Cathodes for Low‐Temperature Solid‐Oxide Fuel Cells

“…[21,25] Recently,N b 5 + has been widely doped into different parent perovskite cathode materials to stabilize the cathode-favored cubic structure and even give ab oost to the ORR activity of the cathodes. [9,[26][27][28][29][30] For example, Zhoue tal. [13] reported ah ighly active SOFC cathode at temperatures below 600 8C after substituting Nb 5 + into Sr(Sc,Co)O 3Àd perovskite oxide,a nd many researchers also substituted Nb 5 + into milestone cathodes, such as (La,Sr)(Co,Fe)O 3Àd [28] and (Ba,Sr)(Co,Fe)O 3Àd .…”

Electrochemical and Catalytic Properties of Fe-Doped SrCo0.9-xNb0.1FexO3-δCathode Materials

“…24,27 Briefly, sample powder is placed on a quartz frit within a quartz tube plug flow micro-reactor. Before each isotope exchange experiment, the sample was pre-treated under 16 O 2 stream at 700 • C in order to ensure that the sample did not contain excess 18 O 2 and that the surface was clean. Based on BET surface area measurements (nitrogen sorption isotherms, Micromeritics ASAP 2020 surface area and porosimetry analyzer, using the standard BET method), each sample was weighed to yield a uniform surface area of 0.1 m 2 .…”

“…The high temperature cubic phase of these SrCoO 3-δ shows very promising oxygen reduction catalytic properties, however above 900 • C this phase is structurally not stable, and exhibits drawbacks mainly through large thermal expansion coefficients and high reactivity with yttria-stabilized zirconia electrolytes. [17][18][19][20] In previous works, Zhou et al 21,22 reported enhanced single phase stability and charge transfer properties of Nb-doped SrCoO 3-δ . In particular, partial substitution of the B-site by high valance cations should lead to a smaller discrepancy in the ionic radius between A-and B-sites, and eventually to stabilized cubic structure.…”