New Rhenium-Doped SrCo1−xRexO3−δ Perovskites Performing as Cathodes in Solid Oxide Fuel Cells

Abstract

In the aim to stabilize novel three-dimensional perovskite oxides based upon SrCoO3−δ, we have designed and prepared SrCo1−xRexO3−δ phases (x = 0.05 and 0.10), successfully avoiding the competitive hexagonal 2H polytypes. Their performance as cathode materials in intermediate-temperature solid oxide fuel cells (IT-SOFC) has been investigated. The characterization of these oxides included X-ray (XRD) and in situ temperature-dependent neutron powder diffraction (NPD) experiments for x = 0.10. At room temperature, SrCo1−xRexO3−δ perovskites are defined in the P4/mmm space group, which corresponds to a subtle tetragonal perovskite superstructure with unit-cell parameters a = b ≈ ao, c = 2ao (ao = 3.861 and 3.868 Å, for x = 0.05 and 0.10, respectively). The crystal structure evolves above 380 °C to a simple cubic perovskite unit cell, as observed from in-situ NPD data. The electrical conductivity gave maximum values of 43.5 S·cm−1 and 51.6 S·cm−1 for x = 0.05 and x = 0.10, respectively, at 850 °C. The area specific resistance (ASR) polarization resistance determined in symmetrical cells is as low as 0.087 Ω·cm2 and 0.065 Ω·cm2 for x = 0.05 and x = 0.10, respectively, at 850 °C. In single test cells these materials generated a maximum power of around 0.6 W/cm2 at 850 °C with pure H2 as a fuel, in an electrolyte-supported configuration with La0.8Sr0.2Ga0.83Mg0.17O3−δ (LSGM) as the electrolyte. Therefore, we propose the SrCo1−xRexO3−δ (x = 0.10 and 0.05) perovskite oxides as promising candidates for cathodes in IT-SOFC.

SrCo1–xRuxO3−δ (x = 0.05, 0.1, and 0.15) Perovskites As Outperforming Cathode Material in Intermediate-Temperature Solid Oxide Fuel Cells

“…A smaller overall polarization resistance of the x = 0.05 Ru-doped perovskite is observed compared to the x = 0.1 sample. At 850 °C, the 10% mol Ru-doped sample presents R p = 0.11 Ω cm 2 and the 5% mol Ru-doped R p = 0.07 Ω cm 2 ; this last sample exhibits extraordinarily low values, comparable to those of other cathodes with good performance such as SrCo 1– x Re x O 3−δ , SrCo 1– x V x O 3−δ , and SrCo 1– x Ti x O 3−δ . , …”

“…All the reflections can be indexed at RT in a superstructure with doubled c -axis, as a = b ≈ a 0 , c ≈ 2 a 0 in the P 4 /mmm space group (No. 123), and the crystal structure was refined in a model derived for other doped-SrCoO 3‑δ oxides. − In this model, Sr atoms are placed at 2 h (1/2,1/2, z ) sites, Co1 at 1 a (0,0,0), Co2 at 1 b (0,0,1/2), and the three kinds of oxygen atoms O1 at 2 f (1/2,0,0), O2 at 2 g (0,0, z ) and O3 at 2 e (1/2,0,1/2) positions. First, Ru atoms were placed together with Co1 resulting in a negative occupancy factor for Ru atoms, for that reason Ru atoms were distributed over the 1 b sites together with Co2 giving a reasonable occupancy factor for both Co and Ru atoms.…”

“…The potential of SrCoO 3−δ oxides may be exploited through the inhibition of this phase transition and the stabilization of a 3C-type perovskite (with a vertex-sharing network of CoO 6 octahedra). In previous works, − this objective was achieved by introducing highly charged cations at the Co sublattice to destabilize the columns of CoO 6 octahedra sharing faces that constitute the competitive 2H polytype.…”

Exsolution of Re-alloy catalysts with enhanced stability for methane dry reforming

“…While LaFeO 3 itself is not active, it provides high oxygen mobility and flexible redox character, properties which are instrumental in designing stable reforming catalyst [33]. The precursor materials reported in this study are LaFeO 3 (LF), LaNi [34][35][36]. The Re that did not enter the perovskite went to form the competing La 3 ReO 8 phase ultimately forming a composite precursor material.…”

Design, Synthesis, Structure and Properties of Ba-Doped Derivatives of SrCo0.95Ru0.05O3−δ Perovskite as Cathode Materials for SOFCs

“…Whereas the cubic phase exhibits an excellent ionic and electronic conductivity, the hexagonal phase has very poor properties and, unfortunately, it is thermodynamically stable, which limits the use of this pure material as a cathode in SOFC. As a strategy to prevent this cubic-to-hexagonal phase transition, it was found that replacing few percentages of Co by aliovalent elements like Re, Nb, Sb or Ti was effective to stabilize the cubic phase in a wide temperature range [9,10,11,12,13]. Recently, we observed that replacing 5% of Co by Ru prevents this unwanted transformation and enhances the catalytic oxygen reduction reaction [14].…”