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Oxygen-electrode-supported solid oxide cells (OESCs) have potential advantages over fuel-electrode-supported cells, including reduced fuel-electrode concentration polarization, better oxygen electrode current collection, and flexibility in the fuel electrode choice. However, there are serious drawbacks including the difficulty of co-firing the oxygen electrode and electrolyte, and oxygen electrode concentration polarization. This paper explores the characteristics of OESCs with La0.8Sr0.2MnO3-d-Zr0.92Y0.16O2-d (LSM-YSZ) electrode-support enhanced by SrTi0.3Fe0.6Co0.1O3-d (STFC) infiltration, thin YSZ electrolyte, and SrTi0.3Fe0.7O3-d (STF) fuel electrodes. The STFC infiltration increases fuel cell maximum power density by >1.5 times and electrolysis current density (at 1.3 V) by >2 times. Cell performance in pure oxygen is compared to that in air, exploring a possible reversible solid oxide cell system configuration where oxygen produced during electrolysis is stored and subsequently used during fuel cell operation. The fuel cell maximum power density is increased from 0.88 W cm-2 in air to 1.37 W cm-2 in oxygen, with limiting current increased from 1.7 to >5.6 A cm-2; the electrolysis performance is essentially unchanged, probably because the electrode air becomes enriched with oxygen during electrolysis. [ABSTRACT FROM AUTHOR]

Sr(Ti0.3Fe0.7)O3−δ (STF) and the associated exsolution electrodes Sr0.95(Ti0.3Fe0.63Ru0.07)O3−δ (STFR), or Sr0.95(Ti0.3Fe0.63Ni0.07)O3−δ (STFN) are alternatives to Ni-based cermet fuel electrodes for solid oxide electrochemical cells (SOCs). They can provide improved tolerance to redox cycling and fuel impurities, and may allow direct operation with hydrocarbon fuels. However, such perovskite-oxide-based electrodes present processing challenges for co-sintering with thin electrolytes to make fuel electrode supported SOCs. Thus, they have been mostly limited to electrolyte-supported SOCs. Here, we report the first example of the application of perovskite oxide fuel electrodes in novel oxygen electrode supported SOCs (OESCs) with thin YSZ electrolytes, and demonstrate their excellent performance. The OESCs have La0.8Sr0.2MnO3−δ–Zr0.92Y0.16O2−δ (LSM–YSZ) oxygen electrode-supports that are enhanced via infiltration of SrTi0.3Fe0.6Co0.1O3−δ, while the fuel electrodes are either Ni-YSZ, STF, STFN, or STFR. Fuel cell power density as high as 1.12 W cm−2 is obtained at 0.7 V and 800 °C in humidified hydrogen and air with the STFR electrode, 60% higher than the same cell made with a Ni-YSZ electrode. Electrolysis current density as high as −1.72 A cm−2 is obtained at 1.3 V and 800 °C in 50% H2O to 50% H2 mode; the STFR cell yields a value 72% higher than the same cell made with a Ni-YSZ electrode, and competitive with the widely used conventional Ni-YSZ-supported cells. The high performance is due in part to the low resistance of the thin YSZ electrolyte, and also to the low fuel electrode polarization resistance, which decreases with fuel electrode in the order: Ni-YSZ > STF > STFN > STFR. The high performance of the latter two electrodes is due to exsolution of catalytic metal nanoparticles; the results are discussed in terms of the microstructure and properties of each electrode material, and surface oxygen exchange resistance values are obtained over a range of conditions for STF, STFN, and STFN. The STF fuel electrodes also provide good stability during redox cycling. [ABSTRACT FROM AUTHOR]

The application of atomic layer deposition (ALD) on solid oxide fuel cell (SOFC) cathodes has previously yielded mixed results and has been seen to depend on the ALD species, catalyst chemistry, catalyst morphology, and the conditions for deposition. Characterized here is the effect of an ALD zirconia coating within an SOFC oxygen electrode: Sr0.5Sm0.5CoO3−δ infiltrated into Gd-doped ceria, Ce0.9Gd0.1O2−δ, scaffolds (SSC–GDC). Island-like ALD-ZrO2 coatings with approximately monolayer coverage initially yield a higher electrode polarization resistance, RP, but thereafter the coated electrodes show lower RP and slower degradation. For example, after ∼1000 hour accelerated ageing tests carried out at 750 °C, SSC–GDC coated with ∼0.3 nm of ALD-ZrO2 showed an RP increase of 18% compared to 30% for uncoated SSC–GDC. Strontium surface segregation was not found to be a significant degradation factor. At 750 °C, a reaction between the Zr-overlayer and the SSC was observed, producing SrZrO3, Co3O4, and SmCoO3. The low RP values achieved suggest that the reactant products were thin enough to be discontinuous and thus not hinder the oxygen surface exchange process, and yet they acted as a barrier to SSC particle coarsening. [ABSTRACT FROM AUTHOR]

Solid oxide cells operated reversibly between fuel cell and electrolysis modes are promising for energy storage with extremely high capacity. La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) has become the dominant oxygen electrode material in electrolysis and reversible operation. However, LSCF has been widely reported to degrade due to Sr surface segregation. The present understanding is that the segregation rate and hence the degradation rate increases with increasing temperature and current density. Here we present a study of LSCF electrode performance and stability carried out with a series of extended life tests (1000 hours) over a range of temperatures and reversing current densities. Although the results at lower temperatures (650–700 °C) show the expected increase in segregation-induced degradation with increasing current density, at higher temperature (750 °C) stability is improved and the electrodes become fully stable at the highest current density of 1.5 A cm−2, maintaining a stable polarization resistance of 0.08 Ω cm2. This unexpected result is explained by the increased electrochemical activity of LSCF at the higher temperature and a very rapid development of a stable surface segregated Sr layer. [ABSTRACT FROM AUTHOR]

In order to assess the durability of La0.6Sr0.4Co0.2Fe0.8O3 oxygen electrodes in reversible solid oxide cells, current switched ~1000 h galvanostatic (0.7, 1.0, and 1.5 A/cm²) life tests were performed on symmetrical Ce0.9Gd0.1O2-electrolyte cells at 700±C. Cell operating voltage and resistance, the latter measured by impedance spectroscopy, were monitored throughout. Degradation was minimal for the 0.7 A/cm² case. For the higher current densities, the cell voltage and resistance increased with time, although the cell appeared to stabilize after ~500 h in the 1.5 A/cm² case. Post-test analyses showed no evidence of electrolyte cracking or delamination for any current. However, 3D imaging revealed measureable microstructural coarsening after 1.5 A/cm² operation that was not present after 0.7 A/cm² operation. Furthermore, the amount of Sr segregated onto LSCF surfaces was higher for the cells operated with current switching versus the as-prepared and zero-current cells. Analysis of the results suggest that much of the degradation was due to decreased oxygen surface exchange rate due to current-enhanced Sr segregation, with a smaller contribution due to microstructural coarsening. The possibility of extrapolating these accelerated tests to longer times is discussed. [ABSTRACT FROM AUTHOR]

In order to improve the cycling stability of β-NbPO5 due to the avoidance of lower voltage irreversible structural transitions, at least 5% Ta5+ is incorporated in β-NbPO5. [ABSTRACT FROM AUTHOR]