RESUMEN

Recently, there have been efforts to use clean and renewable energy because of finite fossil fuels and environmental problems. Owing to the site-specific and weather-dependent characteristics of the renewable energy supply, solid oxide electrolysis cells (SOECs) have received considerable attention to store energy as hydrogen. Conventional SOECs use Ni-YSZ (yttria-stabilized zirconia) and LSM (strontium-doped lanthanum manganites)-YSZ as electrodes. These electrodes, however, suffer from redox-instability and coarsening of the Ni electrode along with delamination of the LSM electrode during steam electrolysis. In this study, we successfully design and fabricate highly efficient SOECs using layered perovskites, PrBaMn2 O5+δ (PBM) and PrBa0.5 Sr0.5 Co1.5 Fe0.5 O5+δ (PBSCF50), as both electrodes for the first time. The SOEC with layered perovskites as both-side electrodes shows outstanding performance, reversible cycling, and remarkable stability over 600 hours.

RESUMEN

The Sr and Fe codoped double perovskites PrBaCo2O5.5+δ (PrBCO) thin films of Pr(Ba0.5Sr0.5)(Co1.5Fe0.5)O5.5+δ (PBSCFO) were epitaxially grown for chemical catalytic studies. The resistance behavior of PBSCFO epitaxial films was monitored under the switching flow of reducing and oxidizing gases as a function of the gas flow time, t, using an electrical conductivity relaxation (ECR) experimental setup. The R(t) vs t relationships determined at various temperatures show the occurrence of two oxidation processes, Co(2+)/Co(3+) ↔ Co(3+) and Co(3+) ↔ Co(3+)/Co(4+). Mathematical fitting of the observed R(t) vs t relationships was carried out using Fick's second law for one-dimensional diffusion of charge carriers to derive the diffusivity D(T) and τ(T) for the two processes at various temperatures, T. The D(T) vs T relationships were analyzed in terms of the Arrhenius relationship to find the activation energies Ea for each process. Oscillations in the dR(t)/dt plots, observed under oxidation reactions, were discussed in terms of a layer-by-layer oxygen vacancy exchange diffusion mechanism. Our work suggests that thin films of LnBCO (Ln = lanthanide) with their A and B sites doped as in PBSCFO are excellent candidates for the development of low or intermediate temperature energy conversion devices and gas sensor applications.

RESUMEN

Renewable energy resources such as solar energy, wind energy, hydropower or geothermal energy have attracted significant attention in recent years. Renewable energy sources have to match supply with demand, therefore it is essential that energy storage devices (e.g., secondary batteries) are developed. However, secondary batteries are accompanied with critical problems such as high cost for the limited energy storage capacity and loss of charge over time. Energy storage in the form of chemical species, such as H2 or CO2, have no constraints on energy storage capacity and will also be essential. When plentiful renewable energy exists, for example, it could be used to convert H2O into hydrogen via water electrolysis. Also, renewable energy resources could be used to reduce CO2 into CO and recycle CO2 and H2O into sustainable hydrocarbon fuels in solid oxide electrolysis (SOE).

RESUMEN

This study focuses on reducing the cathode polarization resistance through the use of mixed ionic electronic conductors and the optimization of cathode microstructure to increase the number of electrochemically active sites. Among the available mixed ionic electronic conductors (MIECs), the layered perovskite GdBa0.5 Sr0.5 CoFeO5+δ (GBSCF) was chosen as a cathode material for intermediate temperature solid oxide fuel cells owing to its excellent electrochemical performance and structural stability. The optimized microstructure of a GBSCF-yttria-stabilized zirconia (YSZ) composite cathode was prepared through an infiltration method with careful control of the sintering temperature to achieve high surface area, adequate porosity, and well-organized connection between nanosized particles to transfer electrons. A symmetric cell shows outstanding results, with the cathode exhibiting an area-specific resistance of 0.006â€…Ω cm(2) at 700 °C. The maximum power density of a single cell using Ce-Pd anode with a thickness of ∼80 µm electrolyte was ∼0.6 W cm(-2) at 700 °C.

RESUMEN

Different layered perovskite-related oxides are known to exhibit important electronic, magnetic and electrochemical properties. Owing to their excellent mixed-ionic and electronic conductivity and fast oxygen kinetics, cation layered double perovskite oxides such as PrBaCo2O5 in particular have exhibited excellent properties as solid oxide fuel cell oxygen electrodes. Here, we show for the first time that related layered materials can be used as high-performance fuel electrodes. Good redox stability with tolerance to coking and sulphur contamination from hydrocarbon fuels is demonstrated for the layered perovskite anode PrBaMn2O5+δ (PBMO). The PBMO anode is fabricated by in situ annealing of Pr0.5Ba0.5MnO3-δ in fuel conditions and actual fuel cell operation is demonstrated. At 800 °C, layered PBMO shows high electrical conductivity of 8.16 S cm(-1) in 5% H2 and demonstrates peak power densities of 1.7 and 1.3 W cm(-2) at 850 °C using humidified hydrogen and propane fuels, respectively.

RESUMEN

A class of double-perovskite compounds display fast oxygen ion diffusion and high catalytic activity toward oxygen reduction while maintaining excellent compatibility with the electrolyte. The astoundingly extended stability of NdBa(1-x)Ca(x)Co2O(5+δ) (NBCaCO) under both air and CO2-containing atmosphere is reported along with excellent electrochemical performance by only Ca doping into the A site of NdBaCo2O(5+δ) (NBCO). The enhanced stability can be ascribed to both the increased electron affinity of mobile oxygen species with Ca, determined through density functional theory calculations and the increased redox stability from the coulometric titration.

RESUMEN

Ba0.5Sr0.5Co0.8Fe0.2O(3-δ) (BSCF) has won tremendous attention as a cathode material for intermediate-temperature solid-oxide fuel cells (IT-SOFC) on the basis of its fast oxygen-ion transport properties. Nevertheless, wide application of BSCF is impeded by its phase instabilities at intermediate temperature. Here we report on a chemically stable SOFC cathode material, La0.5Ba0.25Sr0.25Co0.8Fe0.2O(3-δ) (LBSCF), prepared by strategic approaches using the Goldschmidt tolerance factor. The tolerance factors of LBSCF and BSCF indicate that the structure of the former has a smaller deformation of cubic symmetry than that of the latter. The electrical property and electrochemical performance of LBSCF are improved compared with those of BSCF. LBSCF also shows excellent chemical stability under air, a CO2-containg atmosphere, and low oxygen partial pressure while BSCF decomposed under the same conditions. Together with this excellent stability, LBSCF shows a power density of 0.81 W cm(-2) after 100 h, whereas 25 % degradation for BSCF is observed after 100 h.

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RESUMEN

Cobalt-containing cathodes often encounter problems such as high thermal expansion coefficients (TEC) and poor stability, making them unsuitable for practical use as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). This study focuses on the effects of Cu doping in the Co site of SmBa0.5Sr0.5Co2O5+δ in terms of structural characteristics, electrical properties, electrochemical performance, redox properties, and performance stability as an IT-SOFC cathode material. The TEC value of a SmBa0.5Sr0.5Co1.5Cu0.5O5+δ (SBSCCu50) sample is 12.8 × 10(-6) K(-1), which is lower than that (13.7 × 10(-6) K(-1)) of a SmBa0.5Sr0.5Co2O5+δ (SBSCO) sample at 700 °C. SBSCCu50 showed higher redox stability at lower p(O2) and a more stable cell power output while retaining desirable electrochemical performance, as compared with SBSCO. SBSCCu50 displayed reduced TEC values and enhanced redox and performance stability, as well as satisfactory electrical properties and electrochemical performance under typical fuel cell operating conditions. The results indicate that SBSCCu50 is a promising material as a cathode for IT-SOFCs.

RESUMEN

Solid oxide fuel cells (SOFC) are the cleanest, most efficient, and cost-effective option for direct conversion to electricity of a wide variety of fuels. While significant progress has been made in anode materials with enhanced tolerance to coking and contaminant poisoning, cathodic polarization still contributes considerably to energy loss, more so at lower operating temperatures. Here we report a synergistic effect of co-doping in a cation-ordered double-perovskite material, PrBa0.5Sr0.5Co(2-x)Fe(x)O(5+δ), which has created pore channels that dramatically enhance oxygen ion diffusion and surface oxygen exchange while maintaining excellent compatibility and stability under operating conditions. Test cells based on these cathode materials demonstrate peak power densities ~2.2 W cm(-2) at 600°C, representing an important step toward commercially viable SOFC technologies.

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