Electrochemical performance and anode reaction process for Ca doped Sr2Fe1·5Mo0·5O6-δ as electrodes for symmetrical solid oxide fuel cells

Performance optimization of metal-supported solid oxide fuel cells using cathode and full cell impregnation with La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ electrode

In this study, precursor solutions of La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (LSCFN) symmetric electrode were prepared, and the applications of cathode impregnation and full cell impregnation in the preparation and performance optimization of four-layer metal-supported solid oxide fuel cells (MSCs) were thoroughly investigated. Test results indicate that the polarization impedance of cathode impregnated MSCs under H2 and CH4 atmospheres at 750 °C is approximately 0.1 Ω cm2 and 0.41 Ω cm2, respectively, with power densities of 1115 mW cm-2 and 700 mW cm-2, respectively. Meanwhile, the polarization impedance of full cell impregnated MSCs under the same conditions is 0.12 Ω cm2 and 0.40 Ω cm2, with power densities of 945 mW cm-2 and 840 mW cm-2, respectively. Remarkably, MSCs full cell impregnated LSCFN exhibit outstanding stability performance under CH4 atmosphere in a 100 h stability test. Research on the application of impregnation method for performance optimization of metal-supported cells is relatively scarce. The results reveal the feasibility of simplifying MSCs preparation steps using full cell impregnation method, further promoting the widespread application of metal-supported overall cells.

Squeezing Out Nanoparticles from Perovskites: Controlling Exsolution with Pressure

Nanoparticle exsolution has emerged as a versatile method to functionalize oxides with robust metallic nanoparticles for catalytic and energy applications. By modifying certain external parameters during thermal reduction (temperature, time, reducing gas), some morphological and/or compositional properties of the exsolved nanoparticles can be tuned. Here, it is shown how the application of high pressure (<100 bar H2) enables the control of the exsolution of ternary FeCoNi alloyed nanoparticles from a double perovskite. H2 pressure affects the lattice expansion and the nanoparticle characteristics (size, population, and composition). The composition of the alloyed nanoparticles could be controlled, showing a reversal of the expected thermodynamic trend at 10 and 50 bar, where Fe becomes the main component instead of Ni. In addition, pressure drastically lowers the exsolution temperature to 300 °C, resulting in unprecedented highly-dispersed and small-sized nanoparticles with a similar composition to those obtained at 600 °C and 10 bar. The mechanisms behind the effects of pressure on exsolution are discussed, involving kinetic, surface thermodynamics, and lattice-strain factors. A volcano-like trend of the exsolution extent suggests that competing pressure-dependent mechanisms govern the process. Pressure emerges as a new design tool for metallic nanoparticle exsolution enabling novel nanocatalysts and surface-functionalized materials.

Mechanistic Study on the Corrosion of (La,Sr)(Co,Fe)O3-δ Cathodes Induced by CO2

Solid Oxide Fuel Cell (SOFC) cathodes operating in ambient atmospheric conditions inevitably encounter CO2 contamination, leading to sustained performance deterioration. In this investigation, we examined the impact of CO2 on three variants of (La,Sr)(Co,Fe)O3-δ cathodes and employed the distribution of relaxation times method to distinguish distinct electrochemical processes based on impedance spectra analysis. We meticulously analyzed and discussed the corrosion resistance of these (La,Sr)(Co,Fe)O3-δ cathodes under high CO2 concentrations, relying on the experimental data. Electrochemical impedance spectroscopy results revealed that La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF-6428), La0.4Sr0.6Co0.2Fe0.8O3-δ (LSCF-4628), and La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (LSCFN-46271) cathodes exhibited persistent degradation when exposed to CO2 at temperatures of 650 °C or 800 °C during the durability-testing period. An increase in electrode polarization resistance was observed upon CO2 introduction to the electrode, but electrode performance recovered upon returning to a pure air environment. Furthermore, X-ray diffraction and scanning electron microscopy analyses confirmed that CO2 did not cause permanent damage to the (La,Sr)(Co,Fe)O3-δ cathodes. These findings indicate that the (La,Sr)(Co,Fe)O3-δ cathodes exhibit excellent resistance to CO2-induced corrosion.

Cobalt-Free Double Perovskite Oxide as a Promising Cathode for Solid Oxide Fuel Cells

Double perovskite oxide PrBaFe₂O_5+δ is a potential cathode material for intermediate-temperature solid oxide fuel cells. To improve its electrochemical performance, the trivalent element Ga is investigated to partially replace Fe, forming PrBaFe_2-xGa_xO_5+δ (PBFGx, x = 0.05, 0.1, and 0.15). The doping effects on physicochemical properties and electrochemical properties are analyzed regarding the phase structures, element valence states, amount of oxygen vacancies, content of oxygen species, oxygen surface exchange coefficients (k_chem), electrochemical polarization resistance, and single-cell performance. Specifically, PBFG0.1 exhibits improved k_chem, such as a 19% improvement from 4.09 × 10^-4 to 4.86 × 10^-4 cm s^-1 at 750 °C, due to the increased concentration of reactive oxygen species and oxygen vacancies. Consequently, the interfacial polarization resistance is decreased by 28% from 0.057 to 0.041 Ω cm² at 800 °C. The subreaction steps of the oxygen reduction reaction in the PBFG0.1 cathode are further investigated, which suggests that the oxygen dissociation process is greatly enhanced by doping Ga. Meanwhile, doping Ga increases the peak power density of the anode-supported single cell by 36% from 629 to 856 mW cm^-2 at 800 °C. The single cell with the PBFG0.1 cathode also exhibits good stability in 100 h of long-term operation at 750 °C.

Nanostructured La0.75Sr0.25Cr0.5Mn0.5O3-Ce0.8Sm0.2O2 Heterointerfaces as All-Ceramic Functional Layers for Solid Oxide Fuel Cell Applications

The use of nanostructured interfaces and advanced functional materials opens up a new playground in the field of solid oxide fuel cells. In this work, we present two all-ceramic thin-film heterostructures based on samarium-doped ceria and lanthanum strontium chromite manganite as promising functional layers for electrode application. The films were fabricated by pulsed laser deposition as bilayers or self-assembled intermixed nanocomposites. The microstructural characterization confirmed the formation of dense, well-differentiated, phases and highlighted the presence of strong cation intermixing in the case of the nanocomposite. The electrochemical properties─solid/gas reactivity and in-plane conductivity─are strongly improved for both heterostructures with respect to the single-phase constituents under anodic conditions (up to fivefold decrease of area-specific resistance and 3 orders of magnitude increase of in-plane conductivity with respect to reference single-phase materials). A remarkable electrochemical activity was also observed for the nanocomposite under an oxidizing atmosphere, with no significant decrease in performance after 400 h of thermal aging. This work shows how the implementation of nanostructuring strategies not only can be used to tune the properties of functional films but also results in a synergistic enhancement of the electrochemical performance, surpassing the parent materials and opening the field for the fabrication of high-performance nanostructured functional layers for application in solid oxide fuel cells and symmetric systems.