Electrical properties and sulfur tolerance of La0.75Sr0.25Cr1−xMnxO3 under anodic conditions

Navigating the future of solid oxide fuel cell: Comprehensive insights into fuel electrode related degradation mechanisms and mitigation strategies

Solid Oxide Fuel Cells (SOFCs) have proven to be highly efficient and one of the cleanest electrochemical energy conversion devices. However, the commercialization of this technology is hampered by issues related to electrode performance degradation. This article provides a comprehensive review of the various degradation mechanisms that affect the performance and long-term stability of the SOFC anode caused by the interplay of physical, chemical, and electrochemical processes. In SOFCs, the most used anode material is nickel-yttria stabilized zirconia (Ni-YSZ) due to its advantages of high electronic conductivity and high catalytic activity for H2 fuel. However, various factors affecting the long-term stability of the Ni-YSZ anode, such as redox cycling, carbon coking, sulfur poisoning, and the reduction of the triple phase boundary length due to Ni particle coarsening, are thoroughly investigated. In response, the article summarizes the state-of-the-art diagnostic tools and mitigation strategies aimed at improving the long-term stability of the Ni-YSZ anode.

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.

Rational Design of Perovskite-Based Anode with Decent Activity for Hydrogen Electro-Oxidation and Beneficial Effect of Sulfur for Promoting Power Generation in Solid Oxide Fuel Cells

The poor sulfur tolerance of conventional nickel cermet anodes is particularly concerning for solid oxide fuel cell technology. Herein, we report an innovative anode composed of a samaria-doped ceria (SDC) scaffold and a perovskite La_0.35Ca_0.50TiO_3-δ thin film with a surface modified with strongly coupled and in situ-formed Ni nanoparticles; the anode was prepared via an infiltration-calcination-reduction method. The rational design of such an anode transforms the detrimental effect of sulfur on the cell performance (poisoning) of state-of-the-art Ni cermet anodes into a beneficial effect promoting power generation from H₂. A cell with a Ni + SDC cermet anode and a Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ cathode showed an 18.3% reduction in the power output at 800 °C when the fuel gas was switched from pure H₂ to H₂-1000 ppm H₂S, while a similar cell with this innovative anode showed a power output enhancement of 6.6%. Furthermore, the operational stability was significantly improved. The perovskite phase was found to account for the improved cell power output in the presence of sulfur impurity. The introduction of the nickel nanoparticles further significantly enhanced the electrode activity, while the strong coupling effect of exsolved nickel nanoparticles with the perovskite thin film improved the sulfur tolerance of the nickel phase. As a result, the anode showed both high activity and stability while operating on H₂ fuel with high concentration of H₂S (1000 ppm). The promoting effect of sulfur on the power generation over the perovskite anode is also discussed.

Insights into the Surface Reactivity of Cermet and Perovskite Electrodes in Oxidizing, Reducing, and Humid Environments

Understanding the surface chemistry of electrode materials under gas environments is important in order to control their performance during electrochemical and catalytic applications. This work compares the surface reactivity of Ni/YSZ and La_0.75Sr_0.25Cr_0.9Fe_0.1O₃, which are commonly used types of electrodes in solid oxide electrochemical devices. In situ synchrotron-based near-ambient pressure photoemission and absorption spectroscopy experiments, assisted by theoretical spectral simulations and combined with microscopy and electrochemical measurements, are used to monitor the effect of the gas atmosphere on the chemical state, the morphology, and the electrical conductivity of the electrodes. It is shown that the surface of both electrode types readjusts fast to the reactive gas atmosphere and their surface composition is notably modified. In the case of Ni/YSZ, this is followed by evident changes in the oxidation state of nickel, while for La_0.75Sr_0.25Cr_0.9Fe_0.1O₃, a fine adjustment of the Cr valence and strong Sr segregation is observed. An important difference between the two electrodes is their capacity to maintain adsorbed hydroxyl groups on their surface, which is expected to be critical for the electrocatalytic properties of the materials. The insight gained from the surface analysis may serve as a paradigm for understanding the effect of the gas environment on the electrochemical performance and the electrical conductivity of the electrodes.

Enhancing Sulfur Tolerance of Ni-Based Cermet Anodes of Solid Oxide Fuel Cells by Ytterbium-Doped Barium Cerate Infiltration

Conventional anode materials for solid oxide fuel cells (SOFCs) are Ni-based cermets, which are highly susceptible to deactivation by contaminants in hydrocarbon fuels. Hydrogen sulfide is one of the commonly existed contaminants in readily available natural gas and gasification product gases of pyrolysis of biomasses. Development of sulfur tolerant anode materials is thus one of the critical challenges for commercial viability and practical application of SOFC technologies. Here we report a viable approach to enhance substantially the sulfur poisoning resistance of a Ni-gadolinia-doped ceria (Ni-GDC) anode through impregnation of proton conducting perovskite BaCe0.9Yb0.1O3-δ (BCYb). The impregnation of BCYb nanoparticles improves the electrochemical performance of the Ni-GDC anode in both H2 and H2S containing fuels. Moreover, more importantly, the enhanced stability is observed in 500 ppm of H2S/H2. The SEM and XPS analysis indicate that the infiltrated BCYb fine particles inhibit the adsorption of sulfur and facilitate sulfur removal from active sites, thus preventing the detrimental interaction between sulfur and Ni-GDC and the formation of cerium sulfide. The preliminary results of the cell with the BCYb+Ni-GDC anode in methane fuel containing 5000 ppm of H2S show the promising potential of the BCYb infiltration approach in the development of highly active and stable Ni-GDC-based anodes fed with hydrocarbon fuels containing a high concentration of sulfur compounds.

Application of infiltrated LSCM–GDC oxide anode in direct carbon/coal fuel cells

Hybrid direct carbon/coal fuel cells (HDCFCs) utilise an anode based upon a molten carbonate salt with an oxide conducting solid electrolyte for direct carbon/coal conversion. They can be fuelled by a wide range of carbon sources, and offer higher potential chemical to electrical energy conversion efficiency and have the potential to decrease CO₂ emissions compared to coal-fired power plants. In this study, the application of (La, Sr)(Cr, Mn)O₃ (LSCM) and (Gd, Ce)O₂ (GDC) oxide anodes was explored in a HDCFC system running with two different carbon fuels, an organic xerogel and a raw bituminous coal. The electrochemical performance of the HDCFC based on a 1–2 mm thick 8 mol% yttria stabilised zirconia (YSZ) electrolyte and the GDC–LSCM anode fabricated by wet impregnation procedures was characterized and discussed. The infiltrated oxide anode showed a significantly higher performance than the conventional Ni–YSZ anode, without suffering from impurity formation under HDCFC operation conditions. Total polarisation resistance (R_p) reached 0.8–0.9 Ω cm² from DCFC with an oxide anode on xerogel and bituminous coal at 750 °C, with open circuit voltage (OCV) values in the range 1.1–1.2 V on both carbon forms. These indicated the potential application of LSCM–GDC oxide anode in HDCFCs. The chemical compatibility of LSCM/GDC with carbon/carbonate investigation revealed the emergence of an A₂BO₄ type oxide in place of an ABO₃ perovskite structure in the LSCM in a reducing environment, due to Li attack as a result of intimate contact between the LSCM and Li₂CO₃, with GDC being stable under identical conditions. Such reaction between LSCM and Li₂CO₃ was not observed on a LSCM–YSZ pellet treated with Li–K carbonate in 5% H₂/Ar at 700 °C, nor on a GDC–LSCM anode after HDCFC operation. The HDCFC durability tests of GDC–LSCM oxide on a xerogel and on raw bituminous coal were performed under potentiostatic operation at 0.7 V at 750 °C. The degradation mechanisms were addressed, especially on raw coal.

A redox-stable chromate cathode decorated with in situ grown nickel nanocatalyst for efficient carbon dioxide electrolysis

Ni nanoparticles are anchored on the surface of a chromate substrate by in situ growth, and significantly improve its performance for high-temperature CO₂ electrolysis.

Double perovskites as anode materials for solid-oxide fuel cells

Extensive efforts to develop a solid-oxide fuel cell for transportation, the bottoming cycle of a power plant, and distributed generation of electric energy are motivated by a need for greater fuel efficiency and reduced air pollution. Barriers to the introduction of hydrogen as the fuel have stimulated interest in developing an anode material that can be used with natural gas under operating temperatures 650 degrees C < T < 1000 degrees C. Here we report identification of the double perovskites Sr2Mg(1-x)MnxMoO(6-delta) that meet the requirements for long-term stability with tolerance to sulfur and show a superior single-cell performance in hydrogen and methane.