A ceramic fuel cell in an all solid-state energy conversion device that produces electricity by electrochemically combining fuel and oxidant gases across an ionic conducting oxide. Current ceramic fuel cells use an oxygen-ion conductor or a proton conductor as the electrolyte and operate at high temperatures (>600°C). Ceramic fuel cells, commonly referred to as solid-oxide fuel cells (SOFCs), are presently under development for a variety of power generation applications. This paper reviews the science and technology of ceramic fuel cells and discusses the critical issues posed by the development of this type of fuel cell. The emphasis is given to the discussion of component materials (especially, ZrO2 electrolyte, nickel/ZrO2 cermet anode, LaMnO3 cathode, and LaCrO3 interconnect), gas reactions at the electrodes, stack designs, and processing techniques used in the fabrication of required ceramic structures.

Ceramic Fuel Cells

Recent worldwide interest in building a decentralized, hydrogen-based energy economy has refocused attention on the solid oxide fuel cell (SOFC) as a potential source of efficient, environmentally friendly, fuel-versatile electric power. Due to its high operating temperature, the SOFC offers several potential advantages over polymer-based fuel cells, including reversible electrode reactions, low internal resistance, high tolerance to typical catalyst poisons, production of high-quality waste heat for (among other uses) reformation of hydrocarbon fuels, as well as the possibility of burning hydrocarbon fuels directly. Today, SOFCs are much closer to commercial reality than they were 20 years ago, due largely to technological advances in electrode material composition, microstructure control, thin-film ceramic fabrication, and stack and system design. These advances have led to dozens of active SOFC development programs in both stationary and mobile power and contributed to commercialization or development in a number of related technologies, including gas sensors,1 solid-state electrolysis devices,2 and iontransport membranes for gas separation and partial oxidation.3 Many reviews are available which summarize the technological advances made in SOFCs over the last 15-35 yearssreaders who are primarily interested in knowing the state-of-the art in materials, design, and fabrication (including the electrodes) are encouraged to consult these reviews.4-12 This review focuses on the factors governing SOFC cathode performancesadvances we have made over † Dedicated to Brian Steele, 1929-2003. Researcher, Entrepreneur, Consensus Seeker. 4791 Chem. Rev. 2004, 104, 4791−4843

Factors Governing Oxygen Reduction in Solid Oxide Fuel Cell Cathodes

The generation of energy by clean, efficient and environmental-friendly means is now one of the major challenges for engineers and scientists Fuel cells convert chemical energy of a fuel gas directly into electrical work, and are efficient and environmentally clean, since no combustion is required Moreover, fuel cells have the potential for development to a sufficient size for applications for commercial electricity generation This paper outlines the acute global population growth and the growing need and use of energy and its consequent environmental impacts The existing or emerging fuel cells’ technologies are comprehensively discussed in this paper In particular, attention is given to the design and operation of Solid Oxide Fuel Cells (SOFCs), noting the restrictions based on materials’ requirements and fuel specifications Moreover, advantages of SOFCs with respect to the other fuel cell technologies are identified This paper also reviews the limitations and the benefits of SOFCs in relationship with energy, environment and sustainable development Few potential applications, as long-term potential actions for sustainable development, and the future of such devices are discussed

Solid oxide fuel cells (SOFCs): a review of an environmentally clean and efficient source of energy

Progress in material selection for solid oxide fuel cell technology: A review

The composition and microstructure of cathode materials has a large impact on the performance of solid oxide fuel cells (SOFCs). Rational design of materials composition through controlled oxygen nonstoichiometry and defect aspects can enhance the ionic and electronic conductivities as well as the catalytic properties for oxygen reduction in the cathode. Cell performance can be further improved through microstructure optimization to extend the triple-phase boundaries. A major degradation mechanism in SOFCs is poisoning of the cathode by chromium species when chromium-containing alloys are used as the interconnect material. This article reviews recent developments in SOFC cathodes with a principal emphasis on the choice of materials. In addition, the reaction mechanism of oxygen reduction is also addressed. The development of Cr-tolerant cathodes for intermediate temperature solid oxide fuel cells, and a possible mechanism of Cr deposition at cathodes are briefly reviewed as well. Finally, this review will be concluded with some perspectives on the future of research directions in this area.

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Cathode materials for solid oxide fuel cells: a review

Structure and electrical properties of La1−xSrxCo1−yFeyO3. Part 1. The system La0.8Sr0.2Co1−yFeyO3

Structure and electrical properties of La1 − xSrxCo1 − yFeyO3. Part 2. The system La1 − xSrxCo0.2Fe0.8O3

The effect of quaternary additions of 0.5% Y, 0.5 and 1.0% Th to a base alloy of Ni-10CR-5Al on the oxidation behavior and mechanism was studied during oxidation in air over the range of 1000 to 1200 C. The presence of yttrium decreased the oxidation kinetics slightly, whereas, the addition of thorium caused a slight increase. Oxide scale adherence was markedly improved by the addition of the quaternary elements. Although a number of oxides formed on yttrium containing alloys, quantitative X-ray diffraction clearly showed that the rate-controlling step was the diffusion of aluminum through short circuit paths in a thin layer of alumina that formed parabolically with time. Although the scale adherence of the yttrium containing alloy was considerably better than the base alloys, spalling did occur that was attributed to the formation of the voluminous YAG particles which grew in a mushroom-like manner, lifting the protective scale off the subrate locally. The YAG particles formed primarily at grain boundaries in the substrate in which the yttrium originally existed as YNi9.

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The effect of yttrium and thorium on the oxidation behavior of Ni-Cr-Al alloys

(CeO{sub 2}){sub 0.8}(SmO{sub 1.5}){sub 0.2}(CSO) has been suggested for solid oxide fuel cell (SOFC) applications, because of its higher electrical conductivity and chemical stability, compared to other ceria-based materials. However, CSO is difficult to densify under conditions compatible with other SOFC components. A thin film synthesis technique has been developed for the fabrication of dense CSO films from precursor solutions at relatively low temperatures. Dense, smooth, and homogeneous films were obtained on Pt, single-crystal Si, and La{sub 0.6}Sr{sub 0.4}Co{sub 0.2}Fe{sub 0.8}O{sub 3} (LSCF) substrates by spin-coating a polymeric precursor and subsequent heat-treatment. Crystallization of the film occurred at temperatures as low as 320 C. The developed oxide film did not react with La{sub 0.8}Sr{sub 0.2}MnO{sub 3}, LSCF, or (ZrO{sub 2}){sub 0.84}(YO{sub .15}){sub 0.16}(YSZ) at temperatures up to 1,200 C. When a CSO layer was applied between LSCF and YSZ, a significant improvement in the interfacial resistance was observed. The results suggest that CSO can be used as a buffer layer on YSZ electrolytes for improved performance of high temperature SOFCs.

Synthesis and Characterization of ( CeO2 ) 0.8 ( SmO1.5 ) 0.2 Thin Films from Polymeric Precursors

A method for preparing a substrate coated with a polycrystalline, metal oxide film using polymeric precursors. The oxide films prepared by the method of the present invention are dense (i.e., substantially free of cracks and pinholes) and may be used, for example, as an electrolyte or electrode in intermediate temperature solid oxide fuel cells (SOFCs) or as gas separation membranes.

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M. M. Nasrallah

Papers

Structure and electrical properties of La1−xSrxCo1−yFeyO3. Part 1. The system La0.8Sr0.2Co1−yFeyO3

Structure and electrical properties of La1 − xSrxCo1 − yFeyO3. Part 2. The system La1 − xSrxCo0.2Fe0.8O3

The effect of yttrium and thorium on the oxidation behavior of Ni-Cr-Al alloys

Synthesis and Characterization of ( CeO2 ) 0.8 ( SmO1.5 ) 0.2 Thin Films from Polymeric Precursors

Method of coating a substrate with a metal oxide film from an aqueous solution comprising a metal cation and a polymerizable organic solvent