Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are dee...

Fundamentals and Catalytic Applications of CeO2-Based Materials

Despite being first demonstrated over 160 years ago, and offering significant environmental benefits and high electrical efficiency, it is only in the last two decades that fuel cells have offered a realistic prospect of being commercially viable. The solid oxide fuel cell (SOFC) offers great promise and is presently the subject of intense research activity. Unlike other fuel cells the SOFC is a solid-state device which operates at elevated temperatures. This review discusses the particular issues facing the development of a high temperature solid-state fuel cell and the inorganic materials currently used and under investigation for such cells, together with the problems associated with operating SOFCs on practical hydrocarbon fuels.

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Solid oxide fuel cells

Solid oxide fuel cells (SOFCs) have the promise to improve energy efficiency and to provide society with a clean energy producing technology. The high temperature of operation (500−1000 °C) enables the solid oxide fuel cell to operate with existing fossil fuels and to be efficiently coupled with turbines to give very high efficiency conversion of fuels to electricity. Solid oxide fuel cells are complex electrochemical devices that contain three basic components, a porous anode, an electrolyte membrane, and a porous cathode. In this short review, a survey of the types and properties of materials that have been considered for each of these components is presented with an emphasis on the requirements for operation at intermediate temperature (500−800 °C). Some directions for future research are discussed.

Materials for Solid Oxide Fuel Cells

High temperature solid oxide fuel cells (SOFCs), typified by developers such as Siemens Westinghouse and Rolls-Royce, operate in the temperature region of 850–1000 °C. For such systems, very high efficiencies can be achieved from integration with gas turbines for large-scale stationary applications. However, high temperature operation means that the components of the stack need to be predominantly ceramic and high temperature metal alloys are needed for many balance-of-plant components. For smaller scale applications, where integration with a heat engine is not appropriate, there is a trend to move to lower temperatures of operation, into the so-called intermediate temperature (IT) range of 500–750 °C. This expands the choice of materials and stack geometries that can be used, offering reduced system cost and, in principle, reducing the corrosion rate of stack and system components.This review introduces the IT-SOFC and explains the advantages of operation in this temperature regime. The main advances made in materials chemistry that have made IT operation possible are described and some of the engineering issues and the new opportunities that reduced temperature operation affords are discussed.This tutorial review examines the advances being made in materials and engineering that are allowing solid oxide fuel cells to operate at lower temperature. The challenges and advantages of operating in the so-called ‘intermediate temperature’ range of 500–750 °C are discussed and the opportunities for applications not traditionally associated with solid oxide fuel cells are highlighted. This article serves as an introduction for scientists and engineers interested in intermediate temperature solid oxide fuel cells and the challenges and opportunities of reduced temperature operation.

Intermediate temperature solid oxide fuel cells

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

Physical, chemical and electrochemical properties of pure and doped ceria

This paper gives an extract of available data on the physical, chemical, electrochemical and mechanical properties of pure and doped ceria, predominantly in the temperature range from 200 to 1000°C. Several areas are pointed out where further research is needed in order to make a better basis for the evaluation of the real potential and limits for the practical application of ceria in solid oxide fuel cells and other solid state electrochemical devices.

Physical, Chemical and Electrochemical Properties of Pure and Doped Ceria

The thermal expansion behavior and mechanism of A-site-deficient lanthanum manganite perovskites, La{sub 1{minus}x}MnO{sub 3} (0 < x {le} 0.1), and alkaline earth metal (AE)-doped lanthanum manganite perovskites, La{sub 1{minus}x}AE{sub x}MnO{sub 3} (AE = Ca and Sr, 0 {le} x {le} 0.4), under oxidizing atmospheres have been investigated. The average linear thermal expansion coefficients of the AE-doped lanthanum manganites decreased with increasing Ca content up to 20 mol % and with increasing Sr content up to 10 mol %, and then increased. During the thermal cycle measurement, the La{sub 1{minus}x}MnO{sub 3} (0 {le} x {le} 0.1) perovskite samples and the La{sub 1{minus}x}AE{sub x}MnO{sub 3} perovskites (0 {le} x {le} 0.3) shrank, while no anomalous shrinkage behavior was observed for the La{sub 0.6}AE{sub 0.4}MnO{sub 3} samples. From the results of high-temperature X-ray diffraction analysis, no dependency of cell volume of the perovskites on aging time at selected temperatures and on thermal cycles was observed.

Geoff A. Tompsett

Papers

Physical, chemical and electrochemical properties of pure and doped ceria

Physical, Chemical and Electrochemical Properties of Pure and Doped Ceria

Thermal‐Expansion Behaviors and Mechanisms for Ca‐ or Sr‐Doped Lanthanum Manganite Perovskites under Oxidizing Atmospheres

Fabrication processing condition for dense sintered La0.6AE0.4MnO3 perovskites synthesized by the coprecipitation method (AE=Ca and Sr)