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

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

Impedance and dielectric spectroscopy revisited: Distinguishing localized relaxation from long-range conductivity

▪ Abstract Several recent experimental and numerical investigations have contributed to the improved understanding of the electrochemical mechanisms taking place at solid oxide fuel cell (SOFC) cathodes and yielded valuable information on the relationships between alterable parameters (geometry/material) and the cathodic polarization resistance. Efforts to reduce the polarization resistance in SOFCs can benefit from these results, and some important aspects of the corresponding studies are reviewed. Experimental results, particularly measurements using geometrically well-defined Sr-doped LaMnO3 (LSM) cathodes, are discussed. In regard to simulations, the different levels of sophistication used in SOFC electrode modeling studies are summarized and compared. Exemplary simulations of mixed conducting cathodes that show the capabilities and limits of different modeling levels are described.

Solid Oxide Fuel Cell Cathodes: Polarization Mechanisms and Modeling of the Electrochemical Performance

Electrode polarization is studied by means of a current interruption method with the aid of a reference electrode. In this way anodic and cathodic overpotentials, η, can be measured separately, and the electrolyte polarization (IR drop) can be distinguished from the electrode overpotentials. Platinum paste electrodes are used with several doped ceria electrolytes in oxygen‐argon gas atmospheres. At high , the curves obey the Butler‐Volmer equation, with transfer coefficients of unity, both for anodic and cathodic polarizations. This result implies a charge‐transfer (or activation) mechanism. Study of the exchange current, , as a function of and temperature shows that oxygen for the charge‐transfer process is supplied through adsorbed adatoms on the Pt electrode surface, obeying the Langmuir isotherm. An activation energy of 1.75 eV is obtained for the charge‐transfer step. At low , limiting‐current behavior is obtained for the cathodic polarization, characteristic of a concentration polarization. A scanning electron microscope study of the electrode structure helps to understand the deterioration of electrical properties which occurs when samples are subjected to high temperatures and/or current densities.

A. S. Nowick

Papers

Cathodic and Anodic Polarization Phenomena at Platinum Electrodes with Doped CeO2 as Electrolyte I . Steady‐State Overpotential