The papers included in this issue of ECS Transactions were originally presented in the symposium ¿Ionic and Mixed Conducting Ceramics 6¿, held during the 213th meeting of The Electrochemical Society, in Phoenix, Arizona from May 18 to 23, 2008.

This book provides a state-of-the-art collection of recent papers on interfaces in heterogeneous ceramic systems presented at the 6th Pacific Rim Conference on Ceramic and Glass Technology (PacRim 6) in September of 2005 in Maui, Hawaii. The book is logically divided into 5 sections on interfaces, including theory and modeling, wetting phenomena, heterogeneous interfaces in high-temperature superconductors, bio-interfaces, and new developments in instrumentation that aid in the characterization of interfaces.

Mixed-conducting (electronic and ionic conducting) dense ceramics are used in many applications, including fuel cells, gas separation membranes, batteries, sensors, and electrocatalysis. This paper describes mixed-conducting ceramic membranes that are being developed to selectively remove oxygen and hydrogen from gas streams in a nongalvanic mode of operation (i.e., with no electrodes or external power supply). Ceramic membranes made of Sr-Fe-Co oxide (SFC), which exhibits high combined electronic and oxygen ionic conductivities, can be used for high-purity oxygen separation and/or partial oxidation of methane to synthesis gas (syngas, a mixture of CO and H[sub 2]). The electronic and ionic conductivities of SFC were found to be comparable in magnitude. Steady-state oxygen permeability of SFC has been measured as a function of oxygen-partial-pressure gradient and temperature. For an[approx]3-mm-thick membrane, the oxygen permeability was[approx]2.5 scc[center-dot]cm[sup[minus]2][center-dot]min[sup[minus]1] at 900 C. Oxygen permeation increases as membrane thickness decreases. Tubular SFC membranes have been fabricated and operated at 900 C for[approx]1000 h in converting methane into syngas. The oxygen permeated through the membrane reacted with methane in the presence of a catalyst and produced syngas. We also studied the transport properties of yttria-doped BaCeO[sub 3[minus][delta]] (BCY) by impedance spectroscopy and open-cell voltage (OCV) measurement. Total conductivity of the BCY sample increased from[approx]5 x 10[sup[minus]3][Omega][sup[minus]1][center-dot]cm[sup[minus]1] to[approx]2 x 10[sup[minus]2][Omega][sup[minus]1][center-dot]cm[sup[minus]1], whereas the protonic transference number decreased from 0.87 to 0.63 and the oxygen transference number increased from 0.03 to 0.15 as temperature increased from 600 to 800 C. Unlike SFC, in which the ionic and electronic conductivities are nearly equivalent BCY exhibits protonic conductivity that is significantly higher than its electronic conductivity. To enhance the electronic conductivity and therefore to increase hydrogen permeation, metal powder was combined with the BCY to form a cermet membrane, Nongalvanic permeation of hydrogen through the BCY-cermet membranes was demonstrated and characterized as a function of membrane thickness.

This book provides a comprehensive overview of contemporary research and emerging measurement technologies associated with gas transport in solid oxide fuel cells. Within these pages, an introduction to the concept of gas diffusion in solid oxide fuel cells is presented. This book also discusses the history and underlying fundamental mechanisms of gas diffusion in solid oxide fuel cells, general theoretical mathematical models for gas diffusion, and traditional and advanced techniques for gas diffusivity measurement.