Ionic conduction and applications

Abstract

Solid state ionic conductors are crucial to a number of major technological developments, notably in the domains of energy storage and conversion and in environmental monitoring (such as battery, fuel cell and sensor technologies). Solid state ionic membranes based on fast ion conductors potentially provide important advantages over liquid electrolytes, including the elimination of sealing problems improved stability and the ability to miniaturize electrochemical devices using thin films. This chapter reviews methods of optimizing ionic conduction in solids and controlling the ratio of ionic to electronic conductivity in mixed conductors. Materials are distinguished based on whether they are characterized by intrinsic versus extrinsic disorder, amorphous versus crystalline structure, bulk versus interfacial control, cation versus anion conduction and ionic versus mixed ionic–electronic conduction. Data for representative conductors are tabulated. A number of applications that rely on solid state electrolytes and/or mixed ionic–electronic conductors are considered, and the criteria used to choose such materials are reviewed. Emphasis is placed on fuel cells, sensors and batteries, where there is strong scientific and technological interest. The chapter concludes by considering how solid state ionic materials are likely to be used in the future, particularly in light of the trend for miniaturizing sensors and power sources and the interest in alternative memory devices based on memristors.