Materials for IT-SOFC stacks 35 years R&D: the inevitability of gradualness?

A personal view is presented of developments over the period 1964-1999 that have gradually made possible the fabrication of IT-SOFC stacks operating a t 500 degreesC. Although conceptual IT-SOFC designs were available in the e arly 1960s, their implementation had to await a much better understanding o f various topics including: selection of optimal dopant type and concentrat ion for solid electrolytes; the influence of microstructure on ionic conduc tion in ceramics; and the mechanism of oxygen ion formation and injection i nto solid electrolytes. The latter two topics have benefited immeasurably b y the introduction of relevant instrumental techniques involving the use of frequency response analysers, and dynamic SIMS equipment to measure O-18/O -16 profiles in oxide electrolytes and mixed conductors. The parallel devel opment of hydrocarbon reforming technology has also stimulated interest in IT-SOFC systems as syngas can now be effectively produced from natural gas at intermediate temperatures. With deregulation stimulating the introductio n of distributed (embedded) electric power generation, the commercial futur e of micro-CHP units incorporating IT-SOFC stacks appears assured with entr y into the market expected early in the next millennium. (C) 2000 Elsevier Science B.V. All rights reserved.