During the last three decades, a large number of investigations has be
en reported pertaining to the science and technology of solid oxide fu
el cells (SOFCs) based mainly on the yttria-stabilized zirconia (YSZ)
electrolyte. Because of the problems associated with the high temperat
ure of operation (approximately 1000-degrees-C) of the YSZ-based cells
, there has been a substantial effort to develop alternative electroly
tes with ionic conductivity comparable to that of YSZ at relatively lo
wer temperatures. This review presents a systematic evolution in the a
rea of the development of new electrolytes based on bismuth sesquioxid
e for fuel cell applications at moderate temperatures.