Perspective of perovskite-type oxides for proton conducting solid oxide fuel cells

Solid oxide fuel cell (SOFC) is one of the promising solid-state electrochemical device that converts chemical energy of varied fuels into electricity with high efficiency. However, its market acceptability is hindered due to its high operating temperature (800-1000 degrees C) that is dictated by the use of conventional oxide ion conducting yttria-stabilized zirconia electrolyte and sluggish oxygen reduction reaction properties of conventional Sr-doped LaMnO3 cathodes. Hence, major focus in the field of SOFCs has been directed towards reducing the operating temperature of current SOFCs to intermediate temperatures (500-700 degrees C), with the emphasis on material development for advanced electrolytes and cathodes. Due to the ease of doping on both A and B sites, structural stability, and ability to show both ionic (O2-, H+) and electronic conductivity, perovskite-type ABO(3) (A = Sr, Ba; B = Ce, Zr) ceramics has been the focus of research towards development of proton conducting SOFCs (H-SOFCs). Despite significant developments, there is a general lack of understanding regarding future research directions in this field. In this review article, we first present an overview of crystal structure, dopant composition and its correlation with chemical stability and electrical conductivity followed by existing challenges associated with cathode development for H-SOFCs and achieving high fuel cell performance. We also outline the recent efforts directed towards reducing the H-SOFCs operating temperature.