Development of Potassium Doped, Oxygen Deficient Complex Perovskite Oxides for Solid Oxide Fuel Cell Applications

Abstract

Developing new proton and oxide ion conducting perovskite materials with good chemical stability is of great importance for the performance enhancement of solid state electrochemical devices such as Solid Oxide fuel cells (SOFCs) oxygen separation membranes, hydrogen/oxygen sensors hydrogen permeable membranes etc. The presence of vacant positions in the oxygen sublattice of a material is a necessary condition for the possibility of introducing water into the crystal structure and enhance the proton conductivity. Similarly, the vacant position in oxygen sublattice at high temperature enables the oxide ion conductivity. Complex perovskites of type A3(B1+xB'2-x)O9-3x/2 (A=Ba, Sr, B=Ca, Sr and Ba, B'=Nb, Ta) is one such type of materials which were found to behave as both proton and oxide ion conductors. This dual property in perovskite materials is mainly attributed to the cationic ordering and anionic defects in the form of oxygen vacancies. The new way of improving conductivity of such complex perovskite materials is substitution of lower valent cations thereby creating additional oxygen vacancies and reducing grain boundary resistance. The objective of the present work is to enhance the electrical conductivity and chemical stability of the 1:1 ordered oxygen deficient complex perovskite oxides for intermediate temperature SOFC electrolyte applications. In the present work A1-xKx(B0.50B'0.50)O2.75-δ (A=Ba, Sr, B=Ca, Sr and Ba, B'=Nb, Ta) complex perovskites were synthesised by solid state reaction method. Monovalent potassium was doped in the divalent A site with different degree of substitutions as x= 0, 0.25, 0.50, 0.75 and 1. Perovskites with nominal compositions were prepared by ball milling for longer hours (20h) followed by calcinations and sintering. Based on the results obtained, after structural, morphological and electrical characterizations, the composition which exhibited the highest electrical conductivity and chemical stability is chosen for device fabrication. A single button type SOFC was fabricated using this material as electrolyte and its performance was analysed.