Electrochemical properties of layered perovskite (LnxSr4-x MyFe6yO13+δ; Ln = La, Pr, Sm AND M = Co, Ni) as cathodes forintermediate - temperature solid oxide fuel cells

Abstract

Layered perovskites, Sr4Fe6O13, LaxSr4-xFe6O13, PrxSr4-xFe6O13, Smx Sr4-xFe6O13, Sr4CoxFe6-xO13, and Sr4NixFe6-xO13 have been investigated as cathode materials for intermediate – temperature solid oxide fuel cell (IT-SOFC). All layered oxides were prepared through conventional solid – state reaction method with the respective calcination and sintering temperatures of 850oC for 16 hours and 1185oC for 5 hours and they exhibited a gradual phase transformation from the pure layered phase to the perovskite phase with increasing the dopant content. In addition, the incorporation of Pr, Sm, and Co led to the increasing of electrical conductivity in PSFx, SSFx, and SFCox oxides whereas doping of La and Ni resulted in the transition in electrical conduction from semiconducting to metallic – like behaviours for LSFx and SFNix oxides. XPS analyses and thermogravimetric analyses revealed the different charge compensation mechanisms in lanthanide – and transition metal – containing oxides. The reduction in polarisation resistances with the increased dopant concentration was also observed, in general, for all oxides. The increase in the electrical conductivity and the decrease of the polarisation resistance of the synthesised oxides with increasing the dopant concentration have stemmed from the synergistic effect on the presence of both perovskite and layered phases that provided fast oxide ion diffusion channels and acted as a continuous network for electron transport.