(La,Sr)(Fe,Co)O3-based cathode contact materials for intermediate-temperature solid oxide fuel cells

Abstract

Development of the cathode contact materials (CCMs) for intermediate-temperature solid oxide fuel cells (IT-SOFCs) is a relatively new task promoted by the appearance of full-sized cells, which may operate below 700 °C with sufficient performance, on the market. CCM must ensure a low-resistive interface between interconnect and cathode and is supposed to be sintered at temperatures below 800 °C, as imposed by the specifications of IT-SOFCs and corresponding sealants. The present work is focused on the elaboration of CCMs derived from perovskite-like La0.6Sr0.4Co0.2Fe0.8O3-δ employing two approaches: introduction of the A-site cation vacancies and partial substitution by copper in B sublattice. Both approaches were found to result in a higher electrical conductivity below 800 °C if compared to the parent material. All studied materials exhibit acceptable coefficients of thermal expansion, 13.5–14.8 ppm K−1 at 25–700 °C. Area-specific resistance (ASR) of CCM/chromium barrier (Mn1.5Co1.5O4)/interconnect (Crofer 22APU) assemblies prepared by the screen-printing was measured in air at 660–750 °C. The studies revealed that morphology of CCM powder should be considered as a key parameter in the formation of interfaces with a low resistivity. The best ASR values, below 4 mΩ cm2 at 660–700 °C, were obtained for La0.6Sr0.4Co0.15Cu0.10Fe0.75O3-δ, La0.6Sr0.4Co0.15Cu0.05Fe0.80O3-δ and (La0.60Sr0.40)0.995Co0.20Fe0.80O3-δ as CCMs.