Electrical Conducting Properties of LSF-Based Composites as an Interconnection of Tubular Type of Solid Oxide Fuel Cells

Tubular type of solid oxide fuel cells (SOFCs) is durable under high temperature operation compared to planar type SOFCs where the use of metallic interconnect is inevitable, which deteriorate electrochemical performance by Cr evaporation. On the contrary, development of ceramic interconnection has been a hurdle to fabricate tubular type SOFCs. The ceramic interconnection material must have high electronic conductivity both in oxidizing and reducing atmosphere. A gas-tight microstructure should also be obtained mostly by co-firing with anode or cathode substrates. We have been developing flat-tubular SOFCs from extruded NiO-YSZ tubular substrates. In this study we investigated (La,Sr)FeO₃ (LSF)-based composite materials as the interconnection for tubular SOFCs. La_0.8Sr_0.2FeO_3-δ, a mixed ionic and electronic conductor, was mixed with Gd- or La-doped ceria (GDC or LDC). LSF is a mixed ionic and electronic (hole) conducting material and thus shows low electrical conductivity in reducing (H2) atmosphere. However, composite materials with LSF and ceria showed moderate electrical conductivity by electronic leakage current through doped ceria in reducing atmosphere. LSF-ceria composite and LSF layers were also successfully deposited on NiO-YSZ anode substrate by conventional co-firing process. The area specific resistance of LSF/LSF-GDC bilayer on Ni-YSZ measured in air//H₂ condition was initially ~50 mΩ cm².