31.8: Interconnection

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For the interconnection, an inert and impervious material is needed. It should withstand both oxidising and reducing environments. Lanthanum chromite seems to have the necessary properties in systems operating at 1000 °C. Depending on doping, this material matches the thermal expansion coefficient of LSM. For lower temperatures, metallic based alloys can be used. Again, plasma spraying is the most economic method of applying the interconnect layer on the electrode. Although lanthanum provides cell life times of up to 70,000 h, it is not perfectly inert: it expands in the presence of hydrogen, causing cracking, especially at large planar stacks.

Section of SOFC stack with interconnect. From top to bottom: steel, Ni-mesh, cell, contact paste, interconnect steel (Image courtesy of Forschungszentrum Jülich)

Large lanthanum chromite interconnects are made from fine powder, which is prepared as a mixture of the desired components: lanthanum, strontium and chromium nitrate. This mixture is reacted with glycene at high temperatures. This can be compacted to form plates or extruded to make tubes. It is difficult to sinter the powder to full density.