Chromium Impurity Effects on SOFC Cathodes Using Half-Cell Measurements

Abstract

Solid oxide fuel cells (SOFCs) offer a clean, efficient and environmental-friendly technique to convert chemical energy to electricity . In order to achieve high performance at lower operating temperature, anode-supported planar solid oxide fuel cells are usually preferred. The lower operating temperature enables the deployment of metallic interconnects based on ferritic stainless steel. The leading candidate alloy is Crofer 22 APU which is a state-of-the-art material with good high-temperature stability, high electrical conductivity and low coefficient of thermal expansion. However, the chromia oxide scale that forms on the surface of the Crofer 22 APU alloy reacts with the oxygen and water vapor to form volatile chromium species, chromium trioxide, CrO3, and chromium oxyhydroxide, CrO2(OH)2which deposit on the electrochemically active regions of the cathode. In order to understand the mechanism of chromium poisoning in SOFCs, electrolyte-supported half-cells have been fabricated. 8mol%-yttria-stabilized-zirconia pellets are used as electrolyte by uniaxial pressing. Lanthanum strontium manganite is screen printed on both side of the YSZ pellet, and a silver wire is used as the reference electrode. These half-cells have been tested at different temperatures with different humidity levels in the air, with and without contacting the Crofer 22 APU alloy. Galvanostatic current interruption (GCI) has been employed during the electrochemical test, and after the test, scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX) have been used to detect the composition near the TBPs. Figure 1