Dependence of SOFC cathode degradation by chromium-containing alloy on compositions of electrodes and electrolytes

Although many benefits are expected by reducing the operating temperature of solid oxide fuel cells (SOFCs) with alloy interconnectors, it should be of concern that chromium oxyhydroxide vapor generated from an oxide scale (Cr2O3), which is formed on the surface of most high temperature oxidation-resistant alloys, degrades the performance of the cathode under polarization. We have investigated a relationship between resistance against the Cr poisoning and compositions of electrode and electrolyte to show the possibility of a mitigating the Cr poisoning without reducing the chromium oxyhydroxide vapor pressure. Sr-doped LaMnO3 (LSM) electrode on yttria-stabilized zirconia electrolyte with a current collector made of a Cr-containing alloy showed fast degradation under a polarization, which was due to the precipitation of Cr2O3 at the electrode/electrolyte interface as a result of the reduction of the chromium oxyhydroxide vapor. In the present study, the degradation by the Cr poisoning has been investigated for the LSM electrode on four types of electrolytes. The degree of the degradation was found to depend on the composition of the electrolyte on which the electrode was prepared. This suggests that the electrochemical properties of the electrode/electrolyte interface influence the reduction of the chromium oxyhydroxide vapor. We have found that when La0.6Sr0.4Co0.2Fe0.8O3 and Ce0.8Sm0.2O1.9 were used as the electrode and the electrolyte, respectively, the significant Cr poisoning is not caused even in the presence of the chromium oxyhydroxide vapor at the temperature range from 923 to 1173 K. (C) 2001 The Electrochemical Society. All rights reserved.