Chromium deposition and poisoning in dry and humidified air at (La 0.8Sr 0.2) 0.9MnO 3+ δ cathodes of solid oxide fuel cells

Abstract

Chromium deposition and poisoning on a (La 0.8Sr 0.2) 0.9MnO 3+ δ (LSM) cathode of solid oxide fuel cells in dry and humidified (3% H 2O) air are studied in detail at 900 °C in the presence of a Fe–Cr metallic interconnect. In the absence of interconnect, the LSM cathode shows similar electrochemical activities for the O 2 reduction reaction in the dry and humidified air. However, in the presence of a Fe–Cr metallic interconnect the performance of the LSM cathode in humidified air is much poorer than that in dry air. For example, in the presence of the Fe–Cr metallic interconnect, the increase in the overpotential after polarization at 200 mA cm −2 for 1200 min for the O 2 reduction on an LSM cathode in humidified air is 566 mV, substantially higher than 234 mV measured for the reaction in dry air. Cr deposition in humidified air is also accelerated as compared to that in dry air. The significantly high Cr poisoning and deposition for the reaction in humidified air on the LSM cathode are most likely due to the high partial pressure of the gaseous Cr oxyhydroxide species formed. The results indicate that for SOFCs using Fe–Cr metallic interconnect, the humidity in air on the cathode side should be kept as low as possible.