On the Effect of Surface Treatment to Improve Oxidation Resistance and Conductivity of Metallic Interconnects for SOFC in Operating Conditions

Abstract

Due to the reduction of operating temperature from 1000°C to 800°C, chromia forming alloys are the best candidates for interconnects in Solid Oxide Fuel Cells (SOFCs). These interconnects have to be operational in service conditions, at 800°C in air (cathode side) and in humidified hydrogen (anode side). The performance of the interconnect stainless steels is limited by the oxide scale formation (chromia), the low electronic conductivity of this scale and the possible volatility of chromium oxides. In the field of high temperature oxidation of metals, it is well known that the addition of a nanometric layer made of reactive element oxide such as, La2O3, Nd2O3 and Y2O3 by MOCVD (Metal Organic Chemical Vapor Deposition) on alloy surface resulted in an important improvement in the high temperature oxidation resistance. These coatings are made on metallic alloys in order to form perovskite oxides such as LaCrO3, NdCrO3 and YCrO3, which are expected to present a good conductivity at 800°C in air. However, this temperature looks somewhat too low to guarantee the formation of perovskite oxides and thus to improve the oxidation resistance and electrical conductivity. In fact, XRD analyses revealed that for Y2O3 coatings, perovskite oxides were not formed after oxidation in air at 800°C for 100 hours. The goal of this study is to perform pre-oxidation at 1000°C for 2 hours in air under atmospheric pressure on coated Crofer22APU to pre-form perovskite phases. The so-prepared perovskite were tested in a thermobalance in air. Experiments performed in H2/10%H2O under 150 mbar at 800°C validated the coating influence from the anode side as well as the cathode side. The corrosion products were analyzed after 100 hours ageing at 800°C by SEM, EDX, and XRD. ASR (Area Specific Resistance) was measured for the same times and temperature in air.