Evaluation of ferritic steels for use as interconnects and porous metal supports in IT-SOFCs

Abstract

As a way of reducing the production costs of stacks by replacing ceramic components with metal components with a similar thermal expansion coefficient (TEC), today, much of the research work has focused on SOFCs operating at temperatures of under 800 °C. Some semi-commercial ferritic stainless steels (FSS) satisfy this TEC. Ikerlan has evaluated samples of two of these. Also, AMETEK stainless steel powders were tested in sintered disks until they were completely densified in order to compare results from dense and porous materials. The first tests performed by Ikerlan were conducted with dense samples and included the oxidation test in air at 800 °C and measurements of contact surface electrical resistance (area specific resistance, ASR), to compare electrochemical techniques (electrochemical impedance spectroscopy, EIS) with the traditional four-wire method and indirect measuring of the resistance through current and voltage measurements. An alloy from the last melt manufactured by the company ThyssenKrupp VDM GmbH performed best. These results did not differ greatly from the previous laboratory results attained during alloy development. Only AMETEK powder metallurgy materials were tested as porous bodies, to compare these with these dense materials, and were found to provide much higher oxidation levels, as might be expected. While dense materials can operate under the working conditions of the SOFC, porous materials still need new alloys.