PNNL

Abstract

The requirements for low cost and high-tempurater corrosion resistance for bipolar interconnect plates in solid oxide fuel cell (SOFC) stacks has directed attention to the use of metal plates with oxidation resistant coatings. Candidate coatings must exhibit chemical and thermal-mechanical stability and high electrical conductivity during long-term (>400,000 hrs) exposure to SOFC operatong conditions. The high temperature oxidation resistance and surface electrical donductivity of 304, 440A,a dn Crofer-22 APU steel coupons, with and without multilayer and/or superlattice coatings from a Cr-Al-N system were investigated as a function of exposure in an oxidization atmosphere at high temperatures. The coatins were deposited using large area filtered arc depsition (LAFAD) technology [1], and subsequently annealed in air at 800 degrees C for varying times. Area specific resistance and activation energy for electrical conductivity of oxidized coupons were measured using a 4-point technique with Pt paste for electrical contact between facing oxidized coupon surfaces. The surface compositon, structure and morphology of the coupons were characterized using RBS, nuclear reaction analysis, XPS, SEM, and AFM techniques. The structure of the CRN/CrAlN multilayered superlattice coatings was characterized by TEM. By altering the architecture of the coating layers, both surface electrical conductivity and oxidation resistance [2] improved signigicantly for some of the coated samples tested up to ~100hrs.