Evaluation of Protective Coatings for SOFC Interconnects

Abstract

Chromium poisoning is a widely recognized degradation process in solid oxide fuel cells (SOFC). Stainless steel interconnect plates, in direct contact with the cathode, have been identified as the major chromium source, raising a need for electrically conducting protective coatings for the interconnects. This work evaluates four different manganese-cobalt protective coatings manufactured on thin steel foils, made by three commercial companies and a research centre. Area specific resistance, coating microstructure, and chromium retention are compared. Measurements were done in a humid atmosphere over 1000 hours at 700 °C. An innovative measurement setup was used, in which the coated steel samples are stacked adjacent to thin palladium foils with a screen-printed lanthanum strontium cobalt layer, replicating an SOFC cathode. As a conclusion, TeerCoating Ltd’s and Turbocoating S.p.A’s coatings performed similar to the Sandvik Material Technology’s cerium-cobalt reference coating, and could be employed as such in SOFC applications.

Protective Coatings for Ferritic Stainless Steel Interconnect Materials in High Temperature Solid Oxide Electrolyser Atmospheres

“…For the oxygen side, (Co,Mn) 3 O 4 spinel coatings have been shown to be good candidates with various deposition methods and compositional variations having been tested [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. Ce/Co coatings, deposited as a metallic layer and oxidized to a spinel during operation in the stack, have also showed promising chromium retention and oxidation protection properties [30][31][32][33][34][35].…”

Composite Cu-LaFeO3Conversion Coatings on a 18Cr Ferritic Stainless Steel for IT-SOFC Interconnects: Effect of Long-Term Air Exposure at 700°C on Cr Diffusion Barrier and Electrical Properties

“…13. Briefly, the testing system consists of a multisample stack with the samples electrically connected in series and arranged to form a sandwich structure.…”

“…15 Besides, the method has been previously validated with a commercial Ce/Co coated Sandvik Sanergy HT steel used as benchmark: 13 a very low contact cell unit resistance (ca. 5 m cm −2 ) has been measured at 700…”

In-Situ Observation of Co-Ce Coated Metallic Interconnect Oxidation Combined with High-Resolution Post Exposure Analysis

“…It was later demonstrated that it prevents Cr diffusion to the top layer [11]. Several studies confirmed the beneficial effects of Ce [29] [30], even in the case of discrete particles rather than as a Ce-layer [31]. Ce was also shown to act as diffusion barrier against iron diffusion from the steel [22].…”