Self-healing atmospheric plasma sprayed Mn1.0Co1.9Fe0.1O4 protective interconnector coatings for solid oxide fuel cells

Abstract

Dense coatings on metallic interconnectors are necessary to suppress chromium poisoning of SOFC cathodes. Atmospherically plasma sprayed (APS) Mn1.0Co1.9Fe0.1O4 (MCF) protective layers demonstrated reduced chromium related degradation in laboratory and stack tests. Previous analyses revealed strong microstructural changes comparing the coating's as-sprayed and operated condition. This work concentrates on the layerdensification and crack-healing observed by annealing APS-MCF in air, which simulates the cathode operation conditions. The effect is described by a volume expansion induced by a phase transformation. Reducing conditions during the spray process lead to a deposition of the MCF in a metastable rock salt configuration. Annealing in air activates diffusion processes for a phase transformation to the low temperature stable spinel phase (T < 1050 °C). This transformation is connected to an oxygen incorporation which occurs at regions facing high oxygen partial pressures, as there are the sample surface, cracks and pore surfaces. Calculations reveal a volume expansion induced by the oxygen uptake which seals the cracks and densifies the coating. The process decelerates when the cracks are closed, as the gas route is blocked and further oxidation continues over solid state diffusion. The self-healing abilities of metastable APS coatings could be interesting for other applications.

Chrome Poisoning of Non-Manganiferous Cathode Materials in Solid Oxide Fuel Cells (SOFCs)

“…Finally, to almost fully prevent Cr-poisoning, protective coatings can be applied to the metallic interconnect. These can effectively reduce the volatility of Cr-species and, thus, minimize Cr-related interactions with the cathode material and their influence on the cell performance 21,[75][76][77] .…”

Effect of internal hydrocarbon reforming during coupled operation of a biomass gasifier with hot gas cleaning and SOFC stacks

“…The area of the cathode is 9 × 9 cm², determining the electrochemically active area. All interconnects, cell frames, and top and bottom plates are based on Crofer 22 APU . The metallic parts are sealed by glass sealant (Type 87 ZYBF‐2) .…”

“…All interconnects, cell frames, and top and bottom plates are based on Crofer 22 APU. 38 The metallic parts are sealed by glass sealant (Type 87 ZYBF-2). 37 A MnCo 1.9 Fe 0.1 O 4 (MCF) coating is applied via atmospheric plasma spraying (APS) on all exposed parts of the interconnector on the air side to prevent chromium poisoning.…”

Structure and Electrical Properties of Fe-Mn-Co-O Spinel

“…Low resistance is one of the requirements for IT-SOFC interconnects materials [1][2][3][4][5]. An electrical conductivity study of both materials indicates that their application should minimize electrical resistance at the electrodeinterconnect interface.…”

“…In the case of IT-SOFCs, numerous types of stainless steel have been considered as interconnect materials. Investigations have focused on chromium-rich steel because of its good electrical conductivity, durability and low cost of fabrication [1,2]. Nevertheless, chromium evaporates from the steel core to the remaining parts of SOFC at a rapid rate, subsequently poisoning the electrode materials.…”