Chemical Stability of Ferritic Alloy Interconnect for SOFCs

Abstract

A ferritic alloy interconnect was studied through solid oxide fuel cell ͑SOFC͒ stack operation at intermediate temperatures. Certain pretreatment of the alloy surface proved to be effective for controlling initial degradation of the stack performance, presumably by the formation of stable and conductive oxide scale. Evidences were found that glass sealant containing alkali metals affected the oxidation behavior of the alloy surface not in contact with the cathode material. A thick scale rich in iron tended to be formed at the air side in the vicinity of the glass sealant, while a thinner scale rich in chromium was preferably found in the other. Alkali metal components were found in that thick oxide layer. At the interface between the alloy and the cathode current collector, a strontium chromate, which might cause chromium poisoning at the cathode/electrolyte interface, was formed, and that was found to be distributed over the current collector away from the interface. A thermodynamic equilibrium calculation using a thermodynamic database revealed that the chromium component is highly reactive with alkali or alkali earth metals and forms stable chromates. Some of those chromates are very stable and may hinder the formation of stable oxide scale such as Mn-Cr-O spinels or Cr 2 O 3 , and may cause the severe oxidation of the alloy.

Oxidation and Electrical Behavior of Mn-Co-Coated Crofer 22 APU Steel Produced by a Pack Cementation Method for SOFC Interconnect Applications

“…The deposition of such chromium compounds poisons the cathode's electrochemical activity and results in drastic deterioration in the cell performance. The cathode Cr poisoning phenomenon has been the subject of many research studies [37][38][39][40][41][42][43][44][45][46][47][48][49][50]. Hence, the application of a Mn-Co coating on Crofer 22 APU will reduce cathode poisoning, thereby increasing the efficiency of the fuel cell.…”

Progressive activation of degradation processes in solid oxide fuel cells stacks: Part I: Lifetime extension by optimisation of the operating conditions

“…In an SOFC stack, the cost-effective interconnects, sealants and gas diffusion layers (GDL) amplify material incompatibilities, hence the degradation, because of their lower stability than the MEA materials in the SOFC environment [16]. The transport of contaminants by the gases increases the distance over which detrimental interactions operate [17]. The uneven distributions of temperature, current density, gas composition and overpotential in a stack, induce different local degradation rates.…”

Compression Properties and Leakage Tests of Mica‐Based Seals for SOFC Stacks

“…Chemical reactions have also been reported between glass-ceramics and other stack components. These reactions can include cross-diffusion [3] and excessive surface and internal oxidation at steel-sealant interface [4] as well as increased chromium evaporation from interconnect steels [5].…”