CHAPTER 6 Development of SOFC Interconnect Stainless Steels

Abstract

The chapter introduces components and working principle of solid oxide fuel cells (SOFCs). It is followed by the explanation on the choices of materials focussing on ferritic stainless steels. The review is further made on the required properties of these steels, i.e. low oxidation rate, low chromium species volatilisation rate, high electrical conductivity and good scale adhesion. For the oxidation aspect, the behaviour of stainless steel interconnect in cathode, anode (hydrogen and biogas), and dual atmospheres are described. Surface modification by pre-oxidation and coatings to improve the oxide electrical conductivity and to reduce chromium species volatilisation is finally reviewed.

Mn-Co spinel coatings on Crofer 22 APU by electrophoretic deposition: Up scaling, performance in SOFC stack at 850 °C and compositional modifications

“…The metallic interconnect, during its operation in the oxygen electrode compartment of a solid oxide cells (SOC) stack, reacts with oxygen and steam forming volatile Cr (VI) species that migrate and react at the electrolyte-oxygen electrode three phase boundary, thus "poisoning" the electrochemical activity with detrimental consequences on the stack performance. Chromium poisoning is one of the most important degradation phenomena [1][2][3].…”

Initial stage oxidation corrosion of commercial ferritic stainless steels with different Cr contents at 650 °C for solid oxide fuel cells

“…The element diffusion in the oxide scale and the kinetics of the surface reaction escalate with the increase in temperature. Most investigations focused on SOFCs operating under a high temperature above 750 °C [ [28] , [29] ]. With the development of ceramic technology, the thickness of electrolyte decreases to <10 μm such that the operating temperature of SOFC drops to <750 °C [ 30 ].…”

Fabrication of Mn–Co Alloys Electrodeposited on AISI 430 Ferritic Stainless Steel for SOFC Interconnect Applications

“…An interconnect is a main component that is located between two adjacent repeated units, providing the electrical connection between the SOFCs, and simultaneously transports fuel gases (anode side) and air (cathode side). Ferritic stainless steels are promising materials to use for interconnects, instead of the traditional use of ceramics for interconnects, due to the cost-effectiveness and matching of the thermal expansion coefficient, which is compatible with the electrode materials of the SOFC in the operating temperature range of 650-800 • C [5][6][7][8]. Under this high operating temperature, the exposure of ferritic stainless steels in the cathode and anode atmospheres results in the formation of a chromium oxide (Cr 2 O 3 ) layer at the surface.…”