Abstract
This paper seeks to examine how the Mn–Co spinel interconnect coating microstructure can influence Cr contamination in an oxygen electrode of intermediate temperature solid oxide cells, at an operating temperature of 750 °C. A Mn–Co spinel coating is processed on Crofer 22 APU substrates by electrophoretic deposition, and subsequently sintered, following both the one-step and two-step sintering, in order to obtain significantly different densification levels. The electrochemical characterization is performed on anode-supported cells with an LSCF cathode. The cells were aged prior to the electrochemical characterization in contact with the spinel-coated Crofer 22 APU at 750 °C for 250 h. Current–voltage and impedance spectra of the cells were measured after the exposure with the interconnect. Post-mortem analysis of the interconnect and the cell was carried out, in order to assess the Cr retention capability of coatings with different microstructures.
Highlights
Volatile Cr species released from the steel interconnects of the solid oxide cell (SOC)
Among various proposed materials in the spinel family, perovskites and rare earth oxides, manganese–cobalt spinel coatings have shown a good balance in terms of their chromium blocking capability, matched thermal expansion coefficient, and high electrical conductivity at the SOC operating temperatures (500–850 ◦ C) [3,4]
electrophoretic deposition (EPD) is a fast and versatile process that allows homogeneous layers to be deposited in few seconds, and in a RT condition on complexly shaped steel components [22,23,24]
Summary
Stack, at different oxygen partial pressures, migrate and deposit on the air electrode, leading to a substantial and fast degradation of the electrochemical performance of the SOC cells. Of Mn in the Crofer 22 APU alloy; anyway, the Cr–Mn spinel that develops at the top of the chromia scale has been reported to partially limit, but not completely avoid, the oxygen electrode degradation [1]. In a recently published article by Sabato et al [28], EPD was proved to be an optimal deposition method to coat real dimension SOFC interconnects: despite the numerous corrugated and channeled surfaces on the Crofer 22 APU interconnect, the EPD-deposited Mn–Co spinel-based coating showed great stability and maintained protective properties after the stack test at 850 ◦ C
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