From Ideal to Stack-like Contacting of an SOC

Abstract

The performance of an SOC depends on the testing environment. Regarding single cell tests with ideal contacting (gold and nickel meshes) and inert flow fields (Al2O3), the performance is limited by the intrinsic losses in the cell as contact losses and any poisoning effects are minimized. In an SOC-stack exhibiting metallic interconnectors, the performance is furthermore affected by contact resistances and limitations in gas supply. In this contribution single cell testing is extended to a stack-like contacting applying three different metallic interconnectors (Crofer 22 APU, ASTM 441 and UNS S44330) with and without a cerium-cobalt PVD-coating. Cell performance and losses are analyzed by IV-characteristics, impedance spectroscopy and DRT analysis. For all uncoated interconnectors, significant performance losses due to increased contact losses and air electrode polarization were observed. With the CeCo-coating losses could be drastically reduced leading to a cell performance close to the ideal case for all three steel grades.

Stack-like Contacting in Solid Oxide Cells: Electrochemical Characterization and Modeling

“…9, gas diffusion losses at the air electrode become zero under these conditions. However, in order to be able to compare the measurements with the results from a previous work, 19 a flow rate of 250 sccm air was set at the air electrode as it was also the case there.…”

“…Nevertheless, mounting the cell with an LSCF contact paste in the liquid state as shown in Ref. 19 is also used in this study as a benchmark and for reference purposes.…”

“…[14][15][16][17][18] In addition, a protective coating is beneficial in order to reduce contact losses between the MIC and air electrode. [19][20][21][22] Still, an additional Cathode (air electrode) Contact Layer (CCL) can be applied to minimize the contact losses. 17,[23][24][25][26] Such a CCL can also level out insufficient contacting due to surface roughness related to manufacturing of the MIC and air electrode.…”

“…28,29 In a previous work, a liquid contact paste made of lanthanum-strontium-cobalt-iron oxide (LSCF) applied by screenprinting onto the air electrode was used in combination with a physical vapor deposition (PVD) cerium cobalt (CeCo) coated MIC in order to optimize the cell performance. 19 In this work, a single cell test setup with a stack-like contacting concept using Crofer 22 APU ® as MIC material is investigated. At the air side a protective coating of manganese-cobalt based spinel oxide (MCO) is applied onto the MIC.…”

“…However, stack-like contacting undergoes with degradation effects like Cr-poisoning, 11,[31][32][33][34] corrosion, 35,36 increased contact resistances 19,28,37 and limitations in gas supply. Thus, SOCs were investigated on cell level 38,39 in an inert testing environment with ceramic flow fields and contacted with finely meshed grids in order to observe the cell-intrinsic electrochemical behavior.…”