Oxygen Transport Resistant and Electrically Conductive Perovskite Coatings for Solid Oxide Fuel Cell Interconnects

Abstract

Samples of undoped LaMnO 3 ͑LM͒, Sr-doped LaMnO 3 ͑LSM͒, and Ti-doped LaMnO 3 ͑LTM͒ were fabricated by conventional solid-state ceramic processing methods. The objective of Ti doping was to suppress oxygen vacancy concentration/ion transport, while doping with Sr was to enhance oxygen vacancy concentration/ion transport in relation to undoped LM. Total conductivity, mainly electronic, was measured between 500 and 800°C in air. Coatings of LSM, LM, and LTM, 1 m thick, were deposited on Haynes 230 ͑H230͒ foils by sputtering. Uncoated and coated H230 samples were oxidized in air at 800°C for up to 1080 h. Oxidation kinetics of uncoated and coated samples was studied by measuring oxide scale thickness as a function of time. In all coated samples, oxide scale formed under the coating. All coatings were found to suppress oxidation kinetics. Of the materials studied, LTM was the most protective while LSM was the least protective, in accord with defect chemistry, LTM with the lowest oxygen vacancy concentration and LSM with the highest. Area specific resistance ͑ASR͒ measurements showed that LTM-coated samples exhibited the lowest ASR, while the uncoated ones exhibited the highest ASR, again in accord with defect chemistry. A 15 m LTM coating should be sufficient to ensure a 40,000 h interconnect life at 800°C. A comparison of LTM coating to Mn-Cr-spinel of earlier work shows that LTM coating is ϳ23 times more effective than spinel coating in suppressing oxidation kinetics.

Effects of Plasma-Sprayed La0.7Sr0.3MnO3Coating on Thermally Grown Oxide Scale and Electrical Conductivity of Fe-Cr Interconnect for SOFCs

“…x = k 1 (time) 0.5 . The parabolic growth law represented a diffusion controlled growth, 19,35 which was valid when the oxide scale layer was dense and well-adhered to the substrate. However, further long-term oxidation for 1200 h formed a thick oxide scale layer of 6-7 um, and caused significant cracking and spallation of the oxide scale.…”

“…Further long-term thermal exposure promoted the chemical interactions between the Cr 2 O 3 scale and the LSM coating, and subsequently formed a thick and continuous (Mn,Cr) 3 O 4 layer on the top of Cr 2 O 3 scale. Since (Mn,Cr) 3 O 4 is thermally more stable than Cr 2 O 3 , [8][9][10][11][14][15][16][17][18][19][20][21][22] the (Mn,Cr) 3 O 4 layer in the outer TGO scale prevented further oxygen inward diffusion to the SS430 and reduced the growth rate of TGO scale, resulting in a sub-parabolic growth rate shown in Fig. 7.…”

“…[18][19][20] Two Pt meshes were attached onto each surface of the pre-oxidized samples using Pt paste, and four Pt wires were connected to the meshes. To ensure the adequate contact between sample and Pt mesh, an appropriate load was applied.…”

“…[14][15][16][17][18][19][20][21][22][23][24][25] It is important that the protective coating is as dense as possible to minimize oxidation of underneath Fe-Cr alloy. Thick coatings are obviously more protective than thin coatings when oxidized for long term exposure at high temperatures.…”

Effects of conducting oxide barrier layers on the stability of Crofer® 22 APU/Ca3Co4O9 interfaces

“…This technique has been widely used in the solid oxide fuel cell (SOFC) community with some success. [6][7][8][9][10] Komatsu et al 6 demonstrated that La(Ni,Fe)O 3 resists the uptake of Cr from the chromia scale of nickel alloys such as Inconel 600, and Yang et al 7 have shown that (Mn,Co) 3 O 4 -coated Cr22A can successfully be applied to a SOFC cathode material ((La,Sr)FeO 3 ) to create a stable and conducting interface. The specific purpose of this study was to investigate the effectiveness of these barrier materials when applied to the interface between the thermoelectric material Ca 3 Co 4 O 9 and the CroferÒ 22 APU interconnect alloy.…”