Modification of Surface Oxide Layer of Fe‐Cr‐Al Alloy with Coating Materials for SOFC Applications

Abstract

We investigated the treatment of Fe‐Cr‐Al alloy for application in solid oxide fuel cells (SOFCs). The electrical resistance of the Al2O3‐based surface oxide layer on the alloy decreased and was stable when La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), La0.8Sr0.2MnO3 (LSM), LaNi0.6Fe0.4O3 (LNF), or Pr0.8Sr0.2MnO3 (PrSM) were first coated on the alloy and heat treated at 700 °C in air. The activation energy, calculated from the resistance, also suggested that the surface oxide became more conductive with treatment. The surface oxide layer after treatment had a microstructure of columns growing outward in the same direction, containing small amounts of elements such as Sr, Ni, Fe, La, Mn, and Pr. The microstructure consists of polycrystalline γ‐Al2O3 and small amounts of Al compounds with these elements. In the case of the LNF coating, the formation of NiAl2O4 was observed. The enhanced electrical conductivity may have resulted from the arrangement of the columnar structure, along with the electronic conduction path generated by the reaction of γ‐Al2O3 with these elements.

Durability of LSCF-Coated Fe-Cr-Al Alloy for SOFC Applications

“…Porous alloy was used for the measurement to avoid detachment of the LSCF coating from the alloy surface and obtain stable resistance, and also to decrease the resistance to closer to the practically required value. In this study, it was confirmed that the interfacial resistance for the porous alloy was roughly ten times lower than that for the dense alloy plate because of the increased contact area, 11,12 although it may change depending on the porosity of the alloy and penetration depth of the paste.…”

“…in normal cases, relatively large-size crystalline γ-Al 2 O 3 grew in various directions with much less Sr content (<1 at.%). 11,12 It is assumed that Al ions diffusing outward through γ-Al Figure 5 shows the STEM image and EDS mapping after the test at 900 • C for 3 h in air. The surface oxide layer was composed of aluminum oxide with 5.9 at.% Sr content, and the thickness was approximately 400 nm.…”

“…The lower activation energy may have been caused by the higher Sr content in the Al-rich oxide layer. Assuming that the real contact area between the porous alloy and the LSCF coating was 10 times higher than the apparent area, 11,12 electrical conductivity of the surface oxide layer, from the interior to the exterior of the alloy, can be roughly estimated using the interfacial resistance and the thickness. To compare the interfacial resistance of the Fe-Cr-Al alloy with those of Fe-Cr alloys, the effect of the increased contact area caused by the porous structure should be considered.…”

Metal‐Supported Solid Oxide Electrolysis Cell with Significantly Enhanced Catalysis

“…Advantages of metal‐supported cells over conventional all‐ceramic cells also include low‐cost structural materials (stainless steels) and mechanical ruggedness, showing high potential of MS‐SOCs for mobile and/or intermittent application. In recent years, substantial development of metal‐supported fuel cells (MS‐SOFCs) has resulted in excellent performance and durability, and demonstration of the unique advantages discussed above . Several challenges with MS‐SOFCs have also been identified, and these are also expected to be relevant for electrolysis operation and must be addressed in the future.…”

Enhanced coking resistance of Ni cermet anodes for solid oxide fuel cells based on methane on‐cell reforming by a redox‐stable double‐perovskite Sr 2 MoFeO 6‐δ

“…Nevertheless, the Ni cermet anode needs to be optimized to improve coking resistance. Therefore, substantial efforts have been attempted, such as metal alloying, changing ionic conductor phase, or modifying to the Ni‐based anode surface or the bulk . As we know, coking is caused due to the pyrolysis of hydrocarbon on Ni surface.…”