Spinel MnCo2O4 Research Articles

Preparation and properties of a MnCo2O4 for ceramic interconnect of solid oxide fuel cell via glycine nitrate process

MnCo2O4 powder was prepared by a wet chemistry method using metal nitrates and glycine in an aqueous solution. The phase stability, sintering behavior, thermal expansion and electrical conductivity were examined to characterize powder suitability as an interconnect material in solid oxide fuel cells (SOFCs). X-ray diffraction indicated that the MnCo2O4 spinel synthesized by the glycine nitrate process was stable until 1100 °C and it was possible to obtain a fully densified single phase spinel. On the other hand, the MnCo2O4 synthesized by a solid state reaction decomposed into a cubic spinel and CoO after being sintered at 1100 °C. This might be associated with the reduction of Co3+ in the octahedral site of the cubic spinel phase. MnCo2O4 showed a thermal expansion coefficient comparable to that of other SOFCs components, as well as good electrical conductivity. Therefore, MnCo2O4 is a potential candidate for the ceramic interconnects in SOFCs, provided the phase instability under reducing environments can be improved.

Interface Reactions between Conductive Ceramic Layers and Fe-Cr Steel Substrates in SOFC Operating Conditions

To improve contact resistance and protect the cathode from chromium poisoning, perovskite (La,Sr)CrO3, (La,Sr)CoO3 and spinel MnCo2O4 coatings were applied onto the surfaces of Fe-25Cr (DIN 50049) steel by means of the screen-printing method. The oxidation process of the coated steels under cyclic-oxidation conditions showed high compactness of the protective layer, good adhesion to the metal substrate, as well as acceptable area specific resistance level for SOFC metallic interconnect materials, which was the result of the structural modification of the coating/steel interface reaction, i.e. the formation of an intermediate, chromia-rich multilayer between the conductive coating and the metal substrate. The cross-sectional morphology and nanostructure of interface products formed during long-term thermal oxidation in air and the H2/H2O gas mixture at 1073K were characterized using SEM-EDS and conventional TEM-SAD. Cr-vaporization tests showed that the perovskite and spinel coatings may play the role of barriers that effectively decrease the volatilization rate of chromia species. [doi:10.2320/matertrans.MB201013]

APS Deposition of MnCo2O4 on Commercial Alloys K41X used as Solid Oxide Fuel Cell Interconnect: The Importance of Post Heat-treatment for Densification of the Protective Layer

The continuous contamination of the cathode with chromium released from metallic interconnects speeds up the degradation of the performance of the cell. For this reason Solid Oxide Fuel Cell (SOFC) interconnects are coated with a dense protective layer. This layer plays the role of a diffusion barrier for the chromium evaporation at operating conditions. The deposition of a dense, gas tight and stable MnCo2O4 spinel layer on ferritic alloy using the atmospheric plasma spraying (APS) process is studied. The first experimental results show that the plasma spray process combined with an appropriate post thermal-treatment is suitable to form a dense spinel protective layer.

Influence of the Processing Method on the Quality of the Protective Coatings for SOFC Applications

Protective layers for Solid Oxide Fuel Cells (SOFC) interconnects (IC) were developed. The contacting layers are made of La0.8Sr0.2Mn0.5Co0.5O3 (LSMC) and were prepared by wet powder spraying. In order to avoid IC oxidation and a dramatic increase of ASR, MnCo2O4 spinel protective coatings were processed either by Atmospheric Plasma Spraying (APS) or by a Metal Organic route (MO). The influence of the processing method of these layers on the resistance of their assembly with an IC was investigated on Crofer22APU and F17TNb substrates. The measured ASR is stable after about one hundred hours. Their efficiency in Single Repeated Unit (SRU) configuration was also investigated. The MO process gave the thinnest layer, thereby the lowest resistance. The APS process gives thicker and denser layers, thus preventing completely the chromium diffusion through the cathode, but a slightly higher resistance is observed.

Dense spinel MnCo2O4 film coating by aerosol deposition on ferritic steel alloy for protection of chromic evaporation and low-conductivity scale formation

Conducting ceramic layers with a spinel structure of MnCo2O4 and a thickness of ~3 μm were deposited on ferritic stainless steel (SS) by aerosol deposition (AD), for use as an oxidation-resistant coating layer on the metallic interconnects of a solid oxide fuel cell (SOFC). The microstructural changes in the interface between the MnCo2O4 and SS were analyzed, as were the subsequent electrical conductivity changes at an SOFC operating temperature of 800 °C in air. The coated spinel layers were dense without pores or cracks, and maintained good adhesion even after oxidation at 800 °C for 1,000 h in air atmosphere. Close observation of the interface between the coated spinel oxide and SS substrate indicated the presence of ~1-μm thick, Cr-rich scale formation; however no MnCrCoO4 or MnCr2O4 spinel phase was detected. The area specific resistance (ASR) of the MnCo2O4-coated alloy after heat treatment at 800 °C for 1,000 h was 13.4 mΩ cm2.

Combinatorial Fluorescence XAFS Imaging of Manganese Complex Oxides

Abstract This report demonstrates that novel XAFS (X-ray absorption fine structure) microimaging, which does not require any spatial scans of the sample, can be used to evaluate the chemical states of combinatorial array libraries. The method has been applied to manganese–cobalt spinel MnCo2O4 prepared on the same substrate under different synthesis conditions. The valence numbers of Mn have been studied as a map by obtaining X-ray fluorescence images (1000 × 1000 pixels) as a function of the incident energy of synchrotron X-rays. The advantage of this method is that the whole substrate, i.e., all samples in the library, can be observed in a short time, typically ca. 10 min, which is equivalent to the measuring time for a single sample on the substrate when conventional scanning methods are employed.