Solid Oxide Fuel Cell Interconnect Research Articles

Novel coatings for protecting solid oxide fuel cell interconnects against the dual-atmosphere effect

A key component of a Solid Oxide Fuel Cell (SOFC) is the interconnect, which connects individual fuel cells in series to form a fuel cell stack to reach a desired electrical potential. The interconnect is exposed to air and fuel in parallel, these so-called dual-atmosphere conditions give rise to especially severe corrosion on the air-side. This work investigates coatings to mitigate this effect. Physical Vapour Deposition (PVD) CeCo-coated AISI 441 samples on the air-side and PVD metallic Al- and Al2O3-coated AISI 441 samples on the fuel-side were exposed under dual-atmosphere conditions for up to 7000 h. The evolution of the corrosion products was followed every 1000 h with an optical microscope. Scanning electron microscopy and energy-dispersive x-ray spectroscopy were performed on cross-sections of the samples after 3000 h of exposure. The SEM analysis showed that coating on the air-side improved the sample's life-time by reducing the level of Cr evaporation even in a dual-atmosphere. The use of fuel-side coatings suppressed the dual-atmosphere effect since the coatings formed a barrier to hydrogen permeation. The best results were observed with metallic Al and Al2O3 coating on the fuel-side, which drastically reduced the dual-atmosphere effect. However, the poor conductivity of Al2O3 makes its use as a coating challenging.

Formation mechanism and oxidation behavior of Cu–Mn spinel coating on ferritic stainless steel for solid oxide fuel cell interconnects

Buckling damage and spallation during oxidation are prime challenges in electroplated Cu–Mn oxide spinel coatings prepared for SOFC interconnects. (Cu,Mn)3O4 spinel coating is formed on AISI-430 stainless steel by oxidizing electroplated copper and manganese layers at 750 °C in air. Nickel strike deposition significantly reduces coating spallation. During oxidation at 750 °C, spinel coating hinders chromium migration and improves the oxidation behavior of the alloy by a decrease of 98.9% in the parabolic oxidation rate constant. Formation mechanism of the spinel is investigated, revealing that manganese initially forms MnO, Mn2O3, and Mn3O4. Over the time, copper oxidizes to CuO, and Mn2O3 replaces MnO and Mn3O4. Finally, (Cu,Mn)3O4 spinel forms after 6 h of oxidation by the co-existence of CuO and Mn2O3. It is concluded that manganese oxidation induces buckling damage due to a volume increase of up to 137% in the coating during the earliest stages of the oxidation.

Synthesis of (Cu,Mn,Co)3O4 Spinel: Effects of Citrate-to-Nitrate Ratio on Its Homogeneity and Electrical Properties

The (Cu,Mn,Co)3O4 (CMC) spinel layer is useful in inhibiting Cr vaporization that deteriorates the solid oxide fuel cell performance. The effectiveness of the spinel layer in suppressing volatile Cr species from the metallic interconnects is strongly dependent on layer density, which is influenced by particle size distributions and agglomerations of the spinel powders. Considering that the material properties were influenced by the synthesizing conditions, this study elucidated the influences of citric acid (fuel) on the structure, morphology, and electrical properties of sol–gel derived CMC spinel powders. Dual-phase CMC spinel powders, consisting of cubic CuMnCoO and tetragonal Mn2CoO4, were successfully synthesized at citrate-to-nitrate (CA/MN) ratios of 0.8, 1.0, and 1.2. An undesired CuCo2O4 phase was observed in spinel powders synthesized at a low CA/MN ratio of 0.5. The CA/MN ratio has influenced not only the phase formation of CMC spinel, but also the particle size distributions. The CA/MN ratio of 1.0 yielded the finest CMC spinel with the least agglomerates, which then produced the highest electrical conductivity of 116 Scm−1. Therefore, the CA/MN ratio of 1.0 was recommended for the synthesis of CMC spinel, which can be used in fabricating the protective coating of solid oxide fuel cell interconnects.

Investigation of coated FeCr steels for application as solid oxide fuel cell interconnects under dual-atmosphere conditions

Dual-atmosphere conditions are detrimental for the ferritic stainless steel interconnects used in solid oxide fuel cells, resulting in non-protective oxide scale growth on the air side. In this paper, low-cost steels AISI 441 and AISI 444 and the tailor-made Crofer 22 APU, were investigated at 800 °C and 600 °C under dual-atmosphere conditions: air-3%H2O on one side and Ar-5%H2-3%H2O on the other side. At 800 °C, the uncoated and Ce/Co-coated steels formed protective layers of (Cr,Mn)3O4/Cr2O3 and (Co,Mn)3O4/Cr2O3 respectively on the air side after 336 h. However, at 600 °C, the Ce/Co-coated AISI 441 and AISI 444 showed ∼20–25 μm thick Fe2O3/(Fe,Cr)3O4 oxide scale on the air side after 336 h. Ce/Co coated Crofer 22 APU remained protective after 772 h at 600 °C, indicating better resistance to the dual-atmosphere. The effect of Ce/Co coatings on the air side and the need for coatings on the fuel side are discussed and compared with experimental data.

11–23% Cr steels for solid oxide fuel cell interconnect applications at 800 °C – How the coating determines oxidation kinetics

The present work investigates the low-cost steels AISI 441, AISI 430, and AISI 444 against the tailor-made high Cr steel Crofer 22 APU (22.9 wt% Cr) at 800 °C in simulated solid oxide fuel cell (SOFC) cathode conditions. Furthermore, a low Cr steel, AISI 409 (11.4 wt% Cr) is included in the study. The oxidation, chromium evaporation, and area-specific resistance (ASR) of the uncoated and Ce/Co-coated steels are studied for up to 3000 h. Ce/Co-coated steels showed significant improvement in behaviour compared to their uncoated counterparts. The oxidation and chromium evaporation behaviour between the uncoated steels varied substantially while the Ce/Co coated steels exhibited highly similar behaviour. The area-specific resistance of the coated low-cost steels was on par with Crofer 22 APU. However, 430 formed a continuous silica layer, resulting in a higher ASR after 3000 h. Cross-sections of the uncoated and Ce/Co-coated steels were analysed using a scanning electron microscope and energy dispersive X-ray spectroscopy.

Mn diffusion in the ferritic Fe-25 %Cr Alloy: A First-principles study

The doping manganese (Mn) in the ferritic Fe-Cr alloy could effectively improve its high temperature performance when applied as metallic interconnects of solid oxide fuel cells (SOFCs). A theoretical study of Mn diffusion property in such alloy is implemented. It is found that the substitutional Mn atom prefers to diffuse along the 〈111〉 crystal direction with activation energy of about 0.40 eV. The interstitial Mn atom diffuses across the crystal between two tetrahedral interstitials with activation energy of about 1.37 eV. Under the working temperature of SOFCs at 600℃-800℃, the magnitude of diffusion coefficients mainly varies from 10-15-10-10m2/s which is qualitatively consistent with the experimental result that diffusion rate following the order of DMn > DCr. Our results reveal the diffusion mechanism of Mn atom in the ferritic Fe-Cr alloy at the atomic scale, which provide theoretical guidance for further applications of metallic interconnects in SOFCs.

Highly dense Mn3O4 and CuMn2O4 spinels as efficient protective coatings on solid oxide fuel cell interconnect and their chromium diffusion studies

In this study, we report Mn 3 O 4 and CuMn 2 O 4 spinels as potential protective coating materials on metallic solid oxide fuel cell (SOFC) interconnect SUS430 and their ability to resist chromium diffusion in intermediate temperatures. Powder x-ray diffraction and scanning electron microscopic studies confirm the formation of a single-phase spinel structure with dense microstructure. The high-temperature dc-resistivity measurements show low activation energies for both spinels and demonstrates the ability of good electrical conductivity at intermediate temperatures. The low activation energy at intermediate temperature estimated from electrical studies for both spinels confirm the compatibility of spinels to use as potential protective coating materials. Further, Mn 3 O 4 and CuMn 2 O 4 spinels are coated over ferritic stainless -steel (SUS430 grade) coupon by manual dip coating technique. The cross-section micrographs of both protective coatings show dense microstructures and better adhesion to SUS430. The oxidation kinetics studies show superior resistance to chromium diffusion and post oxidation microstructure characterizations verify the same. Finally, the impact of chromium diffusion on the electrical properties of coated coupons is undertaken by the area-specific resistance (ASR) measurements. The ASR for Mn 3 O 4 coated SUS430 is ~10 mΩ·cm 2 whereas CuMn 2 O 4 coated SUS430 shows ~15 mΩ·cm 2 after 1000 h of oxidation. • Development of spinel based protective coating as protective coating. • Dense microstructure with good adhesion over SUS430. • Better resistance for chromium diffusion at 750 °C. • Compatible ASR up to 1000 hrs oxidation cycle.

Comparison of Cu–Mn and Mn–Co spinel coatings for solid oxide fuel cell interconnects

Electrophoretic deposition (EPD) of protective coatings on solid oxide fuel cell (SOFC) interconnects is an efficient method to mitigate ‘chromium poisoning’, which is a primary reason for degradation of fuel cell performance. Cu–Mn spinels and Mn–Co spinels are the most widely used materials for such coatings. In this study, four spinel coatings were examined; CuMn2O4, CuNi0.2Mn1.8O4, MnCo2O4, and MnFe0.34Co1.66O4. The coatings were evaluated on multiple criteria; including phase stability, microstructural stability, conductivity, Cr gettering ability, ability to act as a diffusion barrier to outward chromium and inward oxygen diffusion, and the ability to limit the increase in the area specific resistance (ASR) during high temperature oxidation exposures. The results showed that, while different coatings have best individual characteristics, overall CuNi0.2Mn1.8O4 was the best candidate for the coatings operating in the intermediate temperature range due to its best sinterability, highest conductivity, lowest ASR, phase stability over the operational temperature range, lower cost and good resistance to outward chromium and inward oxygen diffusion.

Ce-doped (Mn,Co)3O4 coatings for solid oxide fuel cell interconnect applications

In order to improve the electrical conductivity of solid oxide fuel cell (SOFC) interconnect coatings, a series of Ce-doped (Mn,Co)3O4 (Mn1.5-xCo1.5-xCe2xO4+δ, x = 0, 0.025, 0.05, and 0.1) coatings are prepared. The chemical composition, lattice structures, morphology, electrical properties, and weight gain of the coatings are characterized. Experimental results show that doping Ce lowers the area-specific resistance of (Mn,Co)3O4 coatings from 6.83 to 2.62 mΩ cm2 at 800 °C. The electrical conductivity improvement can be attributed to the ion substitution by Ce3+ that turns (Mn,Co)3O4 into (Mn,Co)2CeO4, an N-type semiconductor with a higher electrical carrier density. However, the coatings with heavier doping of Ce exhibit more structural defects due to the lattice parameter reduction and volume shrinkage, which weaken the oxidation resistance of the coatings. This study verifies that doping Ce can effectively improve the electrical conductivity of spinel coatings. The negative influence of doping Ce can be mitigated by modifying the coating preparation technique or by changing the SOFC operating temperature.

High-entropy FeCoNiMnCu alloy coating on ferritic stainless steel for solid oxide fuel cell interconnects

A high-entropy alloy coating of FeCoNiMnCu was prepared on SUS 430 steel via magnetron sputtering for solid oxide fuel cell (SOFC) interconnects application. The coated steels were subject to thermal exposure in air at 800 °C for up to 10 weeks. Phase constituents, microstructure and area specific resistance (ASR) of the coated steel before and after the oxidation testing were investigated. Results indicated the alloy coating was thermally converted into a high-entropy spinel coating of (Fe,Co,Ni,Mn,Cu) 3 O 4 after oxidation and a protective Cr 2 O 3 layer was formed at the steel/coating interface. The (Fe,Co,Ni,Mn,Cu) 3 O 4 spinel coating effectively suppressed growth of Cr 2 O 3 layer and outward diffusion of Cr during the long term exposure. Scale ASR of the coated steel was as low as 6.59 mΩ·cm 2 at 800 °C after 10 weeks. It indicates that (Fe,Co,Ni,Mn,Cu) 3 O 4 is a promising coating material for SOFC metallic interconnects. • A high-entropy alloy coating of FeCoNiMnCu is sputtered on SUS430 steel. • The coating is thermally converted into a high-entropy (Fe,Co,Ni,Mn,Cu) 3 O 4 spinel. • The spinel coating effectively suppresses growth of Cr 2 O 3 and out-diffusion of Cr. • Area specific resistance of coated steel is sufficiently low after long term exposure.

Highly dense (Mn,Co)3O4 spinel protective coating derived from Mn–Co metal precursors for SOFC interconnect applications

The major degradation issues of solid oxide fuel cells (SOFC) are associated with the Cr2O3 scale growth and Cr diffusion of the Cr-based ferritic stainless steel (FSS) interconnects. Although (Mn,Co)3O4 has been proved as a suitable material for protecting FSS interconnects, the porous structure of the coatings prepared with the pre-synthesized spinel weakens the protective capability of the coatings. In this paper, the widely-used pre-synthesized spinel is replaced with metal precursors (Mn and Co powders). Due to the low melting point (≤1290 °C) and the volume expansion during oxidation, the metal precursors, can be effectively sintered at 900 °C in a reducing atmosphere and form dense, well-protective coatings at 850 °C in the air. The samples are characterized with X-ray diffraction (XRD), scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS), and a 4-probe area-specific resistance (ASR) test. Compared with the coatings derived from pre-synthesized spinel, the metal-derived coatings present denser structures with better electrical conductivity (ASR = 5.76 mΩ cm2). The weight gain and ASR measurement results indicate that the metal-derived coatings significantly mitigate the increase of weight gain and ASR by inhibiting scale formation and growth, showing better protective capability for SOFC applications.

Sputtered Fe1·5CoNi0.5 coating: An improved protective coating for SOFC interconnect applications

In an attempt to optimize the properties of FeCoNi coating for planar solid oxide fuel cell (SOFC) interconnect application, the coating composition is modified by increasing the ratio of Fe/Ni. An Fe 1·5 CoNi 0.5 (Fe:Co:Ni = 1.5:1:0.5, atomic ratio) metallic coating is fabricated on SUS 430 stainless steel by magnetron sputtering, followed by oxidation in air at 800°C. The Fe 1·5 CoNi 0.5 coating is thermally converted to (Fe,Co,Ni) 3 O 4 and (Fe,Co,Mn,Ni) 3 O 4 without (Ni,Co)O particles. After oxidation for 1680 h, no further migration of Cr is detected in the thermally converted coating region. A low oxidation rate of 5.9 × 10 −14 g 2 cm −4 s −1 and area specific resistance of 12.64 mΩ·cm 2 is obtained for Fe 1·5 CoNi 0.5 coated steels. • Fe 1·5 CoNi 0.5 coating is deposited on SUS 430 stainless steel by magnetron sputtering. • The tri-layer oxide scale is thermally formed on the Fe 1·5 CoNi 0.5 coated steel. • The oxidation resistance of the steel substrate is improved. • The out-migration of Cr is effectively inhibited. • A low ASR of 12.64 mΩ·cm 2 is exhibited.

Polymer Derived Ceramics based on SiAlOC glasses as novel protective coatings for ferritic steel

In this work, the potential of using Polymer Derived Ceramics based on SiAlOC glasses in the form of protective thin layers was demonstrated on Ferritic Stainless Steel (FSS) Crofer 22APU steel, an alloy often used for intermediate- and low-temperature Solid Oxide Fuel Cells (SOFC’s) interconnects. Microstructural features were investigated by the detailed analysis combining Electron Probe Micro Analysis (EPMA) and Raman Confocal imaging (surface imaging and depth profiling), which revealed the formation of Si-O-Cr bridges, believed to play a crucial role to slow down oxidation of the steel. Additionally, the positive role of aluminum introduced into the SiOC system, which enhances the suppression of the degradation by transport processes. The most crucial value of such findings is the formation of a flexible coating material (SiAlOC glasses) that may be applied on a wide range of FSSs increasing their heat resistance. The application of the combination of methods to determine both chemical (EPMA) and phase (Raman) composition of a multi-layered complex system is also demonstrated.

Fe doped Ni–Co alloy by electroplating as protective coating for solid oxide fuel cell interconnect application

To obtain higher electrical conductivity and lower area specific resistance (ASR), the 10% Fe doped Ni–Co (NCF) alloy was prepared on SUS 430 steel substrate by electroplating for solid oxide fuel cells (SOFCs) interconnects application. Then, the SUS 430 steels and NCF coated steels were oxidized at 800 °C. The microstructure and oxide phase of samples were tested by scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). These results proved that the NCF coated steel achieved the lower oxidation rate of 9.28 × 10−14 g2cm−4s−1 and ASR of 14.72 mΩ cm2.

CrxN/Mn1.7Cu1.3 coating on ferritic stainless steel for solid oxide fuel cell interconnects

CrxN/Mn1.7Cu1.3 dual layer coating was prepared on SUS 430 steel via multi-arc ion plating and magnetron sputtering in sequence for use of solid oxide fuel cell (SOFC) interconnects. The coated steel was exposed to air at 800 °C corresponding to SOFC cathode environment to evaluate the oxidation behavior and electrical property of the surface scale. Results indicated that the Mn1.7Cu1.3 outer layer was thermally converted into Mn1.7Cu1.3O4 spinel outer layer and the CrxN inner layer was gradually oxidized to form a protective Cr2O3 layer at the interface of CrxN and Mn1.7Cu1.3O4. After the CrxN layer was completely oxidized, the surface scale mainly consisted of an outer Mn1.7Cu1.3O4 spinel layer and an inner Cr2O3 layer. Area specific resistance of the surface scale formed on CrxN/Mn1.7Cu1.3 coated steel after 15 weeks oxidation was 17.28 mΩ·cm2. The superior performance of the coated steel benefited from the combination of CrxN barrier layer and Mn1.7Cu1.3O4 spinel.

Cu doped Ni–Co spinel protective coatings for solid oxide fuel cell interconnects application

Four different amount of Cu doped Ni–Co alloy coatings were fabricated on SUS430 substrate by electroplating for solid oxide fuel cells (SOFCs) interconnects application. After oxidation at 800 °C, the microstructure and oxide phase of samples were tested by scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Our experimental results indicated that the Cu addition improved the electrical behavior of Ni–Co alloy coating. Cu doping reduced the activation energy (Ea) of electrons hopping and inhibited the growth of Cr2O3 oxide layer. Furthermore, the oxidation kinetics and electrical properties of the alloy coatings were obtained. These results showed that the 9% Cu doped Ni–Co coated steels achieved the minimum parabolic rate constant (2.05 × 10−14 g2cm−4s−1) and area specific resistance (14.11 mΩ cm2) after the thermostatic oxidation process.

Long-Term Oxidation Behavior of SOFC Interconnects Alloy ZMG232G10 for 40,000 Hours

Solid Oxide Fuel Cell (SOFC) is known as clean and high efficiency co-generation systems. SOFC operates at high temperatures (600 – 900°C), therefore, heat resistant materials are used for SOFC components. For SOFC interconnects that connect between ceramic cells electrically, the required properties are as follows; good oxidation resistance at operating temperature, high electrical conductivity at operating temperature and thermal expansion close to ceramic cells.There are many research works about long term degradation behavior of anode, cathode and electrolyte materials, because the lifetime of SOFC is expected from 40,000 hours (about 5 years) to 90,000 hours (about 10 years). On the other hand, degradation behavior of metal interconnects, that means oxidation behavior of metal interconnects, has not been evaluated sufficiently despite relevance to ohmic loss of SOFC stack.Fe-Cr ferritic alloy for SOFC interconnects “ZMGTM232G10” was developed and its long term oxidation resistance has been evaluated. At this time, we will report 40,000 hours’ oxidation test result about ZMG232G10, for example the changes of oxidation weight gain and microstructure.The alloy was melted with 10kg lab-scale vacuum melting furnace, and then hot forged to bar shape. After that, forged material was cut and cold rolled to sheets with some target thicknesses. Sample sizes cut from sheets are 10mm square with 3mm thickness and 15mm square with 0.3 and 0.5mm thicknesses. The surfaces of samples were ground with #1,000 dry paper.Oxidation test was performed at 850°C in air, which is an accelerated condition compared to 750°C. The test pieces were put in the ceramic containers, and put into electric furnaces. The oxidation weight gain of each test piece was measured after each 500 hours’ oxidation test period. After the measurement, some specimens were cut, plated with Ni, mounted in the resins, ground and polished, and then the cross-sectional microstructures were observed with optical microscope and EPMA and analyzed with EPMA.Figure1 shows the oxidation weight gain of ZMG232G10 vs. exposure time at 850°C in air. In general, oxidation behavior of the alloy with dense oxidation layer is explained with parabolic law. ZMG232G10 with 3mm thickness (bulk sample) showed stable oxidation behavior for 40,000 hours according to parabolic law. However, oxidation behavior of thinner samples deviated from parabolic law, and anomalous oxidation was observed at the edge of the samples.Microstructure of oxide layer of ZMG232G10 consisted of (Mn, Cr, Cu) spinel layer and Cr2O3 layer located beneath spinel layer. Ferrite phase and oxide layer were observed in almost all samples, however martensitic transformation under the oxide layer was observed in thinner sample after long term oxidation test. It indicated that ferrite phase transformed to austenite phase during long-term oxidation test and then austenite phase transformed to martensite during cooling to room temperature. This is the reason why martensite was observed at room temperature.Because the protective oxide layer of ZMG232G10 is mainly Cr2O3, Cr are consumed gradually from the alloy matrix during high temperature oxidation. Then, Cr contents in the alloy matrix were analyzed with EPMA.ZMG232G10 with 3mm thickness contained Cr amount enough to keep protective oxide layer after 40,000 hours oxidation test. However Cr amount in thin samples decreased faster with exposure time than thick one. It was difficult to keep protective oxide layer dense because of less total Cr amount and decreasing Cr in the alloy matrix. As a result, faster oxidation and earlier anomalous oxidation occurred in thin samples than thick one. Furthermore, low Cr content was not able to keep ferrite phase stable and then caused transformation from ferrite phase to austenite phase at high temperature.Through long term oxidation test on ZMG232G10, we obtained the knowledge as follows ; (1) although bulk sample of ZMG232G10 shows stable oxidation behavior according to parabolic law, thin ones show faster oxidation and earlier anomalous oxidation than thick one. (2) In thin samples, ferrite phase may transform to austenite phase in long term oxidation. Both phenomena were caused by less total Cr amount in thin samples and rapid decrease of Cr at high temperature for long term oxidation than thick one. Figure 1

Plasma-sprayed lanthanum-doped strontium titanate as an interconnect for solid oxide fuel cells: Effects of powder size and process conditions

As a key component of the novel bi-layer interconnect for solid oxide fuel cells (SOFC), La-doped SrTiO3 (LST) has been deposited by atmospheric plasma spraying in this study. The effects of powder particle size, hydrogen flow rate and deposition temperature on stoichiometry, microstructure, and properties of LST deposits have been systematically investigated. The preferential vaporization loss of Sr is quantified by the relationship between the droplet size and splat composition, while the droplet size prior to impact is measured by a confocal laser microscopy and the composition of splat is analyzed by the energy-dispersive spectrum of scanning electron microscopy. Thermogravimetric analysis is used to determine the oxygen non-stoichiometry of the deposit. It is found that when the droplet diameter is smaller than 30 µm, the preferential vaporization induced Sr loss is significantly increased up to 45% with decreasing particle size, while it is greatly reduced if the droplet size is larger than 30 µm. Two mechanisms including diffusion-dominated mass transfer and convection-dominated mass transfer are proposed to explain the particle size effect on Sr loss. With increasing H2 flow in plasma gas, the oxygen deficiency in LST deposit is increased. Moreover, the effective bonding at lamellar interfaces is realized by increasing the deposition temperature to higher than the critical bonding temperature. The electrical conductivity of LST deposits is remarkably improved by decreasing Sr loss, increasing oxygen vacancy concentration, and enhancing the lamellar bonding. The LST coatings prepared at a deposition temperature of 450°C with coarse powder particles exhibits a dense microstructure and a conductivity of ~100 S/cm at 850°C in the reducing atmosphere. The results show that by properly optimizing the process conditions, the plasma-sprayed LST coating is a promising candidate to be a part of the bi-layer interconnect for SOFCs.

Synthesis and characterization of Ag-Y co-doped Mn-Co spinel for solid oxide fuel cell application

Mn-Co spinel coating for solid oxide fuel cell interconnects shows a suitable thermal expansion match, acceptable electrical conductivity, and good structural stability. In this paper, the addition of different amounts of Ag and Y as dopants on the physical and electrical properties of the Mn-Co spinel is investigated to improve the coating performance. First, the doped and co-doped powders were successfully synthesized using the Pechini sol-gel method. The synthesized powders were then characterized using X-ray diffraction and field emission scanning electron microscopy. The results confirmed that Ag was not completely doped into the spinel structure and instead acted. as an additive, whereas Y caused Mn3O4 impurity phase formation at higher mol%. Next, the powders were pressed and sintered at different temperatures (950 and 1050 °C) to evaluate the effect of dopants on the sintering and electrical behavior of the samples. Finally, the electrical conductivity of the samples was evaluated using a 2-probe direct current technique. Although results showed that room temperature electrical conductivity increased upon doping, adding Y had a better effect on conductivity than Ag.

A study on the oxidation and electrical behavior of crofer 22 APU solid oxide fuel cell interconnects with Ni-Co-CeO2 composite coating

A protective/conductive coating can be used to limit the formation of chromia in ferritic steel interconnects in solid oxide fuel cells (SOFCs). One of the most promising candidates for restricting chromia formation is the addition of reactive elements oxides to the coating. Here in, Ni-Co-CeO2 composite coating was applied to Crofer 22 APU alloy via the electroless method. The oxidation and electrical behavior of uncoated and coated samples were evaluated at 800 °C. The coating structure was examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results showed Cr2O3-scale thicknesses, and a reduction in oxidation rates for Ni-Co-CeO2-coated samples compared to uncoated samples. Also, area specific resistance (ASR) results indicated that the formation of NiFe2O4, (Mn,Ni)2O4, Co3O4, and CoFe2O4 compositions and the presence of CeO2 reduced ASR. The ASR values of Ni-Co-CeO2 coated and uncoated Crofer 22 APU alloy after 300 h of isothermal oxidation at 800 °C was 11.8 mΩ cm2 and 35.7 mΩ cm2, respectively.