SOFC Interconnect Research Articles

Co-Electrodeposition of Ni/Co–W and Cu/Co–W Alloys on Type 445 Stainless Steel for Application in SOFC Interconnects

Co-Electrodeposition of Ni/Co–W and Cu/Co–W Alloys on Type 445 Stainless Steel for Application in SOFC Interconnects

Physicochemical Properties of (La,Sr)CoO3 Thick Films on Fe-25Cr Steel under Exposure to SOFC Cathode Operating Conditions.

La0.6Sr0.4CoO3 (LSC) coatings with a thickness of 50-100 µm were deposited on Fe-25Cr ferritic stainless steel (DIN 50049) via screen printing. The required suspension had been prepared using fine LSC powders synthesised using EDTA gel processes. In its bulk form, the LSC consisted entirely of the rhombohedral phase with space group R-3c, and it exhibited high electrical conductivity (~144 S·cm-1). LSC-coated steel was oxidised in air at 1073 K, i.e., under conditions corresponding to SOFC cathode operation, for times of up to 144 h. The in situ electrical resistance of the steel/La0.6Sr0.4CoO3 layered system during oxidation was measured. The products formed on the samples after the oxidation reaction resulting from exposure to the corrosive medium were investigated using XRD, SEM-EDS, and TEM-SAD. The microstructural, nanostructural, phase, and chemical analysis of films was performed with a focus on the film/substrate interface. It was determined that the LSC coating interacts with the oxidised steel in the applied conditions, and a multi-layer interfacial zone is formed. Detailed TEM-SAD observations indicated the formation of a main layer consisting of SrCrO4, which was the reaction product of (La,Sr)CoO3, and the Cr2O3 scale formed on the metal surface. The formation of the SrCrO4 phase resulted in improved electrical conductivity of the investigated metal/ceramics layered composite material, as demonstrated by the low area-specific resistance values of 5 mΩ·cm2, thus making it potentially useful as a SOFC interconnect material operating at the tested temperature. In addition, the evaporation rate of chromium measured for the uncoated steel and the steel/La0.6Sr0.4CoO3 layered system likewise indicates that the coating is capable of acting as an effective barrier against the formation of volatile compounds of chromium.

TiC and (Ti,Nb)3SiC2 based dual-layer coating on SUS430 for solid oxide fuel cell interconnects

TiC and crystalline (Ti,Nb)3SiC2 based dual-layer is prepared on SUS430 alloy by DC magnetron sputtering followed by annealing at 1000 °C for 20 h. The oxidation of TiC/TNSC coated alloy at 800 °C for 500 h follows the parabolic law with a low rate constant of 5.4 × 10−15 g2 cm−4 s−1. The formed oxide scale is composed of Cr2O3/MnCr2O4 dominated inner layer and outer layer of Nb-doped TiO2 and SiO2 uniform mixture. Owing to the barrier effect of TiC layer and dense oxide scale, outward diffusion of Cr and Mn is efficiently suppressed, resulting in the low Cr content in the outer oxide layer, which is beneficial to the reduced volatilization of Cr oxide. Furthermore, the ASR of the formed oxide scale at 800 °C is 15.87 mΩ cm2, suggesting excellent conductivity. It is concluded that the TiC/(Ti,Nb)3SiC2 coating can significantly improve the oxidation resistannce and electrical property of SUS430 alloy, endowing it potential application as SOFC interconnect protective coating.

Fabricating a MnCo coating to improve oxidation resistance and electrical conductivity of Crofer22H alloy as SOFC interconnect

The oxidation kinetic behavior of Crofer22H alloy at 700–800 °C was investigated. Due to the high oxidation rate exhibited at 800 °C, the xCr-MnCo dual-structured spinel coating was prepared by magnetron sputtering. The element diffusion behavior of the coating/alloy system was changed by control the formation of Cr layer with different thicknesses on the surface. Appropriately increase the thickness of Cr barrier layer can effectively hinders the Fe outward diffusion and improve the antioxidant performance. Fe doped into Mn–Co spinel increased the electron hopping in the crystal structure. Higher electron hopping and thin Cr2O3 layer reduced the electron resistance.

CoMn2O4 and Cu0.5Co0.5Mn2O4 spinels as efficient protective coating layers on SUS430 for SOFC interconnect

In this study, CoMn2O4 and Cu0.5Co0.5Mn2O4 spinels are examined as protective coatings for chromium diffusion in metallic interconnect of solid oxide fuel cell. Both spinels are prepared by co-precipitation technique in order to obtain high temperature conducting spinels. The spinels obtained after 4 h of calcinations in air at 500 °C exhibit tetragonal crystal structure with average grain size between 90 and 100 nm. Cu0.5Co0.5Mn2O4 spinel exhibits superior electrical conductivity over CoMn2O4 and both display NTCR (negative temperature co-efficient of resistance) behavior illustrating their use as a protective layer on interconnects for fuel cells operating at higher temperatures. Doctor-blade employed spinel coating over SUS430 alloy exhibits good adhesion between protective spinel layer and metallic alloy. Cross section micrographs reveal presence of nanosized and highly dense grains capable to resist the outflow of chromium ions present in SUS430. Mass gain and diffusion rate constant (Kp) was high for CoMn2O4 coated SUS430 illustrating Cu0.5Co0.5Mn2O4 spinel as a better protective coating layer for interconnect application. Chromium outflow is restricted and the same is evident from all cross-section micrographs of spinel coated SUS430 specimens subjected for oxidation up to 1000 h. Estimated thickness of Cr2O3 layer was ∼15 nm for CoMn2O4 whereas Cu0.5Co0.5Mn2O4 coated SUS430 specimen had ∼12.5 μm thickness at the SUS430/spinel interface demonstrating superior resistance to chromium outflow. The area specific resistance was lowest for Cu0.5Co0.5Mn2O4 coated specimen (between 14 mΩcm2 – 15 mΩcm2) followed by CoMn2O4 coated specimen reiterating Cu0.5Co0.5Mn2O4 as efficient protective coating material for SUS430 SOFC interconnect.

Fabrication of Mn–Co Alloys Electrodeposited on AISI 430 Ferritic Stainless Steel for SOFC Interconnect Applications

Mn–Co alloys were electroplated on AISI 430 stainless steel using an electrodeposition technique with the aim to reduce oxidation and chromium volatilization. The electroplating parameters were designed to improve the coating quality. The increased current density with decreased MnSO4 content resulted in a denser coating layer. A sample coated with 0.10 M CoSO4 and 0.50 MnSO4 at 350 mA cm−2 showed the best oxidation resistance after being oxidized at 800 °C for 90 h. The X-ray diffraction (XRD) result revealed that the oxide growth on the surface of the coated samples mainly formed oxides of MnCo2O4, MnCr2O4, and Cr2O3. The chromium volatilization was evaluated by exposing the coated samples to humidified synthetic air at 800 °C for 96 h. The mass flux of Cr volatilization was on the order of 10−11 g cm−2 s−1. Furthermore, different heat treatments in O2 and CO2 atmospheres were compared. Annealing in CO2 at 800 °C for 4 h helped increase the Mn–Co coating density. The relationship between the porosity and its failure behavior was also discussed.

Controlled thermal pre-treatment of ZMG232G10® for corrosion mitigation under simulated SOFC interconnect exposure conditions

The IT-SOFC candidate interconnect material ZMG232G10® was thermally pre-treated in air and in H2 – 3% H2O to mitigate dual atmosphere corrosion. Bare and pre-treated steel samples were exposed to a dual atmosphere exposure condition (dry air/metal/4% H2 – N2 (bal.) + 3% H2O) for 500 h at 600 °C. Corrosion products and oxide morphology developed on the air-exposed surfaces were analyzed. Pre-treatments of the metal in oxidizing (air) and reducing (H2 – 3% H2O) gas atmospheres provide improved passivation against dual atmosphere corrosion compared to bare steel. The uniform and iron-free oxide scale developed during the pre-treatment of alloy in the low pO2 H2 – 3% H2O gas atmosphere provides an effective diffusion barrier against the outward transport of cations and oxidation of iron observed under dual atmosphere conditions.

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.

Development of SOFC Interconnects Based on Industrial Steels with Oxide Coating

This work suggests a method for obtaining heat-resistant protective coatings for 08Kh17T stainless steel that can be used as interconnect material for solid oxide fuel cells. The suggested approach is based on the layer-by-layer precipitation of nickel, cobalt, and manganese, followed by heat treatment in a vacuum and oxidizing atmosphere. XRD results show that the coatings consist of a mixture of metal oxides and compounds with a spinel structure. The obtained coatings demonstrate high resistance to high-temperature oxidation for 100 h. The coating with the ratio of the thicknesses of the cobalt and manganese layers of 1.5/0.5 μm obtained by electrodeposition is the most stable. The specific electrical resistance of this coating is 3.50·10−3 Ω·cm2 after 100 h of exposure at 850 °C, which meets the requirements for SOFC interconnect materials.

Oxidation and Electrical Properties of Cu-Mn3O4 Composite Coating Obtained by Electrodeposition on SOFC Interconnects

Oxidation and Electrical Properties of Cu-Mn3O4 Composite Coating Obtained by Electrodeposition on SOFC Interconnects

The suitability performance of Sr2Fe1.5Mo0.5O6-δ-coated SUS430 for SOFC interconnect application

430 stainless steel (SUS430)-Sr2Fe1.5Mo0.5O6-δ (SFM) composite interconnect materials have been successfully synthesized by a facile powder metallurgy method. SFM powder synthesized by sol–gel method was coated on SUS430 stainless steel matrix and sintered to obtain SUS430-SFM material. After circulating oxidation at 800 °C for 140 h in air, the oxidation rate constant K and current density of the interconnect materials were 3.66 × 10-14 mg2·cm−4·s−1 and 1.296 × 10-7 A·cm−2, lower than those of SUS430 stainless steel. Its conductivity was about 5.8 × 103 S·cm−1, about twice of that of SUS430 sample. This excellent performance is due to the good matching of thermal expansion between the coating and the substrate and the excellent oxidation resistance of the coating.

Novel Ti–Si–C composites for SOFC interconnect materials: Production optimization

This paper presents a first part of research of designing a new Ti–Si–C-based composite for potential application as a solid oxide fuel cells interconnect material. Spark plasma sintering technique was used for the production and the effects of sintering parameters on microstructure, phase composition, as well as mechanical and electrical properties were investigated. Optimization of the sintering conditions then allowed to obtain a fine-grained material with properties (bending strength 433 MPa, hardness of 9.6 GPa, electrical resistance 26 mΩ cm) surpassing those of Crofer steels, materials typically used in the SOFC interconnect applications nowadays. This is a very promising result, yielding our Ti–Si–C composite a serious candidate for new-generation lightweight interconnect materials.

An electrophoretic co-deposition of metal oxides followed by in-situ copper manganese spinel synthesis on AISI-430 for application in SOFC interconnects

Electrophoretic co-deposition of copper and manganese oxides followed by in-situ reactive sintering is investigated as a method of Cu–Mn spinel coating for application in SOFC interconnects. Effect of electrophoretic deposition parameters including time, voltage, solid concentration and dispersant content on the quality and quantity of deposition are examined. A uniform layer of oxides is co-deposited at 100 V, in 10 min, with 10 g/L oxides in ethanol-acetone solution and 1:16 w/w dispersant:oxides. Based on XRD and SEM-EDS results, rate of Fe and Cr diffusion is unacceptable at above 850 °C. 3 h of sintering in air at 800 and 850 °C is best to synthesize spinel without severe Fe–Cr contamination. In a 100-h cyclic oxidation test, coatings prevent chromium poisoning and reduce the oxidation rate by a minimum of two orders of magnitude decrease in the parabolic rate constant of oxidation from 1.34 × 10−12 in uncoated to 8.50 × 10−14 g2 cm−4 s−1 and 32.3% decrease in Cr at.% in the coated samples.

Development of Annealed Mn–Co and Mn–Co–Cu Coated AISI 430 Stainless Steels for SOFC Interconnect Application

Development of Annealed Mn–Co and Mn–Co–Cu Coated AISI 430 Stainless Steels for SOFC Interconnect Application

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

ZMGTM232G10 is Fe-Cr ferritic alloy, which has better oxidation resistance for SOFC interconnects. Oxidation behavior of ZMG232G10 was investigated in air at 750 and 850°C for 40,000 hours. Bulk specimens of ZMG232G10 showed stable oxidation behavior according to parabolic law. However, thinner specimens showed anomalous oxidation behavior for 40,000 hours at 850°C. Furthermore, ferrite to austenite phase transformation was observed in a part of specimens which was oxidized at 850°C. This unstable oxidation behavior resulted from Cr consumption in alloy matrix by oxidation.

Oxidation and volatilisation behaviour of a type 430 stainless steel coated by Mn-Co oxide by slurry method with pre-oxidation for SOFC interconnect application

An AISI 430 stainless steel was coated by Mn-Co spinel using a slurry method. Pre-oxidation before the coating helped reduce the oxidation rate of the coated steel at 800 °C in O2-5%H2O, relating to the formation of the continuous chromia layer which inhibited the outward diffusion of iron to the coating layer. It also helped reduce the mass flux of Cr loss due to the volatilisation. The combined molecular and Knudsen diffusion of the volatile species through the coating layer was suggested to explain the reduced volatilisation rate of the coated sample with pre-oxidation.

Oxidation behavior and electrical conductivity of MAXs phase (Ti,Nb)3SiC2 as a novel intermediate-temperature solid oxide fuel cell interconnect material in anode environment

(Ti,Nb)3SiC2 possesses high oxidation resistance and electrical conductivity in cathode side, endowing it potential application as intermediate-temperature solid oxide fuel cell (IT-SOFC) interconnects. However, the performances of (Ti,Nb)3SiC2 in anode side must be well understood before the application comes true. In this paper, the oxidation resistance and electrical conductivity of (Ti,Nb)3SiC2 in simulated anode reducing atmosphere are systematically investigated. The oxidation kinetics follows parabolic law with a kP value of 7.57 × 10−14 g2 cm−4 s−1. The formed single oxide layer is composed of uniformly distributed Nb-doped rutile TiO2 and amorphous SiO2, without carbon deposition. High partial pressure of H2 and CO in simulated anode reducing atmosphere inhibit the oxidation by H2O and CO2. Nb doping with strengthen the Ti–O bond can also slow down the oxidation rate. ASR of (Ti,Nb)3SiC2 after 605 h cyclic oxidation is 1.6 and 3.7 mΩ cm2 at 800 °C and 500 °C, respectively. The low ASR comes from the induced extra electrons by Nb doping and the dissolution of H2O and H2 in oxide, and the integrated TiO2 conductive network in the scale. (Ti,Nb)3SiC2 exhibits superior performances in simulated anode reducing atmosphere, making it an promising candidate for SOFC interconnect.

High temperature oxidation and chromium volatilisation of AISI 430 stainless steel coated by Mn-Co and Mn-Co-Cu oxides for SOFC interconnect application

An AISI 430 stainless steel was coated by Mn-Co and Mn-Co-Cu oxides, then tested in O2-5%H2O at 800 °C. The coated samples had reduced rates of oxidation and Cr loss due to Cr-species volatilisation with the higher rates for the Mn-Co-Cu oxide coated steel due to more Cr diffusion to the coating layer. The measured rates of Cr loss were in the order of 10–11 g cm–2 s–1. The graphical representation of the mass flux of Cr loss as a function of water vapour content was proposed to help visualise the volatilisation effect.

Effect of W Content on the Oxidation and Electrical Behaviors of Co–W Coatings for SOFC Interconnects Fabricated by Electrodeposition

Effect of W Content on the Oxidation and Electrical Behaviors of Co–W Coatings for SOFC Interconnects Fabricated by Electrodeposition

Thermal conversion and evolution behavior of surface scale on SOFC interconnect steel with sputtered FeCoNi coating

The thermal conversion and evolution of surface scale formed on FeCoNi coated SUS430 steel was investigated in static air at 800 °C under isothermal and cyclic conditions. Fe and Co were preferentially oxidized to (Co,Fe)3O4 on the coating surface. Simultaneously, a thin Cr2O3 layer developed at the steel/coating interface. Then (Ni,Co)O developed beneath the (Co,Fe)3O4 layer, and Co3O4 was formed at the outermost layer. (Fe,Co,Ni)3O4 was formed by a solid-state reaction of thermal converted oxides. The discrete (Ni,Co)O gradually migrated outwards through the alternating process between the formation and decomposition of unstable (Fe,Co,Ni)3O4 and finally aggregated close to the outer surface. The (Fe,Co,Ni)3O4/(Ni,Co)O effectively improved the electrical performance of scale and exhibited adequate compatibility with cathode La0.6Sr0.4Fe0.8Co0.2O3+δ.