Metallic interconnects for SOFC: Characterisation of corrosion resistance and conductivity evaluation at operating temperature of differently coated alloys

One of challenges in improving the performance and cost-effectiveness of solid oxide fuel cells (SOFCs) is the development of suitable interconnect materials. Recent researches have enabled to decrease the operating temperature of the SOFC from 1000 to 800 °C. Chromia forming alloys are then among the best candidates for interconnects. However, low electronic conductivity and volatility of chromium oxide scale need to be solved to improve interconnect performances. In the field of high temperature oxidation of metals, it is well known that the addition of reactive element into alloys or as thin film coatings, improves their oxidation resistance at high temperature. The elements of beginning of the lanthanide group and yttrium are the most efficient. The goal of this study is to make reactive element oxides (La₂O₃, Nd₂O₃ and Y₂O₃) coatings by metal organic chemical vapour deposition (MOCVD) on Crofer 22 APU, AL 453 and Haynes 230 in order to form perovskite oxides which present a good conductivity at high temperature. The coatings were analysed after 100 h ageing at 800 °C in air under atmospheric pressure by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analyses, X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. Area-specific resistance (ASR) was measured in air for the same times and temperature, using a sandwich technique with Pt paste for electrical contacts between surfaces. The ASR values for the best coating were estimated to be limited to 0.035 Ω cm², even after 40,000 h use.     

Solid oxide cells with cermet of silver and gadolinium-doped-ceria symmetrical electrodes for high-performance power generation and water electrolysis

A cermet of silver and gadolinium-doped-ceria (Ag-GDC) is investigated as novel symmetrical electrode material for (ZrO₂)_0.92(Y₂O₃)_0.08 (YSZ) electrolyte-supported solid oxide cells (SOCs) operated in fuel cell (SOFC) and electrolysis (SOEC) modes. The electrochemical performances are evaluated by measuring the current density-voltage characteristics and impedance spectra of the SOCs. The activity of hydrogen and air electrodes is investigated by recording overpotential versus current density in symmetrical electrode cells, respectively in hydrogen and air, using a three-electrode method. Conventional hydrogen electrode, Ni-YSZ, and oxygen electrode, LSCF (La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ)-GDC, are tested as comparison. The results show that, as an oxygen electrode, Ag-GDC is more active than LSCF-GDC in catalyzing both oxygen reduction reaction (ORR) in an SOFC and oxygen evolution reaction (OER) in an SOEC. As a hydrogen electrode, Ag-GDC is more active than Ni-YSZ in catalyzing hydrogen oxidation reaction (HOR) in an SOFC and hydrogen evolution reaction (HER) in an SOEC, especially in high steam concentration. An SOC with symmetrical Ag-GDC electrodes operated in a fuel cell mode, with 3% H₂O humidified H₂ as the fuel, displays a peak power density of 395 mWcm^?2 at 800 °C. Its polarization resistance at open circuit voltage is 0.21 Ω cm². Ag-GDC electrode can be operated even at pure steam. An SOEC operated for electrolyzing 100% H₂O, the current density reaches 720 mA cm^?2 under 1.3 V at 800 °C.     

Improved electrical performance and sintering ability of the composite interconnect La0.7Ca0.3CrO3−δ/Ce0.8Nd0.2O1.9 for solid oxide fuel cells

Significant improvements on sintering characteristic and electrical performance of traditional interconnect La_0.7Ca_0.3CrO_3−δ were presented in this paper. For a composite interconnecting ceramic La_0.7Ca_0.3CrO_3−δ/Ce_0.8Nd_0.2O_1.9, it was found that the addition of Ce_0.8Nd_0.2O_1.9 significantly increased the electrical conductivity of La_0.7Ca_0.3CrO_3−δ both in air and in hydrogen. Among all the investigated specimens, La_0.7Ca_0.3CrO_3−δ with 5 wt% Ce_0.8Nd_0.2O_1.9 possessed the maximal electrical conductivity. In air and hydrogen, the maximal electrical conductivity at 800 °C were 55.4 S cm⁻¹ and 5.0 S cm⁻¹, respectively, which increased significantly as compared with La_0.7Ca_0.3CrO_3−δ under the same conditions. With the increase of Ce_0.8Nd_0.2O_1.9 content the relative density increased, reaching 97.1% from 93.9% of La_0.7Ca_0.3CrO_3−δ. This indicated that Ce_0.8Nd_0.2O_1.9 functioned as an effective sintering aid in enhancing the sinterability of the powders. The average coefficient of thermal expansion at 30-1000 °C in air increased with Ce_0.8Nd_0.2O_1.9 content. Most coefficients of thermal expansion of specimens are compatible with other cell components. The oxygen permeation measurement illustrated a negligible oxygen ionic conduction, indicating it is still an electronically conducting ceramic. Results indicate that this composite is suitable to be used as a high-performance interconnect for intermediate temperature solid oxide fuel cells.     

Electrochemical performance of solid oxide electrolysis cell electrodes under high-temperature coelectrolysis of steam and carbon dioxide

The SOEC electrodes during steam (H₂O) electrolysis, carbon dioxide (CO₂) electrolysis, and the coelectrolysis of H₂O/CO₂ are investigated. The electrochemical performance of nickel-yttria stabilised zirconia (Ni-YSZ), Ni-Gd_0.1Ce_0.9O_1.95 (Ni-GDC), and Ni/Ruthenium-GDC (Ni/Ru-GDC) hydrogen electrodes and La_0.8Sr_0.2MnO_3−δ-YSZ (LSM-YSZ), La_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (LSCF), and La_0.8Sr_0.2FeO_3−δ (LSF) oxygen electrodes are studied to assess the losses of each electrode relative to a reference electrode. The study is performed over a range of operating conditions, including varying the ratio of H₂O/H₂ and CO₂/CO (50/50 to 90/10), the operating temperature (550-800 °C), and the applied voltage. The activity of Ni-YSZ electrodes during H₂O electrolysis is significantly lower than that for H₂ oxidation. Comparable activity for operating between the SOEC and solid oxide fuel cell (SOFC) modes is observed for the Ni-GDC and Ni/Ru-GDC. The overpotential of H₂ electrodes during CO₂ reduction increases as the CO₂/CO ratio is increased from 50/50 to 90/10 and further increases when the electrode is exposed to a 100% CO₂ (800 °C), corresponding to the increase in the area specific resistance. The electrodes exhibit comparable performance during H₂O electrolysis and coelectrolysis, while the electrode performance is lower in the CO₂-electrolysis mode. The activity of all the O₂ electrodes as an SOFC cathode is higher than that as SOEC anodes. Among these O₂ electrodes, LSM-YSZ exhibits the nearest to symmetrical behaviour.     

Electrochemical behaviour of an all-perovskite-based intermediate temperature solid oxide fuel cell

A solid oxide fuel cell (SOFC) has been manufactured using a Ni-modified perovskite and perovskite-based electrolyte and cathode. The SOFC has been investigated for operation at intermediate temperatures (800 °C). The electrical properties of La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ (LSGM) perovskite have been compared to gadolinia-doped ceria (GDC) electrolyte. This has allowed to validate the promising properties of the perovskite electrolyte compared to ceria-based ceramic membranes for operation at intermediate temperatures. The reliability of the Ni-modified La_0.6Sr_0.4Fe_0.8Co_0.2O₃ perovskite-based anode for operation in combination with the LSGM electrolyte and a La_0.6Sr_0.4Fe_0.8Co_0.2O₃ (LSFC) cathode has been studied. A 50 h electrochemical test for the SOFC operating under different fuel feed compositions is reported. The all-perovskite SOFC shows promising fuel-flexibility characteristics.     

Electrode performance and analysis of reversible solid oxide fuel cells with proton conducting electrolyte of BaCe0.5Zr0.3Y0.2O3−δ

Reversible solid oxide fuel cells (R-SOFCs) are regarded as a promising solution to the discontinuity in electric energy, since they can generate electric powder as solid oxide fuel cells (SOFCs) at the time of electricity shortage, and store the electrical power as solid oxide electrolysis cells (SOECs) at the time of electricity over-plus. In this work, R-SOFCs with thin proton conducting electrolyte films of BaCe_0.5Zr_0.3Y_0.2O_3−δ were fabricated and their electro-performance was characterized with various reacting atmospheres. At 700 °C, the charging current (in SOFC mode) is 251 mA cm⁻² at 0.7 V, and the electrolysis current densities (in SOEC mode) reaches −830 mA cm⁻² at 1.5 V with 50% H₂O-air and H₂ as reacting gases, respectively. Their electrode performance was investigated by impedance spectra in discharging mode (SOFC mode), electrolysis mode (SOEC mode) and open circuit mode (OCV mode). The results show that impedance spectra have different shapes in all the three modes, implying different rate-limiting steps. In SOFC mode, the high frequency resistance (R_H) is 0.07 Ωcm² and low frequency resistances (R_L) are 0.37 Ωcm². While in SOEC mode, R_H is 0.15 Ωcm², twice of that in SOFC mode, and R_L is only 0.07 Ωcm², about 19% of that in SOFC mode. Moreover, the spectra under OCV conditions seems like a combination of those in SOEC mode and SOFC mode, since that R_H in OCV mode is about 0.13 Ωcm², close to R_H in SOEC mode, while R_L in OCV mode is 0.39 Ωcm², close to R_L in SOFC mode. The elementary steps for SOEC with proton conducting electrolyte were proposed to account for this phenomenon.     

A new anode material for intermediate solid oxide fuel cells

A new anode material for intermediate temperature solid oxide fuel cells (IT-SOFCs) with a composite of La_0.7Sr_0.3Cr_1−xNi_xO₃ (LSCN), CeO₂ and Ni has been synthesized. EDX analysis showed that 1.19 at% Ni was doped into the perovskite-type La_0.7Sr_0.3CrO₃ and Ce could not be detected in the perovskite phases. Results showed that the fine CeO₂ and Ni were highly dispersed on the La_0.7Sr_0.3Cr_1−xNi_xO₃ substrates after calcining at 1450 °C and reducing at 900 °C. The thermal expansion coefficient (TEC) of the as-prepared anode material is 11.8 × 10⁻⁶ K⁻¹ in the range of 30–800 °C. At 800 °C, the electrical conductivity of the as-prepared anode material calcined at 1450 °C for 5 h is 1.84 S cm⁻¹ in air and 5.03 S cm⁻¹ in an H₂ + 3% H₂O atmosphere. A single cell with yttria-stabilized zirconia (YSZ, 8 mol% Y₂O₃) electrolyte and the new materials as anodes and La_0.8Sr_0.2MnO₃ (LSM)/YSZ as cathodes was assembled and tested. At 800 °C, the peak power densities of the single cell was 135 mW cm⁻² in an H₂ + 3% H₂O atmosphere.     

Optimization of La2O3-containing diopside based glass-ceramic sealants for fuel cell applications

We report on the optimization of La₂O₃-containing diopside based glass-ceramics (GCs) for sealant applications in solid oxide fuel cells (SOFC). Seven glass compositions were prepared by modifying the parent glass composition, Ca_0.8Ba_0.1MgAl_0.1La_0.1Si_1.9O₆. First five glasses were prepared by the addition of different amounts of B₂O₃ in a systematic manner (i.e. 2, 5, 10, 15, 20 wt.%) to the parent glass composition while the remaining two glasses were derived by substituting SrO for BaO in the glasses containing 2 wt.% and 5 wt.% B₂O₃. Structural and thermal behavior of the glasses was investigated by infrared spectroscopy (FTIR), density measurements, dilatometry and differential thermal analysis (DTA). Liquid–liquid amorphous phase separation was observed in B₂O₃-containing glasses. Sintering and crystallization behavior, microstructure, and properties of the GCs were investigated under different heat treatment conditions (800 and 850 °C; 1–300 h). The GCs with ≥5 wt.% B₂O₃ showed an abnormal thermal expansion behavior above 600 °C. The chemical interaction behavior of the glasses with SOFC electrolyte and metallic interconnects, has been investigated in air atmosphere at SOFC operating temperature. Thermal shock resistance and gas-tightness of GC sealants in contact with 8YSZ was evaluated in air and water. The total electrical resistance of a model cell comprising Crofer 22 APU and 8YSZ plates joined by a GC sealant has been examined by the impedance spectroscopy. Good matching of thermal expansion coefficients (CTE) and strong, but not reactive, adhesion to electrolyte and interconnect, in conjunction with a low level of electrical conductivity, indicate that the investigated GCs are suitable candidates for further experimentation as SOFC sealants.     

Ethane dehydrogenation over nano-Cr2O3 anode catalyst in proton ceramic fuel cell reactors to co-produce ethylene and electricity

Ethane and electrical power are co-generated in proton ceramic fuel cell reactors having Cr₂O₃ nanoparticles as anode catalyst, BaCe_0.8Y_0.15Nd_0.05O_3−δ (BCYN) perovskite oxide as proton conducting ceramic electrolyte, and Pt as cathode catalyst. Cr₂O₃ nanoparticles are synthesized by a combustion method. BaCe_0.8Y_0.15Nd_0.05O_3−δ (BCYN) perovskite oxides are obtained using a solid state reaction. The power density increases from 51 mW cm⁻² to 118 mW cm⁻² and the ethylene yield increases from about 8% to 31% when the operating temperature of the solid oxide fuel cell reactor increases from 650 °C to 750 °C. The fuel cell reactor and process are stable at 700 °C for at least 48 h. Cr₂O₃ anode catalyst exhibits much better coke resistance than Pt and Ni catalysts in ethane fuel atmosphere at 700 °C.     

Electrochemical characteristics of solid oxide fuel cell cathodes prepared by infiltrating (La,Sr)MnO3 nanoparticles into yttria-stabilized bismuth oxide backbones

The electrochemical characteristics of the solid oxide fuel cell (SOFC) cathodes prepared by infiltration of (La_0.85Sr_0.15)_0.9MnO_3−δ (LSM) nanoparticles into porous Y_0.5Bi_1.5O₃ (YSB) backbones are investigated in terms of overpotential, interfacial polarization resistance, and single cell performance obtained with three-electrode cell, symmetrical cell, and single cell, respectively. X-ray diffraction confirms the formation of perovskite LSM by heating the infiltrated nitrates at 800 °C. The electrical conductivity of the electrode measured using Van der Pauw method is 1.67 S cm⁻¹, which is acceptable at the typical SOFC operating temperatures. The single cell with the LSM infiltrated YSB cathode generates maximum power densities of 0.23, 0.45, 0.78, and 1.13 W cm⁻² at 600, 650, 700, and 750 °C, respectively. The oxygen reduction mechanism on the cathode is studied by analyzing the impedance spectra obtained under various temperatures and oxygen partial pressures. The impedance spectra under various cathodic current densities are also measured to study the effect of cathodic polarization on the performance of the cathode.     

Oxidation resistance of novel ferritic stainless steels alloyed with titanium for SOFC interconnect applications

Chromia (Cr₂O₃) forming ferritic stainless steels are being developed for interconnect application in Solid Oxide Fuel Cells (SOFC). A problem with these alloys is that in the SOFC environment chrome in the surface oxide can evaporate and deposit on the electrochemically active sites within the fuel cell. This poisons and degrades the performance of the fuel cell. The development of steels that can form conductive outer protective oxide layers other than Cr₂O₃ or (CrMn)₃O₄ such as TiO₂ may be attractive for SOFC application. This study was undertaken to assess the oxidation behavior of ferritic stainless steel containing 1 weight percent (wt.%) Ti, in an effort to develop alloys that form protective outer TiO₂ scales. The effect of Cr content (6–22 wt.%) and the application of a Ce-based surface treatment on the oxidation behavior (at 800 °C in air + 3% H₂O) of the alloys was investigated. The alloys themselves failed to form an outer TiO₂ scale even though the large negative ΔG of this compound favors its formation over other species. It was found that in conjunction with the Ce-surface treatment, a continuous outer TiO₂ oxide layer could be formed on the alloys, and in fact the alloy with 12 wt.% Cr behaved in an identical manner as the alloy with 22 wt.% Cr.     

Characterization of Cu,Ag and Pt added La0.6Sr0.4Co0.2Fe0.8O3−δ and gadolinia-doped ceria as solid oxide fuel cell electrodes by temperature-programmed techniques

Cu, Ag and Pt added La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) and gadolinia-doped ceria (GDC) were analyzed by the temperature-programmed techniques for their characteristics as either the cathode or the anode of the solid oxide fuel cells (SOFCs). Temperature-programmed oxidation using CO₂ was used to characterize the cathode materials while temperature-programmed reduction (TPR) using H₂ and TPR using CO were used to characterize the anode materials. These techniques can offer an easy screening of the materials as the SOFC electrodes. The effects of adding Cu, Ag and Pt to LSCF for the cathodic reduction activity and the anodic oxidation activity are different—Cu > Ag > Pt for reduction and Pt > Cu > Ag for oxidation. The CO oxidation activities are higher than the H₂ oxidation activities. Adding GDC to LSCF can increase both reduction and oxidation activities. The LSCF–GDC composite has a maximum activity for either reduction or oxidation when LSCF/GDC is 2 in weight.     

A cost-effective process for fabrication of metal-supported solid oxide fuel cells

Metal-supported SOFC cells with Y₂O₃ stabilized ZrO₂ as the electrolyte were prepared by a low cost and simple process involving tape casting, screen printing and co-firing. The interfaces were well bonded after the reduction of NiO to Ni in the support and the anode. AC impedance was employed to estimate the cell polarizations under open circuit conditions. It was found that the electrode polarization resistance was high at low temperatures and became equivalent to the ohmic resistance at higher temperatures near 800°°C. The cell performance was evaluated with H₂ as the fuel and air as the oxidant, and maximum power density between 0.23 and 0.80  W/cm² was achieved in the temperature range of 650–800°C, which confirms the applicability of the cost-effective process in fabrication of metal-supported SOFC cells.     

Exploring MnCr2O4–Gd0.1Ce0.9O2-δ as a composite electrode material for solid oxide fuel cell

Symmetrical solid oxide fuel cell (SOFC) adopting the same material at both electrodes is potentially capable of promoting thermomechanical compatibility between near components and lowering stack costs. In this paper, MnCr₂O₄–Gd_0.1Ce_0.9O_2-δ (MCO-GDC) composite electrodes prepared by co-infiltration method for symmetrical electrolyte supported and anode supported solid oxide fuel cells are evaluated at a temperature range of 650–800 °C in wet (3% H₂O) hydrogen and air atmospheres. Without any alkaline earth elements and cobalt, the co-infiltrated MCO-GDC composite electrode shows excellent activity for oxygen reduction reaction but mediocre activity for hydrogen oxidation reaction. With MCO-GDC as the cathode, the Ni-YSZ (Y₂O₃ stabilized ZrO₂) anode supported asymmetrical cell demonstrates a peak power density of 665 mW cm⁻² at 800 °C. The above results suggest MCO-GDC is a promising candidate cathode material for solid oxide fuel cells.     

Ln0.6Sr0.4Co1−yFeyO3−δ (Ln = La and Nd; y = 0 and 0.5) cathodes with thin yttria-stabilized zirconia electrolytes for intermediate temperature solid oxide fuel cells

The electrochemical performances of the solid oxide fuel cells (SOFC) fabricated with Ln_0.6Sr_0.4Co_1−yFe_yO_3−δ (Ln = La, Nd; y = 0, 0.5) perovskite cathodes, thin yttria-stabilized zirconia (YSZ) electrolytes, and YSZ–Ni anodes by tape casting, co-firing, and screen printing are evaluated at 600–800 °C. Peak power densities of ∼550 mW cm⁻² are achieved at 800 °C with a La_0.6Sr_0.4CoO_3−δ (LSC) cathode that is known to have high electrical conductivity. Substitution of La by Nd (Nd_0.6Sr_0.4CoO_3−δ) to reduce the thermal expansion coefficient (TEC) results in only a slight decrease in power density despite a lower electrical conductivity. Conversely, substitution of Fe for Co (La_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ or Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ) to reduce the TEC further reduces the cell performance greatly due to a significant decrease in electrical conductivity. However, infiltration of the Fe-substituted cathodes with Ag to increase the electrical conductivity increases the cell performance while preserving the low TEC.     

YSZ films fabricated by a spin smoothing technique and its application in solid oxide fuel cell

A dense single-layer YSZ film has been successfully fabricated by a spin smoothing method. Followed by a simplified slurry coating, an additional spin smoothing process was conducted to obtain a thinner and smoother film. By employment of high-viscosity slurry including high YSZ content, the film has a suitable thickness by a single coating cycle. With Sm_0.2Ce_0.8O_1.9 (SDC)-impregnated La_0.7Sr_0.3MnO₃ (LSM) cathode and porous NiO–YSZ anode, single solid oxide fuel cell (SOFC) based on an 8-μm-thick YSZ film was obtained. Open-circuit voltage (OCV) of the cell was 1.04 V at 800 °C, and maximum power densities were 676, 965 and 1420 mW cm⁻² at 700, 750 and 800 °C, respectively, using H₂ at a flow rate of 40 mL min⁻¹ as fuel and ambient air as oxidant. The power density could be increased to 1648 mW cm⁻² at 800 °C when the flow rate of H₂ was enhanced to 200 mL min⁻¹.     

Direct methane oxidation over a Bi2O3–GDC system

A novel ceramic system was prepared by adding Bi₂O₃ to gadolinia-doped ceria (GDC). This Bi₂O₃–GDC system was characterized by temperature-programmed and fixed-temperature reaction of methane in the absence of gas-phase oxygen. It was found that adding Bi₂O₃ to GDC can promote the catalytic activity for direct methane oxidation. A Bi₂O₃ loading of 25 wt% in the Bi₂O₃–GDC system maximized the activity of direct methane oxidation. Possible carbon deposition after the reaction can be negligible. In the temperature range of an intermediate-temperature solid oxide fuel cell (SOFC), pre-reduction promotes methane oxidation activity. At temperatures of about 600 °C or lower, only CO₂ and H₂O are produced. However, CO and H₂ can be produced only at a temperature of about 700 °C or higher. This Bi₂O₃–GDC system can be applied to design SOFC anode materials for complete methane oxidation and thus full electricity generation, without syngas cogeneration, at low temperature.     

High performance composite interconnect La0.7Ca0.3CrO3/20 mol% ReO1.5 doped CeO2 (Re = Sm,Gd, Y) for solid oxide fuel cells

This paper reports and discusses composite interconnect materials that were modified from La_0.7Ca_0.3CrO_3−δ (LCC) by addition of Re doped CeO₂ (Re = Sm, Gd, Y) for improved conductivity at relative low temperatures. It is found that the addition of small amounts of RDC (ReO_1.5 doped CeO₂) into LCC dramatically increased the electrical conductivity. For the best system studied, LCC + 5 wt% SDC (Sm_0.2Ce_0.8O_1.9), LCC + 3 wt% GDC (Gd_0.2Ce_0.8O_1.9) and LCC + 3 wt% YDC (Y_0.2Ce_0.8O_1.9), the electrical conductivities reached 687.8, 124.6 and 104.8 S cm⁻¹ at 800 °C in air, respectively. The electrical conductivities of the specimens, LCC + 3 wt% SDC, LCC + 1 wt% GDC and LCC + 2 wt% YDC in H₂ at 800 °C were 7.1, 3.8 and 5.9 S cm⁻¹, respectively. With the increase of RDC content, the relative density increased, indicating that RDC served as an effective sintering aid in enhancing the sinterability of the powders. The average coefficient of thermal expansion (CTE) at 30–1000 °C in air increased with the increase of the RDC content. The oxygen permeation measurements indicated a negligible oxygen ionic conduction, indicating that the efficiency loss of a solid oxide fuel cell by permeation is negligible for the general cell design using LCC + RDC as interconnect. Therefore, the composite materials La_0.7Ca_0.3CrO₃/20 mol% ReO_1.5 doped CeO₂ are very promising interconnecting ceramics for solid oxide fuel cells (SOFCs).     

Characteristic of (La0.8Sr0.2)0.98MnO3 coating on Crofer22APU used as metallic interconnects for solid oxide fuel cell

This study reports the high temperature oxidation kinetics, area specific resistance (ASR), and interfacial microstructure of metallic interconnects coated by (La_0.8Sr_0.2)_0.98MnO₃ (LSM) in air atmosphere at 800 °C. An efficient LSM conductive layer was fabricated on metallic interconnects for solid oxide fuel cells (SOFCs) by using a wet spray coating method. The optimum conditions for slurries used in the wet spray coating were determined by the measurement of slurry viscosity and coated surface morphology. The surface roughnesses of the substrates were increased through sandblast treatment. The adhesive strength of the interface between the coated layer and the metal substrate increased with increased surface roughness of the metallic interconnects. The electrical conductivities of the coated substrates were measured by using a DC two-point and four-wire method under air atmosphere at 800 °C. Of note, the Crofer22APU treated at 1100 °C in N₂ with 10 vol.% H₂ showed long-term stability and a lower ASR value than other samples(heat-treated at 800 °C and 900 °C). After an 8000-h oxidation experiment the coated Crofer22APU substrate, the ASR showed a low value of 23 mΩ cm². The thickness of the coated conductive oxide layer was about 10-20 μm. These results show that a coated oxide layer prevents the formation and the growth of scale (Cr₂O₃ and (Mn, Cr, Fe)₃O₄ layer) and enhances the long-term stability and electrical performance of metallic interconnects for SOFCs.     

Sr2Fe4/3Mo2/3O6 as anodes for solid oxide fuel cells

Sr₂Fe_4/3Mo_2/3O₆ has been synthesized by a combustion method in air. It shows a single cubic perovskite structure after being reduced in wet H₂ at 800 °C and demonstrates a metallic conducting behavior in reducing atmospheres at mediate temperatures. Its conductivity value at 800 °C in wet H₂ (3% H₂O) is about 16 S cm⁻¹. This material exhibits remarkable electrochemical activity and stability in H₂. Without a ceria interlayer, maximum power density (P_max) of 547 mW cm⁻² is achieved at 800 °C with wet H₂ (3% H₂O) as fuel and ambient air as oxidant in the single cell with the configuration of Sr₂Fe_4/3Mo_2/3O₆|La_0.8Sr_0.2Ga_0.83Mg_0.17O₃ (LSGM)| La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF). The P_max even increases to 595 mW cm⁻² when the cell is operated at a constant current load at 800 °C for additional 15 h. This anode material also shows carbon resistance and sulfur tolerance. The P_max is about 130 mW cm⁻² in wet CH₄ (3% H₂O) and 472 mW cm⁻² in H₂ with 100 ppm H₂S. The cell performance can be effectively recovered after changing the fuel gas back to H₂.