Metal-supported Solid Oxide Fuel Cells Research Articles

Degradation analysis of plasma sprayed metal-supported solid oxide fuel cell: The evolution of electrode processes under polarization

Metal-supported solid oxide fuel cells (MS-SOFCs) prepared by plasma spraying exhibit promising potential for scale-up applications, where the key lies in breaking through the challenges of limited lifetime and durability. Although electrochemical impedance spectroscopy (EIS) has been widely used to unfold the complex electrode processes in electrochemical reactions, there are still some concerns concerning the in-depth understanding and scientific evaluation of the degradation mechanism of cell long-term performance. In this study, the contribution of each resistance to the overall performance degradation is separately determined by coupled equivalent circuit model (ECM) based on the deconvolution of recorded EIS data at different DC biases. It is found that the deterioration of cathode surface oxygen exchange and O2− conduction causes more than 64 % of the total resistance increase, followed by the anode charge transfer reaction and gas-phase transport (24.91 %), and then the ohmic resistance (9.73 %). However, the correlation between the output voltage drop of MS-SOFC under load and the gas-phase diffusion resistance gradually increases, indicating a shift in the cell degradation mechanism. Combined with the post-test characterization of the aged cell, it can be inferred that the degradation is mainly attributed to the densification of the anodic microstructure and the cathodic elemental segregation. Additionally, attention should be paid to the effects of the thickening of the metal substrate oxide layer and thermal mismatch on the structural stability of MS-SOFC.

Study on the performance of GDC electrolytes fabricated by atmospheric plasma spraying and vacuum plasma spraying

For metal-supported solid oxide fuel cells (MS-SOFCs), gadolinium-doped ceria (GDC) is one of the most promising electrolyte materials due to its high ionic conductivity. The plasma spraying technique has unique advantages in the preparation of MS-SOFCs, such as high efficiency, low cost, and low thermal impact on the metal support. However, few studies have been conducted on the preparation of dense GDC electrolytes using plasma spraying technology. In addition, it is not clear whether the composition and Ce valence state of GDC change during the plasma spraying process. In order to investigate this issue, GDC electrolytes were fabricated by atmospheric plasma spraying (APS) and vacuum plasma spraying (VPS) techniques. It is found that the GDC electrolyte fabricated by VPS is denser and has better electrochemical performance. The open circuit voltage and maximum power density of the VPS-cell at 600 °C are 0.90 V and 175.7 mW/cm2, respectively, while those of the APS-cell are 0.86 V and 124.8 mW/cm2, respectively. Moreover, the valence state of Ce4+ in the GDC electrolyte remains unchanged after plasma spraying, while the composition of Ce/Gd changes. This work successfully fabricates GDC electrolytes with qualified performance and provides a reference for further optimizing spraying parameters to prepare high-performance MS-SOFC.

Low-Temperature Fabrication of Screen-Printed NiO-YSZ Thin Film Anodic Layer on Metal Substrate via Hot-Pressing for Metal-Supported Solid Oxide Fuel Cells

Low-Temperature Fabrication of Screen-Printed NiO-YSZ Thin Film Anodic Layer on Metal Substrate via Hot-Pressing for Metal-Supported Solid Oxide Fuel Cells

Unravelling the oxidation behaviors of porous stainless steel 430L substrate for metal-supported solid oxide fuel cells

Metal-supported solid oxide fuel cell (MS-SOFC) has been attracting increasing attention due to relatively low materials cost and robust mechanic strength particularly for mobile applications. However, long term stability has been an issue for its application. It is challenging to isolate the degradation behavior and predict maximum lifetime of the metal substrate when assembled as full cell since many parameters may affect cell performance and life expectancy. We systematically investigated and reported the long-term oxidation behavior of porous stainless steel 430 L for up to 1500 h at 800°C under dry and 3 vol% H2O humidified H2/Ar mixture (10 vol% H2) atmosphere to simulate its applications in MS-SOFC. Our results show that the surface oxide scale of the porous 430Lsubstrate in both atmospheres are dominated by Cr2O3 and small amounts of MnCr2O4 or FeCr2O4 spinel oxides depending on the gas conditions, where the oxidation process could be divided into three stages with distinct characteristics. Stepwise surface color change, morphology and thickness of the formed oxide scale, elemental migration and distribution along the bulk alloy/oxide scale interface, and oxidation kinetics as a function of exposure time are systematically and thoroughly studied at high resolution. Based on the measured weight gains and thicknesses, oxidation kinetic parameters are extracted. These kinetic parameters are not only valuable for understanding the oxidation rate of porous 430 L in high temperature applications such as in MS-SOFC, but also can be used to predict the life expectancy of 430 L supported SOFC device which is critical for real and long-term applications.

Breakthrough in atmospheric plasma spraying of high-density composite electrolytes: Deposition behavior and performance of plasma-sprayed GDC-LSGM on porous metal-supported solid oxide fuel cells

The potential application of plasma spraying in the preparation of ceramic electrolyte for porous metal-supported solid oxide fuel cells (SOFCs) is highlighted by its ability to eliminate the need for a high-temperature sintering process. However, the challenge of achieving highly dense electrolytes through plasma spraying remains to be addressed. In this study, a novel electrolyte for porous metal-supported SOFCs (PMS-SOFCs) is developed. This involved the preparation of a highly dense structure of gadolinium-doped ceria (GDC)-lanthanum strontium gallium magnesium oxide (LSGM) composite coating using plasma spraying under atmospheric conditions. The composite electrolyte is prepared using atmospheric plasma spraying (APS). The addition of the low-melting-point LSGM phase enhanced the microstructural densification of the GDC-based composite coating and diminished electron loss in a reducing atmosphere, thereby improving the cell's open-circuit voltage. At 36 kW plasma arc power, the single cell with composite electrolyte exhibited a maximum power density of 371 mw/cm2 at 750 °C and achieved the highest open-circuit voltage (1.03 V) at 600 °C. Moreover, the open-circuit voltage remained stable over a 100-h test. These findings suggest that using APS to deposit a composite electrolyte with added low-melting-point secondary phases presents a promising approach for achieving relatively high OCV in PMS-SOFCs based on cerium oxide electrolytes.

Effect of Low Plasma Spraying Power on Anode Microstructure and Performance for Metal-Supported Solid Oxide Fuel Cells

Effect of Low Plasma Spraying Power on Anode Microstructure and Performance for Metal-Supported Solid Oxide Fuel Cells

Long-Term Oxidation Studies on Porous Stainless Steel 430L Substrate Relevant to Its Application in Metal-Supported SOFC

Metal-supported solid oxide fuel cells (MS-SOFCs) can be used in portable mobile power generators due to their excellent thermal cycling performance, low cost, and strong mechanical strength. The selection and lifetime of the support material are crucial factors that affect the cell’s performance and long-term stability. The oxidizability of porous 430L stainless steel in a dry air atmosphere at 800 °C was systematically studied and reported for up to 1500 h. The aim was to investigate the lifetime of porous stainless steel as a support skeleton in a symmetric MS-SOFC. The substrates were characterized and analyzed using scanning electron microscopy, energy spectroscopy, and X-ray diffractometry after different periods of oxidation. The analysis indicated that the porous substrate’s surface oxides, under dry air conditions, consisted primarily of Fe2O3 and Cr2O3, with small amounts of Fe3O4 and MnCr2O4 spinel. The long-term oxidation process can be divided into two stages with distinct characteristics. However, the oxide flaking phenomenon occurred after 1500 h of exposure. The estimated service life of the stainless steel was consistent with the experimental results, which were around 1500 h. This estimation was based on the measured weight gain and thickness data.

Correction to: Preparation of Plasma Sprayed GDC Electrolytes for Metal-Supported Solid Oxide Fuel Cells

Correction to: Preparation of Plasma Sprayed GDC Electrolytes for Metal-Supported Solid Oxide Fuel Cells

Preparation of Plasma Sprayed GDC Electrolytes for Metal-Supported Solid Oxide Fuel Cells

Preparation of Plasma Sprayed GDC Electrolytes for Metal-Supported Solid Oxide Fuel Cells

Performance optimization of metal-supported solid oxide fuel cells using cathode and full cell impregnation with La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ electrode.

In this study, precursor solutions of La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (LSCFN) symmetric electrode were prepared, and the applications of cathode impregnation and full cell impregnation in the preparation and performance optimization of four-layer metal-supported solid oxide fuel cells (MSCs) were thoroughly investigated. Test results indicate that the polarization impedance of cathode impregnated MSCs under H2 and CH4 atmospheres at 750 °C is approximately 0.1 Ω cm2 and 0.41 Ω cm2, respectively, with power densities of 1115 mW cm-2 and 700 mW cm-2, respectively. Meanwhile, the polarization impedance of full cell impregnated MSCs under the same conditions is 0.12 Ω cm2 and 0.40 Ω cm2, with power densities of 945 mW cm-2 and 840 mW cm-2, respectively. Remarkably, MSCs full cell impregnated LSCFN exhibit outstanding stability performance under CH4 atmosphere in a 100 h stability test. Research on the application of impregnation method for performance optimization of metal-supported cells is relatively scarce. The results reveal the feasibility of simplifying MSCs preparation steps using full cell impregnation method, further promoting the widespread application of metal-supported overall cells.

Low-pressure plasma sprayed dense scandia-stabilized zirconia electrolyte and its effect on SOFC performance

The plasma spraying process has been proven capable of fabricating high-performance metal-supported solid oxide fuel cells (MS-SOFCs), and the critical technology is to prepare dense MS-SOFC electrolytes. Usually, very low-pressure plasma spraying (<1000 Pa) is adopted as it can significantly improve the electrolyte density and air tightness. However, at the same time, it also has the disadvantages of low deposition efficiency and high cost. This paper explores whether it is possible to prepare dense MS-SOFC electrolytes under low-pressure conditions (1000–10000 Pa) with ideal deposition efficiency and cost. Specifically, 4000 Pa and 7000 Pa were chosen to prepare scandia-stabilized zirconia (ScSZ) electrolytes. The effects of spraying pressure and distance on the electrolyte microstructure and cell electrochemical performance were investigated. It was found that the electrolyte prepared at a pressure of 4000 Pa and a spraying distance of 325 mm had the lowest porosity of 3.28%. Meanwhile, the cell exhibited the best electrochemical performance with an open circuit voltage of 1.008 V and a maximum power density of 970 mW/cm2 at 800 °C.

Formation of Dense Yttria-Stabilized Zirconia Thin Film by Aerosol Deposition Method for Metal-Supported Solid Oxide Fuel Cell Applications

Formation of Dense Yttria-Stabilized Zirconia Thin Film by Aerosol Deposition Method for Metal-Supported Solid Oxide Fuel Cell Applications

Flatness Enhancement of Metal-Supported Solid Oxide Fuel Cells with Additional Compensation Layer

Solid oxide fuel cells are high-temperature fuel cells which offer several advantages: high efficiency, fuel flexibility, high-quality waste heat, and the use of non-noble metal catalysts. Metal-supported solid oxide fuel cells, in which the ceramic mechanical support layer is replaced with the metal support, are considered as next-generation solid oxide fuel cells because of their enhanced mechanical/thermal ruggedness compared to conventional ceramic-supported solid oxide fuel cells. However, different thermomechanical behavior of metal support and ceramic layers during sintering makes metal-supported cells vulnerable to warping. Cell warpage must be minimized because it reduces not only uniformity of wet-chemical coating, but also actual contact area between electrode and interconnect, increasing the contact resistance.In this study, causes of metal-supported cell warpage are identified, and the design that can minimize cell warpage is suggested for successful scale-up of metal-supported solid oxide fuel cells. Through thermomechanical and residual stress analyses, it is found that residual stress derived from coefficient of thermal expansion mismatch between electrode layers and the metal substrate is the main cause of the warpage of metal-supported solid oxide fuel cells. Based on these results, a novel design that has thicker metal protection layer on the opposite side of the electrolyte is proposed for minimizing cell warpage due to residual stress. Through the design modification, vertical deformation of 2-inch metal-supported solid oxide fuel cell can be successfully controlled to 17.36% of the previous design. Furthermore, electrochemical evaluation showed a 21% decrease in ohmic ASR and a 25% increase in peak power density after the design modification, implicating reduction of contact resistance as a result of increased contact area by enhanced flatness.

Densification of Plasma-Sprayed YSZ Electrolyte by Suction Filtration Using Submicron/Nanoparticle Suspension for Metal-Supported SOFCs

Atmospheric plasma spraying (APS) is widely used for the fabrication of metal-supported solid oxide fuel cells (MS-SOFCs) due to its cost-effective and fast process. However, the incomplete melting of partial electrolyte particles in the layer-by-layer deposition process leads to a relatively porous electrolyte layer, which causes severe gas leakage and hinders its implementation on MS-SOFCs. In this study, a simple and efficient two-step method is developed to achieve the densification of a plasma-sprayed YSZ electrolyte layer in a tubular MS-SOFC through suction filtration using a YSZ submicron/nanoparticle suspension. The prepared tubular MS-SOFCs were immersed in the YSZ submicron-particle suspension, and the pressure inside the tubular SOFC was reduced to -20 kPa to drive the YSZ submicron particles to fill the pores in the YSZ electrolyte. After suction filtration for 1 h, the gas permeability of the YSZ electrolyte decreased from 2.57×10-5 to 5.84×10-6 by a factor of 4.4, and the pores in the YSZ electrolyte decreased from the micron scale to the submicron scale. Further densification can be achieved by a second suction filtration treatment in the YSZ nanoparticle suspension so that the pores can be further decreased from the submicron scale to the nanoscale, which ensures gas tightness and can be used as the electrolyte of MS-SOFCs.

Steam Reforming Catalytic Layer on Anode-Supported and Metal-Supported Solid Oxide Fuel Cells for Direct Ethanol Operation

A catalyst based on lanthanum chromite with exsolved metallic ruthenium nanoparticles (LaCrO3-Ru) was applied as a catalytic layer for internal ethanol steam reforming of anode-supported and metal-supported solid oxide fuel cells. Both the cermet anode and the metal supports exhibit limited catalytic properties for the ethanol steam reforming reaction. Thus, the LaCrO3-Ru catalysts were optimized for operating temperatures in the 600-700 °C range to promote stable ethanol reforming. The microstructure of the deposited catalytic layer was controlled using pore formers with low burnout temperature, and sintering of the catalytic layer was done in situ during cathode sintering of the metal-supported fuel cell. The performance of the fuel cells was evaluated at 700 °C under hydrogen, anhydrous ethanol, and water/ethanol mixtures. The LaCrO3-Ru catalytic layer had no significant impact on the electrochemical properties of the fuel cells, and samples with the catalytic layer or without it exhibited similar performance in hydrogen. Nonetheless, initial durability tests have shown that the catalytic layer plays a crucial role in the stability of both the anode and the metal-supported fuel cells under ethanol.

Direct Utilization of Pure and Denatured Ethanol in Metal Supported Solid Oxide Fuel Cells

Metal supported solid oxide fuel cells (MS-SOFC) are integrated with high entropy alloy reforming catalyst for direct internal reforming utilization of pure ethanol, methanol, and denatured ethanol to generate electricity. Internal reforming SOFCs have advantages over the external reforming SOFCs in terms of cost, energy efficiency, and space-saving. Performance and durability with denatured ethanol, mimicking the compositions of widely commercially-available bio-ethanol, varies dramatically with the composition of the denaturant. This evaluation of bio-ethanol fuel for SOFC application extends beyond the previous literature focusing on high-purity ethanol. Mitigation of carbon deposition is critical to extend the lifetime of MS-SOFCs operating with ethanol. Conventional Ni catalyst shows rapid carbon deposition, and in contrast the HEA catalyst has excellent resistance to carbon deposition. The HEA also enables complete internal reforming without localized cooling, resulting in high power density >0.8 W/cm2 at 700°C. Long-term operation (500-1000 hours) at the operating temperature of 600-800°C will be presented. Various strategies are applied to improve the cell stability. The effect of impurities and fuel compositions on the cell performance and stability is evaluated. Other degradation factors such as Cr evaporation and catalyst agglomeration are analyzed by SEM-EDS and EIS. It is found that MS-SOFCs are promising for direct utilization of bio-ethanol, offering a path to rapid-start, carbon-neutral operation.

Metal-Supported Solid Oxide Cells for Energy Conversion, Electrolysis, and Chemical Synthesis

This talk will provide an overview and update of performance, durability, and applications of metal-supported solid oxide fuel cell (MS-SOFC) and electrolysis cell (MS-SOEC) technology developed at Lawrence Berkeley National Laboratory (LBNL). The unique LBNL symmetric cell architecture design, with thin zirconia ceramic backbones and electrolyte sandwiched between porous metal supports, offers a number of advantages over conventional all-ceramic cells, including low-cost structural materials (e.g. stainless steel), mechanical ruggedness, excellent tolerance to redox cycling, and extremely fast start-up capability. These features enable a wide variety of applications including vehicle range extenders, electrolysis for intermittent renewables, personal power generators, and distributed generation.With infiltrated catalysts, the catalyst compositions can be easily tailored to a variety of reactions, without re-optimizing the entire cell. Recent efforts have developed catalysts for internal reforming of natural gas and ethanol, steam electrolysis to produce hydrogen, oxidative coupling of methane to synthesize ethylene, and oxygen generation from air. A recent focus is 1000+ hour continuous operation with detailed post-mortem analysis. Progress on cell performance and durability for each of these applications will be discussed.Infiltrated catalysts, however, present a tradeoff between initial performance and long-term stability. Extremely high surface area promotes high electrochemical reaction rates, but also provides high surface energy leading to coarsening and facilitates Cr deposition. Recent approaches to mitigating catalyst coarsening and Cr deposition within the cathode include coatings to prevent Cr evaporation from the stainless steel components, and optimization of infiltrated catalyst processing to stabilize the microstructure during operation. The metal support structure has also been optimized for improved mass transport.

Direct-Fed Ethanol Metal-Supported Solid Oxide Fuel Cell System with Regeneration Process by Air Pulsing

Metal-Supported-SOFC (MS-SOFC) can handle rapid start-up and cool-down without cracking, making it more suitable for mobile applications than a conventional cermet-based SOFC, which is more susceptible to cracking when experiencing thermal shock due to its ceramic component. Despite having more robust mechanical properties, the MS-SOFC still relies on Ni as its anode catalyst, where it can be deactivated due to coking formation if the cell is operated under liquid logistics or hydrocarbon fuels. One of the most effective solutions is introducing a micro-reforming catalyst layer on the anode layer. The micro-reforming catalyst will reform the fuel into H2 and CO mixture called syngas, and then the anode will use the reformatted syngas to run the electrochemical reaction to produce electricity. This method will effectively improve the cell power output, stability, and coking resistance.In this work, we integrated the MS-SOFC with a reforming catalyst through the precursor infiltration method. We infiltrated a non-noble metal-based catalyst with a ceria-zirconia (CZ) into the MS-SOFC. The cell is then operated under direct ethanol fuel at 700 °C with the S/C ratio of 2. The non-noble metal catalyst is less expensive than noble but it also has lower catalytic activity and coking resistance during the cell operation in ethanol. Therefore, a regeneration cycle is necessary to maintain the cell performance and the catalytic activity of the cell. The regeneration cycle is performed by air pulsing directly into the cell’s anode surface to burn off the coking generated during the cell operation. The regeneration process involves a redox cycle that is only possible for a mechanically stable structure like MS-SOFC.Our experimental data showed that the MS-SOFC with infiltrated micro-reforming catalyst was gradually deactivated during the operation under ethanol fuel, indicated by the cell voltage drops due to coking. After the regeneration procedure with air pulsing, the cell voltage was recovered to its original performance. At the same time, the gas chromatograph detects a significant CO2 signal from the effluent gas, suggesting that the carbon removal process was successfully performed. Additionally, we observed an improvement in the cell’s performance under H2 and ethanol fuel. After a long-term constant current stability test, the cell shows up to ~20% and ~25% maximum current density drops under H2 and ethanol fuel, respectively, compared to its initial performance. Upon the cell regeneration with air pulse, the cell’s maximum current density was recovered to its initial performance and showed an improvement up to ~21 and 13% under H2 and ethanol, respectively, compared to its initial performance before the long-term test. This result suggests that some of the carbons might remain within the cell’s functional layer and help improve its conductivity and electrochemical performances. These data clearly show that the air pulsing regeneration process in the MS-SOFC can improve the cell’s lifetime by removing the coking deposit within the anode and enhancing its electrochemical and catalytic activity.-------Figure Caption: Fig 1.(A) The IV pot of the MS-SOFC with reforming catalyst under H2 and (B) ethanol solution (S/C=2) at 700 °C of the MS-SOFC. The IV measurements were taken during its initial screening, after both constant current stability tests, and after both regeneration procedures. (C) Long-term stability test of the cell in ethanol solution under the constant current density of 125 mA/cm2. Figure 1

Effect of Fabrication Processes on Electrochemical Performance of Metal-Supported Solid Oxide Fuel Cells

Metal supported solid oxide fuel cells (MSCs) which have the robust porous metal substrate are expected for the use in some mobilities. MSCs are prepared by various fabrication processes such as sputtering and screen printing. When the electrolyte layer is fabricated by the wet processes, the electrolyte must be sintered with metal substrate at a high temperature. However, it is difficult to obtain the dense electrolyte on porous metal substrate because sintering temperatures of an electrolyte ceramic and a metal material used in substrates are different. In this study, MSCs were fabricated on the sintered porous metal substrates by screen printing and spin coating with high-temperature sintering in reduced atmosphere. The electrochemical performance of MSCs strongly depended on the process conditions. MSCs were prepared by the process which is similar to the process for anode supported cell fabrication. Anode paste including nickel oxide and scandia stabilized zirconia with a weight ratio of 60/40 was coated on the green compact of substrate by screen printing. After drying, the electrolyte layer is coated on it by same procedure. Samples were heat-treated around 400 ºC for 1 h to degrease the organic compounds included in cells. These are finally sintered at 1100 – 1250 ºC in reduced atmosphere. The relationship between the electrochemical performance and the structural property were investigated.In order to obtain dense electrolyte, the shrinkage behavior of porous metal substrates is quite important. Large shrink of substrate can assist the densification of electrolyte in the sintering process. It was found that the degrease temperature affected the shrinkage behavior in sintering process. It was considered that the oxidation of metal particles in substrate affected on the shrinkage. When the sintering temperature were high to obtain the dense electrolyte, Fe and Cr diffused from the substrate to the anode layer. This metal elements diffusion strongly deteriorated the performance of the anode. Additionally, gas atmosphere also affected the metal elements diffusion. When the MSCs are prepared by wet process with high temperature sintering, controlling the sintering behavior of all components by adjusting the process parameter was quite important to low polarization resistance.

Electrochemical Performance and Mechanical Stress Evaluation of Metal-Supported Solid Oxide Fuel Cells Fabricated By Plasma Spray Method

At present, the most common type of SOFC is anode-supported SOFC (AS-SOFC), in which the cell is mechanically supported by the thick fuel electrode layer. Recently, Metal-supported SOFCs (MS-SOFCs) have attracted attention because of their potential for low cost and high mechanical robustness. However, the fabrication process of MS-SOFCs has not been established. The mechanical behavior of the cells under high temperature operation has not been clarified. In this study, we fabricated prototype MS-SOFCs using the plasma spray method. The cell was tested by electrochemical measurements, residual stress measurements, and SEM/EDX to clarify the mechanical behavior of MS-SOFCs under high temperature operation.The layers of anode (NiO-YSZ), electrolyte (LSGM9182), and cathode (LSCF6428) were formed on a metal substrate (SUS430) by atmospheric pressure plasma spraying (APS) to fabricate a single cell of MS-SOFC.Open circuit voltage, AC impedance, and I-V measurements were performed at 600°C, 650°C, and 700°C. The residual stress of LSGM9182 electrolyte was evaluated by cosα method [1] under the cell operation condition using specially designed chamber.The MS-SOFC with thicker electrode layers showed the much lower OCV than that of theoretical. In addition, the electrolyte had vertical cracks between cathode and anode after the 2nd thermal cycle. However the MS-SOFC with thinner electrode layers showed the higher OCV, which was nearly theoretical value, and much better I-V characteristics than the cell with thicker electrodes. Electrochemical impedance measurement revealed the plasma sprayed electrodes showed acceptable performance even though its microstructure was not optimized. The residual stress of LSGM electrolyte in the cell did not change so much during the cell operation. This might be caused by existence of small cracks in the electrolyte layer.This research was financially supported by NEDO.[1] K.Tanaka, Journal of the Society of Materials Science,japan,vol.66,No.7 (2017) 479-487