Metal-supported Solid Oxide Fuel Cells Research Articles

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

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

Ethanol-fueled metal supported solid oxide fuel cells with a high entropy alloy internal reforming catalyst

High-performance metal supported solid oxide fuel cells (MS-SOFC) with an integrated high entropy alloy (HEA) internal reforming catalyst (IRC) are demonstrated for transportation applications using ethanol and methanol as fuels. Addition of the HEA IRC dramatically improves cell performance and stability when using ethanol/water blend fuel. Absence of carbon deposition predicted by thermodynamic calculations is confirmed by Raman spectroscopy analysis of posttest anodes. Optimal catalyst processing (deposition technique, loading, firing temperature) and cell operation conditions (flow rates, temperature, fuel compositions) are explored. Infiltrated HEA reforming catalyst provides a highly porous structure and low catalyst loading (6 mg cm−2). The designed structure and catalysts achieve small mass transport resistances in the fuel electrode (26.2 s m−1) and oxygen electrode (41.6 s m−1). The best ethanol concentration (60:40 v% ethanol: water) provides 0.83 W cm−1 at 700 °C, without carbon deposition. The ethanol-fueled MS-SOFC is operated for 500 h, including five thermal cycles. Cell evolution is similar to that reported previously for hydrogen fuel; nickel aggregation and chromia deposition were the major observed changes, and carbon formation can be avoided even after long-term operation.

NiMo/CZ internal reforming layer for ethanol-fueled metal-supported solid oxide fuel cell

A metal-supported solid oxide fuel cell (MS-SOFC) consisting of infiltrated NiMo/CZ internal reforming catalysts is operated under a direct ethanol feed condition at 700 °C with a steam-to-carbon (S/C) ratio of 2. The additional catalyst functional layer is required to internally reform the ethanol fuel into syngas while preventing the cell's rapid deactivation due to unwanted carbon deposits or coking. Our experimental results show that the cell with NiMo/CZ catalyst shows a higher maximum current density of 0.355 A cm−2 compared to 0.052 A cm−2 for the cell without catalyst at 0.4 V. The constant current stability performance was also improved. The cell with NiMo/CZ can operate for 90 h and shows less carbon deposition than the cell without a catalyst. Adding NiMo/CZ reforming catalyst into the MS-SOFC is a promising solution to enhance the operating lifetime and coke resistance in the ethanol steam reforming fed MS-SOFC system.

Characterization of thin metal‐supported solid oxide fuel cells fabricated through atmospheric Plasma spraying

AbstractIn this study, thin molybdenum‐containing, nickel‐based metal‐supported solid oxide fuel cells (MS‐SOFCs) were fabricated through atmospheric plasma spraying and then characterized. We investigated the change in cell performance associated with the reduction of the Ni–Mo support layer thickness from 200 to 80 µm and reduction of the substrate sintering temperature from 1200 to 1000°C. At a cell voltage of 0.6 V, the measured maximum power density values of a 50 × 50 mm2 MS‐SOFC were 313, 581, 890, and 1098 mW cm−2 at 600, 650, 700, and 750°C, respectively. A 100 × 100 mm2 (commercial‐size) MS‐SOFC and an assembled single‐cell MS‐SOFC stack exhibited electric output power values of approximately 33 and 39 W at 700 and 750°C, respectively, and an effective electrode area of 81 cm2. In a long‐term stability test, the commercial‐size cell and single‐cell stack exhibited a degradation rate of approximately 1% after 1000 h of operation at a current density of 250–300 mA cm−2 and temperature of 700°C. Moreover, a five‐cell MS‐SOFC stack demonstrated a stack power of 180.85 W at 3.792 V (446.5 mW cm−2 at 0.758 V) and 750°C.

Metal-Supported Solid Oxide Fuel Cells: A Review of Recent Developments and Problems

The design of metal-supported solid oxide fuel cells (MS-SOFCs) has again aroused interest in recent years due to their low cost of materials, strength, and resistance to thermal cycling, as well as the advantages of manufacturability. MS-SOFCs are promising electrochemical devices for hydrogen energy. Compared to SOFCs, where ceramic electrodes or electrolytes are used as a carrier base, they are of great interest due to their fast start-up capability, greater reliability, mechanical stability, and resistance to the thermal cycle. MS-SOFCs have many advantages over conventional ceramic-based SOFCs, with the selection of metal-based electrode materials (anode, cathode) and their degradation processes being some of the biggest challenges facing researchers. Therefore, this review reports on the state of the latest research on MS-SOFCs with various structures, discusses the corresponding electrode materials and their existing problems, and puts forward topical issues that need to be addressed in MS-SOFCs.

Failure Mechanism and Optimization of Metal-Supported Solid Oxide Fuel Cells.

A solid oxide fuel cell (SOFC) is a clean, efficient energy conversion device with wide fuel applicability. Metal-supported solid oxide fuel cells (MS-SOFCs) exhibit better thermal shock resistance, better machinability, and faster startup than traditional SOFCs, making them more suitable for commercial applications, especially in mobile transportation. However, many challenges remain that hinder the development and application of MS-SOFCs. High temperature may accelerate these challenges. In this paper, the existing problems in MS-SOFCs, including high-temperature oxidation, cationic interdiffusion, thermal matching, and electrolyte defects, as well as lower temperature preparation technologies, including the infiltration method, spraying method, and sintering aids method, are summarized from different perspectives, and the improvement strategy of existing material structure optimization and technology integration is put forward.

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 internal reforming catalyst for direct utilization of ethanol to generate electricity. MS-SOFCs are operated up to 500 h at 700°C, with water-ethanol blend fuel using high-purity ethanol and denatured ethanol. Performance and durability with denatured ethanol varies dramatically with the composition of the denaturant. Cells operated with three denatured ethanol fuels containing small amount of methanol, isopropanol, and denatonium benzoate demonstrate similar and relative stable performance after stabilization, suggesting that these fuels are fit for MS-SOFC operation. No or minimum carbon deposits are observed on the high entropy alloy-based reforming catalyst layer. Denatured ethanol containing gasoline and toluene leads to fast degradation. MS-SOFCs are promising for direct utilization of denatured ethanol, offering a path to rapid-start, carbon-neutral operation with widely-available fuels.

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. The metal support exhibits 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 catalytic layer had no significant impact on the electrochemical properties of the fuel cell, and samples with and without the catalytic layer exhibited similar performance in hydrogen. Initial durability tests with LaCrO3-Ru layer have shown that the catalytic layer plays a crucial role in the stability of the metal-supported fuel cell under ethanol.

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), while the low gas-tightness of the electrolyte layer prepared by APS hinders its implementation on MS-SOFCs. In this study, a simple two-step method was developed to achieve densification of the plasma-sprayed YSZ electrolyte layer through suction filtration in a YSZ submicron/nanoparticle suspension. After the two-step suction filtration, the gas permeability of the YSZ electrolyte decreased from 4.27×10-6 cm4·gf-1·s-1 to 2.75×10-6 cm4·gf-1·s-1. However, there was no obvious increase in the open circuit voltage (OCV) of the treated cell, which indicated that the gas-tightness of the plasma-sprayed electrolyte should be further improved by optimizing the suction filtration conditions.