Metal-supported Solid Oxide Research Articles

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.

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

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.

A perovskite infiltrated cathode of metal-supported solid oxide electrolysis cell for CO2 electrolysis

Solid oxide electrolysis cells (SOECs) are regarded as a promising technology to realize carbon neutrality since they can electrochemically convert CO2 to CO. This communication reports a feasible structure of a metal-supported solid oxide electrolysis cell (Ms-SOEC) for CO2 electrolysis, where a porous 430 stainless steel substrate is coated with perovskite oxide La0.6Sr0.4Fe0.9Mo0.1O3-δ (LSFM) introduced by the infiltration method. The LSFM catalyst exhibits a uniform distribution and loose accumulation in the porous metal substrate. This Ms-SOEC with a structure of LSFM-430|YSZ|LSCF-SDC shows a current density of 0.90 A cm−2 at 800 °C and 1.5 V with an LSFM loading of 6.0 wt%. Meanwhile, a 10-times thermal cycling operation demonstrates good reliability of the configuration. Overall, the metal-based cathode, where 430 stainless steel acts as the mechanical support and infiltrated LSFM perovskite acts as the electrocatalyst for CO2 electrolysis, could be a viable configuration of Ms-SOECs.

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.

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.

Electrochemical conversion of methane to ethylene, olefins, and paraffins using metal-supported solid oxide cells

Electrochemical oxidative coupling of methane (E-OCM) with Sr2Fe1·5Mo0·5O6−δ (SFM) catalyst is demonstrated with metal-supported solid oxide cells (MS-SOC). SFM anode and Pr6O11 cathode catalysts are loaded into a porous symmetric-architecture cell by infiltration and firing. The most effective chelating agent (citric acid/ethyl glycol) and optimal firing/reducing temperatures (850 °C/750 °C) for the SFM catalyst precursor solution are selected and confirmed by cell testing. Operating temperature, cell voltage, and oxygen concentration at the cathode greatly affect the methane conversion rate and product selectivity by controlling the oxygen ion flow. CH4 conversion of 85.8% is obtained, with C2H4, C2H6, and H2 concentrations of 10.5%, 12.3%, and 25.6% at 800 °C, respectively, in the product exhaust gas. Reasonable stability of the current density and methane conversion is demonstrated during 200 h operation. This research demonstrates technical progress in catalyst and device development for the E-OCM reaction to synthesize valuable chemicals.

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

A Metal-Supported-SOFC (MS-SOFC) has been modified by infiltrating a non-noble metal ceria-zirconia supported cobalt (Co/CZ) internal reforming catalyst to improve its reforming activity and inhibit the carbon deposition or coking under ethanol steam reforming conditions. Non-noble metal catalysts can still be deactivated during long-term cell operation in a severe coking-inducing environment. Therefore, an in-situ regeneration procedure was performed by pulsing air into the anode surface to burn the deposited carbon on the anode and catalyst layer during the cell operation. Upon the cell regeneration steps, the cell voltage was recovered to its initial condition at ~0.8 V, while the peak power density of the cell showed up to 116% recovery under H2 and 111% recovery under ethanol. These data show that the air pulsing regeneration steps in the MS-SOFC can improve the lifetime by removing the coking deposit within the anode and further enhancing its electrochemical and catalytic activity.

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

The LBNL metal-supported solid oxide cell architecture contains zirconia electrolyte and porous backbones co-sintered between porous stainless steel supports. Advantages of this design include low-cost structural materials, mechanical ruggedness, excellent tolerance to redox cycling, and extremely fast start-up capability. These features enable a wide variety of applications including electrolysis for intermittent renewables, distributed power generation, and synthesis of valuable chemicals. Highlights from efforts in these areas are presented.

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.

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.

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

In this study, MSCs were fabricated on the sintered porous metal substrates by wet coating with high temperature sintering in reduced atmosphere. The electrochemical performance of MSCs strongly depended on the process conditions. 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 shrinkage of substrate can assist the densification of electrolyte in the sintering process. It was found that the degrease and sintering temperature affected the shrinkage behavior, and existence of H2O in the atmosphere also affect it. 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. 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.

Development of Multiple Ceramic Coatings on Porous Tubular Metal Support

Dip coating was used to develop anodic half-cell for micro-tubular metal-supported solid oxide fuel cells (MS-SOFCs) economically. Ni–scandia-stabilized zirconia (SSZ) and SSZ were used as anode functional layer and electrolyte, respectively. Successive coatings of the SOFC functional layers were applied onto the porous metallic support using a dip coating technique. Additionally, to prevent delamination between the metal support and anode functional layer, an intermediate layer consisting of stainless steel powder, Ni, and yttria-stabilized zirconia (YSZ) was introduced. After coating, the individual layers were fired in a reducing atmosphere at 1000 °C followed by co-sintering of metal/anode/electrolyte multilayers at 1350°C. Microstructure of the sintered cells was characterized using scanning electron microscopy (SEM). General problems encountered during the fabrication of anodic half-cell for MS-SOFCs by a cost-effective dip coating followed by co-sintering route have been investigated. The sintering conditions and multilayer designs were studied to minimize the metal support oxidation and ceramic layer peeling during co-sintering.

Performance characterization of metal-supported solid-oxide fuel cell stacks at elevated pressure

In this paper, we present results on performance characterization of solid-oxide fuel cell stacks at elevated pressures up to 6 bara. Stacks are designed and built by Ceres Power, Ltd., and are rated at 1- and 5- kWe. Fuel streams include H2/N2 mixtures, synthetic natural-gas reformate, and simulated anode tail-gas recycle. Elevated operating pressure serves to increase stack electrochemical performance, with the most-pronounced gains found up to 4 bara. Pressurized operation reduces the extent of methane conversion, promoting more-uniform internal reforming and cooling within the stack. Such cooling is critical at higher-current conditions. A previously developed one-dimensional computational stack model is used to provide insight into stack operation. Pressurization is found to slightly increase internal thermal gradients, while promoting more-uniform reactant-concentration profiles across the cell, reducing the likelihood of local fuel starvation. The high fuel dilution brought by anode recycle can modestly decrease stack performance; however, this decrease is recovered through elevated-pressure operation at 3 bara. Anode recycle further promotes compositional uniformity across the cell. These results reflect that pressurized operation can promote stack performance, while potentially promoting long-term stack durability through uniformity in stack environmental conditions.

Performance and durability of metal-supported solid oxide electrolysis cells at intermediate temperatures

Performance and durability of metal-supported solid oxide electrolysis cells at intermediate temperatures

Oxidation of porous stainless steel supports for metal-supported solid oxide electrolysis cells

Oxidation of porous stainless steel supports for metal-supported solid oxide electrolysis cells

Optimization of metal-supported solid oxide electrolysis cells with infiltrated catalysts

Metal-supported solid oxide electrolysis cells (MS-SOECs) are being developed for steam-to-hydrogen electrolysis, especially for utilization of dynamic or intermittent electrical power from renewable sources. Various aspects of the electrocatalyst processing and composition, and metal support structure were explored. Catalyst materials, infiltration temperature and infiltration cycles were optimized for high performance and durability. Numerous catalyst materials were screened for both oxygen and steam electrodes. The oxygen catalyst had moderate impact on both initial cell performance and durability. Reducing Ni content in the steam electrode had little effect on durability, but reduced initial performance. Ex-situ XRD analysis and cell assessment of catalyst infiltration temperature revealed that the optimal range is 750–850 °C. The best cell performance and durability was achieved with LSCF-SDC oxygen electrocatalyst and SDC-Ni (60:40 vol%) steam electrocatalyst infiltrated 11 times at 800 °C and operated at 700 °C. At low steam content, a significant mass transport limitation on the steam side results in limiting current behavior. Thinner and more porous metal supports were implemented, and found to improve steam mass transport at low steam content, relevant for SOECs operating under high H2 recycle rate or high steam utilization.

Fabrication, property and performance evaluation of Stainless Steel 430L as porous supports for metal supported solid oxide fuel cells

Metal-supported solid oxide fuel cells (MS-SOFCs) have attracted increasing attention due to their superior mechanical strength, relatively low material cost, and capability of fast thermal cycling, as compared to the conventional all-ceramic solid oxide fuel cell. However, fabrication of MS-SOFCs still remains challenging. This study reports a cost-effective powder metallurgical manufacturing route for producing MS-SOFCs. Stainless steel 430L (SS430L) powder is selected for producing the metal support due to its relatively low cost and good thermal expansion compatibility. MS-SOFC button cells with the SS430L/YSZ|Ni/YSZ|YSZ|LSCF structure were successfully prepared by co-sintering and ultrasonic pyrolytic spraying. We found that the trace oxygen level in the dilute H2/Ar gas mixture could play a drastic role in laboratory sintering of the SS430L support; local oxygen control is essential, particularly to avoid Cr oxidation. The addition of no more than 10% YSZ as a second phase to SS430L substantially minimized over-sintering of the SS430L support, leading to a more porous metallic-type substrate, while the electrical conductivity and thermal expansion were not much affected. The fabricated MS-SOFC button cells with the SS430L/YSZ|Ni/YSZ|YSZ|LSCF structure delivered a maximum power density of 180 mW cm-2 at 800°C with an open-circuit voltage of 1.13 V, using dry hydrogen as the fuel and ambient air as an oxidant. A cell tested at 750°C showed relatively good stability for a period of 140 h. While the performance still needs further optimization, the high OCV and good stability indicated that the reported powder metallurgy route is a promising method, and the relevant experimental details, particularly on producing metallic and oxidation-free porous supports, are critical for the preparation of MS-SOFCs.

Multi-doped ceria-based composite as a promising low-temperature electrolyte with enhanced ionic conductivity for steam electrolysis

A lithium–bismuth–copper co-doped GDC composite (Ce0.712Gd0.178Li0.05Bi0.05Cu0.01O1.801) capable of sintering at ∼750 °C with an electrical conductivity of 29.6 mS cm−1 was developed for the first time for metal-supported solid oxide electrolysers.