Metal-supported Cells Research Articles

Assessment of co-sintering as a fabrication approach for metal-supported proton-conducting solid oxide cells

Proton conducting oxide electrolyte materials could potentially lower the operating temperature of metal-supported solid oxide cells (MS-SOCs) to the intermediate range 400 to 600 °C. The porous metal substrate provides the advantages of MS-SOCs such as high thermal and redox cycling tolerance, low-cost of structural materials, and mechanical ruggedness. In this work, viability of co-sintering fabrication of metal-supported proton conducting solid oxide cells is investigated. Candidate proton conducting oxides including perovskite oxides BaZr0.7Ce0.2Y0.1O3−δ, SrZr0.5Ce0.4Y0.1O3−δ, and Ba3Ca1.18Nb1.82O9−δ, pyrochlore oxides La1.95Ca0.05Zr2O7−δ and La2Ce2O7, and acceptor doped rare-earth ortho-niobate La0.99Ca0.01NbO4 are synthesized via solid state reactive or sol-gel methods. These ceramics are sintered at 1450 °C in reducing environment alone and supported on Fe-Cr alloy metal support, and their key characteristics such as phase formation, sintering property, and chemical compatibility with metal support are determined. Most electrolyte candidates suffer from one or more challenges identified for this fabrication approach, including: phase decomposition in reducing atmosphere, evaporation of electrolyte constituents, contamination of the electrolyte with Si and Cr from the metal support, and incomplete electrolyte sintering. In contrast, La0.99Ca0.01NbO4 is found to be highly compatible with the metal support and co-sintering processing in reducing atmosphere. A metal-supported cell is fabricated with La0.99Ca0.01NbO4 electrolyte, ferritic stainless steel support, Pt air electrode and nanoparticulate ceria-Ni hydrogen electrocatalyst. The total resistance is 50 Ω·cm2 at 600 °C. This work clearly demonstrates the challenges, opportunities, and breakthrough of metal-supported proton-conducting solid oxide cells by co-sintering fabrication.

Development of an Advanced Flexible Solid Oxide Fuel Cell Stack Concept

An advanced flexible solid oxide fuel cell (SOFC) stack concept with the potential for increased reliability, better performance and lower cost is being developed. This stack concept integrates prime-surface interconnects and single cells into a lightweight and compact structure with reliable gas seals for efficient operation at different temperatures depending on selected materials. The concept has several attractive features icluding reduced stack weight and volume, decreased performance losses in stacking, improved sealing, versatility in incorporation of different types of cell construction (for example, conventional sintered cells or thin-film metal supported cells) and flexibility in gas flow configuration. The prime-surface interconnect is a one-piece metal sheet that incorporates both fuel and oxidant flow fields with peaks o one side of the interconnect serving as flow channels (valleys) on the other side; for exampe, the egg-carton shaped prime-surface flow field. The design of the prime-surface interconnect including the key factors impacting on pressure drop, flow uniformity and formability is being evaluated. Hydroforming has been identified as the forming appoach for prime-surface interconnects. Development of metal-supported cells has been initiated. A fabrication process based on sputtering is being developed for producing cells on metal supports for this stack concept.

High Performance (La,Sr)(Co,Fe)O3 Cathodes with Improved Adherence for Metal-Supported Fuel Cells

A novel sintering approach was developed in order to overcome the issue of insufficient adherence of (La,Sr)(Co,Fe)O3 type cathodes in metal-supported solid oxide fuel cells (MSCs). Investigation of the phase stability of the perovskite structure at high temperature in various atmospheres with low oxygen partial pressures provided the basis for the development of a sintering procedure applicable to full-cells. By investigating the layer adherence, time dependent mechanical integrity and reversibility of phase transformations, metal-supported cells with sintered cathodes could be produced reliably and were electrochemically characterized in single cell measurements. The novel sintering approach of such cathodes resulted in a significantly enhanced mechanical stability of the cathode layers. Extensive spallation of the cathode was prevented, which is a substantial improvement in comparison with state-of-the-art MSCs. Furthermore, the electrochemical measurements revealed a beneficial effect regarding the cell performance. Post-test characterization is assumed to provide further information regarding the quality of bonding between cathode and electrolyte. Further investigations cover the implementation of alternative high-performance cathode materials like LSC as well as the combination with optimized anode structures/compositions.

Distribution of Relaxation Times Analysis for Optimization of Anode Thickness in Metal-Supported Microtubular Solid Oxide Fuel Cells

An anode functional layer (AFL) is inserted between anode substrate and electrolyte thin-film to increase the triple phase boundary (TPB) for anode-supported solid oxide fuel cells (SOFCs). On the other hand, better mechanical robustness, redox tolerance, rapid thermal cycling and cost reduction are expected for metal-supported SOFCs. The anode thickness of metal-supported cells (MSCs) is more important than the AFL thickness of anode-supported cells (ASCs), since the metallic substrate does not have TPB. In the present work, the metal-supported microtubular SOFCs with La0.6Sr0.4Co0.2Fe0.8O3(LSCF)-(Ce0.9Gd0.1)O1.95(GDC) cathode, GDC electrolyte, BaCe0.8Y0.2O3- d (BCY) blocking layer and Ni-GDC anode on Ni substrate were investigated. The significant decrease in polarization resistance with increasing the anode thickness from 10 to 16 mm was confirmed by the distribution of relaxation times (DRT) analysis for the metal-supported microtubular SOFCs operated at 550 oC.

Degradation of Metal-Supported Cells with Ni-YSZ or Ni-Ni3Sn-YSZ Anodes Operated with Methane-Based Fuels

The most common solid oxide fuel cell (SOFC) anode material, nickel - yttria stabilized zirconia (YSZ), displays excellent catalytic properties for fuel oxidation and good electronic conductivity. However, nickel-based anodes can cause carbon deposition when hydrocarbon fuels are used [1]. Nickel catalyzes the formation of carbon filaments in the presence of hydrocarbons under reducing conditions, resulting in coverage of the active sites of the anode, and potentially also to dissolution, precipitation, and metal dusting [2]. It is possible to avoid carbon deposition if sufficient steam is present such that the rate of carbon removal is comparable to or faster than the rate of carbon deposition. However, there is a corresponding decrease in electrical efficiency associated with dilution of the fuel. Metals with electronic structures similar to that of carbon may form an alloy with nickel at the surface, thus reducing carbide formation, and as a consequence, coking [3]. Tin, for example, has been reported to reduce carbon deposition on a Ni-YSZ cermet when present in low amounts such as 1 wt.% of tin with respect to nickel [4,5]. However, volatilization of a metallic tin phase at SOFC operating temperatures may present a problem for long term operation. To increase the stability of tin-containing anodes, we fabricated Ni-Ni3Sn-YSZ anodes using a hybrid solution-precursor / suspension plasma spray (SPPS-SPS) process and compared them to nickel-YSZ anodes made using the same process parameters. Thermogravimetric analyses in a 4% CH4 (balance nitrogen) atmosphere showed that the presence of tin in the anode reduced the rate of carbon deposition. Furthermore, higher amounts of tin resulted in less coking. Ni-Ni3Sn-YSZ and Ni-YSZ anodes were incorporated into metal-supported SOFCs that consisted of a porous metal support (Sandvik Sanergy), samaria-doped ceria (SDC) barrier layer, anode as previously described, YSZ electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3-δ-SDC cathode. Cells were tested at 750°C with air as the oxidant and fuel consisting of 65% CH4, 32% H2, and 3% H2O. The cells were held at a current density of 0.15 A·cm-2 for 500 hours. The cell without tin in the anode began to degrade after approximately 200 hours and catastrophically failed at approximately 425 hours. After testing, we observed that the anode had disintegrated, and as a result, the electrolyte and cathode were completely detached from the metal support. On the other hand, the cell with an anode containing tin did not catastrophically fail, and the cell remained intact after 500 hours of operation. Over 500 hours, the cell potential degraded from 0.841 V to 0.743 V, and scanning electron micrographs showed that the anode had delaminated from the electrolyte in some areas. Nonetheless, the cell with the Ni-Ni3Sn-YSZ anode degraded significantly less than the cell containing a Ni-YSZ anode, suggesting that the addition of Ni3Sn to an anode could be a useful strategy for improving durability of SOFC anodes using hydrocarbon fuels.

Development and Evaluation of 3-Layer Metal Supported Solid Oxide Fuel Cell Short Stack

A solid oxide fuel cell (SOFC) is promising technology because of its high electrical efficiency and environmental performance. SOFC can utilize solid ceramic electrolyte, so it can avoid the problems like corrosion, leakage and electrolyte management that often occur in liquid electrolyte. However, these ceramic based SOFC has weakness in external impacts because of its brittleness and relatively low strength. For this problem, metal-supported SOFC has been suggested. Metal supported SOFC refers to SOFC which replace its ceramic support to metal support for enhancing mechanical strength. Metal-support SOFC includes higher mechanical strength, better resistance to vibrates and impacts than conventional SOFC. So, metal-supported SOFC can be applied to movable applications like automobile, train and ship as well as stationary power generation system. In this study, 3-layer metal-supported SOFC short stack was designed and developed for APU (Auxiliary Power Unit) application. The short stack was composed of metal-supported cells, interconnect plates, ceramic sealant, gasket and metal foams. The metal-supported SOFC cell was fabricated by sinter-joining method and dimension of metal-supported SOFC cell was 120 x 80 mm2 and active cathode area was 110 x 70 mm2. For the material of interconnect plates and metal supports, Crofer 22 APU alloy was used which has high resistance to oxidation, low rate of chrome vaporization and good electrical conductivity of its oxide layer. Also, hybrid sealing system of ceramic sealant and sealing gasket were applied for gas tightness. Electrochemical performance of the short stack was evaluated in 800 ℃. The I-V-P characteristics was measured in 1 L/min of hydrogen and 5 L/min of air. Open circuit voltage (OCV) of the short stack was 3.0 V and it showed stable value. The maximum electrical power of the short stack was 23.1 W. In I-V curve, it seems to nearly linear shape which means ohmic resistance governs overpotential of the short stack. This ohmic resistance may originated in current collection from electrodes and it will be further analyzed. Moreover, the short stack was operated for 120 hours in galvanostatic mode with 2.16 A of discharge current. In the beginning, the operation voltage of the short stack was 2 V and there was no rapid initial degradation. Over time, voltage of the short stack was slightly decreased. After 120 hours, voltage of the short stack was 1.81 V and its degradation rate was 9.5 % per 120 hours. This seems to be due to chrome poisoning of cathode and this problem also will be further analyzed. Figure 1

Fabrication of Metal-Supported Solid Oxide Fuel Cells by Sinter-Joining Method with Silver Bonding Layer

Solid oxide fuel cell (SOFC) is an energy conversion device which generates electricity from hydrogen. SOFC is attracting attentions because of its high energy conversion efficiency and low material cost. For these reasons, SOFC are widely studied to be applied to various power generation systems such as stationary power plant, residential power system, auxiliary power unit (APU), etc. For APU applications, high mechanical strength is required to endure mechanical vibration and external shock during the driving of vehicles, which makes ceramic-based SOFC unsuitable. To overcome this limitation, metal-supported SOFC has been proposed. Metal-supported SOFCs are composed of metal substrate which supports ceramic layers of anode, electrolyte, and cathode. For more than past ten years, various types of metal-supported SOFC have been developed in many organizations. However, conventional metal-supported SOFCs had limitations of high cost thin film coating process such as sputtering, plasma spray, etc, sintering at reducing atmosphere, and unsintered cathode. In our research group, metal-supported SOFCs fabricated by sinter-joining method were developed. To fabricate metal-supported SOFCs by sinter-joining method, metal substrates were bonded to conventional ceramic cells by bonding paste composed of mixture of stainless steel, nickel oxide, yittria-stabilized zirconia (YSZ). Recently, silver has been proposed as bonding materials. By using silver as bonding materials, bonding of ceramic cell can be performed at temperature lower than 950 °C at air atmosphere, which enables full sintering of cathode. This has been rarely reported because conventional metal-supported SOFCs were fabricated by sintering at reducing atmosphere to prevent oxidation of metal substrate during the sintering. Furthermore, it is believed that electrical conductivity, thermal conductivity are improved, leading to lower ohmic resistance and better temperature distribution of metal-supported cells. In this work, 5 x 5 cm2 metal-supported SOFCs with silver bonding layer was successfully fabricated. The microstructure of bonding layer was investigated, which showed good adhesion of silver bonding layer. Electrochemical performance and impedance spectra were studied. Power density of 433 mW/cm2, ohmic resistance of 0.52 Ω cm2, polarization resistance of 0.16 Ω cm2 at 800 °C were obtained, and it is believed that high power density was attributed to low polarization resistance by full sintering of cathode. Metal-supported SOFCs fabricated by sinter-joining method showed 10 times higher mechanical strength than conventional ceramic cells.

Effect of Fe doping on the performance of suspension plasma-sprayed PrBa0.5Sr0.5Co2−xFexO5+δ cathodes for intermediate-temperature solid oxide fuel cells

Abstract PrBa 0.5 Sr 0.5 Co 2–x Fe x O 5+δ (PBSCF) (X = 0, 0.3, 0.4, and 0.5) is investigated as cathode material for intermediate-temperature solid oxide fuel cells. Suspension plasma spraying is used as a low cost and large-scale manufacturing process to prepare PBSCF cathodes. Fe substitution effects on the crystal structure and electrochemical performance are characterized. All plasma-sprayed PBSCF cathodes exhibit a pure and stable cubic structure. The suspension plasma-sprayed PBSCF deposits show a porous and fine structure, and the microstructures are insensitive to Fe substitution. Subsequent to Fe doping, the polarization resistance of PBSCF cathodes rapidly decreases for increasing Fe substitution concentration from 0 to 0.4. Further increase of the Fe doping concentration increases the cathode polarization instead. At 600 and 700 °C, a 20% Fe-doped (x = 0.4) PBSCF cathode exhibits remarkably low area-specific polarization resistances (R p ) of 0.074 Ω cm 2 and 0.012 Ω cm 2 , respectively. Moreover, the R p of all cathodes remains almost identical after isothermal annealing at 600 °C for 300 h. Furthermore, the thermally-sprayed porous metal-supported cell assembled with the optimal PBSCF cathode shows excellent performance with peak power densities of 0.37, 0.8, and 1.35 W cm −2 at 500, 600, and 700 °C, respectively.

Development of an Advanced Flexible Solid Oxide Fuel Cell Stack Concept

An advanced flexible solid oxide fuel cell (SOFC) stack concept with the potential for increased reliability, better performance and lower cost is being developed. This stack concept integrates prime-surface interconnects and single cells into a lightweight and compact structure with reliable gas seals for efficient operation at various temperatures depending on selected materials. The concept has several attractive features including reduced stack weight and volume, decreased performance losses in stacking, improved sealing, versatility in incorporation of different types of cell construction (for example, conventional sintered ceramic cells or metal-supported cells) and flexibility in gas flow configuration. The prime-surface interconnect is a one-piece metal sheet that incorporates both fuel and oxidant flow fields with peaks on one side of the interconnect serving as flow channels (valleys) on the other side, for example, the egg-carton shaped prime-surface flow field. The design of the prime-surface interconnect including the key factors impacting on pressure drop, flow uniformity and formability is being evaluated. Hydroforming has been identified as the forming approach for prime-surface interconnects. Development of metal-supported cells has been initiated. A fabrication process based on sputtering is being developed for producing cells on metal supports for this stack concept.

High Performance (La,Sr)(Co,Fe)O3 Cathodes with Improved Adherence for Metal-Supported Fuel Cells

A novel sintering approach was developed in order to overcome the issue of insufficient adherence of (La,Sr)(Co,Fe)O3 type cathodes in metal-supported solid oxide fuel cells (MSCs). Investigation of the phase stability of the perovskite structure at high temperature in various atmospheres with low oxygen partial pressures provided the basis for the development of a specific sintering procedure. After detailed investigation of the layer adherence, time dependent mechanical integrity and reversibility of phase transformations, metal-supported cells with cathodes sintered before cell operation (ex-situ sintering) could be produced reliably and were electrochemically characterized in single cell measurements. The novel sintering approach of such cathodes resulted in a significantly enhanced mechanical stability of the cathode layers. The adherence of the cathode to the electrolyte was considerably stronger, which is a substantial improvement in comparison with state-of-the-art MSCs. Furthermore, the electrochemical measurements revealed a beneficial effect regarding the cell performance.

Distribution of Relaxation Times Analysis for Optimization of Anode Thickness in Metal-Supported Microtubular Solid Oxide Fuel Cells

An anode functional layer (AFL) is inserted between anode substrate and electrolyte thin-film to increase the triple phase boundary (TPB) for anode-supported solid oxide fuel cells (SOFCs). On the other hand, better mechanical robustness, redox tolerance, rapid thermal cycling and cost reduction are expected for metal-supported SOFCs. The anode thickness of metal-supported cells (MSCs) is more important than the AFL thickness of anode-supported cells (ASCs), since the metallic substrate does not have TPB. In the present work, the metal-supported microtubular SOFCs with La0.6Sr0.4Co0.2Fe0.8O3(LSCF)-(Ce0.9Gd0.1)O1.95(GDC) cathode, GDC electrolyte, BaCe0.8Y0.2O3- d (BCY) blocking layer and Ni-GDC anode on Ni substrate were investigated. It was confirmed by the distribution of relaxation times (DRT) analysis that the polarization resistance increased with decreasing the anode thickness from 23 to 10 mm for the metal-supported microtubular SOFCs operated at 550 oC.

Fabrication of Metal-Supported Solid Oxide Fuel Cells by Sinter-Joining Method with Silver Bonding Layer

Solid oxide fuel cell (SOFC) is an energy conversion device which generates electricity from hydrogen. SOFC is attracting attentions because of its high energy conversion efficiency and low material cost. For transportation applications, high mechanical strength is required, which makes ceramic-based SOFC unsuitable. To overcome this limitation, metal-supported SOFC has been proposed. In this work, metal-supported SOFCs are developed by bonding metal substrates to ceramic cells with silver bonding paste. By using silver as bonding materials, bonding was performed at temperature lower than 950 °C at air atmosphere, which enables full sintering of cathode. Furthermore, electrical conductivity, thermal conductivity are improved, leading to lower ohmic resistance and better temperature distribution of metal-supported cells. As a result, 5 x 5 cm2 metal-supported SOFCs with power density of 433 mW cm-2 at 800 °C were fabricated. The metal-supported SOFCs showed 10 times higher mechanical strength than conventional ceramic cells.

Degradation of Metal-Supported Cells with Ni-YSZ or Ni-Ni3Sn-YSZ Anodes Operated with Methane-Based Fuels

Ni-Ni3Sn-YSZ and Ni-YSZ anodes were incorporated into metal-supported SOFCs that consisted of a porous metal support (Sandvik Sanergy), samaria-doped ceria (SDC) barrier layer, anode as previously described, YSZ electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3-δ-SDC cathode. Cells were tested at 750°C with air as the oxidant and fuel consisting of 65% CH4, 32% H2, and 3% H2O. The cells were held at a current density of 0.15 A·cm-2 for 500 hours. The cell without tin in the anode began to degrade after approximately 200 hours and catastrophically failed at approximately 425 hours. After testing, we observed that the anode had disintegrated, and as a result, the electrolyte and cathode were completely detached from the metal support. On the other hand, the cell with an anode containing tin did not catastrophically fail, and the cell remained intact after 500 hours of operation. Over 500 hours, the cell potential degraded from 0.841 V to 0.743 V, and scanning electron micrographs showed that the anode had delaminated from the electrolyte in some areas. Nonetheless, the cell with the Ni-Ni3Sn-YSZ anode degraded significantly less than the cell containing a Ni-YSZ anode, suggesting that the addition of Ni3Sn to an anode could be a useful strategy for improving durability of SOFC anodes using hydrocarbon fuels.

Electrochemical Analysis of Ni Infiltrated Nanoporous GDC Scaffold for Metal Supported SOFCs Anode

Metal-supported SOFCs have been investigated to overcome the disadvantages of ceramic-supported SOFCs, such as mechanical strength and sealing. In the case of ceramic-supported cells, the mechanical support is a brittle ceramic or cermet, and it contains expensive materials. However, metal-supported cells utilize ceramic layers that are only as thick as necessary for electrochemical functioning, thereby compensating for the disadvantages of ceramic-supported cells. The mechanical support is fabricated from inexpensive and robust metals, and the electrochemically active layers are applied directly to the metal support. In other words, metal-supported SOFCs can provide a reduced system cost, easy manufacturing, and operational advantages. These features make metal-supported SOFCs a very promising candidate for commercialization. To improve productivity and accelerate the commercialization, the metal supported SOFCs have to be fabricated at low temperature under oxidized environment. In these days, some metal substrates which can withstand corrosion from ≤1000 °C already have been developed. However, the low fabrication temperature is insufficient for conventional sub-micron scaled NiO/YSZ or GDC to generate smooth electrical and ionic paths. Furthermore, the unsuitable anode can affect to interfaces; and as a result, it can cause decrease of electrical conduction. Therefore, we have tried to apply a wet infiltration technique for anode fabrication. It can fabricate nanosize particles into a porous scaffold at relatively low temperatures and achieve higher performance electrode structures. Then, to substitute the conventional anode, a nanoporous GDC scaffold layer, and the Ni solution were selected as a scaffold and catalyst material, respectively. It is known that the GDC has high ionic conductivity and can be sintered at relatively low temperature. Therefore, it was considered that the GDC could be well matched with the requirements for anode of metal supported SOFC. For investigating the electrochemical performance according to Ni amounts, the half-cell tests were carried out via solatron 1287/1260 device under 97%H2+3%H2O condition. Then, the appropriate Ni infiltrated GDC was applied to the metal-supported SOFC, and the electrochemical performance of infiltrated metal-supported SOFC single cell was measured via the solatron 1287/1260 device.

Layered microstructures based on BaZr0.85Y0.15O3−δ by pulsed laser deposition for metal-supported proton ceramic electrolyser cells

Planar metal-supported cell designs provide cost-effective scaling-up of solid oxide fuel cells and electrolysers. Here, we report on the fabrication of a BaZr0.85Y0.15O3−δ–NiO (BZY15–NiO) composite electrode and BaZr0.85Y0.15O3−δ (BZY15) proton-conducting electrolyte films on metal and ceramic substrates using pulsed laser deposition (PLD). The results demonstrate successful sequential deposition of porous electrode and dense electrolyte structure by PLD at moderate temperatures, without the need for subsequent high-temperature sintering. The decrease in roughness of the metal substrate used for deposition by spray-coating intermediary oxide layers had significant importance to the fabrication of functional layers as thin films. Crystalline porous BZY15–NiO and dense BZY15 films were sequentially deposited at high substrate temperature on metal supports (MS) with or without an electron-conducting barrier oxide layer, e.g. MS/(BZY15–Ni)/(BZY15–NiO)/BZY15 and MS/CeO2/(BZY15–NiO)/BZY15. The different microstructures for electrode and electrolyte were achieved with deposition steps at different substrate temperatures (800, 600 °C) and a gradual decrease in the pressure of O2 in the deposition chamber.

Effect of Anode Thickness on Polarization Resistance for Metal-Supported Microtubular Solid Oxide Fuel Cells

An anode functional layer (AFL) is inserted between anode substrate and electrolyte thin-film to increase the triple phase boundary (TPB) for anode-supported solid oxide fuel cells (SOFCs). On the other hand, better mechanical robustness, redox tolerance, rapid thermal cycling and cost reduction are expected for metal-supported SOFCs. The anode thickness of metal-supported cells (MSCs) is more important than the AFL thickness of anode-supported cells (ASCs), since the metallic substrate does not have TPB. In the present work, the metal-supported microtubular SOFCs with La0.6Sr0.4Co0.2Fe0.8O3(LSCF)-(Ce0.9Gd0.1)O1.95(GDC) cathode, GDC electrolyte, BaCe0.8Y0.2O3-δ (BCY) blocking layer and Ni-GDC anode on Ni substrate were investigated. The significant decrease in polarization resistance with increasing the anode thickness from 10 to 16 μm was confirmed by the distribution of relaxation times (DRT) analysis for the metal-supported microtubular SOFCs operated at 550°C.

A Novel Metal Supported SOFC Fabrication Method Developed in KAIST: a Sinter-Joining Method

Metal-supported SOFCs have been investigated to overcome the disadvantages of ceramic-supported SOFCs, including issues related to mechanical strength and sealing. In the case of ceramic-supported cells, the mechanical support is a brittle ceramic or cermet, and it contains expensive materials. However, metal-supported cells utilize ceramic layers that are only as thick as necessary for electrochemical functioning, thereby compensating for the disadvantages of ceramic-supported cells. The mechanical support is fabricated from inexpensive and robust metals, and the electrochemically active layers are applied directly to the metal support. The metal-supported SOFCs thus can provide a reduced system cost, ease of manufacturing, and operational advantages. Owing to these features, metal-supported SOFCs are a very promising candidate for commercialization. Given the importance of studying worldwide trends in metal-supported SOFC research for performance evaluation, this paper reviews development trends with a focus on fabrication methods. Furthermore, a novel fabrication method developed in KAIST is discussed.

Development of plasma sprayed Ni/YSZ anodes for metal supported solid oxide fuel cells

Solid oxide fuel cells (SOFCs) offer a promising technique for producing electricity by clean energy conversion through an electrochemical reaction of fuel and air. Plasma spraying could be a potential manufacturing route for commercial SOFCs, as it provides a distinct advantage especially in case of metal supported cells (MSCs) by allowing rapid processing at relatively low processing temperatures preventing thus the degradation of the metallic substrate. The objective of this work was to develop nickel/yttria stabilised zirconia (Ni/YSZ) anodes with high porosity and homogeneous phase distribution by atmospheric plasma spraying for MSCs. Various feedstock material approaches were explored in this study, both with single injection as well as separate injection of different feedstock materials , and with and without the use of pore formers to create additional porosity. The advantages and issues with each material route were investigated and discussed. It was shown that agglomerated Ni/YSZ/polyester feedstock material resulted in the best distribution of Ni and YSZ in the anode microstructure with homogeneous porosity. Subsequently, the Ni/YSZ/polyester material route with different amounts and size distributions of polyester was chosen to develop anode symmetrical cells using a commercial zirconia sheet as support for electrochemical testing. The Ni/YSZ/polyester anode powder with 10wt.% standard size polyester exhibited the best electrochemical performance. The results show that plasma spraying of the agglomerated Ni/YSZ/polyester could be a promising route to achieve high performance and rapid production anodes without using the carcinogenic nickel oxide.

Flexible solid oxide fuel cells supported on thin and porous metal

A thin metal (NiFe)-supported SOFC is fabricated by tape casting and co-sintering, and its mechanical flexibility is tested. A single cell, composed of ∼120 μm-thick NiFe-support, ∼30 μm-thick Ni-YSZ (yttria-stabilized zirconia) anode, and ∼15 μm-thick YSZ electrolyte, shows a good mechanical flexibility. With the use of a thin metal (NiFe) support, the degree of bending for the metal-supported cell is much larger than that for the anode- or electrolyte-supported SOFCs as the displacement shows under the mechanical load. The rupture of the cell is also largely prevented due to its flexibility. A thin NiFe-supported cell that operated at 800 °C with a LSCF (La0.6Sr0.4Co0.2Fe0.8O3−δ) cathode shows a power density of ∼430 mW cm−2. This type of cell is promising as a mobile or portable power generator because it is light weight and highly resistant to mechanical shocks.

(Invited) Ce(Mn,Fe)O2/La(Sr)Fe(Mn)O3 Nano Size Film As a Dense Anode for Low Temperature Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) have been attracting much interest as alternative and efficient energy conversion system for next generation. Ni–yttria stabilized zirconia (YSZ) cermets anode film was prepared with laser ablation method. However, large volumetric changes of cermets film and Ni agglomeration cause micro-crack and delaminating thin film in reducing atmosphere. Therefore, investigations for thin film anode have been hardly progressed up to now. We studied dense La(Sr)Fe(Mn)O3-δ (La0.6Sr0.4Fe0.9Mn0.1O3-δ, LSFM) thin ceramic film as an dense anode concept for expanding reaction site from three phase boundary (anode–electrolyte–gas) to two phase one (anode–gas phase) by PLD process. In our previous work, metallic substrate was studied as the porous anode in IT-SOFC. The Ni–Fe substrate exhibited excellent tolerance against thermal-/redox- cycling. Furthermore, the cell using Ni–Fe anodic metal substrate exhibited fairly high power density at intermediate temperature. However, the power density of metal-supported cell was slightly lower than that of cermets-supported cell in our previous study because of limited number of three phase boundary. In order to achieve high power density and stability of intermediate temperature solid oxide fuel cells (IT-SOFC), Ce(Mn,Fe)O2(CMF)-La(Sr)Fe(Mn)O3-δ (LSFM) dense nano-film anode is introduced between Ni–Fe metallic substrate and LaGaO3 base oxide electrolyte. Although it is believed that three phase boundary (TPB) is essentially required for anode active site, the cell using CMF-LSFM mixed conducting thin film anode exhibits reasonable power density comparing with that of the cell with a simple porous Ni–Fe anode, however, slightly decreased comparing with that of LSFM single layer. The maximum power density of the cell having CMF-LSFM film is approximately 2.0 W/cm2 at 973 K. On the other hand, application of double columnar composite of CMF/LSFM shows much smaller anodic overpotential and higher power density at intermediate temperature. Therefore, this study reported the dense film of CMF and LSFM with few 100 nm thickness can be used as dense anode.