Porous Metal Support Research Articles

Progress and Perspectives in the Development of Inorganic-Carbonate Dual-Phase Membrane for CO2 Separation

The inorganic-carbonate dual-phase membrane represents a class of dense membranes that are fabricated using diverse support materials, ranging from metals to ceramics. This dual-phase membrane consists of a porous metal or ceramic support with an introduced carbonate phase within the support pores. Compared with polymer and zeolite membranes, inorganic-carbonate dual-phase membranes exhibit exceptional CO2 selectivity at elevated temperatures (>500 °C), making them an ideal choice for high-temperature CO2 separation in power plant systems. The present paper provides a comprehensive overview of the separation principle, significant models, and preparation techniques employed in carbonate dual-phase membranes for CO2 separation. The present study aims to discuss key factors that limit the CO2 permeation performance and stability of membranes, while also exploring the potential applications of dual-phase membranes in various fields. The identification of key challenges in the future development of the carbonate dual-phase membrane has been highlighted in this work. The future trajectory of research and development should be directed toward overcoming these challenges, encompassing the synthesis technology of membranes, balance optimization of membrane structure and performance, modification of physical and chemical properties of molten carbonate, and advancement in high-temperature sealing techniques, as well as exploration of diverse membrane reactors based on carbonate dual-phase membranes for prospective applications.

Development of Multiple Ceramic Coatings on Porous Tubular Metal Support

Micro-tubular metal supported Solid Oxide Fuel Cell (MS-SOFC) has many advantages over traditional ceramic supported SOFC, such as greater mechanical robustness, better thermal and redox cycling along with low cost of starting material. Among the multiple MS-SOFC fabrication methods, the one involving sequential dip-coating followed by co-sintering has the potential to reduce the fabrication cost further, making it attractive from a commercial production standpoint. However, the co-sintering route is challenging because it requires constrained sintering conditions, high temperatures, and inert atmosphere. Other challenges with the co-sintering route are delamination and cracking of layers, warping of cell, diffusion of Fe and Cr away from metal support, diffusion of Ni from anode, coarsening of Ni in the anode, and lack of complete densification of YSZ electrolyte even at temperatures as high as 1350 °C.In this work, we developed a new ceramic multilayer design on a porous tubular 3D-printed metal support. Scandia Stabilized Zirconia (SSZ) and, Ni and SSZ (Ni-SSZ cermet) were used as electrolyte and anode, respectively. Stainless steel 17-4 PH was identified as the metal support material due to its matching coefficient of thermal expansion with SOFC ceramic materials, low cost and corrosion resistance nature. The dip coating steps and the co-sintering process were optimized so that they could be adopted for a cost-effective fabrication of MS-SOFC. The binder-burnout step was optimized to prevent cracking of the multilayers during the co-sintering process. To avoid delamination and to impede the inter-diffusion of elements, a coating of an intermediate layer made of 17-4 PH stainless steel+Ni+YSZ was introduced between the metal support and the succeeding layers. Preliminary results suggest that the intermediate layer has a potential to prevent delamination and inter-diffusion. Introduction of the debinding step and optimized sintering profiles resulted in the formation of the uniform and dense electrolyte coating. However, certain cell warping was observed after electrolyte sintering, suggesting further improvement is still needed in the support design and ceramic processing.

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.

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.

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.

Metal-Supported Solid Oxide Electrolysis Cells with Coatings to Suppress Chromium Migration

High-temperature electrolysis (HTE) is an efficient technology for converting steam to hydrogen. The performance, durability, and applications of metal-supported solid oxide electrolysis cell technology developed at Lawrence Berkeley National Laboratory (LBNL) will be discussed. 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.An inherent limitation of this design is the intimate contact between the electrode and the porous stainless steel, which is a source of chromium (Cr). Cr migrates from the support to the electrode during cell fabrication and operation, and reacts with the oxygen evolution electrocatalyst (LSCF). This Cr poisoning reduces performance and durability. To overcome this limitation, Cr-blocking coatings have been applied to the porous stainless steel. A variety of coating compositions and deposition techniques have been evaluated. The best coating dramatically reduces the amount of Cr detected in the electrode both after catalyst infiltration at 800°C and after 1000 h continuous operation at 700°C, Fig 1.Other aspects of the MS-SOEC design and operation have been optimized for performance and durability. These include the infiltrated catalyst composition and processing, metal support structure, and operating temperature. Figure 1

Highly selective Pd composite membrane on porous metal support for high-purity hydrogen production through effective ammonia decomposition

In this study, an alumina sol assisted pretreatment method for porous metal supports was investigated for a highly selective Pd composite membrane for ammonia decomposition. Alumina sol made of boehmite was applied to an yttria-stabilized zirconia (YSZ) filled porous Inconel support. Additionally, a vacuum-assisted, two-step electroless plating of Pd drastically increased the hydrogen selectivity. The hydrogen permeation flux and selectivity (H2/N2) measured at 723 K and a transmembrane pressure difference of 100 kPa were 3.40 × 10−1 mol m−2 s−1 and 8,050, respectively. A highly selective Pd composite membrane was applied to a membrane reactor combined with a Ru/Al2O3 catalyst to efficiently produce high-purity hydrogen by ammonia decomposition. The ammonia decomposition test showed that the membrane reactor was able to achieve a high ammonia conversion (99.6%) and a high hydrogen purity (99.99%) with a hydrogen production rate of 0.25 Nm3 h−1 at 745 K and a gauge pressure of 500 kPa. The Pd composite membrane reactor has the advantage of being able to selectively removing hydrogen, increasing the ammonia conversion rate and high-purity hydrogen production via a one-step reaction combined with purification.

Thermochemical energy conversion behaviour in the corrugated heat storage unit with porous metal support

Because of the low charging temperature, salt hydrate-based adsorption thermochemical energy storage (TCES) is currently a significant technology that promises long-term energy storage. A corrugated-shaped heat storage unit (HSU) in which embedding porous metal bracket is proposed in this work to enhance heat transfer between the thermochemical material (TCM) wrapped inside and the heat fluid transfer (HTF) in the external corrugated channel. The thermo-chemical conversion behaviours, including reactive transport processes during dehydration (charging) and hydration (discharging), as well as the influence of parameters, are comprehensively investigated. The numerical results indicate that increasing the HTF temperature facilitates the charging process while the discharging can be promoted by decreasing reaction bed temperature. The time required to complete charging and discharging for the reference cases is 2990 s and 5700 s. For both charging and discharging powers of reactive bed, the values dramatically surge in a short time and then gradually decrease, with the maximum powers of 2638 W and 1866 W, respectively. Boosting evaporation temperature (water vapour pressure) accelerates hydration while the effect of condensation temperature on dehydration is insignificant. The reaction period can be further shortened by heightening the thermal conductivity of TCM, and the porosity also has a distinct influence on the reaction. Compared to the storage unit of a straight external channel without a metal bracket inside, this heat storage module saves 34% and 23% in charging and discharging times. The results of this work provide insights into the prediction and improvement of thermochemical conversion behaviours.

Atmospheric plasma spraying to fabricate metal‐supported solid oxide fuel cells with open‐channel porous metal support

AbstractMetal‐supported solid oxide fuel cells (MS‐SOFCs) have been fabricated by applying phase‐inversion tape‐casting and atmospheric plasma spraying (APS). The effect of the binder amount of the phase‐inversion slurries on the microstructure development of the 430L stainless steel metal support was investigated. The pore structures, the viscosity of the slurry, porosity and permeability of the as‐prepared metal supports are significantly influenced by the amount of the binder. NiO–scandia‐stabilized zirconia (ScSZ) anode, ScSZ electrolyte and La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathode layers were consecutively deposited on the metal support with an ideal microstructure by APS process. The effect of plasma power of the APS on the microstructure of the electrolyte and cathode was investigated. A dense electrolyte layer and a porous cathode layer were successfully obtained at 40 and 6 kW of the APS plasma power, respectively. MS‐SOFCs, with a cell configuration of 430L/Ni‐ScSZ/ScSZ/LSCF, achieved a maximum cell power density of 1079 mW cm−2 at 700°C using humidified H2 as fuel and ambient air as oxidant. The corresponding ohmic resistance and total resistance of MS‐SOFCs was 0.14 and 0.32 Ω cm2, respectively. This work demonstrates the feasibility of fabricating high‐performance MS‐SOFCs with economical and scalable techniques.

Characterization of Stainless-Steel Grids Dedicated to Cost-Effective Metal-Supported IT-SOFC

Metal-Supported Solid Oxide Fuel Cells (MS-SOFCs) have gained significant interest due to their potential advantages (low-cost, tolerance to redox and thermal cycling, robust and manufacturing) over conventional fuel cells. This work focuses on studying corrosion and electrical conductivity of porous metallic supports (stainless steel 316L and FeCrAl alloy) under different temperatures and atmospheres considering physical, chemical and electrical characterizations. Within the studied operating temperature range (500 °C–700 °C), the FeCrAl support resists to corrosion under air and H2. At temperatures higher than 700 °C it forms a layer of alumina. The FeCrAl resistivity generally remains stable under H2 and slowly increases under air. In contrast, the 316L support is only stable at 500 °C under air and at 500 °C and 600 °C under H2. Above these temperatures, the 316L support shows severe corrosion. The resistivity is stable up to 600 °C, increases strongly for the support under air and slightly for the support under H2 with the temperature increase.

Highly Selective Pd Composite Membrane on Porous Metal Support for High-Purity Hydrogen Production Through Effective Ammonia Decompositionhighly Selective Pd Composite Membrane on Porous Metal Support for High-Purity Hydrogen Production Through Effective Ammonia Decomposition

Highly Selective Pd Composite Membrane on Porous Metal Support for High-Purity Hydrogen Production Through Effective Ammonia Decompositionhighly Selective Pd Composite Membrane on Porous Metal Support for High-Purity Hydrogen Production Through Effective Ammonia Decomposition

Single-Atom Co Doped in Ultrathin WO3 Arrays for the Enhanced Hydrogen Evolution Reaction in a Wide pH Range.

Owing to the scarcity of Pt, low-cost, stable, and efficient nonprecious metal-based electrocatalysts that can be applied in a wide pH range for the hydrogen evolution reaction (HER) are urgently required. Herein, a highly efficient and robust HER catalyst that is applicable at all pH values is fabricated, containing isolated Co-single atomic sites anchored in the self-supported WO3 arrays grown on Cu foam. At a current density of 10 mA cm-2, the HER overpotentials are 117, 105, and 149 mV at pH values of 0, 7, and 14, respectively, which are significantly lower than those of the undoped WO3, suggesting superior electrocatalytic H2-evolution activity at all pH values. The catalyst also exhibits long-term stability over a wide pH range, particularly in an acidic medium over 24 h, owing to the excellent anticorrosion properties of WO3. Density functional theory calculations prove that the enhanced HER activity is attributed to the isolated Co sites because these optimize the adsorption energy of H* species on WO3. Moreover, the high electrical conductivity of Co-doped WO3 and the three-dimensional array structure supported on the porous metal support afford a catalyst with suitable HER kinetics to enhance the catalytic performance.

Development of Proton Conducting Ceramic Cells in Metal Supported Architecture

Reliability, long-term stability, lower cost as well as high performance are essential for Solid Oxide Cells (SOC) in fuel-cell and electrolysis applications. Metal-Supported (MS) architecture offers various advantages over state-of-the-art ceramic supported SOCs, such as high tolerance towards thermal/redox cycling that are key features for flexible and reliable operation. Having high potential in many electrochemical applications, Proton-conducting Ceramic Cells (PCC) have been intensively studied and demonstrated promising improvements in the last decade. Different in geometric layout from SOC in terms of steam production in fuel cells and steam supply in electrolysis cells, PCC is advantageous for its low oxygen partial pressure in fuel electrodes, not merely in the electrochemical operation, also in the MS architecture. The challenge in the development of MS-PCC is to find a feasible process to fabricate gas-tight electrolyte on the porous substrate without degrading the metal support. The state-of-the-art PCC electrolyte is based on perovskite oxides that have refractory nature requesting high sintering temperature typically above 1400 °C, which makes it more challenging for MS-PCC than for MS-SOC via sintering method.Our strategy is implementing multilayers combining wet chemical processes below 1000°C for the porous electrode layers and dry Physical Vapor Deposition (PVD) techniques below 800 °C for the gas-tight electrolyte coating. The multilayer approach reducing the pore size stepwise from several tens of μm in the MS down to nm range in the top electrode layer, enables the deposition of 1-μm thick dense perovskite electrolyte by PVD. The paper presents our recent activities in the development of MS-PCC. The state-of-the-art PCC electrolyte, BaZrO3-based perovskite has been chosen and NiO cermet fuel electrodes are developed on the porous metal support. Zr4+ site of BaZrO3 is doped with 10–15 mol% Y3+ to maintain proton conductivity and is partially substituted with Ce4+ for high performance, higher thermal expansion coefficient (TEC) for better match with other components and for better sinterability of the functional layer, while higher Zr content ensures its chemical stability against CO2. Different PVD technologies, namely Pulsed Laser Deposition (PLD) and Electron-Beam Physical Vapor Deposition (EB-PVD), are applied for the electrolyte coating process. Two types of porous metal substrates are investigated: commercial porous metal substrates and metal plates with laser-drilled pores, both of which are made of inexpensive ferritic stainless steel. Pore size, pore distribution and compatibility for electrochemical applications are to be studied and adjusted/considered for improvement in terms of performance and chemical/mechanical stabilities. Protection coating on MS is necessary to prevent/ reduce Cr deposition and interdiffusion into the ceramic layers, as well as to eliminate corrosion of the metal. Obtained half cells are investigated by SEM and X-ray diffraction, some of which are tested for electrochemical performance. The results of the electrochemical tests will be presented in another paper of this conference. In this paper, the results obtained by different PVD techniques and on different types of substrates will be presented and discussed in terms of residual stress, chemical/mechanical stabilities.This work is supported by project DAICHI (EIG CONCERT-Japan), project AH2A (the Research Council of Norway, 268010/E20), project ARCADE (BMBF, 03SF0580A) and project 112CO2 (Horizon2020, 952219). The China Scholarship Council is acknowledged for the Ph.D. fellowship of Haoyu Zheng (201806160173).

(Invited) Metal-Supported Solid Oxide Fuel Cells and Electrolyzers for Low-Cost, Robust, Rapid-Start Systems

This talk will provide an overview of performance, durability, and applications of metal-supported solid oxide fuel cell and electrolysis cell 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.MS-SOFC performance with a variety of fuels will be presented, including hydrogen, ethanol, natural gas, and simulated reformates. The impact of the presence of carbon and internal reforming catalysts on the durability of the cells will be examined. In particular, oxidation of the stainless steel supports in the presence of carbon is analyzed. Scale-up from button cells to 50cm2 will be presented.The case for use of MS-SOECs for dynamic electrolysis operation will be made. Detailed analysis of degradation modes over 1000h of operation with 50/50 steam/H2 informed efforts to improve durability through the use of coatings and catalyst processing techniques.In addition to our long-standing development of zirconia-based metal-supported cells, recent efforts on metal-supported proton-conducting cells are ongoing. Co-sintering of 400-series stainless steel and BZCY-type proton conductors presents a number of challenges, including: Ba evaporation in reducing atmosphere, over-densification of steel at the high temperatures (>1400°C) required for BZCY processing, mismatch of metal and ceramic sintering behavior, and migration of Cr and Si from the steel support into the BZCY layers. Feasibility of new approaches to overcome these challenges will be discussed.

Surface-Modified Titanium Fibers as Durable Carbon-Free Platinum Catalyst Supports for Polymer Electrolyte Fuel Cells

Carbon-based electrodes in polymer electrolyte fuel cells (PEFCs) are prone to corrosion. Therefore, alternative “carbon-free” materials are required. Here, the use of a catalyst-coated porous metal support is proposed as a gas diffusion electrode. As a proof-of-concept, commercially available porous titanium sheets comprising sintered titanium fibers are chemically etched with NaOH, followed by heat treatment. This results in the formation of oxidized titanium nanostructures (such as nanosheets and nanotubes) at the surface. Subsequently, platinum decoration is performed via arc plasma deposition (APD). This porous composite structure is then attached to the membrane, and used as the gas diffusion electrode for PEFC membrane electrode assemblies (MEAs). This concept integrates the catalyst, catalyst support, gas diffusion layer, and current collector in a single structure, cutting down on the number of cell components and reducing total device thickness. The carbon-free nature of this integrated gas diffusion electrode is demonstrated to successfully avoid carbon corrosion during start-stop potential cycling over 60,000 potential cycles. However, further improvements in initial electrochemical activity are still required.

(Invited) Progress in Metal-Supported Solid Oxide Cells with Infiltrated Electrodes

This talk will provide an overview of performance, durability, and applications of metal-supported solid oxide fuel cell and electrolysis cell 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. The metal-supported solid oxide cells achieve high performance at 700°C: >1.5 W/cm2 with 3% humidified hydrogen fuel >1.2 W/cm2 with internal reforming of ethanol fuel >2.6 A/cm2 electrolysis current density at 1.3V and 50%steam/50% hydrogen With infiltrated catalysts, there is a tradeoff between initial performance and long-term stability, as 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 degradation rate has improved to 2.3% kh-1 in fuel cell mode, compatible with the requirements for electric vehicle range extenders. Electrolysis operation, however, results in higher degradation rate. Efforts to identify and mitigate the additional degradation mechanisms in electrolysis mode will be discussed. Scale-up from button cells to 50cm2 is ongoing, and highlights will be presented. In addition to our long-standing development of zirconia-based metal-supported cells, recent exploratory effort has focused on compatibility between stainless steel metal supports and proton-conducting ceramics. Co-sintering of 400-series stainless steel and BZCY-type proton conductors presents a number of challenges, including: Ba evaporation in reducing atmosphere, over-densification of steel at the high temperatures (>1400°C) required for BZCY processing, and migration of Cr and Si from the steel support into the BZCY layers. Feasibility of new approaches to overcome these challenges will be discussed.

High pressure membrane separator for hydrogen purification of gas from hydrothermal treatment of biomass

For hydrogen purification and green hydrogen production in the context of biomass hydrothermal gasification, a palladium membrane system with microchannels on feed and permeate side was studied. The high pressure in the product gas of the hydrothermal process could potentially be used to generate pressurized pure hydrogen on the permeate side. Stabilizing the membrane by an additional porous metal support, experimental verification of the concept was done at feed pressure up to 50 bar and permeate pressure up to 20 bar. The temperatures were varied between 370 °C and 425 °C. The device was found to be highly selective and efficient for pure hydrogen separation. The membrane was characterized regarding the hydrogen flux and a deviation of the permeation from Sievert's law above 30 bars feed pressure was found. Generally, the microchannels on the feed side minimized concentration polarization effects, leading to high hydrogen fluxes with hydrogen feed mixtures and with real gas samples from hydrothermal gasification.

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.

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.

Improvement of corrosion properties of porous alloy supports for solid oxide fuel cells

The development of protective coatings for porous metal supports is critical for sufficient life time for the fuel cells by enabling improved oxidation resistance, reduced chromium evaporation, and increased conductivity of the protective oxide scale. The oxidation of coated and non-coated substrates has been compared, and shows that it is possible to increase the oxidation resistance at 600 °C in air by a factor of 10 and in wet hydrogen by a factor of 1000, after vacuum coating of the porous metal supports by infiltration of a lanthanum–manganese–cobalt solution and fast curing in air at 900 °C. Chromium evaporation is also lowered by a factor of 10 in air at 600 °C. The experiments on pre-coated porous metal supports verify that the coating is well suited to use for metal supported fuel cells prepared by a low temperature fabrication route (below 1100 °C). An alternative coating procedure for coating of the metal supports after co-sintering of the anode and electrolyte has also been investigated and is well suited for the high-temperature fabrication route. For the high temperature fabrication route, the oxidation tests at 600 °C for 500 h in air and 100 h in wet hydrogen showed that post-coating is better than the pre-coating approach since the cell sintering steps has a detrimental effect on the pre-coated samples.