Operating Solid Oxide Fuel Research Articles

In Situ Optical Investigations of Contaminants in Operating Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) can generate electricity efficiently and with broad fuel flexibility, but practical applications require them to be more durable and resistant to degradation when subjected to impurities. In order to better understand poisoning mechanisms and guide strategies for developing more durable materials and devices, we have used operando optical methods combined with electrochemical measurements and exhaust gas analysis to investigate the effects of chlorine and sulfur on Ni/YSZ anodes in high temperature (700 °C) SOFCs. The effects of chlorine contamination were found to be more severe for methane than hydrogen operation based on studies of anode-supported Ni/YSZ SOFCs with 100-300 ppm CH3Cl. Reduced anode activity was indicated by suppressed carbon formation from Raman measurements and fewer oxidation products from infrared emission results. Evidence regarding the degradation mechanism is provided by the differences in recovery for hydrogen and methane. The anode activity is also reduced for operation on methane in the presence of 170 ppm H2S during both electrochemical and stream removal of carbon. Changes in endothermic methane cracking reactions at the anode are monitored with near infrared thermal imaging while gas and surface species are observed with infrared emission spectroscopy, thereby providing some of the first operando studies of sulfur effects on SOFC anodes.

Chromate-Based Oxide Anodes for Low-Temperature Operating Solid Oxide Fuel Cells

Doped-YCrO3 ceramic oxides were investigated as potential anode materials for low-temperature solid oxide fuel cells (LT-SOFC, 400-650°C). This material has shown orthorhombic symmetry with the space group pmmm. Electrical conductivity >1 S/cm at 650°C was measured under reducing gas conditions. The anode-supported SOFCs were prepared by laminating GDC and doped-YCrO3 tapes. A fired half-cell assembly was further deposited with a dense barrier layer made of electrolyte material. The function of the barrier layer at the interface of GDC electrolyte and anode was to prevent the interdiffusion of elements. Furthermore, the LSM/bismuth-based composite low-temperature cathode was deposited on the barrier layer and Ni-GDC precursor was infiltrated on the anode (to introduce catalytic activity for hydrogen oxidation). Peak power density of 700 mW/cm2 (at 2 A/cm2) was obtained at 650°C in H2/3% H2O.

Chromate-Based Oxide Anodes for Low-Temperature Operating Solid Oxide Fuel Cells

Doped-YCrO3- δ ceramic oxides were investigated as potential anode materials for low-temperature solid oxide fuel cells (LT-SOFC, 400-650°C). The studied materials exhibited orthorhombic symmetry and one of the compositions showed an electrical conductivity of 1.7 and 3.5 S/cm at 600°C measured under reducing gases and air, respectively. Ni-GDC nanoparticles were introduced on the surface of the doped-YCrO3- δ ceramic scaffold to achieve catalytic properties for H2 oxidation. The electrochemical properties of the newly developed material were determined using a symmetrical cell. Peak power density of 200 mW/cm2 at 0.4 A/cm2 was achieved at 650°C in H2/3% H2O using an electrolyte-supported SOFC.

In Situ Optical Investigations of Contaminants in Operating Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) can generate electricity efficiently and with broad fuel flexibility, but practical applications require them to be more durable and resistant to degradation when subjected to impurities. In order to better understand poisoning mechanisms and guide strategies for developing more durable materials and devices, we have used operando optical methods combined with electrochemical measurements to investigate the effects of sulfur (170 ppm H2S) on SOFC Ni/YSZ anodes operating on methane at high temperature (700 °C). There is clear evidence of reduced anode catalytic activity based on near infrared thermal imaging which shows not only that the cooling associated with endothermic methane cracking is reduced but also that an elevated temperature is observed that is temporally correlated with drastic electrochemical changes indicative of substantial anode degradation. Mid infrared emission measurements indicate less fuel consumption and fewer oxidation products in agreement with the trend of suppressed anode activity. The effects are compared to similar studies of chlorine contamination where reversibility and degradation mechanism have been mapped out more extensively to show they depend sensitively on temperature and type of fuel; the effects are more pronounced and seem to be promoted in electrochemically active regions for sulfur.

In Situ Optical Investigation of H2s Impact on Carbon Oxidation in Operating Solid Oxide Fuel Cells

While solid oxide fuel cells (SOFCs) promise efficient electricity production and high fuel flexibility, trace sulfur and chlorine constituents commonly found in desirable fuel sources such as syngas and biogas pose challenges. Sulfur poisoning is a well-established phenomenon that can lead to rapid loss of electrochemical performance in SOFCs that operate at high temperatures (650 – 800 °C). State-of-the-art Ni/YSZ (yttrium stabilized zirconia) anodes lose significant catalytic activity upon exposure to even ppm-levels of H2S, but details regarding how the catalyst degrades and the specific effects on electro-catalytic processes remain unclear. One approach to solving this shortcoming is to understand the degradation mechanisms through real time correlation of electrochemical performance with in situ, molecular specific observations. This current study uses infrared emission from the Ni/YSZ anode surface of an operating SOFC to simultaneously characterize 1) gas species using Fourier transform infrared emission spectroscopy (FTIRES) and 2) temperature changes using near infrared (NIR) thermal imaging. These data are collected with electrochemical potential when the SOFC is operated at 75% maximum current at 700 °C using CH4, with and without 170 ppm H2S added. In situ FTIRES measurements show that the CO2 oxidation product and the CO electrochemical intermediate are suppressed when cell potential deteriorates with H2S present. Simultaneous NIR thermal imaging measurements of surface temperatures show that cooling also reflects evolving processes at the anode. After each trial, electrochemical oxidation of deposited carbon showed that H2S also hindered carbon accumulation. These results together have begun to provide direct insight into how sulfur poisoning affects electrochemical processes in SOFCs through correlations of electrochemical potential, surface temperature changes, and gas species at the anode.

Self-Consistent Field Studies of Operating Solid Oxide Fuel Cell Electrodes

not Available.

Interfacial Resistivity of Yttria Stabilized Zirconia in Operating Solid Oxide Fuel Cells

Electrochemical impedance spectroscopy (EIS) has been used to characterize the lateral impedance across the surface of polycrystalline yttria stabilized zirconia (YSZ) electrolytes in functioning solid oxide fuel cells (SOFCs). Experiments varied the applied overpotential of an electrolyte supported, membrane electrode assembly (MEA) operating with (dry) H2 at 775åC and then measured the impedance between two conducting element located on the anode surface. The conducting elements consisted of either porous Au or a porous Ni/YSZ cermet and the distance between elements varied between 0.5 mm and 1.0 mm. Reduced YSZ surfaces (at OCV) showed lower lateral impedance compared to the lateral impedance of a polarized cell. The largest polarization resistances were measured for SOFCs operating steady state at higher cell potentials. Making several assumptions about the extent to which YSZ is reduced by molecular H2, one can estimate a lateral YSZ resistivity of ~10-3-10-4 Ω•cm.

Interfacial Resistivity of Yttria Stabilized Zirconia in Operating Solid Oxide Fuel Cells

not Available.

Short Stack Performance of Intermediate Temperature - Operating Solid Oxide Fuel Cells with Hydrocarbon Fuel Processor

For intermediate temperature operation, we chose an anode-supported, planar type SOFC (Solid Oxide Fuel Cell) design considering mass production with use ferritic stainless steels as cost-effective interconnects. Anode-supported single cells with thin electrolyte layer of YSZ(Yttria-Stabilized Zirconia) were fabricated and short stacks were built and evaluated. We also developed diesel and methane autothermal reforming(ATR) reactors in order to provide fuels to SOFC stacks. Influences of the H2O/C(steam to carbon ratio), O2/C(oxygen to carbon ratio) and GHSV(Gas Hourly Space Velocity) on performances of stacks have been investigated. Performance of the stack operated with a diesel reformer was lower than with using hydrogen as a fuel due to lower Nernst voltage and carbon formation at anode side. The stack operated with a natural gas reformer showed similar performances as with using hydrogen. Effects of various reformer parameters such as H2O/C and O2/C were carefully investigated. We found O2/C is a sensitive parameter to control stack performance.

Characterization of Ln0.8Sr0.2CoO3-δ(Ln=Gd, Nd, Pr, Sm, or Yb) as Cathode Materials for Low-Temperature SOFCs

Perovskites with nominal compositions Ln 0.8 Sr 0.2 CoO 3-δ (Ln=Gd, Nd, Pr, Sm, or Yb) were fabricated as cathode materials using a solid-state reaction method for low-temperature operating Solid-Oxide Fuel Cells (SOFCs). X-ray diffraction analysis and microstructure observation for the sintered samples were performed. The ac complex impedance was measured in the temperature range of 600-900℃ in air and fitted with a Solartron ZView program. The crystal structure, microstructure, electrical conductivity, and polarization resistance of Ln 0.8 Sr 0.2 CoO 3-δ were characterized systematically.

저온 작동형 SOFC Lanthanum Ferrite계 공기극 소재의 전기적 특성

The perovskites with nominal compositions La 0.8 Sr 0.2 Fe 1-x M x O₃ (M=Co, Mn, Ni, x=0.1-0.3) were fabricated by a solid-state reaction method as cathode materials of low-temperature operating Solid Oxide Fuel Cells (SOFCs). X-ray diffraction analysis and microstructure observation for the sintered samples were performed. The ac complex impedance were measured in the temperature range 600?900℃ in air and fitted with a Solatron ZView program. The electrical conductivity and polarization resistance of La 0.8 Sr 0.2 Fe 1-x M x O₃ (M=Co, Mn, Ni, x=0.1?0.3) were characterized systematically. The porosities of the sintered samples were in the range of 25% to 38%. The polarization resistance of La 0.8 Sr 0.2 Fe 0.7 M 0.3 O₃ was 0.291 Ω㎠ at 700℃.

Ba(La)CoO3 Cathode for Intermediate Temperature Operating Solid Oxide Fuel Cell Using LaGaO3 Based Electrolyte

Ba(La)CoO3 Cathode for Intermediate Temperature Operating Solid Oxide Fuel Cell Using LaGaO3 Based Electrolyte

High Performance Electrode for Medium Temperature Operating Solid Oxide Fuel Cells. Activation of La(Sr)MnO<sub>3</sub> Cathode with Highly Dispersed Pt Microcrystals

High Performance Electrode for Medium Temperature Operating Solid Oxide Fuel Cells. Activation of La(Sr)MnO<sub>3</sub> Cathode with Highly Dispersed Pt Microcrystals

High‐Performance Electrode for Medium‐Temperature Operating Solid Oxide Fuel Cells: Polarization Property of Ceria‐Based Anode with Highly Dispersed Ruthenium Catalysts in Gas

Polarization properties of catalyzed anode, which we developed for medium‐temperature operating solid oxide fuel cells, were examined in a synthetic gas containing and . The overpotential was greatly decreased by loading only a small amount of Ru microcrystals onto the mixed conducting oxide, samaria‐doped ceria (SDC), anode layer in both synthetic gas and wet hydrogen atmospheres. It was found that the Ru‐SDC anode exhibited the highest electrocatalytic activities at an optimum oxygen partial pressure in the fuel gas due to high conductivities of both electrons and oxide ions in the SDC. The maximum current density on the Ru‐SDC anode exceeded 1 A/cm2 at all the operating temperatures between 800 and 1000°C at the potential of −0.9 V vs. air reference electrode, when 0.1 mg/cm2 of Ru microcatalysts were loaded on the SDC surface and the appropriate fuel gas was used.

High Performance Catalyzed-Reaction Layer for Medium Temperature Operating Solid Oxide Fuel Cells III. Effects of Composition and Morphology on Performance of Anode and Cathode Layers

Polarization properties of catalyzed-reaction layers, which the authors developed for medium temperature operating SOFC, were greatly improved by controlling their compositions and microstructures. The amount of Pt catalysts loaded on Sr-doped LaMnO{sub 3} (LSM) cathode was reduced down to 1/5 by decreasing size of Pt particles. A large depolarizing effect was observed on the Pt-catalyzed LSM cathode, especially at high current densities. The anodic overpotential for the samaria-doped ceria (SDC) layer was appreciably lowered by applying both highly dispersed Ru microcrystals and 0.1{micro}m-sized SDC particles onto the SDC layer.

High Performance Catalyzed‐Reaction Layer for Medium Temperature Operating Solid Oxide Fuel Cells

New concepts for a high performance catalyzed‐reaction layer for medium temperature operating solid oxide fuel cells were proposed. Mixed conducting oxide particles, samaria‐doped ceria (SDC), were employed as the anode material utilizing highly dispersed noble metal catalysts on their surface. As the cathode material, Sr‐doped (LSM) particles catalyzed with microcrystalline Pt were employed. Performances of the anode or cathode were examined in the cell using yttria‐stabilized zirconia electrolyte at a series of operating temperatures. It was found that the anodic polarization resistance and its activation energy were greatly decreased by loading only a small amount of the catalysts (such as Ru, Rh, and Pt) onto the SDC particles. The polarization loss at the anode showed a minimum value by using the SDC particles with a mean diameter of 1.5 to 2.0 μm. A large depolarizing effect was also observed with a Pt‐catalyzed LSM cathode, especially at high current densities.