Research Interests:
Research Interests:
Research Interests:
Internal steam reforming of methane within solid oxide fuel cells (SOFC) offers a method of improved thermal management and reduced system complexity. Thermal gradient management is dependent upon controlling the reforming activity along... more
Internal steam reforming of methane within solid oxide fuel cells (SOFC) offers a method of improved thermal management and reduced system complexity. Thermal gradient management is dependent upon controlling the reforming activity along the length of the anode. The inherent activity of Ni-YSZ for the steam reforming of methane is highly dependent upon the pretreatment and reduction procedures employed. During
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Abstract Chemical and structural stability of strontium doped lanthanum manganite (LSM) and lanthanum cobalt ferrite (LSCF) cathodes in Cr-containing humidified air has been studied by a combination of experimental and thermodynamic... more
Abstract Chemical and structural stability of strontium doped lanthanum manganite (LSM) and lanthanum cobalt ferrite (LSCF) cathodes in Cr-containing humidified air has been studied by a combination of experimental and thermodynamic approaches. During 100 h tests performed in flowing air (3% H2O) at 1023 K, the electrochemical performance of LSM/yttria doped zirconia (YSZ)/Pt half-cells exhibited a relatively faster degradation in current (I–t) at 0.5 V applied bias than the LSCF/gadolinium-doped ceria (GDC)/Pt half-cells. Cr species from the gas phase deposited predominantly at LSM/YSZ interface while LSCF showed mainly surface deposition throughout the electrode. Raman spectra indicate SrCrO4 formation on the post tested LSCF cathode but not on the post tested LSM cathode. The polarization resistance of the LSM cathode also increased significantly compared to that of the LSCF cathode. A linear programming approach coupled with first-principles thermodynamics suggests that the stoichiometric LSM remains stable and unreacted for the whole range of experimental PCrO3 and temperature conditions whereas the formation of SrCrO4 on LSC cathode is energetically favored at 1023 K supporting the experimental findings.
Research Interests:
Research Interests:
Topography and phase composition of the scales formed on commercial ferritic stainless steel and two experimental nickel-based alloys were studied in atmospheres simulating solid oxide fuel cell (SOFC) environments. Corrosion experiments... more
Topography and phase composition of the scales formed on commercial ferritic stainless steel and two experimental nickel-based alloys were studied in atmospheres simulating solid oxide fuel cell (SOFC) environments. Corrosion experiments were carried out under SOFC dual environment conditions with air on one side of the sample and hydrogen on the other side for 100 h at 700 °C. Post-corrosion
Research Interests:
Over the past several years, advances in materials and fabrication techniques for planar SOFCs have allowed for a reduction in SOFC operating temperatures (e.g., 650-800C)[1]. Consequently, relatively inexpensive ferritic stainless steels... more
Over the past several years, advances in materials and fabrication techniques for planar SOFCs have allowed for a reduction in SOFC operating temperatures (e.g., 650-800C)[1]. Consequently, relatively inexpensive ferritic stainless steels that have good thermal expansion matching with the ceramic cells are now considered to be among the most promising candidate materials for the construction of interconnects in SOFC stacks. To function well in the stacks, the metallic interconnects must demonstrate: (i) Excellent stability over thousands of hours in a very challenging dual environment, as they are exposed simultaneously to a reducing atmosphere (fuel, such as hydrogen) on one side and an oxidizing atmosphere (air) on the other side; (ii) High electrical conductivity through both the bulk material and in-situ formed oxide scales; (iii) Bulk and interfacial thermal mechanical reliability and durability at the operating temperature; (iv) Compatibility with other materials in contact wi...
Research Interests:
Research Interests:
Research Interests:
Morphology-controlled strontianite nanostructures have attracted interest in various fields, such as electrocatalyst and photocatalysts. Basic additives in aqueous strontium solutions is commonly used in controlling strontianite... more
Morphology-controlled strontianite nanostructures have attracted interest in various fields, such as electrocatalyst and photocatalysts. Basic additives in aqueous strontium solutions is commonly used in controlling strontianite nanostructures. Here, we show that trace water also serves an important role in forming and structuring vertically oriented strontianite nanorod arrays on strontium compounds. Using in situ Raman spectroscopy, we monitored the structural evolution from hydrated strontium to strontianite nanorods, demonstrating the epitaxial growth by vapor–liquid–solid mechanism. Water molecules cause not only the exsolution of Sr liquid droplets on the surface but also the uptake of airborne CO2 followed by its ionization to CO32−. The existence of intermediate SrHO+–OCO22− phase indicates the interaction of CO32− with SrOH+ in Sr(OH)x(H2O)y cluster to orient strontianite crystals. X-ray diffraction simulation and transmission electron microscopy identify the preferred-orie...
Research Interests:
Solid oxide electrochemical systems, such as solid oxide fuel cells (SOFC), solid oxide electrolysis cells (SOEC), and oxygen transport membranes (OTM) enable clean and reliable production of energy or fuel for a range of applications,... more
Solid oxide electrochemical systems, such as solid oxide fuel cells (SOFC), solid oxide electrolysis cells (SOEC), and oxygen transport membranes (OTM) enable clean and reliable production of energy or fuel for a range of applications, including, but not limited to, residential, commercial, industrial, and grid-support. These systems utilize solid-state ceramic oxides which offer enhanced stability, fuel flexibility, and high energy conversion efficiency throughout operation. However, the nature of system conditions, such as high temperatures, complex redox atmosphere, and presence of volatile reactive species become taxing on solid oxide materials and limit their viability during long-term operation. Ongoing research efforts to identify the material corrosion and degradation phenomena, as well as discover possible mitigation techniques to extend material efficiency and longevity, is the current focus of the research and industrial community. In this review, degradation processes in...
Research Interests:
Research Interests:
ABSTRACT La0.75Sr0.25)0.95Cr0.7Mn0.3O3 (LSCM) mixed with 8YSZ has promising attributes to function as fuel electrode and electrolyte membrane in high temperature electrochemical devices including solid oxide fuel cell as well as oxygen... more
ABSTRACT La0.75Sr0.25)0.95Cr0.7Mn0.3O3 (LSCM) mixed with 8YSZ has promising attributes to function as fuel electrode and electrolyte membrane in high temperature electrochemical devices including solid oxide fuel cell as well as oxygen transport membrane systems. In this study, electrochemical performance of the symmetrical cells of the configuration LSCM/8YSZ//8YSZ//LSCM/8YSZ is investigated under simulating device operating conditions. Role of temperature (850- 950°C) and bias (0-0.8V) is evaluated on the electrochemical impedance of the symmetrical cells in oxidizing (air) and reducing atmosphere (Ar-3%H2-3%H2O). Higher performance is obtained in oxidizing when compared to reducing atmosphere. Bulk, surface and the electrode/electrolyte interfaces are examined during posttest characterization of the tested cells. No electrode delamination as well as no interface layer or compound formation is identified in the bulk and/or interface in both oxidizing and reducing atmosphere.
ABSTRACT During the operation of tubular solid oxide fuel cells (SOFC) at 1000°C in CH4-H2O fuel, we observed silica deposit formation on the fuel electrode (Ni-YSZ cermet), nickel felt contacts and reforming catalyst surfaces. Silica... more
ABSTRACT During the operation of tubular solid oxide fuel cells (SOFC) at 1000°C in CH4-H2O fuel, we observed silica deposit formation on the fuel electrode (Ni-YSZ cermet), nickel felt contacts and reforming catalyst surfaces. Silica deposition on the fuel electrode resulted in the electrical performance degradation, coverage of the catalyst surface and breakdown of the zirconia skeleton present on the fuel electrode. Sources of silica were identified. A thermohemical model relating to the formation and transport of vapor phase silica species, deposition on the catalytically active surface and interaction with the anode was developed. Vapor transport of silica is considered to take place at the quartz surface in the presence of water vapor. Silica deposition and deactivation of the catalyst is postulated to be due to the dissociation of gaseous hydrated silicious species on the active nickel surface during the reformation of hydrocarbon. Experiments were designed and conducted to validate the mechanism. It is concluded from these experiments that the presence of silica in the solid oxide fuel cell generator and the catalyst support should be eliminated for long term stable operation of cells and generator.
Research Interests:
ABSTRACT Providing adequate and efficient cooling schemes for solid-oxide-fuel-cell (SOFC) stacks continues to be a challenge coincident with the development of larger, more powerful stacks. The endothermic steam-methane reformation... more
ABSTRACT Providing adequate and efficient cooling schemes for solid-oxide-fuel-cell (SOFC) stacks continues to be a challenge coincident with the development of larger, more powerful stacks. The endothermic steam-methane reformation reaction can provide cooling and improved system efficiency when performed directly on the electrochemically active anode. Rapid kinetics of the endothermic reaction typically causes a localized temperature depression on the anode near the fuel inlet. It is desirable to extend the endothermic effect over more of the cell area and mitigate the associated differences in temperature on the cell to alleviate subsequent thermal stresses. In this study, modeling tools validated for the prediction of fuel use, on-cell methane reforming, and the distribution of temperature within SOFC stacks are employed to provide direction for modifying the catalytic activity of anode materials to control the methane conversion rate. Improvements in thermal management that can be achieved through on-cell reforming is predicted and discussed. Two operating scenarios are considered, one in which the methane fuel is fully pre-reformed and another in which a substantial percentage of the methane is reformed on-cell. For the latter, a range of catalytic activity is considered, and the predicted thermal effects on the cell are presented. Simulations of the cell electrochemical and thermal performance with and without on-cell reforming, including structural analyses, show a substantial decrease in thermal stresses for an on-cell reforming case with slowed methane conversion rate.
Research Interests:
A nickel anode electrode fabricated by oxidizing a nickel alloying material to produce a material whose exterior contains nickel oxide and whose interior contains nickel metal throughout which is dispersed the oxide of the alloying... more
A nickel anode electrode fabricated by oxidizing a nickel alloying material to produce a material whose exterior contains nickel oxide and whose interior contains nickel metal throughout which is dispersed the oxide of the alloying material and by reducing and sintering the oxidized material to form a product having a nickel metal exterior and an interior containing nickel metal throughout
Research Interests:
ABSTRACT SummaryA novel glass-mica composite seal was developed based on a previous concept of “infiltrated” mica seals for solid oxide fuel cells. A Ba-Al-Ca silicate sealing glass was mixed with mica flakes to form the glass-mica... more
ABSTRACT SummaryA novel glass-mica composite seal was developed based on a previous concept of “infiltrated” mica seals for solid oxide fuel cells. A Ba-Al-Ca silicate sealing glass was mixed with mica flakes to form the glass-mica composite seals. The glass-mica composite seals were tested for thermal cycle stability in terms of the high temperature leakage under applied compressive stresses. Post mortem analyses were used to characterize the fracture and leak path of the glass-mica composite seals.
Research Interests:
Research Interests:
A novel design of a laboratory built axially rotating collector (ARC) having capability to align electrospun nanofibers have been described. A detailed morphological comparison of such nanofibers orientation and their geometry is done... more
A novel design of a laboratory built axially rotating collector (ARC) having capability to align electrospun nanofibers have been described. A detailed morphological comparison of such nanofibers orientation and their geometry is done using scanning electron microscopy (SEM). For comparison various polymeric solutions were electrospun on conventional static collector as well as ARC. The average diameter of polyvinyl alcohol (PVA) nanofibers was found to be 250 nm while polycaprolactone (PCL) nanofibers were found to be within a range of 600-800 nm. Conducting nanoparticles such as graphene and multi-walled carbon nanotubes (MWNTs) mixed with polymer solutions shown to have a significant influence on the overall geometry of these nanofibers and their diameter distribution. It is evident from the SEM analysis that both graphene and MWNTs in polymer solution play a crucial role in achieving a uniform diameter of nanofibers. Lastly, the formation of the aligned nanofibers using ARC has been mathematically modeled and the electromagnetic field governing the process has been simulated.
Research Interests:
Pacific Northwest National Laboratory (PNNL) is collaborating with government agencies, industries, and academic institutions to develop the technology and knowledge base for SOFC power generation systems capable of near term applications... more
Pacific Northwest National Laboratory (PNNL) is collaborating with government agencies, industries, and academic institutions to develop the technology and knowledge base for SOFC power generation systems capable of near term applications in small distributed generation, mobile auxiliary power and man portable units as well as long term applications in large centralized SOFC/turbine hybrid and reversible power plants operating on coal.
Research Interests: Structural Reliability, Energy Conversion, Fuel Cell, Power Plant, Power Generation, and 10 morePacific Northwest, Solid oxide fuel cell, Knowledge base, Design optimization, Thermal management, Structural Properties, System modeling, Distributed Generators, Department of Energy, and Failure Mechanism
ABSTRACT Providing adequate and efficient cooling schemes for solid-oxide-fuel-cell (SOFC) stacks continues to be a challenge coincident with the development of larger, more powerful stacks. The endothermic steam-methane reformation... more
ABSTRACT Providing adequate and efficient cooling schemes for solid-oxide-fuel-cell (SOFC) stacks continues to be a challenge coincident with the development of larger, more powerful stacks. The endothermic steam-methane reformation reaction can provide cooling and improved system efficiency when performed directly on the electrochemically active anode. Rapid kinetics of the endothermic reaction typically causes a localized temperature depression on the anode near the fuel inlet. It is desirable to extend the endothermic effect over more of the cell area and mitigate the associated differences in temperature on the cell to alleviate subsequent thermal stresses. In this study, modeling tools validated for the prediction of fuel use, on-cell methane reforming, and the distribution of temperature within SOFC stacks are employed to provide direction for modifying the catalytic activity of anode materials to control the methane conversion rate. Improvements in thermal management that can be achieved through on-cell reforming is predicted and discussed. Two operating scenarios are considered, one in which the methane fuel is fully pre-reformed and another in which a substantial percentage of the methane is reformed on-cell. For the latter, a range of catalytic activity is considered, and the predicted thermal effects on the cell are presented. Simulations of the cell electrochemical and thermal performance with and without on-cell reforming, including structural analyses, show a substantial decrease in thermal stresses for an on-cell reforming case with slowed methane conversion rate.
Research Interests:
In this study, octamethylcyclotetrasiloxane (D4) was removed by using a novel modified solid adsorbent of mesoporous silica. The adsorbent was synthesized using inverse micelles with some modifications in the synthesis process... more
In this study, octamethylcyclotetrasiloxane (D4) was removed by using a novel modified solid adsorbent of mesoporous silica. The adsorbent was synthesized using inverse micelles with some modifications in the synthesis process (temperature of gelation) and in the post treatment conditions (calcination temperature and heating rate) with a concomitant improvement of D4 uptake. This is the first report on regulating the textural properties of the mesoporous silica material UCT-14 to develop an active silica adsorbent. These adjustments resulted in an increase of the silica surface area from 391 to 798 m(2).g(-1), which leads to a high capacity (686 mg.g(-1)) of D4-capture for the silica synthesized at 80(o)C, calcined at 450(o)C with the heating rate of 100(o)C.min(-1)(Si-Syn80). This adsorbent showed comparable adsorption performance with the widely used commercial silica gel under dry and humid condition. Recyclability tests on the commercial silica gel and mesoporous silica synthesi...
Research Interests:
Research Interests:
ABSTRACT Hybrid Phlogopite mica seals were evaluated in a combined ageing and thermal cycling test. Two interlayers were investigated: a glass and a metallic foil. Samples were first aged at 800°C for ∼500 or ∼1000 hrs in a simulated SOFC... more
ABSTRACT Hybrid Phlogopite mica seals were evaluated in a combined ageing and thermal cycling test. Two interlayers were investigated: a glass and a metallic foil. Samples were first aged at 800°C for ∼500 or ∼1000 hrs in a simulated SOFC environment, followed by short-term thermal cycling. The results of hybrid mica with glass interlayer showed extensive reaction and poor thermal cycle stability after ageing for 1036 hrs and 21 thermal cycles. Use of the brazing alloy as the interlayer showed no interaction with mica over 504 hrs and reasonable leak rates were maintained through 8 cycles. The leakage development was found to be consistent with fracture surface and microstructure analyses.
Research Interests:
ABSTRACT SummaryA novel glass-mica composite seal was developed based on a previous concept of “infiltrated” mica seals for solid oxide fuel cells. A Ba-Al-Ca silicate sealing glass was mixed with mica flakes to form the glass-mica... more
ABSTRACT SummaryA novel glass-mica composite seal was developed based on a previous concept of “infiltrated” mica seals for solid oxide fuel cells. A Ba-Al-Ca silicate sealing glass was mixed with mica flakes to form the glass-mica composite seals. The glass-mica composite seals were tested for thermal cycle stability in terms of the high temperature leakage under applied compressive stresses. Post mortem analyses were used to characterize the fracture and leak path of the glass-mica composite seals.
Research Interests:
ABSTRACT
ABSTRACT
Research Interests: Method, Cell, Reason, Interior, Temperature, and 13 moreRange, Cracking, Degree, Operation, Electrochemical, Hot, Array, Solid, Electrodes, Electrode, Electrochemical Cell, Electrolyte, and Gas
Description/Abstract The development of solid oxide fuel cell (SOFC) technology represents an opportunity to achieve significant improvements in energy conversion efficiency and reduction of undesirable emissions. However, many technical... more
Description/Abstract The development of solid oxide fuel cell (SOFC) technology represents an opportunity to achieve significant improvements in energy conversion efficiency and reduction of undesirable emissions. However, many technical challenges still need to be ...
This report describes a 24-month effort in the development of a corrosion resistant hardware material for molten carbonate fuel cell (MFC) application. The objective of this program was to identify an inexpensive alloy for MCFC current... more
This report describes a 24-month effort in the development of a corrosion resistant hardware material for molten carbonate fuel cell (MFC) application. The objective of this program was to identify an inexpensive alloy for MCFC current collector/bipolar plate application. For this work, 310S was selected as the base alloy composition and La, Ce and Si were added to improve corrosion resistance. Eight candidate alloys, including 310S and 316L, were screened in MCFC anode and cathode atmospheres. The techniques used include isothermal corrosion, acoustic emission, thermal cycling corrosion, thermogravimetric analyses, electrical surface resistance, and dual atmosphere corrosion testing. Oxide scales formed were analyzed by standard metallographic techniques. The results indicate that COLT-25+ and Crutemp-25 alloys (both containing 25Cr-25Ni and balance Fe) have the best corrosion resistance in the MCFC environment. Rare earth additives, La and Ce, do not appear to improve isothermal or thermal cycling resistance a great deal. Silicon addition appears to improve thermal cycling but not isothermal corrosion resistance. High Mn content (approx.18%) appears detrimental based on this limited investigation. Currently used 316L has the least corrosion resistance of all the alloys tested. Pressurized tests have shown that high pressure (10 atm) reduces corrosion rate in the anode atmosphere whereas it only slightly affects corrosion rate in the cathode atmosphere. 37 refs., 47 figs., 12 tabs.
Research Interests:
Research Interests:
Significant progress in reducing the operating temperature of solid oxide fuel cells (SOFC) from â1000 C to â 750 C may permit the replacement of currently used ceramic interconnects by metallic interconnects in planar SOFCs (PSOFC). The... more
Significant progress in reducing the operating temperature of solid oxide fuel cells (SOFC) from â1000 C to â 750 C may permit the replacement of currently used ceramic interconnects by metallic interconnects in planar SOFCs (PSOFC). The use of metallic interconnects will result in a substantial cost reduction of PSOFCs. The interconnects operate in severe gaseous environments, in which one side of the interconnect can be exposed to hydrogen and the other side to air or oxygen at temperatures up to 800 C. Similar environmental conditions can exist in devices used for separating hydrogen from CO after reforming methane and steam. Type 304 stainless steel was selected for this base line study aimed at understanding corrosion processes in dual gas environments. This paper discusses the oxidation resistance of 304 stainless steel exposed to a dual environment gas at 800 C. The dual environment consisted of air on one side of the specimen and 1% hydrogen in nitrogen on the other side. The surface characterization techniques used in this study were optical and scanning electron microscopy, as well as various x-ray techniques.
Research Interests:
Introduction The conversion of methane and natural gas over the anode of a solid oxide fuel cell followed by electrochemical oxidation of the produced H2 and CO is of interest as a means to increase the overall efficiency of power... more
Introduction The conversion of methane and natural gas over the anode of a solid oxide fuel cell followed by electrochemical oxidation of the produced H2 and CO is of interest as a means to increase the overall efficiency of power generation [1,2]. On-anode steam reforming is ...
The molten carbonate fuel cell (MCFC) wet seal are has been found to experience accelerated corrosion in the presence of molten electrolyte because of simultaneous exposure to reducing and oxidizing atmospheres. Development of protective... more
The molten carbonate fuel cell (MCFC) wet seal are has been found to experience accelerated corrosion in the presence of molten electrolyte because of simultaneous exposure to reducing and oxidizing atmospheres. Development of protective coatings plays an important role in minimizing this corrosion. Various aluminizing processes, such as flame spraying, slurry spraying, pack cementation, and ion vapor deposition, have been
Research Interests:
This chapter contains sections titled: Introduction Experimental Results and Discussion Conclusion Acknowledgement