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Stainless steel wire mesh flow-fields for polymer electrolyte fuel cells

Description: The high cost of fuel cells has delayed their potential widespread use. Stack manufacturers have historically used high-Pt loading membrane/electrode assemblies (MEAs) and intricately machined graphite bipolar plates. We have focused our efforts on decreasing the cost of these components in order to demonstrate an inexpensive, yet high performance PEM fuel cell. This paper describes the design and demonstration of a 100 cm{sup 2} (active area) cell that utilizes ultra-low Pt loading MEAs and inexpensive stainless steel wire screen flow fields.
Date: October 1, 1996
Creator: Zawodzinski, C.; Wilson, M.S. & Gottesfeld, S.
Partner: UNT Libraries Government Documents Department

Advances in tubular solid oxide fuel cell technology

Description: This document provides the functional design criteria for an addition to the 222-S facility. This project will provide space for manipulator repair, equipment and manipulator decontamination and laundry storage. The manipulator repair and storage area will provide for storage of 20 manipulators, an area for receiving potentially contaminated manipulators and an area for the repair of manipulators. The decontamination area will be capable of decontamination of manipulators and shipping casks, pigs, T-handle carriers and other shipping containers. The laundry storage area will provide space for potentially contaminated and clean laundry.
Date: March 1, 1995
Creator: Singhal, S.C.
Partner: UNT Libraries Government Documents Department

Characterization of ceria-based SOFCs

Description: Solid Oxide Fuel Cells (SOFCs) operating at low temperatures (500-700 C) offer many advantages over conventional zirconia-based fuel cells operating at higher temperatures. Cathode performance is being improved by using better materials and/or microstructures. Fabrication of thin dense electrolytes is also necessary to achieve high cell performances.
Date: December 31, 1996
Creator: Doshi, R.; Roubort, J. & Krumpelt, M.
Partner: UNT Libraries Government Documents Department

Recent progress in tubular solid oxide fuel cell technology

Description: The tubular design of solid oxide fuel cells (SOFCs) and the materials used therein have been validated by successful, continuous electrical testing over 69,000 h of early technology cells built on a calcia-stabilized zirconia porous support tube (PST). In the latest technology cells, the PST has been eliminated and replaced by a doped lanthanum manganite air electrode tube. These air electrode supported (AES) cells have shown a power density increase of about 33% with a significantly improved performance stability over the previously used PST type cells. These cells have also demonstrated the ability to thermally cycle over 100 times without any mechanical damage or performance loss. In addition, recent changes in processes used to fabricate these cells have resulted in significant cost reduction. This paper reviews the fabrication and performance of the state-of-the-art AES tubular cells. It also describes the materials and processing studies that are underway to further reduce the cell cost, and summarizes the recently built power generation systems that employed state-of-the-art AES cells.
Date: December 31, 1997
Creator: Singhal, S.C.
Partner: UNT Libraries Government Documents Department

Solid oxide fuel cell commercialization in the United States

Description: This paper discusses aspects of solid oxide fuel cell (SOFC) technology commercialization in the US. It provides the status of the major SOFC developments occurring in the US by addressing both intermediate- and high-temperature SOFC`s, several SOFC designs, including both planar and tubular, and SOFC system configurations. This paper begins with general characteristics, proceeds with designs and system configurations, and finishes with a discussion of commercialization, funding, and policies. The US Department of Energy`s (DOE) Morgantown Energy Technology Center (METC) is the lead US DOE center for the implementation of a Research, Development, and Demonstration Program to develop fuel cells for stationary power. METC`s stakeholders include the electric power and gas industries, as well as fuel cell developers and others. This paper offers some new perspectives on SOFC development and commercialization which come from the broad consideration of the commercialization efforts of the entire fuel cell industry.
Date: March 1, 1995
Creator: Williams, M.C.
Partner: UNT Libraries Government Documents Department

Application of alternating current impedance to fuel cell modeling

Description: AC impedance has provided a useful diagnostic tool in the Los Alamos polymer electrolyte fuel cell (PEFC) program. The author reviews the techniques he has used in ac impedance modeling. These techniques include equation implementation, model simplification and verification, least squares fitting, application of two-dimensional Laplace equation solvers handling complex interfacial boundary conditions, and interpretation of impedance features. The separate features of the complete electrode model are explained by analytic examples.
Date: May 2, 1999
Creator: Springer, T.E.
Partner: UNT Libraries Government Documents Department

Tubular solid oxide fuel cell developments

Description: An overview of the tubular solid oxide fuel cell (SOFC) development at Westinghouse is presented in this paper. The basic operating principles of SOFCs, evolution in tubular cell design and performance improvement, selection criteria for cell component materials, and cell processing techniques are discussed. The commercial goal is to develop a cell that can operate for 5 to 10 years. Results of cell test operated for more than 50,000 hours are presented. Since 1986, significant progress has been made in the evolution of cells with higher power, lower cost and improved thermal cyclic capability. Also in this period, successively larger multi-kilowatt electrical generators systems have been built and successfully operated for more than 7000 hours.
Date: August 1, 1995
Creator: Bratton, R.J. & Singh, P.
Partner: UNT Libraries Government Documents Department

Nondestructive characterization methods for monolithic solid oxide fuel cells

Description: Monolithic solid oxide fuel cells (MSOFCS) represent a potential breakthrough in fuel cell technology, provided that reliable fabrication methods can be developed. Fabrication difficulties arise in several steps of the processing: First is the fabrication of uniform thin (305 {mu}m) single-layer and trilayer green tapes (the trilayer tapes of anode/electrolyte/cathode and anode/interconnect/cathode must have similar coefficients of thermal expansion to sinter uniformly and to have the necessary electrochemical properties); Second is the development of fuel and oxidant channels in which residual stresses are likely to develop in the tapes; Third is the fabrication of a ``complete`` cell for which the bond quality between layers and the quality of the trilayers must be established; and Last, attachment of fuel and oxidant manifolds and verification of seal integrity. Purpose of this report is to assess nondestructive characterization methods that could be developed for application to laboratory, prototype, and full-scale MSOFCs.
Date: January 1, 1993
Creator: Ellingson, W.A.
Partner: UNT Libraries Government Documents Department

Novel carbon-ion fuel cells. Quarterly technical report No. 9, October 1, 1995--December 31, 1995

Description: This report presents research to develop an entirely new, fundamentally different class of fuel cell using a solid electrolyte that transports carbon ions. This fuel cell would use solid carbon dissolved in molten metal as a fuel reservoir and anode; expensive gaseous or liquid fuel would not be required. Thermodynamic factors favor a carbon-ion fuel cell over other fuel cell designs: a combination of enthalpy, entropy, and Gibbs free energy makes the reaction of solid carbon and oxygen very efficient, and the entropy change allows this efficiency to slightly increase at high temperatures. The high temperature exhaust of the fuel cell would make it useful as a ``topping cycle``, to be followed by conventional steam turbine systems.
Date: December 31, 1995
Creator: Cocks, F.H.
Partner: UNT Libraries Government Documents Department

Monolithic solid oxide fuel cell technology advancement for coal-based power generation. Final report, September 1989--March 1994

Description: This project has successfully advanced the technology for MSOFCs for coal-based power generation. Major advances include: tape-calendering processing technology, leading to 3X improved performance at 1000 C; stack materials formulations and designs with sufficiently close thermal expansion match for no stack damage after repeated thermal cycling in air; electrically conducting bonding with excellent structural robustness; and sealants that form good mechanical seals for forming manifold structures. A stack testing facility was built for high-spower MSOFC stacks. Comprehensive models were developed for fuel cell performance and for analyzing structural stresses in multicell stacks and electrical resistance of various stack configurations. Mechanical and chemical compatibility properties of fuel cell components were measured; they show that the baseline Ca-, Co-doped interconnect expands and weakens in hydrogen fuel. This and the failure to develop adequate sealants were the reason for performance shortfalls in large stacks. Small (1-in. footprint) two-cell stacks were fabricated which achieved good performance (average area-specific-resistance 1.0 ohm-cm{sup 2} per cell); however, larger stacks had stress-induced structural defects causing poor performance.
Date: May 1, 1994
Partner: UNT Libraries Government Documents Department

Status of SOFC development in USA

Description: Solid oxide fuel cells represent a highly efficient power generation/cogeneration source in the United States and worldwide. Currently, the US is a leader in this technology in the tubular, monolithic and planar solid oxide fuel cell areas. In addition, research is being conducted in intermediate temperature solid oxide fuel cells. An overview of the status of these technologies, research, and critical issues is presented.
Date: June 1, 1993
Creator: Hooie, D. T.
Partner: UNT Libraries Government Documents Department

Recent progress in zirconia-based fuel cells for power generation

Description: High temperature solid oxide fuel cells based upon yttria-stabilized zirconia electrolyte offer a clean, pollution-free technology to electrochemically generate electricity at high efficiencies. This paper reviews the designs, materials and fabrication processes used for such fuel cells. Most progress to date has been achieved with tubular geometry cells. A large number of tubular cells have been electrically tested, some to times up to 30,000 hours; these cells have shown excellent performance and performance stability. In addition, successively larger size electric generators utilizing these cells have been designed, built and operated since 1984. Two 25 kW power generation field test units have recently been fabricated; these units represent a major milestone in the commercialization of zirconia-based fuel cells for power generation.
Date: December 1, 1992
Creator: Singhal, S. C.
Partner: UNT Libraries Government Documents Department

Synthesis, processing and properties of materials for SOFCs

Description: The synthesis and processing methods of complex oxide materials can significantly influence use in solid oxide fuel cells (SOFCs). This paper discusses (1) effects of powder synthesis and conditioning on fabrication, i.e., sintering, where close, reproducible control of composition and structure are required, and (2) influences on electrical, mechanical, structural and electrochemical properties that can influence SOFC performance. Examples are given for chromites, manganites and related oxides used as interconnections and electrodes in SOFCs. Materials, from source to incorporation into the fuel cell and generator, is a major issue in the development of solid oxide fuel cells (SOFCs). An integral part of this is the synthesis from chemicals and other virgin materials, generally as an oxide or metal powder, which can become a SOFC component. In some instances, such as with electrochemical vapor deposition, the component is formed directly from the chemicals. The synthesized materials are then conditioned and processes prior to fabrication into the fuel cell component, either separately or in conjunction with other material components.
Date: March 1, 1994
Creator: Bates, J. L.; Armstrong, T. A.; Kingsley, J. J. & Pederson, L. R.
Partner: UNT Libraries Government Documents Department

Polymer electrolytes for a rechargeable li-Ion battery

Description: Lithium-ion polymer electrolyte battery technology is attractive for many consumer and military applications. A Li{sub x}C/Li{sub y}Mn{sub 2}O{sub 4} battery system incorporating a polymer electrolyte separator base on novel Li-imide salts is being developed under sponsorship of US Army Research Laboratory (Fort Monmouth NJ). This paper reports on work currently in progress on synthesis of Li-imide salts, polymer electrolyte films incorporating these salts, and development of electrodes and cells. A number of Li salts have been synthesized and characterized. These salts appear to have good voltaic stability. PVDF polymer gel electrolytes based on these salts have exhibited conductivities in the range 10{sup -4} to 10{sub -3} S/cm.
Date: October 1, 1996
Creator: Argade, S.D.; Saraswat, A.K.; Rao, B.M.L.; Lee, H.S.; Xiang, C.L. & McBreen, J.
Partner: UNT Libraries Government Documents Department

Ion and water transport in a Nafion{reg_sign} membrane pore: A statistical mechanical model with molecular structure

Description: With the well established importance of the coupling of water and protons through electroosmotic drag in operating PEFCs the authors present here a derivation of a mathematical model that focuses on the computation of the mobility of an hydronium ion through an arbitrary cylindrical pore of a PEM with a non-uniform charge distribution on the walls of the pore. The total Hamiltonian is derived for the hydronium ion as it moves through the hydrated pore and is effected by the net potential due to interaction with the solvent molecules and the pendant side chains. The corresponding probability density is derived through solution of the Liouville equation. This probability density is then used to compute the friction tensor for the hydronium ion. The authors find two types of contributions: (a) due to the solvent-ion interactions for which they adopt the conventional continuum model; (b) due to the interaction between the pendant charges and the hydronium ion. The latter is a new result and displays the role of the non-uniform nature of the charge distribution on the pore wall.
Date: December 31, 1998
Creator: Paddison, S.J.; Zawodzinski, T.A. Jr. & Paul, R.
Partner: UNT Libraries Government Documents Department

Advanced materials for solid oxide fuel cells

Description: Purpose of the research is to improve the properties of current state- of-the-art materials used for SOFCs. The project includes interconnect development, high-performance cathode, electrochemical testing, and accelerated testing. This document reports results of mechanical tests (bend strength, elastic modulus, fracture strength) of acceptor-substituted lanthanum chromite (interconnect material).
Date: December 31, 1996
Creator: Armstrong, T.R.; Stevenson, J. & Paulik, S.
Partner: UNT Libraries Government Documents Department

Processing of LaCrO{sub 3} for solid oxide fuel cell applications. April 1994--April 1995

Description: A 5-yr program has the objectives of developing LaCrO{sub 3}-based interconnect powders which densify when in contact with anode and cathode materials for solid oxide fuel cells and developing high- performance cathodes, anodes, and interfaces for planar SOFCs. This report is divided into LaCrO{sub 3} sintering studies and SOFC performance studies. Major achievements during the past year included: Developing processing skills for fabricating single cells, incorporating a Pt reference electrode into the electrolyte for separating electrode effects, developing processing-microstructure- property relations for a number of anodes, and developing experimental techniques for measuring cell performance.
Date: July 1, 1995
Creator: Huebner, W. & Anderson, H.U.
Partner: UNT Libraries Government Documents Department

X-ray absorption and electrochemical studies of direct methanol fuel cell catalysts

Description: In order for polymer electrolyte fuel cells to operate directly on methanol instead of hydrogen, methanol oxidation must be catalyzed in the acidic cell environment. Pt-Ru and Pt-Ru oxide are considered to be the most active catalysts for this purpose; Ru enhances the Pt activity for reasons not yet fully understood. XAS and electrochemical techniques were used to study this enhancement. Preliminary results indicate that Ru does effect the d-band occupancy of Pt, which in turn may effect the kinetics of the methanol oxidation reaction on this metal by altering the strength of the Pt-CO bond. Further research is needed.
Date: December 31, 1996
Creator: Zurawski, D.J.; Aldykiewicz, A.J. Jr.; Baxter, S.F. & Krumpelt, M.
Partner: UNT Libraries Government Documents Department

The effect of pressure on solid oxide fuel cell performance

Description: Current work in solid oxide fuel cells (SOFCs) is on cathode-supported, anode-supported, or electrolyte-supported cells. In electrode-supported cells, a thin film (5 to 30 microns) of an electrolyte (YSZ) is deposited on a relatively thick, porous electrode. In electrolyte-supported cells, the electrolyte thickness is typically greater than or equal 150 microns upon which thin electrodes are screen printed. Both types of SOFCs are being explored for hybrid applications, that is, in combination with a gas turbine, for which the exit gases from an SOFC generator must be at a high pressure (3 to 15 atm) for input into a gas turbine. It is necessary to examine the expected performance of an SOFC under a high pressure. Work at Westinghouse Ontario Hydro has shown that the performance improvement at high pressures is greater than that can be expected based on an increased Nernst potential alone. This increased performance can in part be attributed to a lower concentration polarization. The objective of this work was to conduct a preliminary analysis of the effect of pressure on the performance of both cathode-supported and electrolyte-supported cells. Flux equations for transport through porous electrodes are formulated and are solved in combination with those for electrochemical operation of an SOFC for cathode-supported and electrolyte-supported cells. The analysis shows that the overall cell performance increases significantly with increasing pressure in the case of cathode-supported cells due to a lowering of concentration polarization at high pressures. Similar effects (not presented here) are also observed on anode-supported cells. By contrast, only a modest improvement is observed in the case of electrolyte-supported cells, commensurate with the fact that in the latter, the ohmic contribution of the electrolyte is the most dominant one, which is not altered by pressure.
Date: December 1, 1997
Creator: Virkar, A.V.; Fung, K.Z. & Singhal, S.C.
Partner: UNT Libraries Government Documents Department

Verification test of a 25kW class SOFC cogeneration system

Description: Osaka Gas and Tokyo Gas have high expectations for natural-gas-fueled Solid Oxide Fuel Cell (SOFC) cogeneration systems. SOFC offers many advantages for on-site cogeneration systems, such as high electrical efficiency, high quality by-product heat and low emissions. They are now executing a joint development program with Westinghouse Electric Corporation (hereinafter called as WELCO). This program is aimed to verify a 25kW class SOFC cogeneration system. This system, which was modified by replacing previous zirconia porous support tube cells (PST cells) with newly designed air electrode supported cells (AES cells), commenced operation on March 21, 1995. The system has been successfully operated for 13,100 hours as of February 7, 1997. This paper presents the performance evaluation of the new AES cells and the results of system operation at WELCO.
Date: December 31, 1997
Creator: Yokoyama, H.; Miyahara, A. & Veyo, S.E.
Partner: UNT Libraries Government Documents Department

Indirect-fired gas turbine dual fuel cell power cycle

Description: The present invention relates generally to an integrated fuel cell power plant, and more specifically to a combination of cycles wherein a first fuel cell cycle tops an indirect-fired gas turbine cycle and a second fuel cell cycle bottoms the gas turbine cycle so that the cycles are thermally integrated in a tandem operating arrangement. The United States Government has rights in this invention pursuant to the employer-employee relationship between the United States Department of Energy and the inventors.
Date: April 1, 1998
Creator: Micheli, P.L.; Williams, M.C. & Sudhoff, F.A.
Partner: UNT Libraries Government Documents Department