|
> Research, Creativity and Technology Transfer > HiTEC
Projects
Materials Projects
Power Controls
Materials
Advanced Surface Engineering for SOFC Components (Smith Group)
Prof. Smith’s program is a collaborative effort with Dr. Vladimir Gorokhovsky, Arcomac Surface Engineering, Inc., Bozeman, MT, to use advanced surface engineering techniques to fabricate low-cost, corrosion resistant bipolar plates for SOFC stacks operating at 800 oC. We use Arcomac’s large-area filtered arc deposition technology (LAFAD) to coat steel interconnect plates, and characterize the performance of the plates by their area-specific resistance (ASR) in collaboration with Prof. Max Deibert (Chemical Engineering, MSU), and their corrosion resistance and thermal stability using ion beam analysis (IBA). We have studied a variety of coating compositions and multilayer structures. IBA is used to quantify oxidation rates, including oxygen transport parameters, coating composition, thermal stability of the coatings, and vaporization of Cr-containing species from the coatings. We are also studying the mechanisms of Cr poisoning in SOFC operation, and the growth of thin, dense YSZ films on porous YSZ substrates for SOFC applications.
Back to top
Electrode Development & Sulfur Tolerance (Sofie Group)
This activity focuses on the modification of traditional Ni/YSZ systems for anode supported technology with both electrochemically active and inert filler compounds to enhance anode performance while minimizing integration of new anode materials. The objective of the modified anode compositions is to improve durability by improving CTE match, thermal conductivity, and strength as well as achieving higher levels of sulfur tolerance. Further, fundamental studies are being performed to establish the mechanism of sulfur degradation in Ni/YSZ systems using high energy x-ray techniques which may lead to novel anode materials beyond the traditional system including all ceramic approaches.
Back to top
Engineered Pore Structure & Gas Diffusion Characteristics (Sofie Group)
Research activities examining the effects of concentration polarization under high current densities suggest that gas diffusion through thick pore structures limits performance of SOFC’s. Typical electrode structures are fabricated with spherically shaped thermal fugitives (polymer & carbon powder additions). New techniques, based on tape casting technology, are being developed that are capable of generating ordered pore structures without the additions of thermal fugitives. A new tape casting technology (Freeze Tape Casting) is being developed by which a traditional cast tape is solidified uni-directionally solidified through the thickness of the tape. Through the precise control of slurry solids loading, freezing rate, and additives, engineered electrode structures can be fabricated to function as advanced solid oxide fuel cell electrodes that dramatically decrease tortuosity of the gas path. Further, studies are being performed on traditional and freeze tape cast anodes to understand the gas diffusion characteristics associated with concentration polarization.
Back to top
Fuel cell design (Sofie Group)
While traditional anode supported cells (ASC) deliver high performance at relatively moderate temperatures, there are significant disadvantages to the design, including; shrinkage mismatch resulting in cell camber, CTE mismatch resulting in thermal stress, gas diffusion limitations, stack interconnection losses, and reactivity of electrode & electrolyte during sintering thus limiting the selection of potential electrode materials. A new design is being developed that will maintain a balanced symmetry for robustness and utilizing an interleaved micro-textured electrolyte support architecture that more than doubles active cell area while maintaining thin ionic conducting pathways for low area specific resistance (ASR). This new cell concept, developed as the Uni-Cell, is a merging of ASC and electrolyte supported cell (ESC) technology to maximize cell durability and to improve methods for sealing. The intended result is a cell that can be processed with the ease of electrolyte supported technology with low camber and robust mechanical properties. Electrode infiltration will also be utilized to further enhance the properties of this new concept.
Back to top
Measurement and Analysis of SOFC Anode Gas Flow and Tortuosity (Schmidt Group)
Directed by Prof. V. Hugo Schmidt and Dr. Jiaping Han — http://www.physics.montana.edu/eam/sofc/index.htm
This work performs an integrated experimental and theoretical approach to measure and analyze SOFC anode gas flow and tortuosity for various anode structures. The work will help the design of more effective microstructurally engineered electrodes in SOFCs, steam electrolyzers, gas separation membranes, and other high-temperature electrochemical systems. The approach includes theoretical analysis of gas flow equations under SOFC conditions, the construction of a dual opposing flow test apparatus to determine actual diffusivities of counter flowing gases from which tortuosity can be estimated, the application of a new method, magnetic resonance microscopy, to directly measure tortuosity and in-situ interactions of diffusing gases.
Back to top
Metallic Brazed Seals (Sofie Group)
While traditional approaches to SOFC sealing has been focused on compliant and/or rigid glass or glass/ceramic seals, the metallic braze seals may yield a more robust, mechanically stronger, and true hermetic seal. While significant challenges include the elimination of noble metals, shutting off electrical conductivity to prevent shorting of the cells, oxidiation resistance, metal/ceramic bonding, and thermal expansion mismatch, recent research in metallic braze seals shows promise to yield a viable and cost effective approach to SOFC sealing. A copper based braze system is being developed at MSU that forms a chemical and hermetic bond to metal and YSZ components and under the right treatment allows the shutdown of electronic conductivity to negate cell shorting issues. Fillers are also used in this system to control thermal expansion of the metal braze.
Back to top
Research and Development of Hydrogen Separation Membranes (Schmidt Group)
Directed by Prof. V. Hugo Schmidt and Dr. Jiaping Han — http://www.physics.montana.edu/eam/sofc/index.htm
This work is to develop proton conducting materials for intermediate-temperature proton conducting based SOFCs, including synthesis, processing, and characterization of proton conducting ceramics for electrolytes, proton conducting ceramic/electronic conducting ceramic composites for cathodes, and proton conducting ceramic/metal composites for anodes. Typical proton conducting ceramics studied are doped BaCeO3 and doped BaZrO3. Other proton conducting material systems are investigated as well. In addition, we will also develop a variety of other applications based on proton conducting ceramics, such as hydrogen pumps, hydrogen sensors, and steam electrolyzers.
Back to top
Stress in SOFC-related Material Multilayers (Idzerda Group)
In collaboration with Prof. S. Sophie of the MSU Mechanical Engineering Department, we have initiated a research program to examine components of working solid oxide fuel cells to determine methods of material optimization and the mechanism for performance degradation due to operation and poisoning from non-optimal fuel sources. We have constructed a testing station for long-period (>>100 hrs) monitoring of SOFC performance and to quantify degradation for use with variable fuel sources (S, Cl, Si contamination). Simultaneously, we are developing an X-ray compatible, high temperature cell that can work under operational fuel cell temperatures and voltages to characterize the local atomic and electronic structure of these materials. This in-situ X-ray electrochemical cell will be upgraded to include partial pressures of oxygen and/or fuel gas as a working half cell.
Back to top
Synthesis and performance characterization of protective ceramic and cermet coatings on high temperature metal alloys employed as interconnects in planar solid oxide fuel cell (SOFC) systems. (Deibert Group)
Prof. Max Deibert’s group within the Chemical and Biological Engineering (Ch&BE) Department at Montana State University’s High Temperature Electrochemistry Center (MSU-HiTEC) is engaged in high temperature electrochemical materials investigations. Primarily, focus is directed toward the synthesis and performance characterization of protective ceramic and cermet coatings on high temperature metal alloys employed as interconnects in planar solid oxide fuel cell (SOFC) systems. A wide-variety of coating compositions, architectures and deposition techniques are being explored. Coatings are deposited on ferritic steel specimen surfaces and subsequently subjected to SOFC-relevant exposures, e.g. high temperature and cyclic oxidation under controlled atmospheres. The specimens’ surface electronic conductivity, chemical and phase composition, microstructure, adhesion and stability are assessed using a wide-variety of both in-situ and post-mortem analytical techniques for both coated and uncoated materials. Analytical techniques include: time-dependent area specific resistance measurements; surface and cross section reflective optical microscopy; surface and cross-section scanning electron microscopy with energy dispersive x-ray spectroscopy and back-scattered electron diffraction analysis; thermal gravimetric analysis; x-ray diffraction; Rutherford backscattering spectroscopy; x-ray photoelectron spectroscopy; Auger electron spectroscopy; atomic force microscopy; time-of-flight secondary ion mass spectrometry; and others. Combining information from these complimentary techniques yields insight into the oxidation behavior of SOFC metallic interconnects with and without protective coatings, and assists the development of improved coatings and deposition techniques.
At present, the MSU – HiTEC Ch&BE Group consists of graduate student Paul Gannon and undergraduates Preston White, Jorgen Rufner, Edward Musz and Steven Teintze. The high temperature electrochemical materials laboratory is located at 329 Cobleigh Hall (406-994-7380). More information on this group and its current research activities can be accessed at: http://www.chbe.montana.edu/sofc/.
Back to top
X-ray Characterization of Operational SOFC Materials
Y.U. Idzerda
One of the goals of the HiTEC program is to determine the effects of interfacial strain from lattice mismatch at interfaces of technologically relevant SOFC materials. For this work, the interfacial stress is controlled by either depositing SOFC-related films (La0.5Sr0.5CoO3, or LSCO, and La2/3Ca1/3MnO3, or LCMO) grown by pulsed laser deposition (PLD) or metal-organic chemical vapor deposition (MoCVD) on appropriate substrates of known lattice mismatch or by capping thick SOFC-related structures with wedges of overlayers of known lattice mismatch. This latter method allows for the control of the total stress energy with wedge thickness. We have used element and site-specific X-ray spectroscopy and X-ray scattering to study the electronic, chemical, and structural properties of the as grown systems.
By using polarization dependent X-ray absorption spectroscopy (XAS), we have examined the chemical state of different elements of SOFC-related materials at room temperature as a function of the stress within the films created by the substrate or overlayer lattice mismatch that the film is grown under. We have found that as the stress is changed from compressive to tensile stress, the chemical state of the transition metal in the interfacial region changes dramatically, although the structure of the film remains essentially unchanged. The compositional gradient region represents a region where not only the transition metal ion valence is changing, but a region where the oxygen vacancy diffusion is far from optimum, and in some extreme cases where the transition metal valance becomes integer valued, the oxygen vacancy diffusion may become negligible. Through this research, we have identified a novel mechanism that may be a serious bottleneck to SOFC performance whereby the strain energy at an SOFC interface is accommodated and distributed over a larger volume (thickness) by modifying the chemical construction of the SOFC material to improve the lattice mismatch.
Back to top
Power Controls
Combined Heat and Power (CHP) Operation of Fuel Cells (Hashem Nehrir)
In addition to providing electrical power, fuel cells used in power generation applications provide exhaust heat. The heat can be used for a variety of applications. Under this scenario, the efficiency of the fuel cell system can be improved significantly. In this research, physically-based approaches are used to calculate the efficiency of SOFC and PEMFC power generation systems under CHP operation, and to investigate different CHP applications of these fuel cells.
Back to top
DC/DC converter for the SOFC powered residential power system (Gao Group)
Dr. Gao works on the power electronics aspect of SOFC power systems for the HiTEC program. He is developing a new DC/DC converter for the SOFC powered residential power system. The converter boosts the fuel cell voltage to a high level to enable the subsequent DC-AC conversion and provides isolation. The converter utilizes a parasite of the converter for energy conversion and therefore overcomes problems caused by the parasite.
Back to top
Fuel Cell Dynamic Modeling (Nehrir Group)
Physically-based dynamic models have been developed for PEM and solid oxide fuel cells. These models are used to evaluate the fuel cell response under different operating conditions and for a variety of applications.
Back to top
Fuel Cell Load Transient Mitigation (Nehrir Group)
In general, fuel cells are good energy sources under steady-state operation, but they do not respond well under transient conditions. In this research control algorithms are developed so that an auxiliary storage device (such as a battery bank) connected in parallel with the fuel cell power generation system is used to provide power to the load transient and mitigate the transient loads from affecting the fuel cell power plant. As a result, the fuel cell will move slowly from one operating point to another without being negatively affected by the load transient.
Back to top
Fuel Cell Power Generation System Modeling (Nehrir Group)
Models of Fuel cell power plants and power electronic interfacing devices (i.e., DC to DC converters and inverters) have been developed and interconnected. Using the above models, dynamic response and control of fuel cell power generation systems, including hybrid fuel-cell/wind/photovoltaic systems, are investigated in grid-connected and stand-alone configurations.
Back to top
Intelligent Controls in Fuel Cells (Shaw Group)
Investigating how intelligent controls that can be used to mitigate the effects of transients on fuel cell stacks, perform in-situ diagnostics of cells, and mitigate the degradation of cells under certain electrical loads.
Back to top
Modular design approach for DC/AC inverters in large scale SOFC power systems (Gao Group)
Dr. Hongwei Gao’s group is investigating the modular design approach for DC/AC inverters in large scale SOFC power systems and is developing a load sharing control scheme for the modules. The control scheme is expected to be able to lead to even load sharing among all modules at the steady state and transient conditions without requiring communication links.
Back to top
|
