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1. Novel Non-Precious Metals for PEMFC: Catalyst Selection through Molecular Modeling and Durability Studies (Branko N. Popov)
Supported by Department of Energy
Oxygen reduction catalysts with fast reaction rates and good stability are essential for DOEs mission of developing next generation fuel cells. Platinum is still considered the best electrocatalyst for the four-electron reduction of oxygen to water in acidic environments as it provides the lowest overpotentials and the highest stability. But, use of platinum catalysts increases the cost thus necessitating the reduction of Pt loading or the development of Pt-free catalysts. The goal of this project is to demonstrate the potential of the carbon-based electrocatalysts to perform as well as conventional Pt catalysts currently in use in MEAs with a cost at least 50 % less than a target of 0.2 g (Pt loading)/peak kW. The optimization of the catalyst composition is based on durability > 2000 h of continuous operation with less than 10 % power degradation. This work is being performed in collaboration with North Eastern University (NEU) and Case Western Reserve University (CWRU).
The specific objectives are:
(i) To develop highly active and stable carbon-based metal-free catalysts and carbon composite catalysts with strong Lewis basicity to facilitate oxygen reduction.
(ii) To optimize the active reaction sites for ORR as a function of carbon support, surface oxygen groups, nitrogen content, surface modifiers, pyrolysis temperature, porosity, and the concentration of the non-metallic additive.
(iii) To establish clear structure-property relationship using in situ synchrotron based x-ray absorption spectroscopy.
(iv) To conduct steady-state polarization measurements in PEM single cells and dynamic electrochemical tests at membrane electrode interfaces under fully hydrated conditions.
(v) To determine catalyst stability under long-term performance studies.
2. Development of Novel Method to Synthesize Oxygen Electrocatalyst: Catalyst Durability and Sintering Effect Studies (Branko N. Popov)
Supported by NSF/Center for Fuel Cells (USC)
The objective of the proposed research is to decrease the Pt loading (0.01 0.04 mg cm-2 in MEA) and to increase the activity and stability of low Pt catalyst deposited on USC-developed carbon support which is activated with nitrogen and oxygen functional groups. Also, graphitizing carbon support has been shown to prevent carbon corrosion and hence inhibit Pt particle sintering. We focus on stabilizing low Pt and its alloy catalysts by graphitizing the carbon support without losing the active surface area due to graphitization. The effect of surface area and pore size distribution on the activity and stability of Pt-based catalysts will be studied, and eventually modifications of pore size distribution will be done to accomplish enhanced activity and stability.
The specific objectives are:
(i) To synthesize low Pt catalyst on USC carbon composite support activated with different functional groups.
(ii) To synthesize low Pt catalyst on the graphitized carbon support.
(iii) To optimize post-treatment conditions.
(iv) To evaluate durability of low Pt catalyst loaded on USC-developed carbon support.
3. Development of PEM Fuel Cell Electrodes Using Pulse Electrodeposition (Branko N. Popov)
Supported by Faraday Technology, Inc.
Platinum is still considered the best electrocatalyst for the four-electron reduction of oxygen to water in acidic environments as it provides the lowest overpotentials and the highest stability. Increasing the oxygen reduction activity and/or platinum utilization of the gas diffusion electrode can lower the platinum in the electrode. Use of platinum catalysts increases the cost thus necessitating the reduction of Pt loading. Traditionally, platinum salts are reduced chemically by using a reducing agent. The ratio of Pt in carbon can be controlled by the initial concentration of Pt salts. However, when the Pt ratio is over 40 wt%, the colloidal solution is not stable enough to keep the particle size under 4 nm. The oxygen reduction activity depends on the surface area available for reaction and hence on the particle size. Increase in particle size results in the decrease of activity and utilization of platinum. Thus, the Pt/C ratio cannot be increased beyond 40 wt% by the traditional method without losing catalytic activity. Further, this limitation of Pt/C in carbon also imposes a limitation on decreasing the catalyst layer thickness. Since the ion exchange membrane used in PEM fuel cell is a solid type, the contact between membrane and Pt becomes a critical factor to obtain high performance. For this reason, Pt should be placed more close to the surface of electrode. The objective of this project is to develop a novel procedure based on pulse deposition for preparation of PEM fuel cell electrodes.
The specific objectives are:
(i) To develop high Pt/C ratio catalysts with 3-4 nm particle size and an effective catalyst layer thickness of 1-2 microns.
(ii) To optimize the gas diffusion layer through selection of carbon substrate.
(iii) To develop a procedure to coat uniformly a microporous carbon/PTFE/ionomer film on carbon cloth.
(iv) To optimize the hydrophilic character of the film surface.
4. Development of Nanostructured Catalyst for PEM Electrolyzer (Branko N. Popov)
Supported by Faraday Technology, Inc.
Regenerative fuel cell (RFC) is an energy storage device using hydrogen as the energy medium. It is a combination of two separate units for fuel cell and water electrolysis. In the recent years, to overcome the cost involved in using two separate units in RFCs, a more compact and simpler unitized RFC is being explored. In these systems, one electrode is used solely for the oxygen reactions (oxygen evolution in the electrolysis mode, oxygen reduction in the fuel cell mode), whereas the other operates as the corresponding hydrogen electrode (hydrogen evolution in the electrolysis mode, hydrogen oxidation in the fuel cell mode. Despite their apparent advantages, the unitized RFCs are still in their early stages of development because of several limiting factors. In particular, improvement of the kinetics of oxygen electrocatalysis for both reactions - oxygen reduction and water oxidation - is crucial for commercialization of the unitized RFCs.
To overcome the low overall conversion efficiency, we try to develop a unitized RFC system with optimized nanostructured electrocatalyst for the oxygen electrodes. This is accomplished by developing novel bi-functional oxygen electrode. The goal is to develop reversible oxygen electrode which is stable at high cathodic and anodic overvoltages. The peak separation between oxygen reduction and oxygen oxidation is approximately 0.6 V. To increase the reversibility of this electrode it is necessary to decrease this potential difference to less than 0.3 V. To overcome the high irreversibility of oxygen electrode it is necessary do develop multilayer nanostructured electrode materials with optimized porosity and to synthesize a catalyst capable of oxidizing the water at its reversible potential.
The following are the specific objectives:
(i) To develop novel nano-sized Pt alloy catalysts using pulse deposition techniques. The size of the particles (3 -5 nm) is controlled by the pulse current or potential and the duty cycle.
(ii) To fabricate novel gas non-carbon gas diffusion layer with improved kinetics and corrosion resistance properties.
5. Development of Low Cost Bench Scale Coating Process for Preparation of GDL (Branko N. Popov)
Supported by Fuji Photo Film, Inc.
In a PEMFC, the gas diffusion layer, which serves as a current collector, provides reactant gas access from flow-field channels to catalyst layer as well as passage for removal of product water from catalyst layer to flow-field channels. The gas diffusion layer typically adopts a dual-layer structure: the first layer is a macroporous layer of either carbon fiber paper or woven carbon cloth, and the second layer is a thinner microporous layer consisting of carbon black powder and some hydrophobic agent. The microporous layer is needed to provide proper surface pore sizes and also to enhance intimate electronic contact between catalyst layer and macroporous carbon layer. In general, it is desirable for fuel cell to operate at a relatively high current density in order to achieve the highest power output. This requires the gas diffusion layer to efficiently transport reactant gases to catalyst layer at a high rate. However, various problems of mass transport through the gas diffusion layers result from water flooding, dilution of the oxidant concentration and depletion of reactants along the flow channel. Therefore, it is necessary to optimize various physical and chemical properties that govern mass transport through the gas diffusion layers. The objective of this project is to develop the gas diffusion layers for PEMFC that will enhance the catalyst utilization and the overall fuel cell performance.
The specific objectives are:
(i) To investigate the effect of hydrophobic agent (PTFE) in microporous layer of carbon black powder on the characteristics of the gas diffusion layer.
(ii) To study the effect of pore size distribution on mass transport through the gas diffusion layer.
(iii) To establish the relationship between the gas permeability and the pore size distribution of the gas diffusion layer.
(iv) To examine the effect of impregnation methods of the Nafion solution on the fuel cell performance.
(v) To evaluate polarization sources in PEMFC from the cell current-potential relationship measured under various operating conditions.
6. Durability of SOFC Cathode in the Presence of Metallic Interconnects (Branko N. Popov)
Supported by General Electric and Department of Energy
One of the critical components in the SOFC is the interconnect, which permits an in-series voltage connection of individual fuel cell elements. Advances in the design and fabrication of the planar SOFCs resulted in reduction in operating temperatures to an intermediate range of 750oC 850oC that keep the cell power density and durability at the same level as those now operating at higher temperatures (~1000oC). At this temperature range one can use heat resistant alloys for interconnects. Chromium forming ferritic stainless steels are among the most promising alloy candidates due to their higher electronic conductivity, higher heat conductivity, lower cost and easier fabrication than those of a ceramic interconnects. However, the CrO2(OH)2 vapor from the surface oxide scales of metallic interconnects degrades the performance of the SOFC cathode. Increasing the applied pressure of fuel gases has shown enhanced utilization up to 75% which increases the power density. Under these severe conditions, the corrosion of interconnects and the subsequent Cr poisoning is also expected to be high. The overall objectives of the proposed research are: (i) to evaluate the polarization characteristics (increase of overvoltage as a function of time due to Cr poisoning) of LSFC cathodes when alloy is used as an interconnect, (ii) to determine the degradation mechanism of the cathode and the interconnect due to Cr poisoning, and (iii) to study the cathode performance of LSCF electrodes when coated alloy is used as an interconnect.
The specific objectives are:
(i) To evaluate the loss of electrocatalytic activity of LSCF for oxygen reduction as a function of time in the presence of metallic interconnects. The goal is to determine the extent of increase of the overvoltage with time due to growth of the oxide layer and the subsequent Cr poisoning. Impedance spectroscopy will be used to evaluate the variation of the polarization, ohmic and the overall resistance of the cathode/interconnect assembly with time.
(ii) By polarizing the cathode at different oxygen overpotentials to determine the Cr distribution throughout the electrode and electrolyte as a function of time. The change of the Cr distribution as a function of time will be determined by estimating the Cr concentration in the cross-section of the alloy by using EPMA and Fisherscope XDAL. The goal is to estimate any correlation between the overvoltage applied to the cathode and the extent of Cr poisoning.
(iii) To evaluate the Cr poisoning degradation mechanism.
(iv) To develop an efficient protective coating for metallic interconnects. This will be accomplished by studying the electrocatalytic activity for oxygen reduction of LSCF when alloy coated with cobalt base oxide or composites is used as an interconnect.
7. Development of Capacity Fade Model for Li-ion Batteries: Demonstration of the Applicability of Li-ion Batteries for Space Applications (Branko N. Popov)
Supported by NASA
Rechargeable batteries are used on all types of satellites for space applications, ranging from Geostationary Orbit (GEO) to Medium Earth Orbit (MEO) and Low Earth Orbit (LEO). Different orbits induce different constraints on the batteries used. A satellite in LEO uses its batteries far more often than a GEO satellite that is rarely in the Earths shadow cone. Lithium-ion batteries have approximately twice the energy density, both volumetric and gravimetric, of conventional space-qualified batteries such as Ni/H2 and are very promising for space applications. However, there are limited long-term test data available on lithium-ion batteries. The objective of this project is to demonstrate that the first principle model for capacity fade of Li-ion batteries developed in CEE to predict the capacity fade model of lithium-ion batteries is feasible for space application.
The specific objectives are:
(i) To experimentally characterize the cycling behavior of cells as a function of temperature, end of charge voltage and depth of discharge under LEO type conditions.
(ii) To tune the existing model to be operational at different temperatures and to predict the capacity fade and the change in impedance of a battery exposed to constraints of satellite in LEO conditions such as (a) orbit duration approximately 100 minutes, (b) eclipse 30 to 40 min per orbit, (c) number of cycles 12 to 16 per day, approximately 5,000 per year, (d) lifetime 8 years, i.e. 40,000 cycles and (e) depth of discharge 25 and 40 %.
(iii) To evaluate the effect on capacity fade of parameters such as the temperature, the charging rate, the depth of discharge, the end of charge voltage and the overvoltage of the parasitic reaction under LEO type conditions.
8. Development of a New Composite Cathode for Primary Batteries Based on AgV2O5 Doped with Polypyrrole (Branko N. Popov)
Supported by St. Jude Medical Co.
Silver vanadium oxide (SVO) has generated commercial interest in the arena of medical devices, and has become the cathode of choice in lithium primary batteries used to power implantable cardioverter defibrillators. The battery has the following deficiency: (i) the concentration polarization predominates at the electrolyte/electrode interface at high discharge rates, (ii) the resistance at both interfaces at the cathode and at the anode increases with increasing the discharge state, (iii) the battery has very high initial voltage drop, (iv) the rate capability is poor due to diffusion limitations, (v) the load voltage drastically decreases when high current pulses are used, and (vi) at high discharge current densities the resistance of the cell rapidly increases with increase of the discharge state. When high power pulses are used to discharge the battery, the concentration polarization limits the current and the power of the battery thus decreasing its rate capability. The objective of this work is to synthesize cathode materials based on SVO with lower particle to particle resistance, higher stability, low initial voltage drop, higher capacity and higher rate capability than currently available state of the art SVO cathode materials.
The specific objectives of the project are:
(i) To develop SVO composite materials doped with polypyrrole or Sr.
(ii) To synthesize cathode materials with optimized particle size which minimize the particle to particle resistance and improve the rate capability.
(iii) To optimize the stability of the cathode material.
(iv) To correlate the microstructure of the synthesized cathode materials with the electrochemical performance of the materials.
9. Development of Novel Process for Plating Nanostructured Ternary Alloys and Composites for Replacement of Cadmium Coatings (Branko N. Popov)
Supported by Office of Naval Research
Typical navy applications for cadmium plating include coating of steel and aluminum aircraft landing gear components and fasteners. A cadmium electroplate on steel has many advantages such as good lubricity, solderability, and low galvanic corrosion with aluminum. Cadmium plating offers an effective barrier protection to the substrate, especially in the marine environment. Apart from this, cadmium also offers sacrificial protection to the steel components under corroding conditions. However, cadmium deposition from cyanide baths gives rise to unacceptably high hydrogen intake by plated components of high strength, leading to hydrogen embrittlement. Also cyanide waste treatment is very expensive. To improve the barrier properties of zinc coating, research has been aimed at developing effective zinc based coating by alloying zinc with a more noble metal such as nickel. The overall objectives are to develop novel processes for plating nanostructured binary and ternary alloys and composites for replacement of Cd. The goal is by introducing a third element to induce barrier properties to the sacrificial Zn-Ni alloy. Also by introducing a third element in the alloy, the goal is to modify the rate of the hydrogen evolution reaction, the hydrogen proton recombination and adsorption kinetics at the surface in order to inhibit corrosion and impede completely hydrogen penetration in the alloy, thus eliminating the hydrogen embrittlement.
The specific objectives of the project are:
(i) To optimize pulse plating of nanostructured Zn-Ni, and Zn-Ni-SiO2 and Zn-SiO2 composites. The optimization is carried out through corrosion and hydrogen permeation studies and through evaluation of technological properties.
(ii) To optimize dc and pulse deposition of nanostructured Zn-Sn alloys, and Zn-Sn-SiO2 composites. The alloy optimization will be performed through corrosion and hydrogen permeation studies and through evaluation of technological properties.
(iii) To develop galvanostatic dc and pulse plating methods for deposition of nanostructured Zn-Ni-Sn alloys and Zn-Ni-Sn-SiO2 composites.
10. Investigations into the Performance of Various Corrosion Resistant Reinforcement Steels in Highway Bridges (Branko N. Popov)
Supported by South Carolina Department of Transportation
Serviceability and durability of concrete structures exposed to chlorides is seriously affected by corrosion. Concrete protects embedded steel from corrosion through its high alkaline environment. The high pH causes a passive and non-corroding protective oxide film to form on steel. Carbonation or the presence of chloride ions from deicers or seawater can destroy or penetrate the oxide film and consequently initiate corrosion. Several bridges and structures in South Carolina are subjected to severe chloride attack due to exposure to seawater in marine environments and to deicing salts added to bridge decks during winter months. One of the promising solutions pertains to the use reinforcement made of steels of increased corrosion resistance. Such materials include solid stainless steel, stainless steel clad high performance reinforcement, MMFX, and epoxy-coated reinforcing steel, among others. The focus of this project is in evaluating the corrosion performance of various reinforcing steels in lab scale and field studies.
We are studying the following steels as a viable alternative to carbon steel in the five span demonstration bridge to be built in South Carolina: (i) SS 316 clad by SMI and Stelax, (ii) Steel black with zinc anodes, (iii) MMFX 2 Steel and (iv) Steel black bars.
11. Processing of Materials for Improved Biocompatibility (Michael A. Matthews) supported by NIH
12. Material Compatibility with Liquid Carbon Dioxide (Michael A. Matthews) supported by Consolidated Systems Inc.
13. Parametric Studies of BASFs Purification Catalysts (Michael D. Amiridis) supported by BASF Co.
14. Synthesis of Supported Mono- and Multi-metallic Platinum Group Metal Catalysts with Controlled Particle Size and Composition (Michael D. Amiridis) supported by Toyota
15. Novel Bimetallic Catalysts for the Low Temperature Water Gas Shift Reaction (Michael D. Amiridis) supported by BASF Co.
16. Filamenotus Carbon from Waste Methane Streams: Process Development and Scale-Up (Michael D. Amiridis) supported by XLTech Group
17. Fundamental FTIR Studies of the Mechanism of NOx Reduction under FCC Regeneration (Michael D. Amiridis) supported by Grace-Davison
18. Reforming of Jet Fuel for Fuel Cell Applications (Michael D. Amiridis) supported by Boeing
19. Biomolecular and Biomechanical Engineering for Developmental Biology (Michael D. Amiridis) supported by NSF
20. Atomic Scale Design of a New Class of Alloy Catalysts for Reactions Involving Hydrogen (Michael D. Amiridis) supported by DOE
21. Expanding Clean Energy Research and Education Program at the University of South Carolina (Ralph E. White) supported by DOE
22. Life Modeling of Lithium-Ion Cells (Ralph E. White) supported by NRO
23. Rechargeable Lithium Ion Battery Operating Life Model (Ralph E. White) supported by MDA STTR
24. Modification of Ionomer Membranes to Improve Conductivity (Ralph E. White) supported by NSF STTR
25. Design and Manufacturing of Solid Oxide Fuel Cells (John W. Van Zee) supported by SC Research Centers of Economic Excellence Endowed Professorship Program
26. Fuel Cell Research (John W. Van Zee) supported by the State of South Carolina
27. Fuel Cell Design and Performance (John W. Van Zee) supported by DOE
28. Renewable Fuels for the Fuel Cell Economy (John W. Van Zee) supported by SC Research Centers of Economic Excellence Endowed Professorship Program
29. High Performance Electrolyzers for Hybrid Thermochemical Cycles (John W. Weidner) supported by DOE
30. Effect of Structure of Room Temperature Ionic Liquids on Organic Reactions Involving Electrochemically Generated Superoxide Ions (John W. Weidner) supported by NSF
31. REU Site: Green Chemistry in Chemical Engineering (John W. Weidner) supported by NSF
32. Model for a CFx Battery (John W. Weidner) supported by Sandia National Lab.
33. Dynamic Response of a Fuel Cell System on a Variable Frequency AC Power Bus (Roger A. Dougal) supported by NSF
34. Polymer Nanocomposites Research Group (Harry J. Ploehn) supported by USC NanoCenter
35. Polymer Nanocomposites as Future Materials for Defense and Energy Applications (Harry J. Ploehn) supported by Universal Technology Corporation/ AFRL/DOD
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