Debangsu Bhattacharyya and Raghunathan Rengaswamy
Department of Chemical and Biomolecular Engineering, Clarkson University
Energy in the form of electricity remains at the heart of the development of the modern technological civilization. Efficient utilization of the natural resources along with exploration of renewable and alternative energy sources is an important challenge facing this generation. Fuel cells are considered to be a promising candidate as they are not limited by the Carnot efficiency. Solid oxide fuel cell (SOFC) is a high temperature fuel cell 650oC-1000oC with increasing importance for stationary power house applications. High reactivity, comparatively inexpensive anode and cathode material, high power density, high level of usable heat and the possibility of using flexible fuels have made SOFC an attractive choice for utility and industrial applications.
In a tubular solid oxide fuel cell, as the size of the gas flow channels are increased for a given circumferential area, the velocity of the gaseous species decrease. This results in a higher residence time for the reactants thereby increasing the percentage conversion of the reactants. On the other hand, an increase in size leads to a reduction in the pressure drop across the cell. For a given exit pressure, this results in a reduced pressure inside the cell. The decrease in pressure reduces the molar concentration of the reactants at a given temperature affecting the conversion of the reactants and increasing the concentration overpotential of the cell. Therefore an optimum L/D ratio exists for a given circumferential area. In this poster, we will show the use of a detailed two dimensional steady state model for the optimization of the aspect ratio. In another optimization study, a graded loading of Ni at the anode is considered with the objective of reducing the temperature gradient across the cell. In a traditional SOFC, Ni loading in the Ni-YSZ anode remains uniform. If the Ni-loading near the channel is reduced, the diffusion length of the gaseous species will increase resulting in a higher concentration overpotential and a more pronounced temperature gradient towards the anode TPB. In contrast, a higher loading of Ni near the channel will result in a higher overall ohmic resistance of the cell and steeper temperature gradient near the channel. Computaional optimization studies on optimal loading of Ni in the Ni-YSZ anode for the minimization of the temperature gradients will be discussed in this poster.
Brian Bullecks, Debangsu Bhattacharyya, Gregory Campbell and Raghunathan Rengaswamy
Reduction of cost is the key in making PEM fuel cells (PEMFC) commercially viable. For reducing the overall cost of the stack, several approaches can be considered, such as increased power density at the same Pt-loading, reduction of cell hardware, reduction of the cell weight/power ratio etc. In order to reduce cost, we have developed a cylindrical PEMFC which achieves some of the objectives mentioned above. Typical PEM fuel cells are planar. Although the cylindrical geometry has been successfully used in other type of fuel cells such as solid oxide fuel cell (SOFC), it is not common in the case of PEMFC. We will discuss the development of a cylindrical PEMFC that has a higher current density than a planar cell using the same commercial 5 layer MEA and under the same operating conditions. The cell performance is tested using a manual test station (purchased from Electrochem Inc.). The test station consists of a gas management unit, which measures and controls the flow of the reactants to the cell and the back pressure of the channels. The unit also controls the cell temperature. The test station also consists of a humidification unit, which has bubble humidifiers operating at the desired temperature. The unit also maintains the temperatures of the gas transfer lines from the humidifier to the cell to avoid intermediate condensation. The cell performance is tested over a wide range of reactant flows, temperatures and pressures. In the entire range, the cylindrical cell is seen to perform better than the planar cell. The weight of the cylindrical is about ten times lesser than the planar cell. An EIS analysis of the cylindrical cell will also be presented.
Ulaganathan Nallasivam, Sang Youp Chae and Raghunathan Rengaswamy
Clean and efficient conversion of energy to useful forms is an important societal need. This has brought fuel cells into prominence as a potential source for energy conversion. Among the H2-O2 fuel cells, Proton exchange membrane fuel cells (PEMFC) are in an advanced state of development with potential applications in portable power generation. They are also considered the most promising technology for obtaining vehicles with intrinsic possibility of zero emissions. In spite of the advances made in PEMFC, technical advances and breakthroughs are still required to make this technology viable. Cost and reliability are two critical issues in the commercialization of the fuel cell technology.
Achievement of the reliability goals will depend on detailed phenomenological understanding of the various failure modes, and the ability to predict the behavior of fuel cells under these failure modes. Electrochemical impedance analysis (EIS) is an important approach and has been widely used for diagnostics. Several papers exist on the use of EIS for diagnostics and this appears to be the state-of-art in fuel cell diagnostics. Much of the previous work focused individually on a single problem such as flooding, anode poisoning and so on. It is also noted in that with just EIS, there is a risk of confusion when discriminating between flooding and catalyst poisoning.
In this paper, we will present some results on using wavelt analysis of current transients for fault diagnosis in fuel cell systems. We analyze the time-domain properties of the wavelet coefficients at different scales, which represent the frequency information for diagnostics. This provides a combined time-frequency analysis that is missing in pure spectral or pure time domain analysis. Experimental results on the proposed approach will be presented.
D. M. Goodale and P. A. Amodeo
The State University of New York College of Agriculture and Technology At Cobleskill
Fossil fuel use reduction is on the minds of many as the cost of a single barrel of crude oil rises to over $80. Currently, there are several alternative energy production possibilities. Each alternative depends on current land use modification. This poster will present a unique alternative energy idea with its focus on biowaste conversion into bioenergy through gasification. Although the concept of gasification is not new, the technology presented in this poster is truly innovative. The focal point of this highly efficient technology is its diverse biowaste feedstocks, which include animal, municipal, green, paper, biological and cafeteria wastes. Each of these biowaste examples are part of daily life and are traditionally spread on the land for decomposition or trucked to a landfill for burial or incineration.
A team of scientists based at SUNY Cobleskill is establishing a research and demonstration project to assess the efficiency of converting biowaste into alternative energy using the patent-pending Biomass Energy Solutions, Inc. gasifying system. Summarily, the collaborators will evaluate the physical and chemical analysis of biowaste to ascertain the quality and thermal energy of the biogas (syngas). Mathematical modeling will be employed to demonstrate the relationships among process variables. Modeling outcomes will be used to identify and manage intermediate research objectives to ensure efficient utilization of time and resources. Clarifying feedstock handling parameters will be the basis for optimizing operations through automated controls. Emphasis will be placed on maximizing energy rich products (hydrogen and/or methane) while minimizing or eliminating harmful emissions.
Matt Ganter, Chris Schauerman, Roberta DiLeo, Chris Sira, Brian Landi and Ryne Raffaelle
NanoPower Research Labs and Rochester Institute of Technology
Carbon nanotubes (CNTs) have been shown to possess various electrical, mechanical, and thermal properties that make them ideal for use in energy conversion and storage devices. CNT electrodes have been fabricated using both purified single wall carbon nanotubes (SWNTs) synthesized by laser vaporization and multi wall carbon nanotubes (MWNTs) synthesized by injection chemical vapor deposition (CVD). The details of the synthesis and purification procedures used in the production of the electrodes will be described; as well as an overview of the required characterization techniques (i.e. SEM, Raman, TGA, UV-Vis). Carbon nanotube "papers" were investigated as a replacement to conventional carbon electrodes in both PEM fuel cells and Lithium ion batteries. The high electrical conductivity and large surface area allow improved Li+ intercalation and cycleablility when compared to conventional graphite anodes in a rechargeable Li ion battery application. Similar CNT papers also provided increased PEM fuel cell performance when used as electrodes due to their porous nature, high conductivity and catalytic surface area, and ability to act as a metal catalyst support. The results from CNT papers used in each of these applications will be presented.
Nathan Darling, Annick Anctil, Brian Landi, James Worman, and Ryne Raffaelle
Functionalized semiconducting quantum dots (QDs) are being investigated as multifunctional additives in polymer photovoltaic devices. Quantum dots are capable of size-dependent optical absorption and acting as exciton dissociation centers and as a means of carrier transport in conjugated polymers. Generally, polymer photovoltaic devices rely solely on photon absorption by the conducting polymer and as such are bandgap(Eg)-limited (typically > 2 eV) in regard to solar spectrum conversion. Therefore, QDs with optical bandgaps below the conducting polymer Eg can allow composite devices to absorb a larger portion of the solar spectrum. However, the performance of the organic solar cells is primarily limited by charge transfer. In an effort to resolve this, quantum dots (QD) will be functionalized through different ligand exchange approaches. Functionalized QDs can be used directly in bulk heterojunctions or attached to other nanomaterials such as carbon nanotubes to assist in carrier transport. In this work II-VI and III-V QDs such as CdSe, InAs and Pbse have been functionalized using pyridine and aminothiophenol (ATP) ligands. Solar cells have been fabricated by dispersing the QDs into Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and Poly (3-hexylthiophene) (P3HT). Results on the device performance based on their spectral response and 1 sun air mass 1.5 current-voltage measurements will be presented.
Andrew Merrill, Annick Anctil, Oxana Petrichenko, Brian Landi, and Ryne Raffaelle
The development of lightweight polymeric solar cells which incorporate nanostructured materials has been receiving considerable attention by the scientific community recently. This development has been driven by the overarching goal of producing large area cost-effective photovoltaic arrays for terrestrial energy production. Typically, these devices comprise multiple polymer layers sandwiched between a transparent conductive electrode and a back metal contact. Optimization of layer thicknesses, polymer morphology, and nanomaterial concentrations represent significant challenges. Optimization of these device parameters are aimed at enhancing the exciton dissociation and carrier transport, and will ultimately translate into the overall efficiency of the device. The present work has investigated the properties of the Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate (PEDOT-PSS) layer including the relationship between thickness and device performance. In addition, we have evaluated the increase in electrical conductivity in the PEDOT-PSS layer through incorporation of carbon nanotubes. The dependence on the cell performance of the molecular weight conducting polymer absorber layers (e.g. poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene]- MEH-PPV) has also been student. A strong correlation between, this molecular weight, and subsequent thermal annealing, has been demonstrated on overall device performance. The power conversion efficiency results from simulated air mass zero and spectral response for each of these processing designs will be highlighted and the feasibility of such devices for terrestrial use will be discussed.
Ryan Aguinaldo, Cory Cress, Seth Hubbard, John Anderson, and Ryne Raffaelle
NanoPower Research Labs (NPRL) and Rochester Institute of Technology
The efficiency of state-of-the-art (SOA) crystalline solar cells consisting of III-V multi-junction architectures has recently surpassed 40% under solar concentration. Using a detailed balance approach, our theoretical model results indicate that the bandgap of the middle junction in such devices is slightly larger than ideal, causing it to be the limiting component within the current-matched stack. The incorporation of an InAs quantum dot (QD) array within the middle junction has been suggested as a viable means to improve the photo-generated current within this layer, resulting in a large improvement in the overall device efficiency. Historically these devices were cost prohibitive for terrestrial applications; however, their high efficiency, demonstrated reliability (in the harsh space environment), and new concentrator solar array designs have provide credence for use of this technology on earth.
The development of InAS QD solar cells (QDSC) requires a fundamental understanding of InAs QD arrays, the behavior of such structures within a single or multijunction SC, and a means to predict the performance of the devices in both space and terrestrial environments. We are developing theoretical methodologies to provide this understanding and to give incite with regards to material selection and device structure optimization. A first approach consists of detailed balance calculations, which provide performance limits of the QDSCs based on thermodynamic considerations. Additionally, single and multiple junction device simulations are being developed which solve the coupled 2-D Poisson's and continuity equations under various light intensities and external biases. A large experimental data set consisting of the spectral response, current-voltage characteristics, thermal response, and radiation tolerance of InAs QD arrays and single junction GaAs p-type / intrinsic / n-type (pin) SCs, in which InAs QDs are incorporated in the intrinsic region, has been compiled. Based on this data, we are utilizing parameter extraction techniques to ascertain the critical operational parameters which are subsequently incorporated in our 2-D device simulations enabling us to fit our experimental data, and therefore realistically predict the performance of novel QDSC structures. These modeling results will be discussed in the context of the applicability of InAs QDSC in space and terrestrial environments.
J. Zhang, K. Sasaki, M.B. Vukmirovic, M.H. Shao, J.X. Wang, M. Mavrikakis*, R.R. Adzic
Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973
*Department of Chemical & Biological Engineering, University of Wisconsin
Electrocatalytic oxygen reduction reaction has been the focus of considerable attention because of its slow kinetics and the need for better electrocatalysts with decreased Pt content for fuel cell cathodes. One promising way to make progress on these major difficulties is by using electrocatalysts made with a Pt monolayer supported on suitable substrates. We demonstrated this concept by synthesizing a new class of electrocatalysts, consisting of Pt and mixed metal-Pt monolayer on.pdf" substrates and Pt monolayer on non-noble metal - noble metal core-shell substrates. These electrocatalysts have up to twenty times higher Pt-mass specific activity than the commercial Pt catalysts. Mixed metal-Pt catalysts owe their enhanced activity to reduction of Pt-OH formation while electrocatalysts consist of Pt monolayer on core-shell substrates owe their enhanced activity to electronic and geometric effects introduced by core-shell substrates.
Christopher Bailey, Ross Robinson, Seth M. Hubbard and Ryne Raffaelle
Recent proposals have pointed to alternate approaches to improving solar cell efficiency using nanostructured materials such as quantum dots and quantum wires. Insertion of quantum dots (QDs) into the intrinsic region of a single junction p-type/intrinsic/n-type (PIN) solar cell leads to formation of an intermediate band within the bandgap of the host. This approach takes advantage of the extended absorption spectrum of the QDs and allows for enhancement of the short circuit current and overall efficiency improvements. Initial theoretical predictions for conversion efficiency using QD enhancement are near 63%. This is almost double the 33% maximum efficiency of a single junction solar cell. Improving the efficiency of solar cells is a paramount concern in the space photovoltaic community. Additionally, with recent developments in solar concentrator technology, these ultra-high efficiency cells are becoming a more feasible option for terrestrial applications.
In this work, QD enhanced solar cells were grown using organometallic vapor phase epitaxy. QD growth was first optimized for both dot size and quality. Four standard GaAs PIN cell structures were then grown consisting of a standard PIN cell without QDs, cells with both 1 and 5 layers of QD in the i-region and a cell with 5 layers of strain compensated QDs in the i-region. An array of solar cells was fabricated on each type of QD structure and power conversion efficiency and spectral response were evaluated for each type of structure. The dependence of efficiency and spectral response on the type of QD structure will be highlighted. Feasibility of this solar cell design for both terrestrial concentrator and space power application will be discussed.
Platinum Nanofiber Network as PEMFC Electrodes
Zexuan Dong, Jianglan Shui and James C. M. Li
University of Rochester
For commercialization of proton-exchange membrane fuel cells (PEMFCs), the durability of electrode catalyst must be significantly improved. PEMFCs typically use carbon supported Pt nanoparticles for both anode and cathode. But the catalytic surface area and hence the efficiency of the fuel cell gradually decreases due to Pt nanoparticle migration and agglomeration during the fuel cell operation. Recent studies showed that the particle growth was accelerated during a potential sweep test. In this study, two kinds of nano-fiber Pt electrode are prepared and compared with commercial Pt/C (5 wt.% Pt nanoparicles E-TEK) in terms of their durability in PEMFC during potential cycling. X-ray diffraction (XRD), transmission electron microscopy (TEM) and inductively coupled plasma-mass spectroscopy (ICP-MS) are used to characterize the catalysts before and after the potential sweep test.
Lynn Rice, Zhouying Zhao, Harry Efstathiadis and Pradeep Haldar
College of Nanoscale Science & Engineering, University at Albany
Due to a strong demand for renewable energy and a widespread and growing interest in organic semiconductor based devices, organic solar cells have been objects of increasing interest and development during the last decade. Organic solar cells offer a range of advantages over traditional, silicon based photovoltaic devices including their low cost, light weight, and processability on large area flexible substrates. Among organic photovoltaic systems, composed of blends of conductive polymers acting as electron donors (p type materials) and materials exhibiting high reduction potentials acting as electron acceptors (n type materials), the poly-3-hexylthiophene/ phenyl-C61-butyric acid methyl ester (P3HT/PCBM) bulk heterojunction is considered to be a model system. In this system, which has developed record efficiencies (6%) among polymeric photovoltaics, the conjugated polymer P3HT acts as an electron donor and the fullerene derivative PCBM is the electron acceptor. By spin casting blend films of these materials onto indium tin oxide coated glass substrates along with a layer of poly-3,4, ethylenedioxythiophene polystyrenesulfonate (PEDOT-PSS) and depositing aluminum as a front contact and cathode, we have synthesized polymeric photovoltaic devices that are up to 2% efficient in power conversion. Herein, the fabrication (using non-vacuum methods) and the characterization by photocurrent-voltage measurements, atomic force microscopy, scanning electron microscopy, and ellipsometry of these 2% percent efficient organic solar cells is presented.
Brittany Higgins, Manisha Rane-Fondacaro, Pradeep Haldar, Vasantha Amarakoon, Herbert Giesche
College of Nanoscale Science & Engineering, University at Albany & Alfred University
Solid oxide fuel cells (SOFC) are a highly efficient energy source that provide clean conversion of energy into electricity. Currently, high temperature SOFCs operating at approximately 1000°C are the dominating form of SOFC. High temperature operation yields high efficiency, but limits the material selection of electrodes and interconnects. Low temperature operation reduces the ionic conductivity of the electrolyte and hence lowers the SOFC efficiency. Gadolinia doped Ceria (GDC) is an electrolyte candidate for intermediate temperature SOFC (IT-SOFC) due to its high ionic conductivity in the range of 450°C-600°C. However, Ce4+ reduces to Ce3+ in low oxygen partial pressure, thus increasing the electronic conductivity. Electron trapping layers are introduced in the structure in order to decrease the electronic conductivity. Alternating nano-layers (Al2O3 /CoO/GDC) were deposited onto quartz substrates using RF sputter deposition in order to produce uniform dense layers. The purpose of this study is to examine the effects of alternating insulating nano-layers with a conducting nano-layer of GDC. Deposition temperatures was varied between room temperature and 600°C to determine its effect on conductivity. The conductivity of GDC was studied as a function of temperature and oxygen partial pressure using 2-probe impedance spectroscopy. The composite electrolyte was characterized using SEM-EDS, AES, and X-ray diffraction used to determine the effects of processing parameters on density, grain size, and conductivity.
Jeff Wells, Erin Bedford, Harry Efstathiadis and Pradeep Haldar
College of Nanoscale Science & Engineering, University at Albany
Solar energy has the potential to be a clean and efficient alternative to traditional energy sources. The technology to make high-efficiency solar cells is available, but the cost of materials and manufacturing is currently too great to be considered a practical replacement for everyday purposes. Traditional cells are silicon based and have the disadvantages of being expensive and inflexible. In response, an environmentally friendly CIGS solar cell has been produced. The p-type absorber layer is made from sputtered copper, indium and gallium, followed by selenization. The traditional n-type absorber layer is made of cadmium sulfide (Eg ~ 2.4 eV), but the toxicity of the cadmium sulfide makes it harmful to the environment. Zinc sulfide, which has a slightly larger band gap (Eg ~ 3.7 eV), could be a viable replacement of CdS that could also enhance the CIGS cell performance. An efficiency of 18.6% has been achieved by Nakada and NREL using ZnS, deposited by chemical bath deposition (CBD).
The goal of our project is to produce a CIGS solar cell of high efficiency and low manufacturing cost over large areas; this requires the use of low-cost, non-vacuum processes. Our research was focused on the use of CBD to deposit the ZnS buffer layer. Up to 7 µm-thick, continuous, and homogeneous ZnS films were deposited on glass substrates at room temperature, from zinc sulfate (ZnSO4), ammonia (NH3) and thiourea (SC(NH2)2),. The film growth rate was found to be 24 nm/min.. Scanning electron microscopy, energy dispersion spectroscopy, Auger electron spectroscopy, Uv-vis spectroscopy, and spectroscopic ellipsometry were used to characterize the resulting films. By adjusting the deposition parameters such as bath temperature, concentration, time, and PH, the film growth was optimized in terms of growth rate, composition, and impurities such as oxygen and nitrogen. The film characteristics deposited on CIGS/Mo/glass along with properties of the ZnS/CIGS interface will also be reported.
Understanding electrochemical phenomena and manipulating electrochemical active sites at the nanometer scale are some of the major benefits that nanotechnology provides to fuel cells. In this work a non-vacuum, aerosol assisted deposition (AAD) method has been developed, to grow highly oriented nanoparticles and thin continuous films of platinum, as well as pure Pt oxide on a variety of substrates. Platinum nanoparticles of various sizes were successfully synthesized on Si, silicon dioxide coated Si substrates and carbon nanotubes. The size and density of the nanoparticles was found to depend strongly on the process parameters. The particles showed preferential orientation of (111) that was independent of substrate used. The resulting nanoparticles were characterized by Scanning Electron Microscopy (SEM), X-Ray Diffraction Spectroscopy (XRD), X-Ray Photoelectron Spectroscopy (XPS) and catalytic activity using half-cell Current-Voltage measurements in order to obtain information about their morphology, crystallinity, composition and performance. Pt oxide films were obtained by controlling the deposition parameters. Identification of the pure oxide films was performed by XRD and XPS and their morphology was characterized by SEM. Therefore the method developed can deposit uniform coatings of highly oriented, pure Pt nanoparticles, Pt films and Pt oxide films without the need of any substrate pretreatment and without altering the structure and features of the substrate (e.g. porosity, specific area). This technique has the potential for designing and fabricating high performance nanoengineered fuel cell electrodes with reduced platinum loading and improved catalyst utilization.
Thin film solar cells based on polycrystalline silicon (poly-Si) are one of the most promising approaches to substantially reduce production costs of photovoltaic devices. Silicon has the advantage of being an abundant material, nontoxic, and stable and the disadvantage of low absorption characteristics can be overcome by advanced light trapping structures. For efficient cost reduction of photovoltaic devices, cheap foreign substrates such as glass ought to be employed. In the present work, successful high deposition rate (70nm/min) of silicon films by e-beam evaporation technique is reported. E-beam evaporation of silicon was selected because it provides a much higher deposition rate than all other low-temperature deposition methods such as RF sputtering and plasma enhanced chemical vapor deposition. Non-doped silicon films were deposited by e-beam evaporation (ATC ORION 8-E system) on Si wafers and on borofloat glass substrates at the substrate temperature range from room temperature (RT) to 700oC at 10-7 Torr process pressure. The e-beam voltage and current were kept constant at 75kV and 0.2A, respectively. Characterization of resulting film properties has been performed to determine their dependence on deposition parameters by cross section scanning electron microscopy, spectroscopic ellipsometry, Raman spectroscopy, atomic force microscopy, and Auger electron spectroscopy. Raman spectra of the films deposited at RT showed a broad peak at around 480 cm-1, which is typical spectrum of an amorphous film. The oxygen and nitrogen concentration in the bulk of the films was found to be below the detection limit of AES while the surface root-mean-square roughness of a 500nm-thick film was found to be about 1nm. The properties of films deposited at 700oC and the aluminum-induced crystallization of a-Si on glass substrates, for producing continuous poly-Si films at low temperatures, will be reported.
Microwave Synthesis of Rare Earth Stabilized Zirconia
Brandon J. Striker, Gary Del Regno & Vasantha R.W. Amarakoon
NYS Center for Advanced Ceramic Technology (CACT) at Alfred University
Rare earth oxides including dysprosia, gadolinia,europia, and samaria were researched as potential zirconia stabilizers. The powders were synthesized through a modified sol-gel process,which utilized dissolved hydrated nitrate solutions, or hydroxide solutions, of the rare earth oxides and zirconia n-propoxide. The powders were both calcined and later sintered using 2.45GHz microwave radiation and conventional procedures. Particular emphasis explored microwave calcinations and sintering compared to conventionally processed materials.X-ray diffraction patterns illustrated crisper, sharp peaks corresponding to the cubic and tetragonal phases compared to conventional processing.The patterns gathered suggest there may be additional phenomena creating higher order micro-crystallinity in the microwave processed samples. Information including XRD phase information, grain size, and ionic conductivity for the stabilized zirconia samples will be presented.
Investigation of CuO stabilized Zirconia as an Electrolyte for Solid Oxide Fuel Cell Applications
Lee Crumley, Gary Del Regno & Vasantha R.W. Amarakoon
NYS Center for Advanced Ceramic Technology (CACT) at Alfred University
Copper oxide stabilized Zirconia materials having molarconcentrations of CuO of 10,15,20,25, and 30% were subjected to multiple tests to determine if a stable lattice structure could be formed using either conventional or microwave calcination and sintering processes. The purpose of this investigation was to confirm previous work in this area and to determine if these materials could be utilized for solid oxide fuel cells (SOFC). These materials were synthesized from a sol-gel precipitation method to yield nano-sized particles. Calcinations of powders were performed at 600 C using both conventional and microwave heating. Pelletized samples were sintered at 1600 C conventinally and at 1650 C in the microwave furnace. X-ray diffraction data and environmental scanning electron microscopy confirmed the formation of tetragonal nano-grain particles of CuO stabilized Zirconia powders, and indicated crystalline de-stabilization after sintering. Conductivity measurements were performed and illustrated the possibility of this material as being potentially viable for electrolyte applications in solid oxide fuel cells.
Fabrication of CeO2/Al2O3 Nano Composites for SOFC Applications
Vasantha R.W. Amarakoon, Rajalekshmi Chockalingam & Herbert Giesche
NYS Center for Advanced Ceramic Technology (CACT) at Alfred University
Gadolinium doped Cerium Oxide is a potential electrolyte for use in intermediate operating temperature (500°C-600°C) solid oxide fuel cells (SOFC). Although they are superior oxygen ion conductors, they are prone to reduction at lower oxygen partial pressure; thus showing n-type electronic conductivity reducing the efficiency of the SOFC. Nano-crystalline processing offers a new route for synthesizing CeO2/Al2O3. Composites can be designed with unique interfacial characteristics to overcome these limitations without reducing the overall ionic conductivity of the electrolyte. CeO2/Al2O3 nano-composites were prepared using a sol-gel chemical synthesis technique. These powders were calcined, dry pressed and consolidated using both conventional and microwave sintering procedures. X-ray diffraction, SEM, TEM/EDS microstructure and electrical conductivity measurements were used to determine the effect of composition, sintering procedure on the microstructure and properties of Gd doped CeO2/Al2O3 composites. 4-Point DC conductivity as well as AC impedance spectroscopy measurements as a function of Po2 and temperature were used to determine the electron trapping behavior of CeO2/Al2O3 composites in comparison to Gd doped CeO2 samples. Improvements in electrical and mechanical properties of composite materials indicate their usefulness as candidate electrolyte materials for low temperature SOFC applications.
Similar nano-crystalline coating and microwave sintering techniques are being used to fabricate a variety of nano-composite ceramics for electrical, optical, mechanical and thermal applications such as IC substrates, cutting tools, light emitting diodes and non lead piezoelectrics.
Seth L Knupp, Wenzhen Li, Odysseas Pachos, Thomas Murray, Pradeep Haldar
College of Nanoscale Science and Engineering at the University at Albany
In the Proton Exchange Membrane Fuel Cells (PEMFCs), degradation of the stack voltage and cost are two main factors hindering the commercialization. Degradation of the cell voltage is primarily due to the oxidation of the carbon support which results in dissolution and aggregation of the catalytic Pt nanoparticles. We show methods of preparing highly dispersed Pt nanoparticle on elevated surface area carbon supports which will prolong the cells lifetime. Platinized carbon nanotubes and carbon nanofibers are prepared using intermittent microwave irradiation (IMI) and conventional refluxing method and characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy. The two preparation techniques showed similar results and they were both able to form crystalline nanoparticles less then 3nm in diameter. Support morphology and diameter were found to have a great effect on the average particle size. Platinum loading also had a great effect on particle size and agglomeration was prevalent.
Derrick Mott, Peter Njoki, Lingyan Wang, Jin Luo, and Chuan-Jian Zhong
College Department of Chemistry, State University of New York at Binghamton
Fuel cells are becoming increasingly attractive power sources for mobile and stationary applications such as on-board electric power sources for advanced propulsion systems, non-polluting electric vehicles and portable devices because of the high conversion efficiencies and low pollution. Fuel cell components enable fuel cell commercialization. Catalysts constitute one of the key components in these devices (~30% of the cost for fuel cell manufacturing). A key challenge to the ultimate commercialization of fuel cells is thus the development of active, robust and low-cost catalysts. We have been developing novel nanostructured multimetallic catalysts to address this challenge. One example area of our research is the design and engineering of bimetallic/trimetallic nanoparticles with controlled size, shape, composition, and morphological properties. The understanding of the surface properties versus bulk properties of such nanostructured catalysts is essential for exploiting their synergistic electrocatalytic properties for both cathode and anode reactions in fuel cells. This poster describes the recent findings of our investigations using novel synthetic/processing approaches and advanced characterization techniques. Results for some of the promising nanostructured catalysts (e.g., Au, AuPt, PtNiFe, etc) with controlled sizes (2-5 nm) and alloy composition and phase properties will be discussed. The results have revealed some important insights into the understanding of the relationship between the electrocatalytic properties (activity, stability and cost) and the nanostructural properties of the catalysts. In partnerships with scientists and engineers in industries (e.g., Honda, NSC Technology, etc), we are also investigating a number of critical issues related to practical fuel cell applications of the nanostructured catalysts.
Wentao Wang, Tianhua Yu, Pradeep Haldar
College of Nanoscale Science and Engineering at the University at Albany
A new screen printing paste was developed for preparation of catalyst coated membrane (CCM) using screen printing technique. It has a very long shelf life and can avoid catalyst and CCM ignition during the preparation process. A 15-micron continuous and uniform catalyst layer can be deposited directly on a Na+ Nafion 112 membrane in one pass with this screen printing paste. The SEM images show that the CCM made with this method exhibits better catalyst layer uniformity compared with the CCM made with spraying coating method. A simplified CCM preparation process was developed based on this new screen printing paste. The new CCM fabrication process looks attractive to replace the conventional thin film decal membrane electrode assembly (MEA) preparation methods.
C. Dangler, M. Rane, P. Haldar
College of Nanoscale Science and Engineering at the University at Albany
In order to maximize the capacitance and thus the energy density of electrochemical double layer capacitors (EDLC) activated carbon electrodes have been investigated. High surface area, mesoporous, activated carbon, has been bound with Teflon 6C to form freestanding electrodes. Brunauer-Emmett-Teller method (BET) surface area measurements, performed before and after electrode fabrication, show that 80% of the surface area is retained during the fabrication process. Electrochemical characteristics of the electrodes were determined using a half-cell test with 1M H2SO4 as the electrolyte. Specific capacitance values of 15 F/g have been achieved.
Hazem Tawfik1, 2, Yue Hung 1, and Devinder Mahajan2, 3, 4
1Farmingdale State College, State University of New York, Farmingdale, NY 11735
2Advanced Energy Research and Technology Center (AERTC), Stony Brook University, Stony Brook, NY 11794-2275
3Materials Science and Engineering Department, Stony Brook University, Stony Brook, NY 11794-2275
4Energy Sciences and Technology Department, Brookhaven National Laboratory, Upton, NY 11973
Metallic bipolar plates offer an attractive alternative for PEM fuel cell operation because of their higher mechanical strength, easier manufacturability, and lower interface contact resistance than graphite composites that are currently considered the industry standard. Unlike graphite, metals have excellent potential for cost effective high volume manufacturing techniques such as stamping and die casting fabrication processes.
In our study of bipolar plates for PEM, six single PEM fuel cells were identically deigned, manufactured and operated under similar conditions 70oC, 96% R.H. and 10 psi pressure for both hydrogen and Air (Oxygen) as reactant gases. Four out of the six cells were fabricated of aluminum bipolar plates that were coated with high corrosion resistant carbide-based alloy. The other two cells were fabricated of graphite composites to provide a reference of comparison and benchmarking for PEM fuel cell performance. Both metal and graphite PEM cells showed steady performances with no power degradation, however the average electric power output from the metallic cell considerably exceeded that produced with graphite. This is attributed to the bulk and interfacial contact resistances (ICR) of the corrosion-resistant coatings on the aluminum bipolar plates that are considerably lower than graphite composite. Samples of byproduct water produced during the single fuel cells operation were also collected and tested for the existence of trace metals (such as chromium, nickel, carbon, iron, sulfur and aluminum) using mass spectroscopy.
Samples of the bipolar plates and the Membrane Electrode Assembly (MEA) were collected and tested from both the cathode and the anode side of a single cell after one thousands hours of normal operation under cyclic loading. Samples from both the anode and the cathode were subjected to Scanning Electron Microscopy (SEM) measurements to detect any surface changes. The measurements were supper imposed to identify the locations and zones of anomalies to conduct further analysis focused on these zones. X-ray Diffraction (XRD) analysis was also performed on samples obtained from the same samples of the MEA that was in operation for 1000 hours with metallic bipolar plate based fuel cell. The analysis of the SEM measurements indicated the possibility of the dissociation and dissolution of nickel chrome that is used as a binder for the carbide based corrosion resistant coating with the substrate. The X-ray study suggested that the tendency for the catalyst growth could result in power degradation.
Glenn Musano 1Hazem Tawfik 1,2, , and Devinder Mahajan2, 3, 4
Thamarai selvi Devarajana, Seiichiro Higashiyab, Manish Ranea, Jeremy Snydera, John T. Welchb and Pradeep Haldara
aCollege of Nanoscale science and Engineering, University at Albany, NY bDepartment of Chemistry
The electronics industry is constantly demanding portable energy storage devices that are smaller, lighter, more powerful, and higher in energy than the previous generation. Electrochemical capacitors have show themselves as a viable energy storage alternative. EDLC has long cycle life and high power density compared to batteries. However they have low energy density. This research attempts to increase the energy density of EDLC without compensating power density. Since energy is proportional to square of decomposition voltage, various electrolytes which can give high decomposition potential were synthesized and tested. Small volume EDLC test cells were developed. EDLC performance was calculated using Cyclic voltammetery, Constant current charge/discharge and Electrochemical impedance spectroscopic techniques.
Navaneetha Santhanam, Larry Walker
Biological and Environmental Engineering, Cornell University, Ithaca NY
A rapid high-throughput cellulase binding assay using microwell plates was developed to quantify cellulose- bound fractions of fluorescently labeled Thermobifida fusca cellulases Cel5A, Cel6B and Cel9A alone or in synergistic mixtures. These cellulases were labeled with Alexa Fluor 594, Alexa Fluor 350 and Alexa Fluor 488, respectively, without losses in activity on bacterial micro-crystalline cellulose. Controlled experiments were conducted (1) to ascertain whether individual labeled cellulases could be accurately quantified using microwell plates; (2) to investigate whether the fluorescent signal of one labeled cellulase could be reliably filtered from the signals of other labeled cellulases in ternary mixtures to accurately quantify individual cellulases; (3) to verify the thermostability of fluorescent signals of the labeled cellulases; and (4) to assess cooperative or competitive cellulase binding in ternary mixtures. Experiments clearly demonstrated that the microwell plate reliably yielded accurate measurements of cellulase concentrations in single cellulase reactions as well as in multi-cellulase mixtures. In addition, the fluorescent signals remained stable at 50°C over the entire 4h time course of the experiments. This high-throughput measurement system also revealed 13% greater binding for Cel6B-AF350 and 11% lower binding for Cel9A-AF488 than what was observed when these cellulases were reacted with cellulose alone.
Stephane Corgie, Corinne Rutzke, Larry Walker
Stephane Corgie, Ed Evans, Larry Walker