bluuebunny/crossref_metadata_2025_split huggingface dataset:
The DOE National Hydrogen Storage Project: Recent Progress in On-Board Vehicular Hydrogen Storage
Authors: Read Carole , Petrovic John , Ordaz Grace , Satyapal Sunita 
Published: April 2011

ABSTRACTHydrogen is under consideration by several countries for its potential as an energy carrier for transportation applications. In order to compete with vehicles in use today, hydrogen-powered vehicles will require a driving range of greater than 300-miles in order to meet customer needs and expectations. For the overall vehicular light-duty fleet, this dictates that a range of 5 to 13 kg of hydrogen be stored on-board (assuming a fuel cell power plant) within stringent system weight, volume, and cost constraints. Vehicular hydrogen storage thus constitutes a major scientific and technological challenge. To meet this challenge, the U.S. Department of Energy (DOE) initiated a “National Hydrogen Storage Project” with roughly 40 universities, 15 companies and 10 federal laboratories, actively engaged in hydrogen storage research. Centers of Excellence in metal hydrides, chemical hydrides, and carbon-based materials have been established, as well as independent university and industry projects in the areas of new concepts/materials, hydrogen storage testing, and storage system analysis. Recent technical progress in each of these areas is discussed.
High Throughput Screening of Complex Hydrides for Hydrogen Storage
Authors: Lewis Gregory , Sachtler J. W. Adriaan , Low John J. , Lesch David A. , Faheem Syed A. , Dosek Paul M. , Knight Lisa M. , Jensen Craig M. 
Published: April 2011

ABSTRACTThe discovery that dopants, such as Ti, cause NaAlH4 to reversibly desorb H2 at mild conditions has spurred a great deal of research into complex metal hydrides. However, no complex hydride meets the targets for automotive hydrogen storage. Our approach is to accelerate the rate of discovery of improved hydrides and dopants through the combination of Virtual High Throughput Screening (VHTS) and Combinatorial Synthesis and Screening (CSS). Our CSS methods will allow us to screen thousands of samples in a year. These samples will be prepared by ball milling mixtures of hydrides and dopants similar to the established method of preparing Ti doped NaAlH4. VHTS exploits a molecular mechanics method to screen a thousand phases in a month. The combination of combinatorial methods and VHTS will help us discover the most promising complex hydrides for hydrogen storage. We will show the results of our medium throughput CSS and VHTS as applied to the NaAlH4–LiAlH4 – Mg(AlH4)2 mixed alanate compositions.
Hydrogen Storage in Carbon Nanoscrolls: A Molecular Dynamics Study
Authors: Coluci Vitor , Braga Scheila F. , Baughman Ray H. , Galvão Douglas S. 
Published: April 2011

ABSTRACTWe carried out molecular dynamics simulations with Tersoff-Brenner potentials in order to investigate the hydrogen uptake mechanisms and storage capacity of carbon nanoscrolls (CNSs). CNSs are jelly roll-like structures formed by wrapping graphene layers. Interlayer adsorption is an option for this material, which does not exist for single and multiwalled carbon nanotubes. We analyzed the processes of hydrogen physisorption and uptake mechanisms. We observed incorporation of hydrogen molecules in both external and internal scroll surfaces. Insertion in the internal cavity and between the scroll layers is responsible for 40% of the total hydrogen adsorption at 77 K.
Corrosion Resistance of TiN Coatings Prepared by Filtered Cathodic Vacuum Arc Process
Authors: Wu Jin-Bao , Tsai Yin-Wen , Shih Chin-Te , Li Mei-Yi , Leu Ming-Sheng , Lai Chiou-Chu 
Published: April 2011

ABSTRACTFor the purpose of developing the corrosion-resistant and low-cost metallic bipolar plates for direct methanol fuel cell (DMFC), Ti mesh, stainless steel and Si(100) were coated with TiN by using the filtered cathodic vacuum arc system (FCVA). These TiN films have received considerable attention because of its high anti-corrosion behavior and low contact-resistance. In order to improve the corrosion protective ability of TiN films and decrease pinholes of coating, growth modifications such as thickness of the coatings and bias applied to substrates have also been carried out. The microstructures and composition of TiN film were identified by the instrumental analyses such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The corrosion behavior of TiN coatings was studied in 0.5 M H2SO4 solutions by using potentiodynamic polarization method. The DC bias of −150 V was applied to the substrates to achieve a dense structure of approximately 400 nm coating of TiN, so that good corrosion protection of the Ti mesh and stainless steel substrates can be achieved. The TiN coating on stainless steel exhibited excellent corrosion behavior especially in lower corrosion current than 2×10−7 A/cm2.
Ruthenium-Iridium Oxide Films Prepared by MOCVD and their Electrocatalytic Activity for Oxygen Evolution
Authors: Torres M.Z. Figueroa , Garduño M. Hesiquio , Estrada E. M. Arce , García J. R. Vargas 
Published: April 2011

ABSTRACTRuthenium-iridium oxide films were prepared in an horizontal hot-wall MOCVD apparatus and their electrocatalytic activity was investigated in the oxygen evolution reaction. Metal-acetylacetonates were used as precursors and oxygen as the reactant gas. Appropriate deposition conditions for obtaining bi-metallic oxide films were found to be deposition temperature (Tdep), 673 K and total pressure (Ptot), 133.32 Pa. X-Ray diffraction (XRD), Rietveld refinement and scanning electron microscopy (SEM) results demonstrated that the MOCVD method is a viable alternative to grow RuxIr1−xO2 films consisted of a single-phase with a very homogeneous distribution of elements. The electrocatalytic activity of the RuxIr1−xO2 films was investigated by cyclic voltammetry and anodic polarization curves in a 0.5 M H2SO4 solution at room temperature. The single-phase Ru0.4Ir0.6O2 films showed to be very promising for the oxygen evolution reaction due to a synergistic effect.
Properties of Carbon-doped TiO2 (Anatase) Photo-Electrodes
Authors: Enache Cristina S. , Schoonman Joop , van de Krol Roel 
Published: April 2011

ABSTRACTTo enhance the visible light absorption of anatase TiO2 photo-electrodes, the material was doped with carbon by two different methods: i) by spray pyrolysis under a CO2 atmosphere, and ii) by a post-deposition thermal treatment in a hexane-containing environment. For the hexane-treated samples, most of the carbon is located at the surface, from which it can be removed by re-oxidation at elevated temperatures. In addition, both methods seem to result in the presence of small amounts of carbon in the bulk of the material, as deduced from a small red-shift of the absorption edge of TiO2.
New Directions for Nanoscale Thermoelectric Materials Research
Authors: Dresselhaus M. S. , Chen Gang , Tang M. Y. , Yang R. G. , Lee H. , Wang D. Z. , Ren Z. F. , Fleurial J. P. , Gogna P. 
Published: April 2011

ABSTRACTMany of the recent advances in enhancing the thermoelectric figure of merit are linked to nanoscale phenomena with both bulk samples containing nanoscale constituents and nanoscale materials exhibiting enhanced thermoelectric performance in their own right. Prior theoretical and experimental proof of principle studies on isolated quantum well and quantum wire samples have now evolved into studies on bulk samples containing nanostructured constituents. In this review, nanostructural composites are shown to exhibit nanostructures and properties that show promise for thermoelectric applications. A review of some of the results obtained to date are presented.
New Directions in Bulk Thermoelectric Materials Research: Synthesis of Nanoscale Precursors for “Bulk-Composite” Thermoelectric Materials
Authors: Tritt Terry M. , Zhang Bo , Gothard Nick , He Jian , Ji Xiaohua , Thompson Daniel , Kolis Joe 
Published: April 2011

ABSTRACTOver a decade ago it was predicted that nano-scaled thermoelectric (TE) materials might have superior properties to that of their bulk counterparts. Subsequently, a significant increase in the figure of merit, ZT (ZT > 2), has been reported for nano-scaled systems such as superlattice and quantum dot systems constituently based on those more commonly used bulk TE materials (e.g., Bi2Te3 and PbTe). However, the challenge remains to achieve these higher performance results in bulk materials in order to more rapidly incorporate them into standard TE devices. Recent theoretical work on boundary scattering of phonons in amorphous materials indicates that micron and submicron grains could be very beneficial in order to lower the lattice thermal conductivity and yet not deteriorate the electron mobility. The focus in this paper will be to highlight some of our new directions in bulk thermoelectric materials research. Thermoelectric materials are inherently difficult to characterize and these difficulties are magnified at high temperatures. Specific materials will be discussed, especially those bulk materials that exhibit favorable properties for potential high temperature power generation capabilities. One potentially fruitful research direction is to explore whether hybrid TE materials possess possible enhanced TE properties. These “engineered” hybrids include materials that exhibit sizes from on the order of a few nanometers to hundreds of nanometers of the initial materials. These initial materials are then incorporated into a bulk structure. A discussion of some of the future research directions that we are pursuing is highlighted, including some bulk materials, which are based on nano-scaled or hybrid composites. The synthesis techniques and the synthesis results of many of these nano-scale precursor materials will be a primary focus of this paper.
Thermoelectric and Thermomagnetic Transport in PbTe with Nanoscale Structures
Authors: Heremans Joseph P. 
Published: April 2011

ABSTRACTQuantum-dot superlattices (QDSLs) have demonstrated thermoelectric figure of merit (ZT) values double those of classical bulk materials, providing the proof that nanoscale materials can address this age-old limitation on thermoelectric technology. Since QDSL materials can only be obtained in thin-film form, the development of bulk materials with nanoscale inclusions would be useful for many large-scale applications. Nanometer-scale inclusions in lead chalcogenides are known to improve the thermoelectric figure of merit through a combination of two factors: a strong decrease in lattice thermal conductivity, and an increase in the Seebeck coefficient over that of bulk PbTe for a given carrier concentration. This paper focuses on experimental results obtained on two types of PbTe nanocomposites, namely samples prepared by sintering powders with nanometer-sized grains, and samples prepared with nanoprecipitates of metallic Pb. The results are analyzed using the “method of four coefficients.” At each measurement temperature there are four unknowns. These are the carrier concentration, the mobility, the carrier effective mass, and the energy dependence of the relaxation time Tau, which is modeled by a power law: Tau proportional to energy to power Lamda. Therefore, at each temperature, four measurements are taken: the electrical conductivity, and the Hall, Seebeck and transverse Nernst-Ettingshausen coefficients. This analysis concludes that the effect of the nanoscale inclusions on the power factor is due to an increase in the scattering parameter λ, and that the nanoscale inclusions affect the electron scattering in such a way as to increase the Seebeck coefficient.
Nanostructuring and its Influence on the Thermoelectric Properties of the AgSbTe2-SnTe Quaternary System
Authors: Androulakis Ioannis , Pcionek R. , Quarez E. , Palchik O. , Kong H. , Uher C. , Dangelo J. J. , Hogan T. , Tang X. , Tritt T. , Kanatzidis Mercouri 
Published: April 2011

ABSTRACTThe structural and thermoelectric properties of the AgSbTe2-SnTe quaternary system were studied. Powder averaged x-ray diffraction of Ag0.85SnSb1.15Te3 indicates a cubic NaCl-type structure in contrast with the single crystal refinements, which point towards tetragonal symmetry. Furthermore, high-resolution electron microscopy imaging revealed the system to be a nano-composite formed by thermodynamically driven compositional fluctuations rather than a solid solution as it was viewed in the past. The lattice thermal conductivity attains very low values, which is in accord with recent theories on thermal transport in heterogeneous systems. The charge transport properties of the system exhibit a rich physical behavior highlighted in the coexistence of an almost metallic carrier concentration (∼5×1021 cm−3) with a large thermoelectric power response of ∼160 μV/K at 650 K. This is attributed to a heavy hole effective mass that is almost six times that of the electron rest mass.
Design of Heterostructures for High Efficiency Thermionic Emission
Authors: Bian Zhixi , Shakouri Ali 
Published: April 2011

ABSTRACTWe use two heterostructure designs to improve the energy conversion efficiency of solid-state thermionic devices. The first method is to use a non-planar heterostructure with roughness in order of electron mean free path. This has some combined benefits of increased effective interface area, and reduced total internal reflection for the electron trajectories arriving at the interface. Monte Carlo simulations of various geometries show that the electrical conductivity and thermoelectric figure of merit can be improved for non-planar barrier compared to the planar counterpart. The second method is to use planar high barrier heterostructures with different effective masses for charge carriers in emitter and barrier regions. When an electron passes from a lower effective mass emitter and arrives at a barrier with higher effective mass, since both the lateral momentum and total energy are conserved, part of the lateral energy is coupled to the vertical direction and the electron gains momentum in the direction perpendicular to the interface to enter the barrier region. For high potential barriers, the improvement of thermionic current is about the same as the ratio of the effective masses of the two materials, which can be a factor of 5-10 for typical heterostructure material systems.
Characterization of Thermoelectric Power Generation Modules Made from New Materials
Authors: Short Jarrod L. , D'Angelo Jonathan , Downey Adam D. , Pajor Michael A. , Timm Ed , Schock Harold , Kanatzidis Mercouri G. , Hogan Timothy P. 
Published: April 2011

ABSTRACTLead-Antimony-Silver-Tellurium (L-A-S-T) materials, synthesized at Michigan State University, show promising thermoelectric properties at high temperatures for use in power generation applications. Recent scaled-up quantities of L-A-S-T show a ZT=1.4 at 700 K approaching the figure of merit for samples made in small quantities. These materials are of great interest for power generation applications with hot side temperatures in the range of 600-800 K. Developing these materials into working devices requires minimization of the thermal and electrical parasitic contact resistances, so various fabrication methods are under investigation. To examine each method, a new measurement system has been developed to characterize these devices under various load and temperature gradients. An introduction to the system will be presented, as well as results for devices made of the L-A-S-T materials.
Study on the Filling Fraction Limit of Impurities in CoSb3
Authors: Shi X. , Zhang Wenqing , Chen Lidong , Yang Jihui 
Published: April 2011

ABSTRACTComplex crystals such as skutterudites have interstitial voids in the lattice that can be filled by various impurity atoms. The filling fraction limit (FFL) for the intrinsic voids in the lattice of CoSb3 is studied by density functional methods. The FFL is shown to be determined not only by the interaction between the impurity and host atoms but also by the formation of secondary phases between the impurity atoms and one of the host atoms. A model is proposed to quantitatively explain the phenomenon. The predicted FFLs for Ca, Sr, Ba, La, Ce, and Yb in CoSb3 are in excellent agreement with reported experimental data. Detailed analysis reveals the existence of a quantitative relationship between the repulsive interaction of impurity atoms and their charge state. A correlation between the FFL of an impurity atom and its charge state and electronegativity is discovered.
Synthesis and thermoelectric power factor of LSCO perovskites
Authors: Rodriguez Julio E. 
Published: April 2011

ABSTRACTMeasurements of Seebeck coefficient, S(T) and electrical resistivity, ρ(T) on polycrystalline La2−xSrxCuO4+d(LSCO) (0<x≤0.2) samples are reported. The Seebeck coefficient is positive in whole measured temperature range (77K and 300K) and it decreases with Sr content. At room temperature S(T) changes from 400 μ/K for the samples with the lowest levels of Sr to 30 μV/K for the samples with the highest Sr levels. The behavior of S(T) fits to Heikes model, which describes the behavior of Seebeck coefficient in systems where the correlated hopping is present. With the Sr content, the electrical resistivity changes its behavior from semiconducting to metallic and it took values from 2.4 to 10−3Ωcm. From S(T) and rho(T) measurements the thermoelectric power factor, PF was obtained. The maximum values for PF were about 5 μW/K2cm in the samples where x= 0.03, which are comparable to the typical values for conventional thermoelectric semiconductors. The structural and morphological properties of the samples were studied by x-ray diffraction analysis and Scanning Electron Microscopy (SEM) respectively. The behavior of transport properties opens de possibility of considering this family of perovskite-compounds as a thermoelectric material which works below room temperature.
Progress on the Fabrication and Characterization of High Efficiency Thermoelectric Generators
Authors: Hogan Timothy P. , Downey Adam D. , Short Jarrod , D'Angelo Jonathan J. , Quarez Eric , Androulakis John , Poudeu Pierre F. P. , Kanatzidis Mercouri G. , Timm Ed , Sarbo Kim , Schock Harold 
Published: April 2011

ABSTRACTHigh efficiency thermoelectric modules are of great interest for power generation applications where hot side temperatures of approximately 800K exist. The fabrication of such modules requires a multidisciplinary effort for the optimization of the material compositions, the engineering of the module systems, modeling and fabrication of the devices, and constant feedback from characterization. Pb-Sb-Ag-Te (LAST) and Pb-Sb-Ag-Sn-Te (LASTT) compounds are among the best known materials for this temperature range. Modeling of these materials and possible cascaded structures shows efficiencies of 14% can be achieved for low resistance contacts. Using antimony we have achieved contact resistivities less than 20 µΩ·cm2. Here we give a detailed presentation on the procedures used in the fabrication of thermoelectric generators based on these new materials. We also present the characterization systems and measurements on these generators.
Electron work function at grain boundary and the corrosion behavior of nanocrystalline metallic materials
Authors: Li D. Y. 
Published: April 2011

ABSTRACTDue to their high grain boundary density, nanocrystalline materials possess unusual mechanical, physical and chemical properties. Extensive research on nanocrystalline materials has been conducted in recent years. Many studies have shown that corrosion, one of important properties of nanocrystalline materials, is crucial to their applications. In this article, the activity of electrons at grain boundaries of metallic surfaces is analyzed based the electron work function (EWF), the minimum energy required to attract electrons from inside a metal. It is demonstrated that at grain boundaries, the electron work function decreases, indicating that at a grain boundary, electrons are more active. As a result, the surface becomes more electrochemically reactive. Such increase in electrochemical reactivity has negative effect on the corrosion resistance of nanocrystalline materials. However, for a passive nanocrystalline metal or alloy, the nanocrystalline structure is beneficial to its corrosion resistance through rapid formation of a protective passive film. The mechanisms responsible for the variation in EWF at grain boundary and effects of nanocrystallization on corrosion are discussed in this article.
Statistical Mechanics: Undamaged ⇐-radiation-⇒ Damaged Atomic Lattice Density Evolution and Stochastic Deformation Functional
Authors: Stout Ray B. , Stout Natasha K. 
Published: April 2011

AbstractThe deformation kinematics for radiation damage response of bulk materials is presently semi-empirical and phenomenological based on a continuum mechanics supposition: there exists a function space of continuous functions to describe material displacement, strain, strain-rate metrics by using the mathematics of differential calculus. Existing data being assembled from tests on nano-length-scale(NLS) samples provide objective evidence that the continuum mechanics supposition is not an adequate generic mathematical description for radiation damage response in surface-dominated material structures at NLS. An alternative approach will be described that uses concepts and methods from classical statistical mechanics and describe deformation kinematics as a stochastic accumulation of discrete damage events at atomic lattice nano-length-scales. Although radiation damage deformation at a lattice length-scale in solids is mechanistically different from velocity scattering developed by Boltzmann for a kinetic theory of gases, the two problem areas are technically similar and in some simply cases there are useful mathematical analogs. The technical similarities and mathematical analogs will be used to define probability density functions (number per unit volume functions) for undamaged and damaged “size and size change” lattice species (similarity to a probability density function for atomic velocities in gas theory). In general, equations for undamaged and damaged lattice density function evolution are Boltzmann-type equations, which can be approximated and solved for simple cases of radiation induced material damage. Using a path integral approach and the two probability density functions, a stochastic functional will be derived for the relative deformation between any two arbitrary spatial points in a radiation damaged material. Given the relative deformation as an explicit functional of the undamaged and damaged lattice density functions, the kinematics metrics of relative velocity, strain, strain rate, etc., will also be functionals. In the case of radiation damage and annealing, the two lattice density functions are analog expressions to those commonly used to model “birth and death” population evolution.