bluuebunny/crossref_metadata_2025_split huggingface dataset:
New Strategies on SOFC
Authors: Ruiz-Morales Juan Carlos , Peña-Martínez Juan , Marrero-López David , Pérez-Coll Domingo , Canales-Vázquez Jesús , Irvine John T.S. , Núñez Pedro 
Published: April 2011

AbstractFuel Cells are highly promising energy conversion systems for the new energy scenario. Particularly, Solid Oxide Fuel Cells (SOFCs) have been extensively studied during the last few years as a result of the increasing interest in the development of more efficient, and environmentally friendly ways of energy generation, as well as a consequence of their fuel flexibility. This work shows some strategies to improve the efficiency of SOFCs through the use of new anode materials, a novel method of microstructural optimisation by means of polymeric templates, using composites or cermets-based materials or applying a new concept in SOFC, e.g. the Symmetrical SOFC (SFC).
Electrochemical Characterization of La2-xPrxNiO4+x for Application as Cathodes in Intermediate Temperature SOFCs
Authors: Kim Gun Tae , Jacobson Allan J 
Published: April 2011

AbstractThe electrochemical properties of perovskite-type materials, Ln2NiO4+δ (Ln = La, Pr) as cathodes on Ce0.9Gd0.1O3 (CGO) and YSZ electrolytes were studied from 400 to 700 °C under different oxygen partial pressures (pO2 = 0.01-1 atm) by using AC impedance spectroscopy. These oxide electrodes yielded lower area specific resistance (ASR) compared to manganite perovskites. Ln2NiO4+δ (Ln = La, Pr) on CGO showed similar electrochemical performance though La2NiO4 (LNO) has a smaller ASR than Pr2NiO4 (PNO). The polarization resistance of LNO on YSZ was 2 orders higher than that on CGO. The interfacial resistance between the electrode and electrolyte was much smaller for LNO on CGO than for LNO on YSZ.
Impedance Analysis of Electrochemical NOx Sensor Using a Au/Yttria-Stabilized Zirconia (YSZ)/Au cell
Authors: Woo Leta Y. , Martin L. Peter , Glass Robert S. , Gorte Raymond J. 
Published: April 2011

AbstractAn electrochemical cell employing a YSZ electrolyte and two Au electrodes was utilized as a model system for investigating the mechanisms responsible for impedancemetric NOx (NO and NO2) sensing. The cell consists of two dense Au electrodes on top of a porous/dense YSZ bilayer structure (with the additional porous layer present only under the Au electrodes). Both electrodes were co-located on the same side of the cell, resulting in an in-plane geometry for the current path. The porous YSZ appears to extend the triple phase boundary and allows for enhanced NOx sensing performance, although the exact role of the porous layer is not completely understood. Impedance data were obtained over the frequency range of 0.1 Hz to 1 MHz, and over a range of oxygen (2 to 18.9%) and NOx (10 to 100 ppm) concentrations, and temperatures (600 to 700 °C). Data were fit with an equivalent circuit, and the values of the circuit elements were obtained for different concentrations and temperatures. Changes in a single low-frequency arc were found to correlate with concentration changes, and to be temperature dependent. In the absence of NOx, the effect of O2 on the low-frequency resistance could be described by a power law, and the temperature dependence described by a single apparent activation energy at all O2 concentrations. When both O2 and NOx were present, however, the power law exponent varied as a function of both temperature and concentration, and the apparent activation energy also showed dual dependence. Adsorption mechanisms are discussed as possibilities for the rate-limiting steps.
Impedancemetric Technique for NOx Sensing Using a YSZ-Based Electrochemical Cell
Authors: Martin L. Peter , Woo Leta Y. , Glass Robert S. 
Published: April 2011

AbstractAn impedancemetric technique for NOx sensing using a yttria-stabilized zirconia (YSZ) electrochemical cell is reported. The cell consists of a dense YSZ substrate disk with two YSZ/metal-oxide electrodes deposited on the same side. The cell is completely exposed to the test gas (no air reference). The NOx and O2 response of the cell were evaluated during constant-frequency operation at frequencies in the range from 1 to 1000 Hz. At 10 Hz, the NOx response (as measured by phase angle shift) is shown to be linear with concentration over the range from 8-50 ppm, with comparable response to both NO and NO2. A method of operation is described which enables compensation for the O2 response at oxygen concentrations greater than approximately 4%. This mode of operation allows the sensor to provide sub-10 ppm detection of NOx irrespective of the O2 concentration. The sensor exhibits good stability during continuous operation for more than 150 hr. It was observed that the O2 response of the cell may be too slow to be of practical use, taking several minutes to equilibrate after changing the concentration by a few percent. However, data will be presented which demonstrate that this response is related to the metal oxide used for the electrode, and that more rapid response times can be achieved by modification of the electrode material.
Iron Phosphates as Cathodes of Lithium-Ion Batteries
Authors: Wang Shijun , Whittingham M. Stanley 
Published: April 2011

ABSTRACTThis study focusses on optimizing the parameters of the hydrothermal synthesis to produce iron phosphates for lithium ion batteries, with an emphasis on pure LiFePO4 with the olivine structure and compounds containing a higher iron:phosphate ratio. Lithium iron phosphate (LiFePO4) is a promising cathode candidate for lithium ion batteries due to its high theoretical capacity, environmentally benign and the low cost of starting materials. Well crystallized LiFePO4 can be successfully synthesized at temperatures above 150 °C. The addition of a reducing agent, such as hydrazine, is essential to minimize the oxidation of ferrous (Fe2+) to ferric (Fe3+) in the final compound. The morphology of LiFePO4 is highly dependent on the pH of the initial solution. This study also investigated the lipscombite iron phosphates of formula Fe1.33PO4OH. This compound has a log-like structure formed by Fe-O octahedral chains. The chains are partially occupied by the Fe3+ sites, and these iron atoms and some of the vacancies can be substituted by other cations. Most of the protons can be ion-exchanged for lithium, and the electrochemical capacity is much increased.
High Performance of Lithium Iron Phosphates for HEV with Quality Control Made by Magnetometry
Authors: Julien Christian M , Mauger Alain , Zaghib Karim , Gendron François 
Published: April 2011

ABSTRACTOptimized LiFePO4 positive electrode for Li-ion batteries was obtained after severe control of the fundamental properties of material. The nanoscopic structure and magnetic properties of a series of carbon-coated LiFePO4 particles prepared under various conditions were analyzed with XRD, FTIR, Raman and SQUID magnetometry. We evaluate intrinsic and extrinsic properties. The existence of low content of nano-sized ferromagnetic particles was evidenced by magnetic measurements in samples grown from iron(II) oxalate; such ferromagnetic clusters do not exist in the optimised samples grown from FePO4(H2O)2. Other impurity phases such as Fe2P, Li3Fe2(PO4)3, FeP2O7 were also detected for particular conditions of preparation. The impact of the carbon coating on the electrochemical properties is reported. Li-ion cells show excellent cyclability after 200 cycles at 60 °C without iron dissolution.
Novel Nanoporous Carbon Derived from Coal Tar Pitch/polyethylene Glycol Diacid Blends as Electrodes for Ultracapacitors
Authors: Rajagopalan Ramakrishnan , Perez Keith , Foley Henry 
Published: April 2011

ABSTRACTNanoporous carbon materials with high surface area (1500 – 2000 m2/g) and narrow pore size distribution ranging from 1 – 3 nm were synthesized using polyfurfuryl alcohol/polyethylene glycol diacid and coal tar pitch/polymer blends. Electrical double layer capacitance of synthesized carbon was measured using cyclic voltammetry. There is a strong correlation between the surface area of the carbon and the specific capacitance. Carbon that had surface area smaller than 1000 m2/g had specific capacitance less than 50 F/g while the carbons having surface area from 1000 – 1500 m2/g showed specific capacitances in the order of 200 -250 F/g. It was shown that the mesoporosity and macroporosity in the parent carbon are critical for both activation and as well as the specific capacitance of the material. The use of these carbons in EDLCs was also demonstrated by fabricating a two-electrode ultracapacitor.
Mesoporous Carbon Materials as Electrodes for Electrochemical Double-Layer Capacitor
Authors: Park Sea , Liang Chengdu , Sheng Dai , Dudney Nancy , DePaoli David 
Published: April 2011

ABSTRACTNanostructured carbon materials with a regular array and narrow size distribution of mesopores have been synthesized at Oak Ridge National Laboratory via the self-assembly of block copolymers as soft templates. One promising application for these materials is as electrodes for electrochemical double-layer capacitors. To evaluate the performance, electrodes were prepared by coating the precursor onto fibrous carbon paper, followed by curing and pyrolysis at 850°C. The resulting mesoporous carbon has a surface area of 310 m2/g and an average pore size of 8.5 nm. Results from cyclic voltammetry and impedance spectroscopy experiments using a sulfuric acid electrolyte showed high specific capacitance values of up to 300 F/g. For comparison, a commercially available aerogel carbon coated paper was also examined.
Titania-German Nanocomposites for Quantum Dot Solar Cells
Authors: Goyal Amita , Hazra Sukti , Shah S. Ismat 
Published: April 2011

ABSTRACTSeveral new photovoltaic semiconductor materials and technologies have been developed due to the increasing need for renewable energy sources. Quantum dot (QD) based solar cell is potentially one of the best contenders. We have developed a thermodynamically stable nanocomposite (stable up to 900°C) titania-germanium (TiO2-Ge) which shows promise as the active layer for QD solar cells. In TiO2-Ge nanocomposites Ge nanodots are distributed in a TiO2 matrix. Due to the 3-D quantum confinement effect, tailoring of the optoelectronic properties is relatively easily done by simply varying the Ge nanodots size. Ge is particularly advantageous since its Bohr radius is relatively large, 25 nm. In this paper results of the variation of the optoelectronic properties of TiO2-Ge nanocomposites as a function of the nanostructure parameters are presented. TiO2-Ge nanocomposite thin films were synthesized using RF magnetron sputtering. The structural studies (by XRD, HRTEM) established the fact that the Ge concentration in the composite target governs the size of the Ge nanodots whereas RF sputtering power controls the density of Ge nanodots in the nanocomposite films. The optical spectroscopic studies showed that the variation of the size of Ge nanodots in the TiO2-Ge films shifts the absorption edge from ∼ 0.66 eV (infrared) to ∼ 2.3 eV (blue-green). Similarly, dark conductivity also varies in a wide range of 10−7 - 10−2 Scm−1 by altering the concentration as well as the structural phase (amorphous or crystalline) of Ge.
Plasma Synthesis of Highly Monodisperse Ge Nanocrystals and Self-Assembly of Dense Nanocrystal Layers
Authors: Gresback Ryan , Holman Zak , Kortshagen Uwe 
Published: April 2011

ABSTRACTGermanium nanocrystals have been synthesized using a low-pressure, nonthermal plasma approach. The nanocrystal size can be adjusted between 4-20 nm by varying the plasma parame-ters, and the size distribution is relatively narrow with standard deviations of 10-20% of the av-erage crystal size. Stable colloidal solutions of the germanium crystals have been prepared by grafting organic alkene ligands onto the nanocrystal surfaces. When drop-cast from solution onto TEM grids, the nanocrystals form densely packed films.
Copper Chalcopyrite Film Photocathodes for Direct Solar-Powered Water Splitting
Authors: Marsen Bjorn , Dorn Susanne , Cole Brian , Rocheleau Richard E. , Miller Eric L. 
Published: April 2011

ABSTRACTIn search of an efficient semiconductor material for direct photoelectrochemical (PEC) hydrogen production, chalcopyrite films in the Cu(In,Ga)Se2system (CIGS) with bandgaps of 1.3-1.65 eV have been evaluated. The films have been fabricated by 2-stage and 3-stage co-evaporation processes. Film samples have been fabricated into CIGS/CdS solar cells for evaluation of solid-state device properties, and into CIGS photocathodes for evaluation of the photoelectrochemical hydrogen-production characteristics. The PEC current-potential scans of the photocathodes in 0.5M sulfuric acid show photocurrents of 18-27 mA/cm2under simulated AM1.5 global light (100 mA/cm2) at sufficient cathodic potential bias. In terms of fill factor of the photocurrent curves, electrodes with molybdenum back contact are superior to SnO2:F back contact because of better conductivity. The morphology as seen in scanning electron micrographs is unchanged after initial PEC testing in the cathodic regime, suggesting films are stable.
Conjugated Polymer-Based Flexible Photovoltaic Cells with Controlled Nanostructures
Authors: Kim Myung-Su , Kim Jin-Sung , Cho Jae Cheol , Shtein Max , Guo L. Jay , Kim Jinsang 
Published: April 2011

ABSTRACTWe demonstrate that conjugated polymers (CPs)-based flexible solar cells with well-defined interdigitated donor-acceptor interfaces enhance charge separation and transport. The welldefined straight donor-acceptor interfaces are achieved successful application of nanoimprinting technology to rationally designed energy harvesting and hole transporting conjugated polymers. Nanoimprinting enables the precise and direct nano-scale control of the shape of the donoracceptor interface on both rigid and flexible substrates. Comparison between the performances of the solar cells having imprinted different feature sizes revealed that the short circuit current can be systematically increased by the interfacial area of the heterojunction without affecting the open circuit voltage. The results also showed that the vertically oriented heterojunction facilitate charge transport and allow synergistically improved fill factor, open circuit current, and ensuing energy conversion efficiency beyond the gain of the interfacial area of the heterojunction.
Electrical Response of Wet Chemically Grown ZnO Nanorods for Photovoltaic Application
Authors: Tornow Julian , Schwarzburg Klaus 
Published: April 2011

ABSTRACTWet chemically prepared arrays of ZnO nanorods in electrolyte solution were investigated with respect to their capacitive behavior. The ZnO nanorod electrode could be well described by a frequency independent capacitive and a conductive element in parallel. The capacitive element is determined as space charge capacitance in the nanorods. However the dependency of the nanorod electrodes capacitance on the applied voltage bias is more complicated than for flat semiconductor electrodes.
Microcrystalline SiO and its Application to Solar Cell
Authors: Piromjit Channarong , Yotsaksri Decha , Pingate Nirut , Sichanugrist Porponth 
Published: April 2011

ABSTRACTAs microcrystalline silicon oxide (μc-SiO) is reported to be more promising material than microcrystalline silicon carbide for the application to solar cells, both of high efficiency amorphous (top cell) and microcrystalline (bottom cell) silicon solar cells fabricated on tin oxide coated glass substrate have been developed by using μc-SiO p-layer and buffer i-layer. High VHF frequency of 60 MHz and carbon dioxide gas are used for their deposition. ZnO deposited by DC sputtering is coated on Asahi's type U tin oxide in order to promote the crystallization of the μc-SiO p-layer. It was found that the top cell with this novel mc-SiO p-layer has higher cell efficiency than the one with normal SiO p-layer. Furthermore, the microcrystalline bottom cell with novel μc-SiO p-layer and μc-SiO buffer layer has higher performance than the one with normal μc-Si p-layer. Up to now, an efficiency of more than 15% has been achieved with a-SiO/a-SiGe/μc-Si tandem cell.
Analytical TEM Observations of Au-Pd Nano-particles Prepared by Sonochemical Techniques
Authors: Akita Tomoki , Hiroki Taiei , Tanaka Shingo , Kojima Takao , Kohyama Masanori , Iwase Akihiro , Hori Fuminobu 
Published: April 2011

ABSTRACTThe structure of Au-Pd bimetallic nanoparticles prepared by sonochemical technique was investigated by an analytical transmission electron microscopy. The core (Au)-shell (Pd) structure was clearly confirmed by the intensity profile of annular dark field scanning transmission electron microscopy (ADF-STEM). The line-scan analysis of energy dispersive X-ray spectroscopy (EDS) in STEM mode also revealed the Au core-Pd shell structure. The selected area electron diffraction pattern from the Au-Pd nanoparticles indicated the possibility that the crystal lattice of Pd shell is expanded and coincident with the crystal lattice of Au core.
Measurement of Moisture Migration Kinetics in Environmental Scanning Electron Microscopy
Authors: Tang Xiaohu , Rooij Mario de 
Published: April 2011

ABSTRACTVolume change of cereal materials caused by moisture migration is studied by Environmental Scanning Electron Microscopy (ESEM) using videomicroscopy and stereoscopy in combination with image processing. It is shown that the in situ volume change can be monitored by following the change of projection area, assuming isotropic volume change. Also the volume change measured by stereoscopy matches well with the measurement of the projection area change by videomicroscopy (after normalization). It is concluded that volume changes more in a higher relative humidity (RH) region with more active kinetic behavior. The exact volume change in between two relative humidities can be obtained by interpolating the equilibrium volumes. All the sorption/desorption curves can be well described by the ‘parallel exponential kinetics’ model (PEK model), which described two independent, parallel processes.
Electrical and Optical Modelling of Thin-Film Silicon Solar Cells
Authors: Zeman Miro , Krc Janez 
Published: April 2011

AbstractToday amorphous and microcrystalline silicon based solar cells use surface-textured substrates for enhancing the light absorption and buffer and graded layers in order to improve the overall performance of the cells. Tandem and triple-junction configurations are utilized to assure better use of the solar spectrum and, thus, achieve higher conversion efficiencies of the devices. Resulting structures of the solar cells are complex and computer modeling has become an essential tool for a detailed understanding and further optimization of their optical and electrical behavior.The performance limits of tandem and triple-junction silicon based solar cells are studied by simulations using the optical simulator SunShine developed at Ljubljana University and the opto-electrical simulator ASA developed at Delft University of Technology. First, both simulators were calibrated with realistic optical and electrical parameters. Then, they were used to study the required scattering properties, absorption in non-active layers, antireflective coatings, the crucial role of the wavelength selective intermediate reflector, and a careful current matching in order to indicate the way for achieving a high photocurrent, more than 15 mA/cm2 for a tandem a-Si:H/ìc-Si:H and 11 mA/cm2 for a triple-junction a-Si:H/a-SiGe:H/ìc-Si:H solar cells. By optimizing electrical properties of the layers and interfaces, for example using a p-doped a-SiC layer with a larger band gap (EG > 2 eV) and introducing buffer layers at p/i interfaces, the extraction of the charge carriers, the open-circuit voltage and the fill factor of the solar cells are improved. The potential for achieving the conversion efficiency over 15% for the a-Si:H/ìc-Si:H and 17 % for the triple-junction a-Si:H/a-SiGe:H/ìc-Si:H solar cells is demonstrated.
Comparative Study of Hot-Wire Chemical Vapor Deposition onto (100) Si Near 600°C: Epitaxial and Polycrystalline Silicon Films
Authors: Teplin Charles W. , Branz Howard M. , Jones Kim M. , To Bobby , Iwaniczko Eugene , Stradins Paul 
Published: April 2011

AbstractPreviously, we reported improved silicon epitaxy by hot-wire chemical vapor deposition (HWCVD) between about 600 and 650°C. Such temperatures are compatible with the thickening of large-grained Si seed layers on borosilicate glasses or other inexpensive substrates. Here, we provide detailed real-time spectroscopic ellipsometry (RTSE) and x-ray diffraction (XRD) analysis of two films grown near 600°C. A film grown at 594°C shows breakdown to a polycrystalline phase, while a film grown at 627°C is entirely epitaxial. Transmission electron microscopy (TEM) of this epitaxial film shows dislocation defects that originate at the substrate/film interface, suggesting that an optimized surface preparation could yield lower defect densities.
Microwave Activation of Dopants & Solid Phase Epitaxy in Silicon
Authors: Thompson Douglas C. , Decker J. , Alford T. L. , Mayer J. W. , Theodore N. David 
Published: April 2011

AbstractMicrowave heating is used to activate solid phase epitaxial re-growth of amorphous silicon layers on single crystal silicon substrates. Layers of single crystal silicon were made amorphous through ion implantation with varying doses of boron or arsenic. Microwave processing occurred inside a 2.45 GHz, 1300 W cavity applicator microwave system for time-durations of 1-120 minutes. Sample temperatures were monitored using optical pyrometery. Rutherford backscattering spectrometry, and cross-sectional transmission electron microscopy were used to monitor crystalline quality in as-implanted and annealed samples. Sheet resistance readings show dopant activation occurring in both boron and arsenic implanted samples. In samples with large doses of arsenic, the defects resulting from vacancies and/or micro cluster precipitates are seen in transmission electron micrographs. Materials properties are used to explain microwave heating of silicon and demonstrate that the damage created in the implantation process serves to enhance microwave absorption.
Optimisation of Microcrystaline Silicon Deposited by Expanding Thermal Plasma Chemical Vapor Deposition for Solar-Cell Application
Authors: Jimenez Zambrano Raul , van Swaaij R.A.C.M.M. , van de Sanden M.C.M. 
Published: April 2011

AbstractThe causes for the porosity of the microcrystalline material deposited by the expanding thermal plasma (ETP) chemical vapor deposition (CVD) technique have been investigated through IR-absorption measurements. The role of impinging ions on the structure of the material is discussed in relation to the hydrogen bounding configuration (microcrystalline factor). The ion energy is controlled through external RF biasing. Correlation between biasing and reduction of porosity is presented. The influence of high deposition pressure is as well studied, related with changes in a-Si structure.
Phase Control and Stability of Thin Silicon Films Deposited from Silane Diluted with Hydrogen
Authors: van Elzakker Gijs , Šutta Pavol , Tichelaar Frans D. , Zeman Miro 
Published: April 2011

AbstractHydrogen dilution of silane during the rf-PECVD growth of a-Si:H absorber layers is used to suppress light-induced degradation of a-Si:H solar cells. The increased stability of cells and films deposited using hydrogen dilution is verified in an accelerated degradation experiment. At higher hydrogen dilutions the early phase transition to the microcrystalline phase complicates the growth of fully amorphous films as absorbers with a sufficient thickness. In a systematic study on the influence of various deposition conditions on the material properties the pressure is identified as an important factor for controlling the structural phase evolution of the films.