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Records with Subject: Materials
Showing records 1 to 25 of 122. [First] Page: 1 2 3 4 5 Last
Dicyanovinyl and Cyano-Ester Benzoindolenine Squaraine Dyes: The Effect of the Central Functionalization on Dye-Sensitized Solar Cell Performance
Simone Galliano, Vittoria Novelli, Nadia Barbero, Alessandra Smarra, Guido Viscardi, Raffaele Borrelli, Frédéric Sauvage, Claudia Barolo
December 3, 2018 (v1)
Subject: Materials
Keywords: central functionalization, dye-sensitized solar cells, NIR-sensitizers, squaraines
In order to achieve a greater light absorption in the near-infrared (NIR) region with a panchromatic spectral response and to suppress the photo-isomerisation phenomenon, we herein report the design, synthesis, spectroscopic and electrochemical characterization of novel centrally functionalized symmetric benzoindolenine squaraine dyes. These molecules have shown different photoelectrical conversion properties, depending on the dicyanovinyl and cyano-ester group substitution on the squaric core unit and on the extension of the π-conjugation.
Metamaterial Absorber Comprised of Butt-Facing U-Shaped Nanoengineered Gold Metasurface
Masih Ghasemi, Pankaj Kumar Choudhury
November 28, 2018 (v1)
Subject: Materials
Keywords: complex optical mediums, metamaterial absorbers, nanostructured mediums, plasmonic resonators
The paper reports spectral features of the absorbed electromagnetic (EM) waves in a new kind of multilayered plasmonic metamaterial thin film comprised of homogenous layers of copper and silicon as the bottom and the middle sections (of the thin film), respectively, and the inhomogeneous U-shaped nanoengineered gold layer as the top. Each unit cell of the top metasurface consists of one upside and one downside U-shaped (butt-facing) structure. The absorbance of EM waves is simulated in the wavelength range of 200−1500 nm under different incidence angles considering the wave as being transmitted from the metasurface side. The low-order TE and TM modes are taken into account for the estimation of wave absorbance under varying metasurfaces as well as silicon layer thicknesses. It has been found that the nanoengineered gold layer causes higher confinement of power in silicon, which can be further controlled by suitably adjusting its thickness. Further, the increased thickness of metasurfac... [more]
Effect of Coal Rank on Various Fluid Saturations Creating Mechanical Property Alterations Using Australian Coals
Mandadige Samintha Anne Perera, Ashani Savinda Ranathunga, Pathegama Gamage Ranjith
November 28, 2018 (v1)
Subject: Materials
Keywords: CO2 saturation, coal rank, mechanical properties, N2 saturation, water saturation
During CO₂ sequestration in deep coal seams, the coal mass may be subjected to various fluid (CO₂, N₂, etc.) saturations. Therefore, in order to maintain the long-term integrity of the process, it is necessary to identify the mechanical responses of preferable coal seams for various fluid saturations. To date, many studies have focused on the CO₂ saturation effect on coal mass strength and less consideration has been given to the influence of other saturation mediums. Hence, this study aims to investigate coal’s mechanical responses to water and N₂ saturations compared to CO₂ saturation and to determine the effect of coal-rank. A series of unconfined compressive strength (UCS) tests was conducted on Australian brown and black coal samples saturated with water and N₂ at various saturation pressures. An advanced acoustic emission (AE) system was utilized to identify the changes in crack propagation behaviors under each condition. According to the results, both CO₂ and water act similarly... [more]
High Stable, Transparent and Conductive ZnO/Ag/ZnO Nanofilm Electrodes on Rigid/Flexible Substrates
Qiaoxia Zhang, Yanghua Zhao, Zhenhong Jia, Zhengfei Qin, Liang Chu, Jianping Yang, Jian Zhang, Wei Huang, Xing’ao Li
November 28, 2018 (v1)
Subject: Materials
Keywords: flexible, oxidization-induced effect, transparent electrode, ZnO/Ag/ZnO
Here, highly transparent, conductive, and stable ZnO/Ag/ZnO electrodes on transparent rigid glass and flexible substrates were prepared by facile, room-temperature magnetron sputtering, in which the continuous Ag layers were obtained by means of oxidization-induced effect under an Ar atmosphere with tiny amounts of O₂. The results showed an appropriate amount of O₂ was beneficial to form continuous Ag films because of the adsorption of oxygen between the ZnO and Ag layers. When the concentration of O₂ in the Ar atmosphere was 2.0%⁻3.0%, ZnO (40 nm)/Ag (10 nm)/ZnO (40 nm) films on rigid glass showed visible-range transmittance of 94.8% and sheet resistance of 8.58 Ω·sq−1, while the corresponding data on flexible PET substrates were 95.9% and 8.11 Ω·sq−1, respectively. In addition, the outstanding electrodes remained stable for more than six months under air conditioned conditions. The electrodes are fully functional as universal rigid/flexible electrodes for high-performance electronic... [more]
Controlled Al3+ Incorporation in the ZnO Lattice at 188 °C by Soft Reactive Co-Sputtering for Transparent Conductive Oxides
Salvatore Sanzaro, Antonino La Magna, Emanuele Smecca, Giovanni Mannino, Giovanna Pellegrino, Enza Fazio, Fortunato Neri, Alessandra Alberti
November 28, 2018 (v1)
Subject: Materials
Keywords: Al doped ZnO (AZO), co-sputtering, doping, dye-sensitized solar cells (DSCs), low temperature, transparent conductive oxide (TCO)
Transparent conductive oxide (TCO) layers, to be implemented in photo-anodes for dye-sensitized solar cells (DSCs), were prepared by co-deposition of ZnO and Al using pulsed-direct current (DC)-magnetron reactive sputtering processes. The films were deposited at low deposition temperatures (RT-188 °C) and at fixed working pressure (1.4 Pa) using soft power loading conditions to avoid intrinsic extra-heating. To compensate the layer stoichiometry, O₂ was selectively injected close to the sample in a small percentage (Ar:O₂ = 69 sccm:2 sccm). We expressly applied the deposition temperature as a controlling parameter to tune the incorporation of the Al3+ species in the targeted position inside the ZnO lattice. With this method, Aluminum-doped Zinc Oxide films (ZnO:Al) were grown following the typical wurtzite structure, as demonstrated by X-ray Diffraction analyses. A combination of micro-Raman, X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE) analyses has shown... [more]
A Multi-Component Additive to Improve the Thermal Stability of Li(Ni1/3Co1/3Mn1/3)O₂-Based Lithium Ion Batteries
Qingsong Wang, Lihua Feng, Jinhua Sun
November 28, 2018 (v1)
Subject: Materials
Keywords: electrolyte, lithium ion battery (LIB) safety, multi-component (MC) additive, thermal stability
To improve the safety of lithium ion batteries, a multi-component (MC) additive (consisting of vinylene carbonate (VC), 1,3-propylene sulfite (PS) and dimethylacetamide (DMAC)) is used in the baseline electrolyte (1.0 M LiPF₆/ethylene carbonate (EC) + diethyl carbonate (DEC)). The electrolyte with the MC additive is named safety electrolyte. The thermal stabilities of fully charged Li(Ni1/3Co1/3Mn1/3)O₂ (NCM) mixed with the baseline electrolyte and safety electrolyte, respectively, are investigated using a C80 micro-calorimeter. The electrochemical performances of the NCM/baseline electrolyte/Li and NCM/safety electrolyte/Li half cells are evaluated using galvanostatic charge/discharge, cyclic voltammetry and alternating current (AC) impedance. The experimental results demonstrate that the fully charged NCM-safety electrolyte system releases less heat and reduces the main sharp exothermic peak value to a great extent, with a reduction of 40.6%. Moreover, the electrochemical performance... [more]
A Computational Analysis of Functionally Graded Anode in Solid Oxide Fuel Cell by Involving the Correlations of Microstructural Parameters
Chao Wang
November 28, 2018 (v1)
Subject: Materials
Keywords: conventional non-graded electrodes, functionally graded electrodes (FGEs), microstructural parameters correlations, numerical simulation, solid oxide fuel cells (SOFCs)
Functionally-graded electrodes (FGEs) have shown great potential in improving solid oxide fuel cells’ (SOFCs) performance. In order to produce predictions of real FGE operations, a comprehensive numerical model that takes into account all the microstructure parameters, together with two sub model correlations, i.e., porosity-tortuosity, and porosity-particle size ratio, is utilized, aiming to provide a novel approach to demonstrate the advantages of FGEs for SOFCs. Porosity grading and particle size grading are explored by using this implemented model as a baseline. Multiple types of grading cases are tested in order to study the FGEs at a micro-scale level. Comparison between the FGEs and conventional non-graded electrodes (uniform random composites) is conducted to investigate the potential of FGEs for SOFCs. This study essentially focuses on presenting a new perspective to examine the real-world FGEs performance by involving the correlations of physically connected micro-structural... [more]
Low-Temperature, Chemically Grown Titanium Oxide Thin Films with a High Hole Tunneling Rate for Si Solar Cells
Yu-Tsu Lee, Fang-Ru Lin, Ting-Chun Lin, Chien-Hsun Chen, Zingway Pei
November 28, 2018 (v1)
Subject: Materials
Keywords: band alignment, chemically grown, heterojunction, hole tunneling, titanium oxide
In this paper, we propose a chemically grown titanium oxide (TiO₂) on Si to form a heterojunction for photovoltaic devices. The chemically grown TiO₂ does not block hole transport. Ultraviolet photoemission spectroscopy was used to study the band alignment. A substantial band offset at the TiO₂/Si interface was observed. X-ray photoemission spectroscopy (XPS) revealed that the chemically grown TiO₂ is oxygen-deficient and contains numerous gap states. A multiple-trap-assisted tunneling (TAT) model was used to explain the high hole injection rate. According to this model, the tunneling rate can be 10⁵ orders of magnitude higher for holes passing through TiO₂ than for flow through SiO₂. With 24-nm-thick TiO₂, a Si solar cell achieves a 33.2 mA/cm² photocurrent on a planar substrate, with a 9.4% power conversion efficiency. Plan-view scanning electron microscopy images indicate that a moth-eye-like structure formed during TiO₂ deposition. This structure enables light harvesting for a high... [more]
Cobalt-Based Electrolytes for Dye-Sensitized Solar Cells: Recent Advances towards Stable Devices
Federico Bella, Simone Galliano, Claudio Gerbaldi, Guido Viscardi
November 27, 2018 (v1)
Subject: Materials
Keywords: cobalt complex, cobalt electrolyte, dye-sensitized solar cell, polymer electrolyte, quasi-solid electrolyte, stability
Redox mediators based on cobalt complexes allowed dye-sensitized solar cells (DSCs) to achieve efficiencies exceeding 14%, thus challenging the emerging class of perovskite solar cells. Unfortunately, cobalt-based electrolytes demonstrate much lower long-term stability trends if compared to the traditional iodide/triiodide redox couple. In view of the large-scale commercialization of cobalt-based DSCs, the scientific community has recently proposed various approaches and materials to increase the stability of these devices, which comprise gelling agents, crosslinked polymeric matrices and mixtures of solvents (including water). This review summarizes the most significant advances recently focused towards this direction, also suggesting some intriguing way to fabricate third-generation cobalt-based photoelectrochemical devices stable over time.
Fabrication and Characterization of CH₃NH₃PbI3−x−yBrxCly Perovskite Solar Cells
Atsushi Suzuki, Hiroshi Okada, Takeo Oku
November 27, 2018 (v1)
Subject: Materials
Keywords: crystal structure, microstructure, perovskite, photovoltaic property, solar cell
Fabrication and characterization of CH₃NH₃PbI3−x−yBrxCly perovskite solar cells using mesoporous TiO₂ as electron transporting layer and 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene as a hole-transporting layer (HTL) were performed. The purpose of the present study is to investigate role of halogen doping using iodine (I), bromine (Br) and chlorine (Cl) compounds as dopant on the photovoltaic performance and microstructures of CH₃NH₃PbI3−x−yBrxCly perovskite solar cells. The X-ray diffraction identified a slight decrease of crystal spacing in the perovskite crystal structure doped with a small amount of I, Br, and Cl in the perovskite compounds. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) showed the perovskite crystal behavior depended on molar ratio of halogen of Pb, I, Br and Cl. Incorporation of the halogen doping into the perovskite crystal structure improved photo generation, carrier diffusion without carrier recombina... [more]
Chemical Analysis of Different Parts of Date Palm (Phoenix dactylifera L.) Using Ultimate, Proximate and Thermo-Gravimetric Techniques for Energy Production
Ramadan A. Nasser, Mohamed Z. M. Salem, Salim Hiziroglu, Hamad A. Al-Mefarrej, Ahmed S. Mohareb, Manawwer Alam, Ibrahim M. Aref
November 27, 2018 (v1)
Subject: Materials
Keywords: date palm, Energy, proximate analysis, thermo-gravimatric analysis, ultamiate analysis
The objective of the study was to analyze chemical structure of date palm (Phoenix dactylifera L.) by employing ultimate, proximate and thermo-gravimetric techniques. Samples from different anatomical parts of date palm, namely trunk, frond base, frond midrib, leaflets, coir, fruit stem, date stone, and fruit empty bunches were considered for the experiments. Based on the findings in this work palm leaflet samples gave the highest amount of extractives content (32.9%), followed by date palm stone specimens with 31.5%. Cellulose content values of 32.8% and 47.5% were obtained for date palm stone and palm coir samples, respectively. Overall the hemicellulose contents of all samples were relatively similar to those of typical wood or non-wood lignocellulosic materials with the two exceptions of palm coir and palm leaflets. Both palm coir and palm leaflet specimens had 12.6% and 16.1% hemicellulose content. Volatile matter values of 74.3% and 87.5% were determined for leaflets and fruit em... [more]
Lithium Ion Batteries—Development of Advanced Electrical Equivalent Circuit Models for Nickel Manganese Cobalt Lithium-Ion
Alexandros Nikolian, Yousef Firouz, Rahul Gopalakrishnan, Jean-Marc Timmermans, Noshin Omar, Peter van den Bossche, Joeri van Mierlo
November 27, 2018 (v1)
Subject: Materials
Keywords: begin of life (BoL) parameters, cell characterization, dynamic discharge pulse test (DDPT), equivalent circuit model (ECM), lithium ion, Modelling, nickel manganese cobalt (NMC), validation profile, worldwide harmonized light vehicle test procedure (WLTC)
In this paper, advanced equivalent circuit models (ECMs) were developed to model large format and high energy nickel manganese cobalt (NMC) lithium-ion 20 Ah battery cells. Different temperatures conditions, cell characterization test (Normal and Advanced Tests), ECM topologies (1st and 2nd Order Thévenin model), state of charge (SoC) estimation techniques (Coulomb counting and extended Kalman filtering) and validation profiles (dynamic discharge pulse test (DDPT) and world harmonized light vehicle profiles) have been incorporated in the analysis. A concise state-of-the-art of different lithium-ion battery models existing in the academia and industry is presented providing information about model classification and information about electrical models. Moreover, an overview of the different steps and information needed to be able to create an ECM model is provided. A comparison between begin of life (BoL) and aged (95%, 90% state of health) ECM parameters (internal resistance (Ro), pola... [more]
How the Starting Precursor Influences the Properties of Polycrystalline CuInGaSe₂ Thin Films Prepared by Sputtering and Selenization
Greta Rosa, Alessio Bosio, Daniele Menossi, Nicola Romeo
November 27, 2018 (v1)
Subject: Materials
Keywords: Cu(In,Ga)Se2 (CIGS), precursors, sputtering, thin-film solar cell
Cu(In,Ga)Se₂ (CIGS)/CdS thin-film solar cells have reached, at laboratory scale, an efficiency higher than 22.3%, which is one of the highest efficiencies ever obtained for thin-film solar cells. The research focus has now shifted onto fabrication processes, which have to be easily scalable at an industrial level. For this reason, a process is highlighted here which uses only the sputtering technique for both the absorber preparation and the deposition of all the other materials that make up the cell. Particular emphasis is placed on the comparison between different precursors obtained with either In₂Se₃ and Ga₂Se₃ or InSe and GaSe as starting materials. In both cases, the precursor does not require any heat treatment, and it is immediately ready to be selenized. The selenization is performed in a pure-selenium atmosphere and only lasts a few minutes at a temperature of about 803 K. Energy conversion efficiencies in the range of 15%⁻16% are reproducibly obtained on soda-lime glass (SLG... [more]
Inorganic p-Type Semiconductors: Their Applications and Progress in Dye-Sensitized Solar Cells and Perovskite Solar Cells
Ming-Hsien Li, Jun-Ho Yum, Soo-Jin Moon, Peter Chen
November 27, 2018 (v1)
Subject: Materials
Keywords: charge selective material, charge transport material, dye-sensitized solar cell, inorganic material, p-type semiconductor, perovskite solar cell
Considering the increasing global demand for energy and the harmful ecological impact of conventional energy sources, it is obvious that development of clean and renewable energy is a necessity. Since the Sun is our only external energy source, harnessing its energy, which is clean, non-hazardous and infinite, satisfies the main objectives of all alternative energy strategies. With attractive features, i.e., good performance, low-cost potential, simple processibility, a wide range of applications from portable power generation to power-windows, photoelectrochemical solar cells like dye-sensitized solar cells (DSCs) represent one of the promising methods for future large-scale power production directly from sunlight. While the sensitization of n-type semiconductors (n-SC) has been intensively studied, the use of p-type semiconductor (p-SC), e.g., the sensitization of wide bandgap p-SC and hole transport materials with p-SC have also been attracting great attention. Recently, it has been... [more]
Preparation and Characterization of Tetra-Imidazolium Hydroxide Polyphenylene Membranes via Nickel Catalyzed C⁻C Coupling Polymerization
Hohyoun Jang, Soonho Lee, Jaeseong Ha, Kunyoung Choi, Taewook Ryu, Kyunghwan Kim, Heung-Seok Jeon, Whangi Kim
November 27, 2018 (v1)
Subject: Materials
Keywords: alkaline fuel cell, anion exchange membrane, imidazolium, nickel catalyst, polyphenylene
Imidazolium hydroxide anion exchange membranes functionalized with conjugated tetraphenylethylene moieties were synthesized via Ni(0) catalyzed polymerization by sequential chloromethylation, substitution with imidazoliums and ion exchange. Moreover, with their pendant benzoyl groups the copolymers showed high molecular weight, durability, thermo-oxidative stability, high solubility in polar aprotic solvents and strong chemical and thermal stability in comparison to alkyl quaternary ammonium-functionalized polymers. The proposed polymer membranes, without ether linkages, demonstrated improved performance in ion exchange capacity, water uptake, ion conductivity, and thermal stability. The polymer membranes were studied by ¹H-NMR (Nuclear Magnetic Resonance) spectroscopy, thermogravimetric analysis, water uptake, ion exchange capacity and ion conductivity. Surface morphologies were assessed by atomic force microscope (AFM). The synthesized polymers may have applications as fuel cell memb... [more]
How the Chlorine Treatment and the Stoichiometry Influences the Grain Boundary Passivation in Polycrystalline CdTe Thin Films
Alessio Bosio, Greta Rosa, Daniele Menossi, Nicola Romeo
November 27, 2018 (v1)
Subject: Materials
Keywords: cadmium telluride, chlorine treatment, close-spaced sublimation, grain boundaries passivation
The absorption coefficient of CdTe is large enough to assure that all of the visible light is absorbed in a thickness on the order of 1 µm. High efficiency devices are fabricated by using close-spaced sublimation (CSS)-deposited CdTe films with a thickness in the range of 6⁻8 µm. In order to decrease the thickness of the CdTe film, a novel approach has been used. On top of the CdTe film, whose thickness is reduced to 2⁻3 μm, another CdTe layer is deposited by RF sputtering, with a thickness of 100⁻200 nm. The purpose of this approach is to fill up the voids, which tend to form when a low thickness-CdTe film is deposited by close-spaced sublimation. Using this CdTe double layer, solar cells, with an efficiency greater than 15%, were reproducibly obtained. Since the CdTe layer deposited by the CSS technique shows a p-type behavior, whereas the layer deposited by sputtering is n-type, it is supposed that the formation of a p-n junction into the grain boundaries, which makes a mirror for t... [more]
Towards Renewable Iodide Sources for Electrolytes in Dye-Sensitized Solar Cells
Iryna Sagaidak, Guillaume Huertas, Albert Nguyen Van Nhien, Frédéric Sauvage
November 27, 2018 (v1)
Subject: Materials
Keywords: dye-sensitized solar cells (DSC), ionic liquids, liquid electrolyte, sugar-based iodide sources
A novel family of iodide salts and ionic liquids based on different carbohydrate core units is herein described for application in dye-sensitized solar cell (DSC). The influence of the molecular skeleton and the cationic structure on the electrolyte properties, device performance and on interfacial charge transfer has been investigated. In combination with the C106 polypyridyl ruthenium sensitizer, power conversion efficiencies lying between 5.0% and 7.3% under standard Air Mass (A.M.) 1.5G conditions were obtained in association with a low volatile methoxypropionitrile (MPN)-based electrolyte.
Lightweight Borohydrides Electro-Activity in Lithium Cells
Daniele Meggiolaro, Luca Farina, Laura Silvestri, Stefania Panero, Sergio Brutti, Priscilla Reale
November 27, 2018 (v1)
Subject: Materials
Keywords: borohydrides, conversion reactions, lithium-ion batteries, negative electrodes
As a substitute for graphite, the negative electrode material commonly used in Li-ion batteries, hydrides have the theoretical potential to overcome performance limits of the current state-of-the-art Li-ion cells. Hydrides can operate through a conversion process proved for some interstitial hydrides like MgH₂: MxAy + n Li = x M + y LimA, where m = n/y. Even if far from optimization, outstanding performances were observed, drawing the attention to the whole hydride family. Looking for high capacity systems, lightweight complex metal hydrides, such as borohydrides, deserve consideration. Capacities in the order of 2000⁻4000 mAh/g can be theoretically expected thanks to the very low formula unit weight. Although the potential technological impact of these materials can lead to major breakthroughs in Li-ion batteries, this new research field requires the tackling of fundamental issues that are completely unexplored. Here, our recent findings on the incorporation of borohydrides are presen... [more]
Synergistic Optimization of Thermoelectric Performance in P-Type Bi0.48Sb1.52Te₃/Graphene Composite
Dewen Xie, Jingtao Xu, Guoqiang Liu, Zhu Liu, Hezhu Shao, Xiaojian Tan, Jun Jiang, Haochuan Jiang
November 27, 2018 (v1)
Subject: Materials
Keywords: Bi0.48Sb1.52Te3, graphene, microstructure, synergistic optimization, thermoelectrical materials
We report the synergistic optimization of the thermoelectric properties in p-type Bi0.48Sb1.52Te₃ by the additional graphene. Highly dense Bi0.48Sb1.52Te₃ + graphene (x wt%, x = 0, 0.05, 0.1 and 0.15) composites have been synthesized by zone-melting followed by spark plasma sintering. With the help of scanning electron microscopy, the graphene has been clearly observed at the edge of the grain in the composites. Due to the additional graphene, the composites show an improved power factor of 4.8 × 10−3 Wm−1K−2 with modified carrier concentration and suppressed lattice thermal conductivity. Consequently, synergistic optimization in electrical and lattice properties by additional graphene leads to a great improvement in the figure of merit ZT (1.25 at 320 K).
S-Rich CdS1−yTey Thin Films Produced by the Spray Pyrolysis Technique
Shadia J. Ikhmayies
November 27, 2018 (v1)
Subject: Materials
Keywords: CdS/CdTe solar cells, CdSxTe1−x solid solution, interdiffusion, photoluminescence, spray pyrolysis
Understanding the properties of CdSTe ternary alloys is important because they always form at the interface between the CdS window layer and CdTe absorber layer in CdS/CdTe solar cells due to the intermixing. This interdiffusion is necessary because it improves the device performance. Experimental work has been devoted to studying Te rich p-type CdSxTe1−x alloys, but there is a lack of studies on S-rich n-type CdS1−yTey solid solutions. In this work, a review of the structure, morphology, and optical properties of the S-rich n-type CdS1−yTey thin films produced by the spray pyrolysis technique on glass substrates is presented.
Gas-Phase Mass-Transfer Resistances at Polymeric Electrolyte Membrane Fuel Cells Electrodes: Theoretical Analysis on the Effectiveness of Interdigitated and Serpentine Flow Arrangements
Elisabetta Arato, Marzia Pinna, Michela Mazzoccoli, Barbara Bosio
November 27, 2018 (v1)
Subject: Materials
Keywords: gas flow mode, Modelling, polymeric membrane fuel cells, transport phenomena
Mass transfer phenomena in polymeric electrolyte membrane fuel cells (PEMFC) electrodes has already been analyzed in terms of the interactions between diffusive and forced flows. It was demonstrated that the whole phenomenon could be summarized by expressing the Sherwood number as a function of the Peclet number. The dependence of Sherwood number on Peclet one Sh(Pe) function, which was initially deduced by determining three different flow regimes, has now been given a more accurate description. A comparison between the approximate and the accurate results for a reference condition of diluted reactant and limit current has shown that the former are useful for rapid, preliminary calculations. However, a more precise and reliable estimation of the Sherwood number is worth attention, as it provides a detailed description of the electrochemical kinetics and allows a reliable comparison of the various geometrical arrangements used for the distribution of the reactants.
Thermo-Economic Analysis of Zeotropic Mixtures and Pure Working Fluids in Organic Rankine Cycles for Waste Heat Recovery
Florian Heberle, Dieter Brüggemann
November 27, 2018 (v1)
Subject: Materials
Keywords: energy conversion systems, Organic Rankine Cycle (ORC), thermo-economic analysis, waste heat recovery, working fluids, zeotropic mixtures
We present a thermo-economic analysis of an Organic Rankine Cycle (ORC) for waste heat recovery. A case study for a heat source temperature of 150 °C and a subcritical, saturated cycle is performed. As working fluids R245fa, isobutane, isopentane, and the mixture of isobutane and isopentane are considered. The minimal temperature difference in the evaporator and the condenser, as well as the mixture composition are chosen as variables in order to identify the most suitable working fluid in combination with optimal process parameters under thermo-economic criteria. In general, the results show that cost-effective systems have a high minimal temperature difference ΔTPP,C at the pinch-point of the condenser and a low minimal temperature difference ΔTPP,E at the pinch-point of the evaporator. Choosing isobutane as the working fluid leads to the lowest costs per unit exergy with 52.0 €/GJ (ΔTPP,E = 1.2 K; ΔTPP,C = 14 K). Considering the major components of the ORC, specific costs range betw... [more]
Electrochemical Mechanism for FeS₂/C Composite in Lithium Ion Batteries with Enhanced Reversible Capacity
Shengping Wang, Jingxian Yu
November 27, 2018 (v1)
Subject: Materials
Keywords: composites, electrochemical measurements, electrochemical properties
Nanoscale FeS₂ was synthesized via a simple hydrothermal method and was decorated by hydrothermal carbonization (FeS₂@C). The structural properties of the synthesized materials detected by X-ray diffraction (XRD), together with the morphologies characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the hydrothermal carbonization only had an impact on the morphology of pyrite. Additionally, the electrochemical performance of the coated pyrite in Li/FeS₂ batteries was evaluated by galvanostatic discharge-charge tests and electrochemical impedance spectroscopy (EIS). The results showed that the initial capacity of FeS₂@C was 799.2 mAh·g−1 (90% of theoretical capacity of FeS₂) and that of uncoated FeS₂ was only 574.6 mAh·g−1. XRD and ultraviolet (UV) visible spectroscopy results at different depths of discharge-charge for FeS₂ were discussed to clarify the electrochemical mechanism, which play an important part in Li/FeS₂ batteries.
Advances in Thin-Film Si Solar Cells by Means of SiOx Alloys
Lucia V. Mercaldo, Iurie Usatii, Paola Delli Veneri
November 27, 2018 (v1)
Subject: Materials
Keywords: mixed-phase materials, plasma enhanced chemical vapor deposition (PECVD), silicon oxide, solar cells, thin-film Si
The conversion efficiency of thin-film silicon solar cells needs to be improved to be competitive with respect to other technologies. For a more efficient use of light across the solar spectrum, multi-junction architectures are being considered. Light-management considerations are also crucial in order to maximize light absorption in the active regions with a minimum of parasitic optical losses in the supportive layers. Intrinsic and doped silicon oxide alloys can be advantageously applied within thin-film Si solar cells for these purposes. Intrinsic a-SiOx:H films have been fabricated and characterized as a promising wide gap absorber for application in triple-junction solar cells. Single-junction test devices with open circuit voltage up to 950 mV and ~1 V have been demonstrated, in case of rough and flat front electrodes, respectively. Doped silicon oxide alloys with mixed-phase structure have been developed, characterized by considerably lower absorption and refractive index with r... [more]
Progress on Low-Temperature Pulsed Electron Deposition of CuInGaSe₂ Solar Cells
Massimo Mazzer, Stefano Rampino, Enos Gombia, Matteo Bronzoni, Francesco Bissoli, Francesco Pattini, Marco Calicchio, Aldo Kingma, Filippo Annoni, Davide Calestani, Nicholas Cavallari, Vimalkumar Thottapurath Vijayan, Mauro Lomascolo, Arianna Cretì, Edmondo Gilioli
November 27, 2018 (v1)
Subject: Materials
Keywords: CuInGaSe2 (CIGS), photovoltaics, pulsed electron deposition, thin films
The quest for single-stage deposition of CuInGaSe₂ (CIGS) is an open race to replace very effective but capital intensive thin film solar cell manufacturing processes like multiple-stage coevaporation or sputtering combined with high pressure selenisation treatments. In this paper the most recent achievements of Low Temperature Pulsed Electron Deposition (LTPED), a novel single stage deposition process by which CIGS can be deposited at 250 °C, are presented and discussed. We show that selenium loss during the film deposition is not a problem with LTPED as good crystalline films are formed very close to the melting temperature of selenium. The mechanism of formation of good ohmic contacts between CIGS and Mo in the absence of any MoSe₂ transition layers is also illustrated, followed by a brief summary of the measured characteristics of test solar cells grown by LTPED. The 17% efficiency target achieved by lab-scale CIGS devices without bandgap modulation, antireflection coating or K-dop... [more]
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