Bilateral energy conferenceCC
Materials for electrochemical energy conversion - from modular to large-scale energy generation and storage
Electrochemical energy generation and storage is becoming an area of increasing interest, due to factors related to the increased penetration of renewable energy, limitations related to intermittency of renewable energy, limitations in other energy storage approaches, and the high theoretical efficiencies possible with most electrochemical devices. An emphasis has grown in the scale of deployment and both modular, dispersed solutions and large-scale approaches are being investigated. Many of the approaches are still highly dependent on materials advances as key enabling elements.
Electrochemical energy conversion devices include batteries (primary and secondary), fuel cells, electrolyzers, and flow batteries. Historically, these devices have been primarily investigated for their use at relatively low energy or power levels with few examples that have approached the megawatt or megawatt-hour level. In order to make a greater impact on the electrical energy system the scale of these devices and their deployment needs to increase significantly. Traditional large scale electricity generating approaches, such as natural gas, coal and nuclear power plants have significant benefits (on a per KW basis) tending towards larger scales. Electrochemical devices typically have reduced gains in the economy of scale and make smaller distributed systems another interesting potential approach. Cost competitiveness remains a barrier for larger wide spread adoption of these technologies, and materials approaches are being pursued.
Electrochemical energy conversion devices have the ability to fit into larger energy systems in a number of ways. They can serve as sources of electricity generation from fuels (fuel cells), they can convert electrical energy in chemical form (electrolyzers), or they store electrical energy for some period of time and return electricity back at some later time (secondary batteries, flow batteries, reversible fuel cells).
In the area of energy generation, fuels (most notably natural gas) can be directly converted by fuel cells into electrical energy, often with useful heat (combined heat and power) as a valuable byproduct. Solid oxide fuel cells (SOFCs), molten carbonate fuel cells (MCFCs), phosphoric acid fuel cells (PAFCs) including those based on polybenzimidazole(PBI) and proton exchange membrane fuel cells (PEMFCs) have all been explored for their applicability in energy generation.
In the area of electrochemical conversion of electrical energy to fuel, specifically water electrolyzers, the scale of deployment to enable functions such as load leveling needs to be increased significantly. A number of new projects/programs are looking into the possibility of large scale electrolysis. The historic approach has been focused on aqueous potassium hydroxide as an electrolyte, although increasing interest in being given in the areas of solid oxide, proton exchange membrane, and alkaline membrane electrolysis. Each of these approaches has different limitations ranging from struggles with intermittent/high temperature operation to efficiency/precious metal catalysis to durability and lifetime.
In the area of electrical energy storage (secondary batteries, flow batteries, reversible fuel cells) the direct competition is with technologies such as pumped hydro and compressed air. These competing technologies don’t scale well down to small sizes and are limited geographically available. Depending on the specific technology the issues range from cost, durability, energy density and/or efficiency.
Contributions are sought in all areas where electrochemical energy devices are being investigated.
Topics to be covered by the symposium:
- Polymer electrolyte fuel cells, including high temperature PBI/phos acid systems
- Alkaline membrane fuel cells
- Solid oxide fuel cells
- Flow batteries
- Membranes, electrolytes, separators
Bryan S. Pivovar
National Renewable Energy Laboratory
15013 Denver West Parkway
Golden, CO 80401
Phone: +1 303 275 3809
Fax: +1 303 275 3840
Institut Charles Gerhardt de Montpellier UMR 5253
CNRS - Universite Montpellier II
Aggregates, Interfaces and Materials for Energy
Place Eugene Bataillon, Building 15, CC 1502
34095 Montpellier cedex 5
Phone : +33 467 14 3330
Fax : +33 467 14 3304
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Authors : E. A. Kotomin, R. Merkle, Yu. A. Mastrikov, M.M. Kuklja, J. Maier
Affiliations : Max Planck Institute for Solid State Research, Heisenbergstr., Stuttgart, Germany; Institute for Solid State Physics, University of Latvia, Riga, Latvia, Materials Science and Engineering Dept., University of Maryland, College Park, USA
Resume : In this talk, we discuss calculated from first principles the atomic and electronic structure of oxygen vacancies, their formation and migration energies in the bulk and in the surface layer, the defect-induced electronic density redistribution, and dependence of defect properties on the chemical composition of the (Ba,Sr)(Co,Fe)O3 (BSCF) (Fe/Co ratio). Our calculations confirm that the O-vacancy formation and, in particular, migration energies in BSCF are considerably smaller than in similar (La,Sr)MnO3 (LSM) and (La,Sr)(Co,Fe)O3 (LSCF) perovskites which explains its good performance. The gradual increase of these energies with an increase of the iron content is explained by analysis of the calculated density of the states. We discuss also briefly the problem of complex perovskites stability with respect to the decomposition into mixture of cubic and hexagonal phases or parent perovskites and oxides. Based on the calculated formation and migration energies of oxygen vacancies and adsorbed oxygen atoms at the LSM surface, we calculated the rates of elementary steps in ORR and suggested different scenatios of this process in LSM, BSCF, LSCF as a function surface coverage with adsorbed atoms and oxygen vacancy concentration. We predict that in both LSCF and BSCF perovskites the dissociation of surface peroxide or superoxide ion occurs with assistance of Vo, their encounter being the rate- determining step. M. Kuklja, E. Kotomin, R. Merkle et al, PCCP 15, 5443 (2013).
Poster Session : Bryan Pivovar and Deborah Jones
Authors : Doohun Kim, Yoon-Cheol Ha, Chuhyun Cho, Won-jae Lee, Chil-Hoon Doh
Affiliations : Battery Research Center, Korea Electrotechnology Research Institute, Chagwon, Republic of Korea
Resume : A novel technique of electrical explosion has been used for nanomaterial synthesis by a single-step process. However, it was known that in principle the electrical explosion of Si is not possible due to the fact that applying a high voltage on Si wire having relatively high electrical resistance leads to a current flow through surface plasma formed along the wire which disables the resistive heating of Si. In this presentation, we will show the successful application of electrical explosion to silicon nanoparticle synthesis and the electrochemical properties of Si/C nanocomposites derived from the nanoparticles. The electrical explosion of Si was successfully applied using a liquid media to suppress the unfavorable surface plasma generation. The physical and chemical properties of the produced materials were analyzed by XRD, FE-SEM, HR-TEM and the performances of the Si/C composites as an anode for Li ion batteries were investigated by electrochemical charge/discharge measurements. The Si/C composites obtained under the explosion in hexane and ethanol consist of a core-shell structure with a compact graphitic carbon on the Si particle surface which cause detrimental effects against Li ion diffusion. However, we found that Si explosion in methanol minimized the formation of the carbon phase on the surface of nano-sized Si. The Si/C nanocomposite after a simple pyrolysis with carbon precursor showed a high capacity with an excellent cycle performance.
Authors : Jong-Won Lee, Beom-Kyeong Park, Nurhadi S. Waluyo, Seung-Bok Lee, Tak-Hyoung Lim, Seok-Joo Park, Rak-Hyun Song
Affiliations : New and Renewable Energy Research Division, Korea Institute of Energy Research, 152 Gajeong-ro, Yuseong-gu, Daejeon, 305-343, Republic of Korea
Resume : Solid oxide fuel cells (SOFCs) offer several advantages over low-temperature fuel cells, e.g., high thermodynamic efficiency, fast electrode kinetics, and direct use of hydrocarbon fuels. An interconnect provides electrical connection between adjacent cells and separates fuel and oxidant gases. The interconnects can be divided broadly into two categories ceramic and metallic interconnects. A thin and gastight ceramic layer is deposited onto a porous support, and metallic interconnects are coated with conductive ceramics to improve their surface stability. Here, we report on SOFC interconnect coatings based on perovskite-type oxides. A dual-layer ceramic interconnect is first discussed that consists of an n-type conducting (Sr,La)TiO3 layer on the anode side and a p-type conducting (La,Sr)FeO3 layer on the cathode side. Then, protective perovskite coatings of (La,Sr)MO3 (M = transition metals) on metallic interconnects are presented, which are capable of mitigating oxide scale growth and inhibiting Cr evaporation. The synthesis of perovskite oxides and their electrical/thermal expansion properties are discussed in detail, followed by a description of coating processes. We demonstrate that the dense interconnect or protective layers are fabricated by a simple and cost-effective coatingsintering process and they exhibit low resistance and high stability under SOFC operating conditions.
Authors : Jong Deok Park, Sung Ho Lee, and Haekyoung Kim
Affiliations : School of Materials Science and Engineering, Yeungnam University, Gyeungsan, South Korea
Resume : With the expanding need for large electrical energy storage systems in connection with renewable energy sources, flow batteries, have been enormously considered due to their high flexibility in upgrade and low cost associated with scale-up. Of all the flow batteries, vanadium redox flow battery (VRFB) use of same element in both half-cell solutions that overcomes the inherent issue of cross contamination by diffusion of different ions across the membrane. Together with the absence of any toxic emissions, the vanadium redox flow battery has demonstrated its uniqueness in terms of safety and long life cycle. Typical chargedischarge reactions of a VRFB involve two vanadium redox couples, V(II)/V(III) and V(IV)/V(V), in the negative and positive half-cells, respectively. In a fashion similar to most batteries, electrons are transferred between the two electrodes through the external circuit during the charge and discharge processes. In a VRFB, the ion exchange membrane is a key component as an ionic conductor and separator: it not only provides an ionic conduction pathway between the two electrolytes but also prevents mixing of the negative and positive electrolytes. The crossover of ions through the membrane, with the diffusion of vanadium ions from one half-cell to the other due to the concentration gradients between the two electrolytes, will result in self-discharge and thus the loss of the chemical energy. In this study, the hybrid membrane of inorganic materials with perfluorinated organic membrane were fabricated and characterized in terms of ionic conductivity and permeability. The ionic conductivity was measured with four point probe method and the permeability was measured with UV spectroscopy. The hybrid membrane exhibited similar ionic conductivity with perfluorinated organic membrane and 30% lower permeability than perfluorinated organic membrane.
Authors : Hyunuk Kim, Young-Ju Lee, Sung-Jin Lee, Yong-Sik Chung2, Yoonjong Yoo*
Affiliations : Korea Institute of Energy Research;2Chonbuk National University
Resume : Carbon papers (CPs) were fabricated using wet-laying carbon fibers (CFs) and polyacrylonitrile (PAN) fibers. Scanning electron microscopy revealed that the PAN fibers tightly interconnected the CF junctions with the pores. The tensile strength of the carbon webs (CWs) increased as the fraction of PAN fibers used as the binder increased. The CW fabricated with 0.15 wt.% PAN fibers had a tensile strength six times greater than that of a bare CW. Moreover, by mixing the CFs with PAN fibers in water, the CFs separated from each other in the webs due to the interruption of hydrophobicity between the CFs. After the CWs were pyrolyzed at 1200 C in the presence of a phenolic resin, the PAN fibers maintained their morphology due to their high carbon content. The resistance of the CPs with high PAN fiber content was significantly lower than that of a bare CP due to the interconnection of the CFs by the carbonized PAN fibers.
Authors : Arbi Fattoum, Mourad Arous
Affiliations : Research Unit: Materials Environment and Energy, chemistry department, faculty of sciences 2112 Gafsa, Tunisia; Laboratory of Composite Materials, Ceramics and Polymers, physics department, faculty of sciences 3038 Sfax, Tunisia.
Resume : In this work we investigated composite electrolytes of 25 and 50 mol% cross linked polyvinyl alcohol by oxalic and citric acids for fuel cell application. We studied the effects of crosslinking on thermal, structural, conductivity and dielectric relaxations. The glass transition temperature is increased indicating the decrease of the local mobility of the polymer chains. X-ray diffraction showed the decrease of the cristallinity degree. The Ac conductivity studied between 10-1Hz and 1MHz showed a power law response in the high frequency range. This behavior characterizes the charge transport in disordered materials. At low frequencies the Ac conductivity is governed by the electrode/sample interface polarization. The dc conductivity is thermally activated and the activation energy is deduced from an Arrhenius fitting. The use of the dielectric permittivity indicates the presence of a relaxation process attributed to electrode/sample interface polarization and another relaxation process attributed to alpha relaxation of the polyvinyl alcohol matrix.
Authors : Veerapandian Ponnuchamy ; Stefano Mossa ; Valentina Vetere
Affiliations : INAC/SPrAM/GT ; INAC/SPrAM/GT ; CEA / DRT/DEHT/LCPEM, CEA-Grenoble, 17 Rue des Martyrs, 38054 Grenoble, France.
Resume : The electrolyte plays an important role in Lithium ion batteries(LIB's). Organic solvents such as cyclic and linear carbonates are commonly used in LIB's. It is very important to investigate the structure and dynamics of Li+ ion in pure and mixed solvent compositions. Although there are some DFT studies of Li+ ion with single solvent, in several applications mixtures of three solvent are used to improve stability and transport properties. Here we focus on three carbonates such as cyclic ethylene carbonate(EC), propylene carbonate(PC) and linear dimethyl carbonate(DMC). The DFT method provides a detailed account for the electronic structures of carbonates and Li+ ion including clusters Li+(S)n (S=EC,PC,DMC n=1-4) and mixed cluster Li+(EClDMCmPCn) (l+m+n=4) in gas phase as well as in solvent environment and including the effect of PF6- anion. The results show that carbonates mainly interact through the intermolecular Li+ --O=C. We have studied the coordination shell around Li+ for three solvents. We have investigated the Mulliken charges and vibrational modes with solvent molecules varying from 1 to 4 and thermodynamics properties used to clarify the stability of clusters.Study of clusters of EC and PC reveals that PC tends to substitute EC in the solvation shell. These DFT calculations were performed at the level of GGA/PBE using TZP basis. This study will be used to develop Molecular Dynamics studies that will help to understand the transport properties of Li+ ion in LIB's.
Authors : Adriana Balan (1), Alexandra Trefilov(1), Catalin Luculescu(2), Stefan Iordache(1), Ioan Stamatin(1)
Affiliations : (1)University of Bucharest, Faculty of Physics, 3Nano-SAE Research Centre, P.O.Box MG-38, 077125 Magurele, Romania (2) National Institute for Lasers, Plasma, and Radiation Physics, 409 Atomistilor Street, RO-77125, MG-36, Magurele-Ilfov, Romania
Resume : The aim of this study is to design a hybrid electrolyte with a three-layer structure: a proton conducting polymer layer on one side of a resorcinol-formaldehyde (RF) porous structure, while the other is impregnated with an anion conducting polymer. The sandwich structure enables protons generated at the anode to progress toward the center and meet hydroxyl ions created at the cathode to form water, which is directed through the porous RF network. The hybrid electrolyte ensures an efficient water management by preventing water presence at electrode sites and, hence, related problems: corrosion, low fuel efficiency. Specific structural features are identified by means of Fourier transform infrared spectroscopy, while information on the polymer/porous RF network interfaces are revealed by scanning electron microscopy. Electrochemical characteristics are studied through electrochemical impedance spectroscopy. Further on, the hybrid electrolyte is tested in H2/air fuel cell system, with a Pt catalyst load of 1mg/cm^2 at both anode and cathode, reaching a maximum current density of 400-600mA/cm^2 at a voltage of 0.6-0.7V.
Authors : Catalin Ceaus(1), Adriana Balan(1), A.M. Iordache(1), *Ioan Stamatin(1), Catalin Luculescu(2)
Affiliations : (1)University of Bucharest, Faculty of Physics, 3Nano-SAE Research Centre PO Box MG-38, Bucharest-Magurele, Romania (2)National Institute for Lasers, Plasma, and Radiation Physics, 409 Atomistilor Street, RO-77125, MG-36, Magurele-Ilfov, Romania *corresponding author: email@example.com
Resume : Looking for high quality graphene and their mass production, today are devised a series of experimental methods from basics (e.g. scotch tape method, kish graphite, high pyrolitic graphite) to graphene oxide reduction with different reducing agents (hydrazine, tetraborohydrides). Few studies deal with graphite exfoliation at moderate pressures and temperature (close to 4000C) in different solvents (e.g. water, ethanol, tetrahydofuran, DMF, methanol). On the other hand, the expandable graphite (intumescent graphite) is a stack of intercalated graphene with different inercalants like nitric, sulphuric, acetic compounds. The graphene result from a high oxidative process of intercalation such as nitric-sulphuric acids followed by flash heating at high temperatures (up to 4000C) to insert sulphate compounds (sometimes referred to as graphite bisulphate). Based on these considerations, this study deals with graphite exfoliation in few layers (up to five layers) graphene using reactive species developed by water and ethanol in different mixtures under criticalsupercritical conditions, at a set temperature and time. Structural investigation by atomic force microscopy, Raman spectroscopy and scanning electron microscopy reveal structures with a single to a few layers (up to five) of graphene. Cyclic voltammetry, performed in a three electrode cell, in acidic and basic media, shows few reversible peaks in the range 750mV - 570mV (in 0.1M HClO4)... This report provides a simple and low-cost approach for the production of pure graphene sheets, with a wide range of applications: fuel cells, supercapacitors, solar cells, electrochemical sensors.
Authors : A. Cucu, E. C. Serban, A. Balan, C.Ceaus, A-M Ducu, L. Popovici, I. Stamatin
Affiliations : University of Bucharest, Faculty of Physics, 3Nano-SAE Research Centre, MG-38, Bucharest-Magurele, Romania
Resume : Major drawbacks in fuel cells performance is determined by the oxygen reduction reaction (ORR) which is sluggish than the hydrogen oxidation reaction (HOR). Extensive researches made over the past decades have focused in improving the ORR kinetics by using different catalysts: noble metals (Pt), alloys, carbon materials, quinone, transition metals chalcogenides, transition metals carbides and heteropolyacids. One approach is to utilize heteropolyacids (HPA) as potential cathode mediators, due to their acidic and redox properties, their potential to carry complex counter-cations (e.g. H+, H3O+, H5O2+) and their thermal stability. Three types of heteropolyacids: phosphomolibdic acid, phosphotungstic acid and tungstosilicic acid where studied as redox mediators in the cathodic chamber. The experimental set-up consists of a bicameral fuel cell with Nafion membrane. The anodic chamber acts as the source of hydrated protons at a given potential (equivalent with a reversible hydrogen electrode); the cathode chamber contains the aqueous HPA mediators recirculate in different conditions of flow and oxygen concentration. Electrochemical impedance spectroscopy, cyclic voltammetry and polarization curves were carried out to identify kinetics mechanisms related to ORR improvement.
Authors : E. C. Serban, A. Balan, A. M. I. Trefilov, A. Cucu and I. Stamatin
Affiliations : University of Bucharest, Physics Department, 3Nano-SAE Research Centre, Atomistilor Street, Nr. 405, P.O Box 38, Bucharest-Magurele, 07712, Romania,
Resume : Urea Fuel Cells employ a non-toxic, non-flammable and transport-friendly (without pressurization need) fuel that can be easily recovered from waste water. The present study investigates the urea fuel cells performance, using a new membrane-electrode assembly based on an anion exchange resin in a polyvinyl alcohol polymer matrix. Composite membrane intrinsic properties are studied in terms of ion-exchange capacity (IEC), water content, transport number, and thermal stability. Results show an IEC and water content increase with resin content, while polymer glass transition temperature and melting points shift due to hydrogen bonding between polymer and resin. Urea fuel cell testing is performed using Pt/C at both anode and cathode, for different urea concentrations, ranging from 1 to 7 M.
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Authors : Vijay Shankar Rangasamy 1*, Savitha Thayumanasundaram 1, Jin Won Seo 2, Jean-Pierre Locquet 1
Affiliations : 1. Department of Physics and Astronomy, KU Leuven, Bus 2414, Celestijnenlaan 200D, 3000 Leuven, Belgium; 2. Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg 44 - bus 2450, B-3001 Leuven, Belgium
Resume : We report the vibrational properties and the changes in the degree of crystallinity of poly(ether ether ketone) (PEEK) membranes by using Fourier transform infrared (FTIR) spectroscopy. The changes in the vibrational modes of the functional groups present in the polymer due to sulfonation and the incorporation of functionalized silica particles are discussed. From the infrared spectra, the incorporation of sulfonic acid group in the polymer chain as well as in the functionalized silica nanoparticles was confirmed. We have attempted a non-destructive method to calculate the crystallinity of polymers by measuring the variations in the peak area intensity of the characteristic out-of-plane vibrations of the aromatic rings in the PEEK polymer with respect to a crystallinity-insensitive reference peak. These values were correlated to the crystallinity values calculated by Differential Scanning Calorimetry (DSC). High degree of sulfonation (DS) values decreased the crystallinity of the polymer, indicating the crystalline-to-amorphous phase transition in the polymer, which explains the improved ionic conductivity at high DS values. Keywords: SPEEK, FTIR, sulfonation, silica, crystallinity, DSC
Authors : Timothy N. Lambert,* Danae J. Davis, Julian A. Vigil, and Steven Limmer
Affiliations : Department of Materials, Devices, and Energy Technologies, Sandia National Laboratories, Albuquerque, New Mexico 87185, Fax: 505-844-7786; Tel.: 505-284-6967; *Email: firstname.lastname@example.org
Resume : Reversible oxygen electrochemistry is vital to numerous future renewable energy technologies, such as fuel cells, metal-air batteries, and electrolyzers. Active electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are known; however, they are typically expensive and based on rare materials such as Pt (for ORR) and Ir or IrOx (for OER). These can also suffer from reaction poisoning and poor electrochemical selectivity, further decreasing their utility. Therefore, catalyst materials that are highly active, stable, and cost-effective are needed. We have recently begun developing catalysts for oxygen electrochemistry in aqueous electrolytes. We will present on Cu-α-MnO2 nanowire electrocatalysts and demonstrate how various Cu-ion doping amounts alter the nanowire surface area, crystalline lattice, conductivity, and the manganese oxidation state; we then rationalize how these factors impact the activity for the ORR. We will demonstrate that when blended with a graphene-like carbon, Cu-α-MnO2 compares well to the Pt/C benchmark for the ORR in alkaline electrolyte. We will also present on our new porous Co3O4 and NixCo3-xO4 spinel films. Electrocatalytic data shows performance rivaling that of commercial benchmarks and recent literature catalysts for both the ORR and the OER. These electrocatalysts hold much promise for improving the efficiency of devices reliant on reversible oxygen electrochemistry. This work was supported by Sandia National Laboratories: Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energys National Nuclear Security Administration under Contract DE-AC04-94AL85000.
Authors : Chinmoy ranjan, Zoran Pavlovic, Robert Schloegl
Affiliations : Max Planck Institute for Chemical Energy Conversion
Resume : Non noble metal "earth abundant" electrocatalysts will significantly reduce the costs and make it possible to use electrochemical water splitting (electrolysis) on a very large scale. Non noble metal catalysts can be an effective replacement even if their electrochemical activities are a fraction of their noble metal counterparts. If these catalysts can be developed to an extent where their operational lifetime would become comparable to their noble metal counterparts, a large part of the problem would be solved. MnO2 is earth abundant and well known for catalyzing oxygen evolution. A form of MnOx cluster is known to catalyze water oxidation in photosynthesis. The problem is that the catalyst comes with a significant corrosion problem. Besides that MnO2-xnaturally exists in various polymorphs, with various amounts of defects each of which is known to have a different electrocatalytic performance. Poor ballistic electronic conduction (important for good electrode materials) is also a prevalent issue with these oxides. These catalysts although with immense potential remain a long way from successful implementation within electrolysers. In order to understand the limitations of this catalyst under the operational conditions, it is important to study this material in situ. Setup for in situ Surface Enhanced Raman Spectroscopy is used for tracking the structural changes of hydrous MnOx. Electrodeposition of MnOx on the surface of Au was achieved by passing an anodic current of 50 mC/cm2 at 1,6V. The resulting MnO2 phase could be termed as the alpha/MnO2 phase. The structural integrity of the MnOx was studied by following the Mn-O-Mn stretching various potential ranges in various electrolytes. Onset of phase changes and corrosion could be clearly established. Beside this, other methods such as XRD, SEM, TEM where applied to study these thin films.
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Lithium Batteries : Mike Toney and Stefan Adams
Authors : Johanna Nelson Weker, Nian Liu, Joy C. Andrews, Yi Cui, Michael F. Toney
Affiliations : Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA Department of Materials Sciences, Stanford University, Stanford, CA
Resume : Germanium has a significantly higher theoretical energy storage capacity (1600 mAhg-1) than the carbon-based anodes (372 mAhg-1) presently used in Li-ion batteries and Ge has relatively high electronic conductivity and room temperature Li-ion diffusivity. Yet large volume changes during operation severely limit Ge anode lifetimes. To understand the dynamics and failure mechanism of these and other electrode materials, it is essential to image batteries under operating conditions. Here we show significant size dependence on the cycling characteristics of micron-sized Ge particles employing hard X-ray microscopy during typical battery operation. We found smaller Ge particles experience volume expansion before their larger counterparts. However, these small particles rapidly lose electrical contact and only the largest particles contribute to the battery capacity in the second cycle. Finally, we found particles with larger surface area to volume ratios have greater volume changes during lithiation. Our results demonstrate the significant value in high resolution imaging of batteries under operating conditions and suggest possible strategies to mitigate capacity fade in Ge and Si anodes.
Authors : Marketa Zukalova, Barbora Laskova, Arnost Zukal, Milan Bousa, Ladislav Kavan
Affiliations : J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic
Resume : TiO2 (B) is metastable monoclinic modification of titanium dioxide. Zukalova et al. found that Li-insertion into TiO2 (B) is characterized by unusually large faradaic pseudocapacitance. This peculiar effect was ascribed to Li-accommodation in open channels of TiO2 (B) structure allowing fast Li-transport in TiO2 (B) lattice along the b axis (perpendicular to (010) face). Analysis of cyclic voltammograms of Li insertion into TiO2 (B) and anatase provides information about capacitive contributions to overall charge of Li-storage. The enhancement of 30% is found in capacitive contributions (normalized to the total stored charges) in TiO2 (B) compared to that in anatase, in spite of ca. three times smaller surface area of the former. Different charging mechanism explains facilitated Li- insertion in TiO2 (B). The difference is caused mainly by pseudocapacitive Li-storage in the bulk TiO2 (B). Deconvolution of cyclic voltammograms also indicates different capacitive contributions of the two voltammetric peaks, S1 and S2 of TiO2 (B). These results provide novel insight into the Li-storage in TiO2 (B) and its difference from that in anatase. This work was supported by the Grant Agency of the Czech Republic (contract No. 108/12/0814).
Authors : D. Safanama,* R. Prasada Rao,* Y. Hu,* N. Sharma,** S. Adams*
Affiliations : * National University of Singapore Department of Materials Science and Engineering;** University of New South Wales, School of Chemistry
Resume : In view of power limitations of organic Li-air batteries, we explore aqueous Li-air batteries with highly soluble discharge products enhancing power performance and energy efficiency, but requiring an electrolyte membrane to prevent a direct contact of Li to the aqueous catholyte. Here we design and test a composite membrane synergizing the robustness of ceramic electrolytes with the flexibility of polymer electrolytes and simplifying design compared to existing multilayer membranes. The optimized membrane contains 70wt% of the NASICON-type high stability electrolyte LAGP (conductivity 5×10^-4 Scm-1) in a polymer matrix of 18wt% PVDF, 6wt% PEO and 6wt% LiBF4. After immersion in acidified 1 M LiCl solution for one month the membrane shows no sign of significant swelling or change in conductivity. An aqueous Li-air cell employing a Li anode, the composite membrane, the catholyte on glass fibre separator and a Pt-impregnated CNT air cathode is constructed and the performance in ambient air is studied. With the LiCl catholyte it showed an open circuit voltage of 3.0 V and the curve has a plateau around 2.9 V (vs. Li). At a constant current density of 1 mAcm-2, the first discharge and charge capacity are 350 and 250 mAh per g of carbon, respectively in the voltage range of 1.0-3.8 (vs. Li/Li+) with low polarization (0.2 V). To investigate the origin of the limited cyclability, the by-products formed during discharge are analyzed by in situ synchrotron studies.
Authors : C.C. H. TRANa, C. DAMASa, A. BENITEZ DE LA TORREb, C. MEDELb, M. CRUZb, J. MORALESb, F. GHAMOUSSa, F. TRAN VANa, A. MERYa, D. FARAHATa, J. SANTOS?PENAa
Affiliations : aLaboratoire de Physicochimie des Mat?riaux et Electrolytes pour l??nergie, Campus de Grandmont, Universit? Fran?ois Rabelais, 37200 Tours (France) bDepartamento de Quimica Inorg?nica e Ingenier?a Qu?mica, Universidad de C?rdoba, Campus de Rabanales, 14071 C?rdoba (Spain)
Resume : Needs of electrochemical energy storage devices have driven great interest in batteries and electrochemical capacitors. Nowadays, RuO2 is the most important oxide-based electrode for electrochemical capacitors. However, ruthenium oxide is quite expensive and other transition metal oxides are currently been investigated as cheaper alternatives. In this context, MnO2 is the most plausible choice . Exploration of these oxides in capacitor devices has shown that, as for RuO2, there is a limited contribution of the electrochemical double layer to the total capacitance, its high value being mostly associated to fast redox reactions taking place at the electrode/electrolyte interface. Therefore, and unlike for traditional carbonaceous materials used as supercapacitor electrodes where the charge storage relies on the electrochemical double layer, the role of mesoporosity in transition metal oxide has been somewhat omitted. In this contribution, we show the synthesis and characterization of mesoporous manganese oxides. Their preparation involved a simple, slow thermal decomposition of an oxalate containing manganese (II) ions . For comparison purposes we have also studied manganese oxide obtained by different original methods including: - the oxidation of alkenes assisted by CTAMnO4 (CTA= cetyltrimethylammonium)  - the oxidation of alcohol, dimethylformamide, ethylene glycol, and glycerol by KMnO4 [4,5]. The latter syntheses would lead to micro or macroporous materials with different particles aggregation than found for the mesoporous oxides. We analyzed the effect of mesoporosity on the electrochemical performances of the different systems synthesized, in terms of capacitance, device resistance and cycling efficiency with aqueous electrolytes. Furthermore, influence of the alkenes hydrophobic chain, the counter-ion of MnO4- group, and, in general, of the reductor agent on the morphology of the final manganese oxide are also determined according to specific and porosity determination by BET analysis and SEM imaging. In addition, several electrochemical techniques, including electrochemical impedance spectroscopy and cyclic voltammetry, have been applied for this research to determine electrochemical performances of these different materials. After the study on three electrode cells, such oxides were tested as positive electrodes in front of negative electrodes based on activated carbon.  D. B?langer, T. Brousse, J.W. Long, The Electrochemical Society Interface (2008) 49?52.  L. Guo, H. Arafune, N. Teramae, Langmuir 29 (2013) 4404?4412.  S. Dash, S. Patel, B. K. Mishra, Tetrahedron 65 (2009) 707?739.  J-L. Liu, L-Z. Fan, X. Qu. Electrochim. Acta 66 (2012) 302?305.  Y-T. Wang, A-H. Lu, W-C. Li. Microp. Mesop. Mater. 153 (2012) 247?253.
Authors : Madjid Arab1*, Ali Hallaoui1,2, Abdeljalil Benlhachemin2, Jean Raymond Gavarri1
Affiliations : 1Université du Sud-Toulon Var, IM2NP, UMR CNRS 6242, BP 20132, 83957, La Garde, France 2 Université Ibn Zohr, LME, BP 32/S Agadir, Maroc
Resume : In this study, we develop tungstate materials as electrocatalysts sensors systems allowing the degradation of pollutant. In this work, tungsten trioxide (WO3) was prepared by electrodeposition and used as anode for electrochemical degradation of Rhodamin B dye in aqueous solution. Oxide film was prepared using a facile one-pot chronoamperometry approach, from an electrolytic solution containing an equimolar mixture of Na2WO4.2H2O and H2O2. Several parameters were optimized to deposit these thin films such as the precursor concentration, current density, substrate, time deposit. X- Ray Diffraction (DRX) analyze was used to identified the oxide structure, scanning electron microscopy (SEM) coupled with EDX for morphological studies. The synthesized films were applied for the electrodegradation of organic pollutants by anodic oxidation. The Rhodamin B is deteriorated by electrochemical root using the three-electrode assembly: the working electrode based on WO3 thin film, Platinum foil as counter electrode and saturated calomel electrode as the reference. Many parameters were varied to find the optimal conditions for the degradation (supporting electrolyte, current density, temperature). Ultraviolet spectroscopy and chemical oxygen demand measurements were conducted to follow degradation rate and study the reaction kinetics of Rhodamin B degradation. Keywords: Electrodeposition, Tungsten oxide, Anodic oxidation, Rhodamin B, Reaction kinetics.
Authors : C. Cherkouk, M. Zschornak, J. Hanzig, M. Nentwich, F. Meutzner, M. Urena, T. Leisegang, D. C. Meyer
Affiliations : Institut für Experimentelle Physik, Technische Universität Bergakademie Freiberg, Leipziger Straße 23, 09596 Freiberg, Germany Fraunhofer-Technologiezentrum Halbleitermaterialien, Am-St.-Niclas-Schacht 13, 09599 Freiberg
Resume : Unpredictable risk of nuclear power energy and, in particular, the energy turnaround in Germany have renewed interest on green power based energy and material conversion, and solutions for efficient energy storage. Electrochemical energy storage technologies are of particular importance due to high achievable energy densities. Especially all-solid-state batteries, which were previously reserved for low power energy devices, such as microchips, wireless sensors or low-power medical applications, offer greater potential in respect to energy density, safety and autarchic power supply for short and long term operation applications. These aspects and new concepts of electrochemical storage technologies are in the focus of a joint research project CryPhysConcept coordinated by the TU Bergakademie Freiberg. This contribution presents a new solid-state battery concept, based on oxide material that aims to use oxygen defect migration in a crystal as electromotive force to store (and release) electric energy. Furthermore, a solid-state air-battery based on thin-film technology containing an oxygen cathode, is addressed in this work. Since the efficiency of metal-air batteries is significantly limited by the activation of oxygen reduction reaction (ORR) as well as of the ion and electron conductivities, an adequate porosity to allow air oxygen to readily diffuse through the cathode material as well as a controlled metal doping is required. The ion implantation of promising transition metal oxides is a key technology to achieve this goal. A co-implanted with Ni2+- and Co2+-ions strontium titanate (SrTiO3) oxide material combined with millisecond flash lamp annealing to create metal clusters, which act as active centres, is used to improve catalytic properties. The depth profile of the samples is characterized by means of Rutherford backscattering spectrometry (RBS) and X-ray diffraction (XRD). The oxygen catalytic properties of the implanted crystalline SrTiO3 will be demonstrated. FEM-simulations are used to improve functionality.
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