913 resultados para biochars, lithium-sulfur batteries, microporous structure, bamboo carbon–sulfur composites
Resumo:
Energy issues have always been a subject of concern to people. During the past 30 years, rechargeable Li-ion batteries (LIBs) have been widely used in portable electronic devices and power tools because of their high energy density and efficiency among practical secondary batteries. While the unevenly distribution of Lithium sources and the increasing cost of lithium-raw material can not satisfy the requirement for further cost reduction, especially for the grid-scale energy storage. Post-lithium ion batteries as promising replacement for LIBs have attracted wide attention, owing to their high abundant resources and adequate insertion potential. Similar with Li-ion batteries, finding a suitable electrode material is the key for the research and application of the post-Li ion batteries. In our project, we focus our study on Prussian blue analogues (PBAs), with formula AxM[M(CN)6]1-yyzH2O (0x2, 0<y<1), where A is alkali-metal ion, M and M are transition metal ions, represents the M(CN)6 vacancy, which are archetype of metal-organic framework, with 3D frameworks which allow for a facile insertion/ extraction of ions with negligible lattice strain. By substituting the metal sites with different transition metals, we can get a series of compounds that can be used as both cathode and anode material for both Li-ion and post-Li batteries. The most commonly studied PBAs are metal haxacyanoferrate, with the carbon-sites of -CN- ligands fix connected with Fe. Here, we synthesized three different PBAs: manganese hexacynoferrate (MnHCF), zinc hexacynoferrate (ZnHCF) and titanium hexacynoferrate (TiHCF), using co-precipitation method, and their electrochemical properties were tested in both aqueous Na+, K+, Mg2+, Zn2+ and organic Li+, Na+ electrolytes. Various X-ray techniques were employed to study their electronic and structural properties of electrodes and electrochemical reaction mechanism during cycling.
Resumo:
Gas sorption by coal is closely related to its physical and chemical properties, which are, in turn, governed by coal type and rank. The role of coal type (sensu maceral composition) is not fully established but it is clear that coal type may affect both adsorption capacity and desorption rate. Adsorption capacity is closely related to micropore (pores <2 nm) development, which is rank and maceral dependent. Adsorption isotherms indicate that in most cases bright (vitrinite-rich) coals have a greater adsorption capacity than their dull (often inertinite-rich) equivalents. However, no differences, or even the opposing trend, may be observed in relation to coal type. Desorption rate investigations have been performed using selected bright and dull coal samples in a high pressure microbalance. Interpretation of results using unipore spherical and bidisperse pore models indicate the importance of the pore structure. Bright, vitrinite-rich coals usually have the slowest desorption rates which is associated with their highly microporous structure. However, rapid desorption in bright coals may be related to development of extensive, unmineralised fracture systems. Both macro-and micro-pore systems are implicated in the more rapidly desorbing dull coals. Some dull, inertinite-rich coals may rapidly desorb due to a predominance of large, open cell lumina. Mineral matter is essentially nonadsorbent to coal gases and acts as a simple diluent. However, mineral-rich coals may be associated with more rapid desorption. Coal rank and type (maceral composition) per se do not appear to be the critical factors in controlling gas sorption, but rather the influence they exert over pore structure development. (C) 1998 Elsevier Science B.V.
Resumo:
The tetraalcohol 2,3,5,6-endo,endo,endo,endo-tetrakis(hydroxymethyl]bicyclo[2.2.1]heptane (tetol, 1) has been prepared and crystallises readily as the lithium(I) complex [Li(1)(2)]Cl, forming an oligomeric multi-chain structure in which pairs of alcohols from two crystallographically independent tetol molecules bind lithium ions tetrahedrally. However, formation of monomeric structures in solution is inferred from electrospray mass spectroscopy, which has also shown evidence of exchange of lithium ion in the complexed species by added alkaline earth ions. (C) 2000 Elsevier Science S.A. All rights reserved.
Resumo:
A mobilidade considerada um dos factores chave na sustentabilidade e desenvolvimento de qualquer economia. Em Portugal essa realidade no diferente. Em 2011 verifica-se que 41% do consumo global de combustveis pertence ao sector rodovirio [1] o que evidencia a sua relevncia na economia do pas. No que concerne aos veculos de traco elctrica, comearam a surgir nos finais do sc. XIX, e no incio do sc. XX nos Estados Unidos da Amrica representavam 38% dos veculos [2]. Diversos factores econmicos e tecnolgicos conduziram a um crescente desinteresse por parte da indstria em investir na produo deste tipo de veculos. Contudo com a introduo de baterias de ies de ltio em veculos de traco elctrica, torna-os viveis e competitivos. Neste trabalho proposto o desenvolvimento de um sistema de gesto de baterias de ies de ltio do tipo LiFePO4 para aplicao em veculos elctricos. O sistema dever assegurar a proteco das baterias e indicar o estado de carga das mesmas. Este sistema permitir uma optimizao no uso deste gnero de baterias, proporcionar uma melhor utilizao, aumentando a sua vida til. O sistema ir ser aplicado e testado experimentalmente no veculo elctrico ecolgico (Veeco). No mbito do projecto Veeco foi projectado e construdo um banco de ensaios utilizado na anlise do comportamento das baterias, e determinar quais os requisitos necessrios para o sistema de gesto desenvolvido. Foi tambm projectado e realizado um sistema de aquisio e processamento de dados que permite obter informaes acerca da bateria, dados que estaro disponveis no interface Homem-mquina do Veeco.
Resumo:
Coffee fruit processing is one of the most polluting activities in agriculture due to the large amount of waste generated in the process. In this work, coffee parchment was employed as precursor for the production of carbons activated with ZnCl2 (CAP). The material was characterized using N2 adsorption/desorption at 77 K, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The material showed a surface area of 521.6 mg-1 and microporous structure. CAP was applied as adsorbent for the removal of methylene blue dye in aqueous medium. The adsorption capacity was found to be about 188.7 mg g-1.
Resumo:
Direct methanol fuel cells (DMFCs) without external pumps or other ancillary devices for fuel and oxidant supply are known as passive DMFCs and are potential candidates to replace lithium-ion batteries in powering portable electronic devices. This paper presents the results obtained from a membrane electrode assembly (MEA) specifically designed for passive DMFCs. Appropriated electrocatalysts were prepared and the effect of their loadings was investigated. Two types of gas diffusion layers (GDL) were also tested. The influence of the methanol concentration was analyzed in each case. The best MEA performance presented a maximum power density of 11.94 mW cm-2.
Resumo:
Zorflex activated carbon fibers (ACF), reference FM100 198B, are used before and after an oxidizing procedure with H3PO4 to study the adsorption of Pb2+. The point of zero charge was determined for the modified and unmodified fiber giving values of 2.3 and 4.3, respectively. After oxidizing the ACF, the fiber showed to have a greater Pb2+ adsorption capacity in comparison with the unmodified fiber, which is related with the acid sites increase, where lead was mainly adsorbed. Determination of the BET area was carried out by nitrogen physisorption at 77K. ACFs presented superficial areas between 1000 and 1500 m/g showing mostly, a microporous structure. The preliminary design of an adsorbent using the modified fiber is presented where the fiber superior physicochemical properties over the unmodified one are observed.
Resumo:
Ajoneuvojen tiukentuneet pstrajoitukset, sek ajoneuvojen kokonaishytysuhteen parantamisen tarve ohjaavat ajoneuvovalmistajia kehittmn uusia ratkaisuja. Energiavarastojen kytt ajoneuvoissa on yleistynyt ja niiden kytll voidaan saada huomattava energiasst. Tss kandidaatintyss on esitelty erilaisia energiavarastoja ja niiden verkkoon liittmist. Ppaino tyss on akkujen ja superkondensaattorien rinnankytkennss. Energiavarastot pyritn kytkemn mahdollisimman vhll tehoelektroniikalla verkkoon. Esimerkkitapaukseksi on otettu litium-ioni akkujen ja superkondensaattorien rinnankytkent vaihtojnnitteeseen pelkll invertterill.
Resumo:
Akkuteknologia on kehittynyt viime vuosina erityyppisten litium-ioniakkujen hallitessa markkinoita. Uutta teknologiaa kaupallisissa litium-pohjaisissa akuissa edustavat litium-polymeeri- ja litium-rautafosfaattiakut. Tyn tarkoituksena oli selvitt soveltuvatko litium-polymeeri- ja litium-rautafosfaattiakut kannettavaan audiolaitteeseen ja verrata nit Ni-Cd- ja Ni-Mh-akkuihin sek LiCoO2- ja LiMnO4-kemian litium-ioniakkuihin. Kyseisten akkutyyppien soveltuvuutta kannettavaan audiolaitteeseen ei kirjallisuudessa ole juuri tutkittu. Ty toteutettiin kirjallisuustutkimuksena.
Resumo:
Tss kandidaatintyss tutkittiin shk- ja hybridiajoneuvojen akkujen uusiokytt. Tutkimus toteutettiin kirjallisuustyn. Tavoitteena oli selvitt voidaanko shk- ja hybridiajoneuvojen akkuja uusiokytt, mit ongelmia mahdollisesti uusiokyttn liittyy, minklaisissa sovelluksissa kytettyj akkuja voisi kytt ja uusiokytetnk kyseisenlaisia akkuja jo nykyn. Tyss esiteltiin mys yleisimpi akkutekniikoita sek niiden kierrtyst. Tutkimuksessa havaittiin, ett akuissa on runsaasti kapasiteettia jljell ajoneuvokytn jlkeen. Uusiokytss akku voi kest jopa yht paljon kytt kuin ajoneuvokytss. Ongelmat uusiokytss liittyvt akkujen vaihtelevaan kuntoon ja kapasiteettiin. Ennen uusiokytt akut tulisi tarkastaa ja jos mahdollista, poistaa huonokuntoiset ja vialliset kennot. Kytettyjen akkujen uusiokyttn soveltuvista laitteistoista on tehty muutamia prototyyppej, jotka ovat teholtaan ja kapasiteetiltaan hyvin vaihtelevia. Sopivalla valvontajrjestelmll varustettuna kytettyj akkuja voitaneen kytt mys olemassa olevissa, akkuja sisltviss jrjestelmiss. Kytettyj akkuja voitaneen kytt muun muassa uusiutuvan energian varastointiin, shkverkon kulutushuippujen kompensointiin ja shkajoneuvojen pikalatauksen puskurina. Etenkin litiumioniakkujen uusiokytt on jrkev, koska kierrtys ei ole kovin tehokasta ainakaan viel.
Resumo:
Tss diplomityss tarkasteltiin Nissan Leaf -shkauton kytetyn litiumakun soveltuvuutta UPS-varavirtalaitteen energialhteeksi. Kun akku on heikentynyt niin ettei sen kapasiteetti en ole riittv autokyttn, sit voidaan kuitenkin viel hydynt muissa sovelluksissa, kuten UPS-laitteessa. Ty sai alkunsa osana GreenDataNet-projektia, jossa pyritn kehittmn datakeskuksiin ymprist vhemmn kuormittavia ratkaisuja kyttmll uusiutuvia energialhteit, akkujen uusiokytll, sek energianhallinnan optimoinnilla. Tyss kytiin lpi akun ja sen ohjausjrjestelmn ominaisuuksia, kerrottiin UPS:in ohjelmistoon tehdyist muutoksista sek esitettiin testitulokset. Lopputuloksena todettiin akun sopivan muuten hyvin UPS-kyttn, mutta vaadittu pivittinen kennojnnitteiden tasaus ja sen aiheuttama katkos energian saatavuuteen heikent UPSin kyttvarmuutta kuorman suojauksessa. Lopussa esitettiin muutamia ehdotuksia tmn ongelman korjaamiseksi.
Resumo:
Le LiFePO4 est un matriau prometteur pour les cathodes des batteries au lithium. Il possde une bonne stabilit haute temprature et les prcurseurs utiliss pour la synthse sont peu couteux. Malheureusement, sa faible conductivit nuit aux performances lectrochimiques. Le fait de diminuer la taille des particules ou denrober les particules dune couche de carbone permet daugmenter la conductivit. Nous avons utilis une nouvelle mthode appele synthse par voie fondue pour synthtiser le LiFePO4. Cette synthse donne des gros cristaux et aucune impuret nest dtecte par analyse Rayon-X. En revanche, la synthse de LiXFePO4 donne un mlange de LiFePO4 pur et dimpuret base de lithium ou de fer selon lexcs de fer ou de lithium utilis. La taille des particules de LiFePO4 est rduite laide dun broyeur plantaire et plusieurs paramtres de broyage sont tudis. Une couche de carbone est ensuite dpose sur la surface des particules broyes par un traitement thermique sur le LiFePO4 avec du -lactose. Linfluence de plusieurs paramtres comme la temprature du traitement thermique ou la dure du chauffage sont tudis. Ces expriences sont ralises avec un appareil danalyse thermogravimtrique (ATG) qui donne la quantit de chaleur ainsi que la variation de masse durant le chauffage de lchantillon. Ce nouveau chauffage pour la couche de carbone donne des chantillons dont les performances lectrochimiques sont similaires celles obtenues prcdemment avec la mthode de chauffage pour la couche de carbone utilisant le four tubulaire.
Resumo:
The formation of novel structures by the passage of an electric current through graphite is described. These structures apparently consist of hollow three-dimensional graphitic shells bounded by curved and faceted planes, typically made up of two graphene layers. The curved structures were frequently decorated with nano-scale carbon particles, or short nanotubes. In some cases, nanotubes were found to be seamlessly connected to the thin shells, indicating that the formation of the shells and the nanotubes is intimately connected. Small nanotubes or nanoparticles were also sometimes found encapsulated inside the hollow structures, while fullerene-like particles were often seen attached to the outside surfaces. With their high surface areas and structural perfection, the new carbon structures may have applications as anodes of lithium ion batteries or as components of composite materials.
Resumo:
Thin films of MnO(2) nanoparticles were grown using the layer-by-layer method with poly (diallyldimetylammonium) as the intercalated layer. The film growth was followed by UV-vis, electrochemical quartz crystal microbalance (EQCM), and atomic force microscopy. Linear growth due to electrostatic immobilization of layers was observed up to 30 bilayers, but electrical connectivity was maintained only for 12 MnO(2)/PPDA bilayers. The electrochemical characterization of this film in 1-butyl-2,3-dimethyl-imidazolium (BMMI) bis(trifluoromethanesulfonyl)imide (TFSI) (BMMITFSI) with and without addition of a lithium salt indicated a higher electrochemical response of the nanostructured electrode in the lithium-containing electrolyte. On the basis of EQCM experiments, it was possible to confirm that the charge compensation process is achieved mainly by the TFSI anion at short times (<2 s) and by BMMI and lithium cations at longer times. The fact that large ions like TFSI and BMMI participate in the electroneutrality is attributed to the redox reaction that occurs at the superficial sites and to the high concentration of these species compared to that of lithium cations.
Resumo:
Seeking a greater appreciation of cheese whey was developed to process the hydrogenation of lactose for the production of lactitol, a polyol with high added value, using the catalyst Ni / activated carbon (15% and 20% nickel), the nitride Mo2N, the bimetallic carbide Ni-Mo/ activated carbon and carbide Mo2C. After synthesis, the prepared catalysts were analyzed by MEV, XRD, laser granulometry and B.E.T. The reactor used in catalytic hydrogenation of lactose was the type of bed mud with a pressure (68 atm), temperature (120 oC) and stirring speed (500 rpm) remained constant during the experiments. The system operated in batch mode for the solid and liquid and semi-continuous to gas. Besides the nature of the catalyst, we studied the influence of pH of reaction medium for Mo2C carbide as well as evaluating the character of the protein inhibitor and chloride ions on the activity of catalysts Ni (20%)/Activated Carbon and bimetallic carbide Ni-Mo/Activated Carbon. The decrease in protein levels was performed by coagulation with chitosan and adsorption of chloride ions was performed by ion exchange resins. In the process of protein adsorption and chloride ions, the maximum percentage extracted was about 74% and 79% respectively. The micrographs of the powders of Mo2C and Mo2N presented in the form of homogeneous clusters, whereas for the catalysts supported on activated carbon, microporous structure proved impregnated with small particles indicating the presence of metal. The results showed high conversion of lactose to lactitol 90% for the catalyst Ni (20%)/Activated Carbon at pH 6 and 46% for the carbide Mo2C pH 8 (after addition of NH4OH) using the commercial lactose. Monitoring the evolution of the constituents present in the reaction medium was made by liquid chromatography. A kinetic model of heterogeneous Langmuir Hinshelwood type was developed which showed that the estimated constants based catalysts promoted carbide and nitride with a certain speed the adsorption, desorption and production of lactitol
