Effect of Carbon Nanotubes on the Na+ Intercalation Capacity of Binder Free Mn2V2O7-CNTs Electrode: A Structural Investigation

Improvements in sodium intercalation in sodium cathodes have been debated in recent years. In the present work, we delineate the significant effect of the carbon nanotubes (CNTs) and their weight percent in the intercalation capacity of the binder-free manganese vanadium oxide (MVO)-CNTs composite electrodes. The performance modification of the electrode is discussed taking into account the cathode electrolyte interphase (CEI) layer under optimal performance. We observe an intermittent distribution of the chemical phases on the CEI, formed on these electrodes after several cycles. The bulk and superficial structure of pristine and Na+ cycled electrodes were identified via micro-Raman scattering and Scanning X-ray Photoelectron Microscopy. We show that the inhomogeneous CEI layer distribution strongly depends on the CNTs weight percentage ratio in an electrode nano-composite. The capacity fading of MVO-CNTs appears to be associated with the dissolution of the Mn2O3 phase, leading to electrode deterioration. This effect is particularly observed in electrodes with low weight percentage of the CNTs in which the tubular topology of the CNTs are distorted due to the MVO decoration. These results can deepen the understanding of the CNTs role on the intercalation mechanism and capacity of the electrode, where there are variations in the mass ratio of CNTs and the active material

Efeito miragem aplicada a eletroquímica

Orientador: Franco DeckerDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb WataghinResumo: Nesta tese nós apresentamos aspectos teóricos e experimentais da técnica Miragem aplicada à eletroquimica. Nós mostramos como o efeito Miragem pode ser utilizado para medidas calorimétricas e refratomélricas nos eletrólilos, discutindo os efeitos térmicos Peltier e Joule e as variações dinâmicas dos perfis de concentração existentes nos eletrólitos. A partir dos resultados á possível. através de modelos, deduzir os coeficientes de difusão das espécies iônicas, a potência térmica envolvida durante uma reaçãoeletroquimica, e a contribuição do eletrólito suporte no índice de refração do elelrólitoAbstract: In this thesis we present theoretical and experimental aspects of the Mirage technique applied to electrochemistry. We have shown how, the Mirage effect can be used for calorimetric and refratometric measurements in the eletrolyte, discussing the thermal Peltier and Joule effects and the dynamic variations of the concentration profiles in the electrolyte. Starting from the results it is possible, with the use of models, to deduce the diffusion coefficients of the ionic species, the power involved during an electrochemical reaction and the contribution of' the support electrolyte to the electrolyte refraction indexMestradoFísicaMestre em Físic

Structural Characterization and Analysis of Intercalation and Insertion Compounds

In the field of solid-state chemistry, the class of materials represented by intercalation and insertion compounds (IIC) deserves particular interest for a variety of reasons. These range from the versatility of the synthetic procedures for producing IICs, to the plethora of applications in which IICs can be adopted as active functional materials. Indeed, IICs are practically unique in modulating reversibly (or quasi reversibly) their chemical-physical properties in a wide range of values through reactions that do not require extreme conditions of realization in terms of pressure, temperature and chemical ambient. The continuous development of IICs for diverse advanced technologies requires an adequate portfolio of investigation techniques for a meaningful characterization of IICs, with a special emphasis to the determination of their crystal structure and the definition of their chemical composition. Indeed, IICs undergo severe structural and compositional changes due to the reaction of insertion/intercalation during operation. The aim of this Research Topic is to achieve a full comprehension of intercalation/insertion phenomena in the IICs of practical interest. Indeed, such understanding is crucial for the diagnosis and optimization of intercalation/insertion materials in the specific areas of their applications. At this regard the structural characterizations of IICs by means of in-situ/in-operando techniques represent a very important aspect to cover. The contributors to this Research Topic are invited to submit either Original Research or Review articles on the following themes: • structural characterization of IICs employed as active materials in advanced technologies and devices of interest in electrochemistry, catalysis, magnetism, optics, biology and medicine among others • preparation of new and innovative IICs • analysis of the reactivity of IICs • modelling of IICs and evaluation of their stability • study of the different types of transitions occurring in IICs • description of alternative techniques for the non-invasive and non-destructive analysis of IICs • determination of electronic, optical and conduction properties of IICs

Electrochemical Evidence of Strong Electronic Interaction of PtRu on Carbon Nanotubes with High Density of Defects

We show that carbon nanotubes (CNTs) with high density of defects can present a strong electronic interaction with nanoparticles of Pt-Ru with average particle size of 3.5 +/- 0.8 nm. Depending on the Pt-Ru loading on the CNTs, CO and methanol oxidation reactions suggest there is a charge transfer between Pt-Ru that in turn provokes a decrease in the electronic interaction taking place between Ru and Pt in the PtRu alloy. The CO stripping potentials were observed at about 0.65 and 0.5 V for Pt-Ru/CNT electrodes with Pt-Ru loadings of 10 and 20, and 30 wt %, respectively. (C) 2008 The Electrochemical Society. [DOI: 10.1149/1.2990222] All rights reserved.Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[06/07253-8]Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[04/07085-2]CNP

Short-range order in solid and liquid KBr probed by EXAFS

Br K-edge EXAFS spectra of solid and liquid KBr have been performed and analysed using advanced techniques for data analysis (GNXAS). Structural results on solid KBr at room temperature and near melting are compared with molecular dynamics (MD) simulations and diffraction data. The first-neighbour distribution is found to be strongly asymmetric even at room temperature, as also shown by MD simulations. This confirms the existence of important anharmonic effects in solid KBr. MD simulations are in agreement with EXAFS data at room temperature. For solid KBr near melting, anharmonic effects become very important. In comparison with MD calculations, the rise of the first-neighbour peak is found to be steeper, while the foot of the first-neighbour distribution is found to be slightly shifted toward longer distances. Experimental short-range partial pair distribution functions g(BrK) and g(BrBr) are derived in liquid KBr for the first time. The first peak of the g(BrK) distribution is accurately determined and found to be in good agreement with MD simulations, confirming a slight contraction of the most probable Br-K distance in the liquid phase. The first peak of the g(BrBr) distribution, measured with less accuracy, is found to be sharper and slightly shifted to longer distances, lowering the overlap with the first-neighbour K shell

Micro/nanostructured carbon composite modified with a hybrid redox mediator and enzymes as a glucose biosensor

A carbon micro/nanostructured composite based on cup-stacked carbon nanotubes (CSCNTs) grown onto a carbon felt has been found to be an efficient matrix for enzyme immobilization and chemical signal transduction. The obtained CSCNT/felt was modified with a copper hexacyanoferrate/polypyrrole (CuHCNFe/Ppy) hybrid mediator, and the resulting composite electrode was applied to H(2)O(2) detection, achieving a sensitivity of 194 +/- 15 mu A mmol(-1) L. The results showed that the CSCNT/felt matrix significantly increased the sensitivity of CuHCNFe/Ppy-based sensors compared to those prepared on a felt unrecovered by CSCNTs. Our data revealed that the improved sensitivity of the as-prepared CuHCNFe/Ppy-CSCNT/felt composite electrode can be attributed to the electronic interactions taking place among the CuHCNFe nanocrystals, Ppy layer and CSCNTs. In addition, the presence of CSCNTs also seemed to favor the dispersion of CuHCNFe nanocrystals over the Ppy matrix, even though the CSCNTs were buried under the conducting polymer layer. The CSCNT/felt matrix also enabled the preparation of a glucose biosensor whose sensitivity could be tuned as a function of the number of glucose oxidase (GOx) layers deposited through a Layer-by-Layer technique with an sensitivity of 11 +/- 2 mu A mmol(-1) L achieved at 15 poly(diallyldimethylammoniumchloride)/GOx bilayers. (C) 2011 Elsevier Ltd. All rights reserved.FAPESP[proc. 05/59560-9]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP[06/07253-8]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Modeling volatile organic compounds (voc`s) adsorption onto cup-stacked carbon nanotubes (cscnt) using the linear driving force model

Modeling volatile organic compounds (voc`s) adsorption onto cup-stacked carbon nanotubes (cscnt) using the linear driving force model. Volatile organic compounds (VOC`s) are an important category of air pollutants and adsorption has been employed in the treatment (or simply concentration) of these compounds. The current study used an ordinary analytical methodology to evaluate the properties of a cup-stacked nanotube (CSCNT), a stacking morphology of truncated conical graphene, with large amounts of open edges on the outer surface and empty central channels. This work used a Carbotrap bearing a cup-stacked structure (composite); for comparison, Carbotrap was used as reference (without the nanotube). The retention and saturation capacities of both adsorbents to each concentration used (1, 5, 20 and 35 ppm of toluene and phenol) were evaluated. The composite performance was greater than Carbotrap; the saturation capacities for the composite was 67% higher than Carbotrap (average values). The Langmuir isotherm model was used to fit equilibrium data for both adsorbents, and a linear driving force model (LDF) was used to quantify intraparticle adsorption kinetics. LDF was suitable to describe the curves

New synthesis method for a core-shell composite based on ?-Bi2O3@PPy and its electrochemical behavior as supercapacitor electrode.

New composite based on polypyrrole (PPy) and bismuth oxide (?-Bi2O3) was investigated as supercapacitor electrode. The ?-Bi2O3 was obtained by hydrothermal route at 500 ?C for 2 h. Cyclic voltammetry was used to electropolymerize PPy on graphite electrode (GE) or on GE/?-Bi2O3. The X-ray diffraction profile of Bi2O3 revealed the ?-Bi2O3 monoclinic structure with space group P21/c. The scanning and transmission electron microscopy images showed that PPy coated ?-Bi2O3. Raman spectra showed that PPy inhomogeneously coated ?-Bi2O3, but it was still possible to obtain a ?-Bi2O3@PPy core-shell hybrid composite with highly ordered ?-Bi2O3 with electronic interaction between the oxide and the polymer chain of the polymer. The GE/?-Bi2O3@PPy composite electrode (type I supercapacitor) displayed a predominantly capacitive profile with low impedance values and good electrochemical stability after 50 charge and discharge cycles. The specific capacitance of ?-Bi2O3@PPy composite was found in the range of 634 to 301 F g-1 to gravimetric current of 3 and 10 A g-1, respectively