Oxidação eletroquímica do herbicida tebutiuron utilizando eletrodo do tipo DSA

Tebuthiuron (TBH) is a herbicide widely used in different cultures and known for its toxic effects. Electrochemical methods are promising for removing pollutants such as pesticides. This study showed the degradation of TBH using a DSA® anode operated at current densities of 50 to 200 mA cm-2. Removal presented pseudo-first order kinetics while high-pressure liquid chromatography (UV detection) showed two peaks, ascribed to degradation intermediates. The maximum percentage of total organic carbon removed was 12.9%. Ion chromatography revealed that higher concentrations of nitrate and nitrite ions formed with increasing current density.

Glycerol oxidation on nickel based nanocatalysts in alkaline medium – Identification of the reaction products

In this work, carbon supported nickel based nanoparticles were prepared by impregnation method and used as anode electrocatalysts for the glycerol conversion. These metallic powders were mixed with a suitable amount of a Nafion/water solution to make catalytic inks which were then deposited onto the surface of carbon Toray used as a conductive substrate. Long-term electrolyses of glycerol were carried out in alkaline medium by chronoamperometry experiments. Analysis of the oxidation products was performed with ion-exclusion liquid chromatography which separates the analytes by ascending pKa. The spectroscopic measurements have shown that the cobalt content in the anode composition did contribute to the CAC bond cleavage of the initial molecule of glycerol.

Characterization of nanostructured material images using fractal descriptors

This work presents a methodology to the morphology analysis and characterization of nanostructured material images acquired from FEG-SEM (Field Emission Gun-Scanning Electron Microscopy) technique. The metrics were extracted from the image texture (mathematical surface) by the volumetric fractal descriptors, a methodology based on the Bouligand-Minkowski fractal dimension, which considers the properties of the Minkowski dilation of the surface points. An experiment with galvanostatic anodic titanium oxide samples prepared in oxalyc acid solution using different conditions of applied current, oxalyc acid concentration and solution temperature was performed. The results demonstrate that the approach is capable of characterizing complex morphology characteristics such as those present in the anodic titanium oxide.

Advanced lithium and lithium-ion rechargeable batteries for automotive applications

The worldwide demand for a clean and low-fuel-consuming transport promotes the development of safe, high energy and power electrochemical storage and conversion systems. Lithium-ion batteries (LIBs) are considered today the best technology for this application as demonstrated by the recent interest of automotive industry in hybrid (HEV) and electric vehicles (EV) based on LIBs. This thesis work, starting from the synthesis and characterization of electrode materials and the use of non-conventional electrolytes, demonstrates that LIBs with novel and safe electrolytes and electrode materials meet the targets of specific energy and power established by U.S.A. Department of Energy (DOE) for automotive application in HEV and EV. In chapter 2 is reported the origin of all chemicals used, the description of the instruments used for synthesis and chemical-physical characterizations, the electrodes preparation, the batteries configuration and the electrochemical characterization procedure of electrodes and batteries. Since the electrolyte is the main critical point of a battery, in particular in large- format modules, in chapter 3 we focused on the characterization of innovative and safe electrolytes based on ionic liquids (characterized by high boiling/decomposition points, thermal and electrochemical stability and appreciable conductivity) and mixtures of ionic liquid with conventional electrolyte. In chapter 4 is discussed the microwave accelerated sol–gel synthesis of the carbon- coated lithium iron phosphate (LiFePO 4 -C), an excellent cathode material for LIBs thanks to its intrinsic safety and tolerance to abusive conditions, which showed excellent electrochemical performance in terms of specific capacity and stability. In chapter 5 are presented the chemical-physical and electrochemical characterizations of graphite and titanium-based anode materials in different electrolytes. We also characterized a new anodic material, amorphous SnCo alloy, synthetized with a nanowire morphology that showed to strongly enhance the electrochemical stability of the material during galvanostatic full charge/discharge cycling. Finally, in chapter 6, are reported different types of batteries, assembled using the LiFePO 4 -C cathode material, different anode materials and electrolytes, characterized by deep galvanostatic charge/discharge cycles at different C-rates and by test procedures of the DOE protocol for evaluating pulse power capability and available energy. First, we tested a battery with the innovative cathode material LiFePO 4 -C and conventional graphite anode and carbonate-based electrolyte (EC DMC LiPF 6 1M) that demonstrated to surpass easily the target for power-assist HEV application. Given that the big concern of conventional lithium-ion batteries is the flammability of highly volatile organic carbonate- based electrolytes, we made safe batteries with electrolytes based on ionic liquid (IL). In order to use graphite anode in IL electrolyte we added to the IL 10% w/w of vinylene carbonate (VC) that produces a stable SEI (solid electrolyte interphase) and prevents the graphite exfoliation phenomenon. Then we assembled batteries with LiFePO 4 -C cathode, graphite anode and PYR 14 TFSI 0.4m LiTFSI with 10% w/w of VC that overcame the DOE targets for HEV application and were stable for over 275 cycles. We also assembled and characterized ―high safety‖ batteries with electrolytes based on pure IL, PYR 14 TFSI with 0.4m LiTFSI as lithium salt, and on mixture of this IL and standard electrolyte (PYR 14 TFSI 50% w/w and EC DMC LiPF 6 50% w/w), using titanium-based anodes (TiO 2 and Li 4 Ti 5 O 12 ) that are commonly considered safer than graphite in abusive conditions. The batteries bearing the pure ionic liquid did not satisfy the targets for HEV application, but the batteries with Li 4 Ti 5 O 12 anode and 50-50 mixture electrolyte were able to surpass the targets. We also assembled and characterized a lithium battery (with lithium metal anode) with a polymeric electrolyte based on poly-ethilenoxide (PEO 20 – LiCF 3 SO 3 +10%ZrO 2 ), which satisfied the targets for EV application and showed a very impressive cycling stability. In conclusion, we developed three lithium-ion batteries of different chemistries that demonstrated to be suitable for application in power-assist hybrid vehicles: graphite/EC DMC LiPF 6 /LiFePO 4 -C, graphite/PYR 14 TFSI 0.4m LiTFSI with 10% VC/LiFePO 4 -C and Li 4 T i5 O 12 /PYR 14 TFSI 50%-EC DMC LiPF 6 50%/LiFePO 4 -C. We also demonstrated that an all solid-state polymer lithium battery as Li/PEO 20 –LiCF 3 SO 3 +10%ZrO 2 /LiFePO 4 -C is suitable for application on electric vehicles. Furthermore we developed a promising anodic material alternative to the graphite, based on SnCo amorphous alloy.

Deposizione elettrochimica di esacianoferrato di rame tramite un metodo "a due step"; caratterizzazione e valutazione delle prestazioni

In this thesis we have identified two electrochemical procedures for preparing two compounds of copper hexacyanoferrate (CuHCF) films with different compositions and structures. The deposition were carried out using a “two steps” method consisting in electrochemical oxidation of previously deposited metallic copper on carbon substrates (glassy carbon and graphite foil electrodes) in K3[Fe(CN)6] solution. Both films, CuHCF-methodA and CuHCF-methodB, were characterized by cyclic voltammetry (GC) and their study using XANES spectroscopy revealed evidence of different structures. Additionally, insertion and extraction of different cations (Na+, K+, Mg2+, Al3+ and Cs+) were performed and the results indicate that CuHCF-methodA has slightly better performances and operational stability than CuHCF-methodB. Data from galvanostatic charge-discharge tests confirme the latter observation. An application for amperometric detection of H2O2 and SEM micrographs are also reported for both films (method A and B). Comparing these results with a previous work of our research group, seems that the deposition of two different compounds using methodA and methodB is due to the different stoichiometry of ions Cu2+ e [Fe(CN)6]3– created near electrode surface during the dissolution step.

Combined Secondary Ion Mass Spectrometry Depth Profiling and Focused Ion Beam Analysis of Cu Films Electrodeposited under Oscillatory Conditions

The recrystallization behavior of Cu films electrodeposited under oscillatory conditions in the presence of plating additives was studied by means of secondary ion mass spectrometry (SIMS) and focused ion beam analysis. When combined with bis-(sodium-sulfopropyl)-disulfide (SPS), Imep levelers (polymerizates of imidazole and epichlorohydrin) show characteristic oscillations in the galvanostatic potential/time transient measurements. These are related to the periodic degradation and restoration of the active leveler ensemble at the interface. The leveler action relies on adduct formation between the Imep and MPS (mercaptopropane sulfonic acid)-stabilized CuI complexes that appear as intermediates of the copper deposition when SPS is present in the electrolyte. SIMS depth profiling proves that additives are incorporated into the growing film preferentially under transient conditions during the structural breakdown of the leveler ensemble and its subsequent restoration. In contrast, Cu films electrodeposited in the presence of a structurally intact Imep–CuI–MPS ensemble remain largely contamination free.

High-Resolution Chemical Depth Profiling of Solid Material Using a Miniature Laser Ablation/Ionization Mass Spectrometer

High-resolution chemical depth profiling measurements of copper films are presented. The 10 μm thick copper test samples were electrodeposited on a Si-supported Cu seed under galvanostatic conditions in the presence of particular plating additives (SPS, Imep, PEI, and PAG) used in the semiconductor industry for the on-chip metallization of interconnects. To probe the trend of these plating additives toward inclusion into the deposit upon growth, quantitative elemental mass spectrometric measurements at trace level concentration were conducted by using a sensitive miniature laser ablation ionization mass spectrometer (LIMS), originally designed and developed for in situ space exploration. An ultrashort pulsed laser system (τ ∼ 190 fs, λ = 775 nm) was used for ablation and ionization of sample material. We show that with our LIMS system, quantitative chemical mass spectrometric analysis with an ablation rate at the subnanometer level per single laser shot can be conducted. The measurement capabilities of our instrument, including the high vertical depth resolution coupled with high detection sensitivity of ∼10 ppb, high dynamic range ≥10(8), measurement accuracy and precision, is of considerable interest in various fields of application, where investigations with high lateral and vertical resolution of the chemical composition of solid materials are required, these include, e.g., wafers from semiconductor industry or studies on space weathered samples in space research.

Layer-by-layer grown scalable redox-active ruthenium-based molecular multilayer thin films for electrochemical applications and beyond

Here we report the first study on the electrochemical energy storage application of a surface-immobilized ruthenium complex multilayer thin film with anion storage capability. We employed a novel dinuclear ruthenium complex with tetrapodal anchoring groups to build well-ordered redox-active multilayer coatings on an indium tin oxide (ITO) surface using a layer-by-layer self-assembly process. Cyclic voltammetry (CV), UV-Visible (UV-Vis) and Raman spectroscopy showed a linear increase of peak current, absorbance and Raman intensities, respectively with the number of layers. These results indicate the formation of well-ordered multilayers of the ruthenium complex on ITO, which is further supported by the X-ray photoelectron spectroscopy analysis. The thickness of the layers can be controlled with nanometer precision. In particular, the thickest layer studied (65 molecular layers and approx. 120 nm thick) demonstrated fast electrochemical oxidation/reduction, indicating a very low attenuation of the charge transfer within the multilayer. In situ-UV-Vis and resonance Raman spectroscopy results demonstrated the reversible electrochromic/redox behavior of the ruthenium complex multilayered films on ITO with respect to the electrode potential, which is an ideal prerequisite for e.g. smart electrochemical energy storage applications. Galvanostatic charge–discharge experiments demonstrated a pseudocapacitor behavior of the multilayer film with a good specific capacitance of 92.2 F g−1 at a current density of 10 μA cm−2 and an excellent cycling stability. As demonstrated in our prototypical experiments, the fine control of physicochemical properties at nanometer scale, relatively good stability of layers under ambient conditions makes the multilayer coatings of this type an excellent material for e.g. electrochemical energy storage, as interlayers in inverted bulk heterojunction solar cell applications and as functional components in molecular electronics applications.

Electrochemical analysis of the performance of carbon supported Pd nanoparticles for direct formic acid fuel cells: from gold supported electrodes to catalyst-coated membranes

In this work carbon supported Pd nanoparticles were prepared and used as electrocatalysts for formic acid electrooxidation fuel cells. The influence of some relevant parameters such as the nominal Pt loading, the Nafion/total solids ratio as well as the Pd loading towards formic acid electrooxidation was evaluated using gold supported catalytic layer electrodes which were prepared using a similar methodology to that employed in the preparation of conventional catalyst coated membranes (CCM). The results obtained show that, for constant Pd loading, the nominal Pd loading and the Nafion percentage on the catalytic layer do not play an important role on the resulting electrocatalytic properties. The main parameter affecting the electrocatalytic activity of the electrodes seems to be the Pd loading, although the resulting activity is not directly proportional to the increased Pd loading. Thus, whereas the Pd loading is multiplied by a factor of 10, the activity is only twice which evidences an important decrease in the Pd utilization. In fact, the results obtained suggest the active layer is the outer one being clearly independent of the catalytic layer thickness. Finally, catalyst coated membranes with Pd catalyst loadings of 0.1, 0.5 and 1.2 mg cm-2 were also tested in a breathing direct formic acid fuel cell.

Feasibility of electrochemical chloride extraction from structural reinforced concrete using a sprayed conductive graphite powder–cement paste as anode

This article summarizes research on the application of a conductive cement paste as an anode in the now classical technique of electrochemical extraction of chlorides applied to a concrete structural element by spraying the paste on the surface of a concrete structural element, a pillar. Sprayed conductive cement paste, by adding graphite powder, is particularly useful to treat sizable vertical surfaces such are structural supports. Outcomes indicate that this kind of anode not only provides electrochemical chloride removal with similar efficiency, but also is able to retain moisture even without the use of a continuous dampening system.

Electrochemical generation of oxygen-containing groups in an ordered microporous zeolite-templated carbon

Zeolite templated carbon (ZTC) was electrochemically oxidized under various conditions, and its chemistry and structural evolution were compared to those produced by conventional chemical oxidation. In both oxidation methods, a general loss of the original structure regularity and high surface area was observed with increasing amount of oxidation. However, the electrochemical method showed much better controllability and enabled the generation of a large number of oxygen functional groups while retaining the original structure of the ZTC. Unlike chemical treatments, highly microporous carbons with an ordered 3-D structure, high surface area (ranging between 1900 and 3500 m2/g) and a large number of oxygen groups (O = 11,000–3300 μmol/g), have been prepared by the electrochemical method. Some insights into the electrooxidation mechanism of carbon materials are proposed from the obtained polarization curves, using ZTC as a model carbon material.

Tailoring the Surface Chemistry of Activated Carbon Cloth by Electrochemical Methods

This paper presents a systematic study of the effect of the electrochemical treatment (galvanostatic electrolysis in a filter-press electrochemical cell) on the surface chemistry and porous texture of commercial activated carbon cloth. The same treatments have been conducted over a granular activated carbon in order to clarify the effect of morphology. The influence of different electrochemical variables, such as the electrode polarity (anodic or cathodic), the applied current (between 0.2 and 1.0 A) and the type of electrolyte (HNO3 and NaCl) have also been analyzed. The anodic treatment of both activated carbons causes an increase in the amount of surface oxygen groups, whereas the cathodic treatment does not produce any relevant modification of the surface chemistry. The HNO3 electrolyte produced a lower generation of oxygen groups than the NaCl one, but differences in the achieved distribution of surface groups can be benefitial to selectively tune the surface chemistry. The porous texture seems to be unaltered after the electro-oxidation treatment. The validity of this method to introduce surface oxygen groups with a pseudocapacitive behavior has been corroborated by cyclic voltammetry. As a conclusion, the electrochemical treatment can be easily implemented to selectively and quantitatively modify the surface chemistry of activated carbons with different shapes and morphologies.

Efficiency of a conductive cement-based anodic system for the application of cathodic protection, cathodic prevention and electrochemical chloride extraction to control corrosion in reinforced concrete structures

This article describes the research carried out regarding the application of cathodic protection (CP) and cathodic prevention (CPrev), in some cases with a pre-treatment of electrochemical chloride extraction (ECE), on representative specimens of reinforced concrete structures, using an anodic system consisting of a graphite-cement paste applied as a coating on the surface. The aim of this research is to find out the competence of this anode for the aforementioned electrochemical treatments. The efficiency of this anode has been clearly demonstrated, as well as its capability to apply a combined process of ECE and after CP.

Electrochemical characteristics of ordered mesoporous carbon used as electrode material in Li-ion battery

Ordered mesoporous carbon CMK-5 was comprehensively tested for the first time as electrode materials in lithium ion battery. The surface morphology, pore structure and crystal structure were investigated by Scanning Electronic Microscopy (SEM), N-2 adsorption technique and X-ray diffraction (XRD) respectively. Electrochemical properties of CMK-5 were studied by galvanostatic cycling and cyclic voltammetry, and compared with conventional anode material graphite. Results showed that the reversible capacity of CMK-5 was 525 mAh/g at the third charge-discharge cycle and that CMK-5 was more compatible for quick charge-discharge cycling because of its special mesoporous structure. Of special interest was that the CMK-5 gave no peak on its positive sweep of the cyclic voltammetry, which was different from all the other known anode materials. Besides, X-ray photoelectron spectroscopy (XPS) and XRD were also applied to investigate the charge-discharge characteristics of CMK-5.

Synthesis of ordered nanoporous carbon and its application in Li-ion battery

Ordered nanoporous carbon (ONC) was comprehensively tested for the first time as electrode material in lithium-ion battery. Structure characterization shows the order nanoporous structure and tiny crystallite structure of as-synthesized ONC. The electrochemical properties of this carbon were studied by galvanostatic cycling and cyclic voltammetry. Of special interest is that ONC gave no peak on its positive sweep of the cyclic voltammetry, which was different from other known anode materials. Besides, X-ray photoelectron spectroscopy (XPS) and XRD were also used to investigate the electrochemical characteristics of ONC. (c) 2006 Elsevier Ltd. All rights reserved.