A soluble-lead redox flow battery with corrugated graphite sheet and reticulated vitreous carbon as positive and negative current collectors

A soluble-lead redox flow battery with corrugated-graphite sheet and reticulated-vitreous carbon as positive and negative current collectors is assembled and performance tested. In the cell, electrolyte comprising of 1 center dot 5 M lead (II) methanesulfonate and 0 center dot 9 M methanesulfonic acid with sodium salt of lignosulfonic acid as additive is circulated through the reaction chamber at a flow rate of 50 ml min (-aEuro parts per thousand 1). During the charge cycle, pure lead (Pb) and lead dioxide (PbO2) from the soluble lead (II) species are electrodeposited onto the surface of the negative and positive current collectors, respectively. Both the electrodeposited materials are characterized by XRD, XPS and SEM. Phase purity of synthesized lead (II) methanesulfonate is unequivocally established by single crystal X-ray diffraction followed by profile refinements using high resolution powder data. During the discharge cycle, electrodeposited Pb and PbO2 are dissolved back into the electrolyte. Since lead ions are produced during oxidation and reduction at the negative and positive plates, respectively there is no risk of crossover during discharge cycle, preventing the possibility of lowering the overall efficiency of the cell. As the cell employs a common electrolyte, the need of employing a membrane is averted. It has been possible to achieve a capacity value of 114 mAh g (-aEuro parts per thousand 1) at a load current-density of 20 mA cm (-aEuro parts per thousand 2) with the cell at a faradaic efficiency of 95%. The cell is tested for 200 cycles with little loss in its capacity and efficiency.

Surface study of vitreous carbon obtained from glassy carbon powder

This work presents a surface study of monolithic vitreous (or glassy) carbon - MVC - obtained from vitreous carbon powder. Defective MVC pieces are crushed in a ball mill and size classified by sifting. The MVC powder is mixed with furfuryl-alcohol resin and compacted in a mould using a hydraulic press. Samples with different powder granulometries are produced in this way and carbonized in a furnace under nitrogen atmosphere. Complete carbonization of the powder is achieved in only one day and losses due to breakage of the pieces is less than 5%. These results compare very favorably with respect to traditional MVC production methods where full carbonization may require up to seven days and losses due to breakage can be as high as 70%. After carbonization, samples are sanded and polished. Surface roughness and microstructure are characterized by light microscopy. Porosity is quantified from micrographs using ImageJ software and nanometric height variations are measured by atomic force microscopy. © 2012 Materials Research Society.

Treatment of Reticulated Vitreous Carbon by Dielectric Barrier Discharge Plasma for Electrodes Production

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Synthesis and characterization of polyarylacetylene for use in the monolithic vitreous carbon processing

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A novel method of electrodepositing highly dispersed nano palladium particles on glassy carbon electrode

The volumetric behavior of a chloride complex of palladium was studied at a glassy carbon electrode (GCE). The Pd-IV complex existing on the GCE surface was found, which was proposed to form an octahedral surface complex through coordination to the oxygen atom of an oxygen functional group on the pretreated GCE surface. The ferri/ferrocyanide redox couple was used as a probe to examine the activity of the GCE. X-ray photoelectron spectroscopy provided the evidence of the surface complex existing on the GCE. Highly dispersed Pd particles can be obtained when the surface complexes were reduced electrochemically to Pd atoms. The Pd particles obtained in this way were in nanometer scale and exhibit high catalytic activity towards the oxidation of hydrazine. (C) 1997 Elsevier Science Ltd.

Effect of furfuryl alcohol addition on the cure of furfuryl alcohol resin used in the glassy carbon manufacture

Glassy carbon can be manufactured practically without pores, named Monolithic Vitreous Carbon (MVC) or presenting up to 98% in transport pore volume, foam form, denominated Reticulated Vitreous Carbon (RVC). The glassy carbon processing is affected by some processing parameters, among them it can be cited the resin viscosity. The present work involves the optimization of RVC manufacture by monitoring the polyurethane (PU) foam impregnation with furfuryl alcohol resin with different viscosity values, which were obtained by dilution of the resin with different amounts of furfuryl alcohol. The resin samples used in the PU impregnation were characterized by thermal and rheological analyses. These results were correlated with scanning electron microscopy observations and compression test results of the impregnated polyurethane foam. The results show that the rheological behavior of the resin has significant influence on the polymerization step, affecting the homogeneity of impregnated foam and, consequently, its final properties, mainly the mechanical one. The impregnated foam prepared with the furfuryl alcohol resin diluted with 10% of furfuryl alcohol (eta = 11.4 Pa s) showed higher compression values (0.26 MPa). (c) 2007 Wiley Periodicals, Inc.

Electrochemical deposition of silver in room-temperature ionic liquids and its surface-enhanced Raman scattering effect

The use of room-temperature ionic liquids (RTILs) as media for electrochemical application is very attractive. In this work, the electrochemical deposition of silver was investigated at a glassy carbon electrode in hydrophobic 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) and hydrophilic 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) RTILs and in KNO3 aqueous solution by cyclic voltammetric and potentiostatic transient techniques. The voltammograms showed the presence of reduction and oxidation peaks associated with the deposition and dissolution of silver from AgBF4 in both BMIMPF6 and BMIMBF4, resembling the redox behavior of AgNO3 in KNO3 aqueous solution. A crossover loop was observed in all the cyclic voltammograms of these electrochemical systems, indicating a nucleation process. From the analysis of the experimental current transients, it was shown that the electrochemical deposition process of silver in these media was characteristic of 3D nucleation with diffusion-controlled hemispherical growth, and the silver nucleation closely followed the response predicted for progressive nucleation in BMIMPF6 and instantaneous nucleation in KNO3 aqueous solution, respectively.

IN-SITU SCANNING TUNNELING MICROSCOPIC STUDY OF NICKEL ELECTRODEPOSITION ON HOPG

The early stages of the electrodeposition of nickel on highly oriented pyrolytic graphite (HOPG) were investigated by in situ scanning tunnelling microscopy, scanning electron microscopy and electrochemical measurements. Experimental results showed that t

Changed reactivity of the 1-bromo-4-nitrobenzene radical anion in a room temperature ionic liquid

Radical anions of 1-bromo-4-nitrobenzene (p-BrC6H4NO2) are shown to be reactive in the room temperature ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, ([C(4)mPyrr][NTf2]), by means of voltammetric measurements. In particular, they are shown to react via a DISP type mechanism such that the electrolysis of p-BrC6H4NO2 occurs consuming between one and two electrons per reactant molecule, leading to the formation of the nitrobenzene radical anion and bromide ions. This behaviour is a stark contrast to that in conventional non-aqueous solvents such as acetonitrile, dimethyl sulfoxide or N,N-dimethylformamide, which suggests that the ionic solvent promotes the reactivity of the radical anion, probably via stabilisation of the charged products.

Approaches for multicopper oxidases in the design of electrochemical sensors for analytical applications

We report an effective approach for the construction of a biomimetic sensor of multicopper oxidases by immobilizing a cyclic-tetrameric copper(II) species, containing the ligand (4-imidazolyl)ethylene-2-amino-1-ethylpyridine (apyhist), in the Nafion (R) membrane on a vitreous carbon electrode surface. This complex provides a tetranuclear arrangement of copper ions that allows an effective reduction of oxygen to water, in a catalytic cycle involving four electrons. The electrochemical reduction of oxygen was studied at pH 9.0 buffer solution by using cyclic voltammetry, chronoamperometry, rotating disk electrode voltammetry and scanning electrochemical microscopy techniques. The mediator shows good electrocatalytic ability for the reduction of O(2) at pH 9.0, with reduction of overpotential (350 mV) and increased current response in comparison with results obtained with a bare glassy carbon electrode. The heterogeneous rate constant (k(ME)`) for the reduction of O(2) at the modified electrode was determined by using a Koutecky-Levich plot. In addition, the charge transport rate through the coating and the apparent diffusion coefficient of O(2) into the modifier film were also evaluated. The overall process was found to be governed by the charge transport through the coating, occurring at the interface or at a finite layer at the electrode/coating interface. The proposed study opens up the way for the development of bioelectronic devices based on molecular recognition and self-organization. (C) 2010 Elsevier Ltd. All rights reserved.

Evaluation of different electrochemical methods on the oxidation and degradation of Reactive Blue 4 in aqueous solution

The oxidation of a reactive dye, Reactive Blue 4, RB4, (C.I. 61205), widely used in the textile industries to color natural fibers, was studied by electrochemical techniques. The oxidation on glassy carbon electrode and reticulated vitreous carbon electrode occurs in only one step at 2.0 < PH < 12 involving a two-electron transfer to the amine group leading to the imide derivative. Dye solution was not decolorized effectively in this electrolysis process. Nevertheless, the oxidation of this dye on Ti/SnO2/SbOx (3% mol)/RuO2 (1% mol) electrode showed 100% of decolorization and 60% of total organic carbon removal in Na2SO4 0.2 M at PH 2.2 and potential of +2.4 V. Experiments on degradation photoelectrocatalytic were also carried out for RB4 degradation in Na2SO4 0.1 K PH 12, using a Ti/TiO2 photoanode biased at +1.0 V and UV light. After 1 h of electrolysis the results indicated total color removal and 37% of mineralization. (c) 2004 Elsevier Ltd. All rights reserved.

Voltammetric sensor for sodium nitroprusside determination in biological fluids using films of poly-L-lysine

Sodium nitroprusside (NP), a commercial vasodilator, can be pre-concentrated on vitreous carbon electrode modified by films of 97.5%: 2.5% Poly-L-lysine (PLL): glutaraldehyde (GA). This coating gives acceptable anion exchange properties whilst giving the required improvement of adhesion to the glassy carbon electrode surface. Linear response range and detection limit on nitroprusside in B-R buffer pH 4.0, were 1 x 10(-6) to 2 x 10-(5) mol L-1 and 1 x 10(-7) mol L-1, respectively. The repeatability of the proposed sensor, evaluated in term of relative standard deviation, was measured as 4.1% for 10 experiments. The voltammetric sensor was directly applied to determination of nitroprusside in human plasma and urine samples and the average recovery for these samples was around 95-97% without any pre treatment.

A Chloro-Bridged Linear Chain Imine-Copper(II) Complex and Its Application as an Enzyme-Free Amperometric Biosensor for Hydrogen Peroxide

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Viscosity, pH, and moisture effect in the porosity of poly(furfuryl alcohol)

The poly(furfuryl alcohol) is highly indicated to obtain advanced carbonaceous materials due mainly to its good carbon yield (around 50%) and a controllable cure reaction. In the processing of some carbonaceous materials, such as monolithic vitreous carbon, it is necessary to make sure that the material has the smallest porosity to be used in nobler applications such as heart valves and aerospace integrated systems. In this manuscript, a design of experiments was used to study the influence of viscosity, pH, and moisture in the porosity of the cured material. This study shows that the moisture exerts a significant influence on the porosity and the trend of the results lead to conclude that lower viscosity and moisture, and the use of non-neutralized poly(furfuryl alcohol) resins lead to obtain materials with better quality. © 2012 Wiley Periodicals, Inc.

Produção e caracterização de carbono vítreo monolítico a partir das resinas poliarilacetileno e furfurílica

Pós-graduação em Engenharia Mecânica - FEG