Showing papers by "Centro de Investigación y Desarrollo Tecnológico en Electroquímica published in 2011"

Nanosized IrO2 electrocatalysts for oxygen evolution reaction in an SPE electrolyzer

Abstract: Nanosized IrO2 electrocatalysts (d ~ 7–9 nm) with specific surface area up to 100 m2 g−1 were synthesized and characterized for the oxygen evolution reaction in a solid polymer electrolyte (SPE) electrolyzer. The catalysts were prepared by a colloidal method in aqueous solution and a subsequent thermal treatment. An iridium hydroxide hydrate precursor was obtained at ~100 °C, which was, successively, calcined at different temperatures from 200 to 500 °C. The physico-chemical characterization was carried out by X-ray diffraction (XRD), thermogravimetry–differential scanning calorimetry (TG–DSC) and transmission electron microscopy (TEM). IrO2 catalysts were sprayed onto a Nafion 115 membrane up to a loading of 3 mg cm−2. A Pt catalyst was used at the cathode compartment with a loading of 0.6 mg cm−2. The electrochemical activity for water electrolysis of the membrane-electrode assemblies (MEAs) was investigated in a single cell SPE electrolyzer by steady-state polarization curves, impedance spectroscopy and chrono-amperometric measurements. A maximum current density of 1.3 A cm−2 was obtained at 1.8 V and 80 °C for the IrO2 catalyst calcined at 400 °C for 1 h. A stable performance was recorded in single cell for this anode catalyst at 80 °C. The suitable catalytic activity and stability of the most performing catalyst were interpreted in terms of proper combination between nanostructure and suitable morphology.

Electrodeposition and corrosion behavior of Zn coatings formed using as brighteners arene additives of different structure

Abstract: This study examined the effect of the molecular structure of the aliphatic chain in arenes (phenyl + aliphatic chain) used as brightener additives on the reduction kinetics, morphology and corrosion resistance of Zn coatings formed by reduction of Zn(II) ions in a chloride electrolytic bath. Three such brighteners were tested—benzylideneacetone (BDA), benzylacetone (BA) and butylbenzene (BB)—dissolved in polyethyleneglycol (MW200) PEG 200 , in order to determine the influence of the phenyl, carbonyl and/or C = C double bond present in these compounds on the zinc reduction process. The results showed that, in the presence of PEG 200 alone, the reduction rate (j 0 ) of Zn(II) ions was higher than in the absence of additives. By contrast, in the presence of the brightener-PEG 200 mixtures, the values of j 0 were lower, leading to a reduction in the size of the Zn clusters. Among the brighteners tested, no significant differences were observed in the values of j 0 as a function of the molecular structure of the arene aliphatic chain. SEM analysis revealed a change in the Zn coating morphology from hexagonal crystals with a (101) preferred orientation in the absence of additives, to flakes grouped in hemispherical clusters with (002), (100) and (101) crystallographic orientations when PEG 200 or brightener-PEG 200 mixtures were present in the electrolytic bath. In addition, the cluster size decreased in accordance with the j 0 values. The comparison of the values of corrosion current density indicates that there are no significant differences between them.

Coexistence of intramolecular ligand-mediated and through hydrogen-bond magnetic interactions in a chain of dicopper(II) units.

Abstract: The reaction of 2,8-dimethyl-5,11-bis(pyridin-2-ylmethyl)-1,4,5,6,7,10,11,12-octahydroimidazo[4,5-h]imidazo[4,5-c][1,6]-diazecine (dimp) with copper(II) nitrate in water produces the compound [Cu(2)(dimp)(H(2)O)(2)(NO(3))(2)](NO(3))(2). The single-crystal X-ray structure shows the formation of hydrogen-bonded chains in the lattice that are formed by dicopper(II) units doubly connected by nitrate/water bridges. Within the one-dimensional chains, the Cu ions are separated by either intramolecular or intermolecular distances of 7.309(2) A or 6.255(2) A, respectively. The magnetic susceptibility data revealing weak antiferromagnetic exchange interactions between the copper(II) ions were interpreted by considering two possible models, namely, an isolated dinuclear and a 1-D chain picture. The latter leads to an alternation J(1) = -11.6 and J(2) = -3.0 cm(-1) along the chain. In order to clarify the relative strengths of the exchange couplings through hydrogen bonds and via the bridging dimp ligand, solution EPR studies and quantum chemical calculations were carried out. EPR studies unambiguously conclude on the existence of an exchange interaction J(a) mediated by the dinucleating dimp ligand, while the through-H coupling J(b) is physically absent in solution. On the basis of dinuclear units extracted from the X-ray data, J(a) was estimated around -5.0 cm(-1) from DFT-based calculations (M06 functional), whereas J(b) is negligible. In contrast, wave function configuration interaction calculations (DDCI) support a description where both inter- and intramolecular pathways coexist with a preeminent role of H bonds with J(a) = -2.8 and J(b) = -10.4 cm(-1). Not only are these values very consistent with the extracted set of parameters (J(1), J(2) = -11.6, -3.0 cm(-1)) but the possibility to generate leading exchange coupling through weak bonds is evidenced by means of wave function-based calculations.

Surface modification of acrylonitrile-butadiene-styrene (ABS) with heterogeneous photocatalysis (TiO2) for the substitution of the etching stage in the electroless process

Abstract: The acrylonitrile-butadiene-styrene (ABS) is the most commonly used copolymer in industry for metallizing. The process in solution used for depositing metallic films on non-conductive substrates is known as electroless, which is an autocatalytic procedure. However, the sulfo-chromic admixture used to modify the ABS surface, in the first step of this process, is not environmentally suitable due to the use of Cr (VI), and its utilization implies a risk of severe damage to living beings. For this reason, a study of an alternative surface treatment with substantially lower levels concerning environmental impact is presented in this work, which is based on a photocatalytic reaction that is initiated on the copolymer surface by TiO 2 nanoparticles (30 nm), as a suspension, under UV exposure. After surface conditioning with the photocatalytic treatment was conducted, the substrates were metallized in two different ways: electroless process or dynamic chemical process (DCP), with a subsequent conventional electrolytic deposit. The DCP does not need a surface activation with palladium ions, unlike electroless process, which simplified the procedure by reducing directly both, the effluents and the costs. The prepared substrates were characterized using: scanning electron microscopy (SEM), atomic force microscopy (AFM), atomic force acoustic microscopy (AFAM), mechanic profilometry, optical interference profilometry, profilometry by AFM, and a cross cut tape test. The results obtained with the proposed pre-treatment stage are shown and compared with those obtained in the conventional electroless process.

Morphological rational operator for contrast enhancement

Abstract: Contrast enhancement is an important task in image processing that is commonly used as a preprocessing step to improve the images for other tasks such as segmentation. However, some methods for contrast improvement that work well in low-contrast regions affect good contrast regions as well. This occurs due to the fact that some elements may vanish. A method focused on images with different luminance conditions is introduced in the present work. The proposed method is based on morphological transformations by reconstruction and rational operations, which, altogether, allow a more accurate contrast enhancement resulting in regions that are in harmony with their environment. Furthermore, due to the properties of these morphological transformations, the creation of new elements on the image is avoided. The processing is carried out on luminance values in the u′v′Y color space, which avoids the creation of new colors. As a result of the previous considerations, the proposed method keeps the natural color appearance of the image.

Spectroscopy of free-base N-confused tetraphenylporphyrin radical anion and radical cation.

Abstract: The radical anions and radical cations of the two tautomers (1e and 1i) of 5,10,15,20-tetraphenyl N-confused free-base porphyrin have been studied using a combination of cyclic voltammetry, steady state absorption spectroscopy, and computational chemistry. N-Confused porphyrins (NCPs), alternatively called 2-aza-21-carba-5,10,15,20-tetraphenylporphyrins or inverted porphyrins, are of great interest for their potential as building blocks in assemblies designed for artificial photosynthesis, and understanding the absorption spectra of the corresponding radical ions is paramount to future studies in multicomponent arrays where electron-transfer reactions are involved. NCP 1e was shown to oxidize at a potential of Eox 0.65 V vs Fc+|Fc in DMF and reduce at Ered −1.42 V, while the corresponding values for 1i in toluene were Eox 0.60 V and Ered −1.64 V. The geometries of these radical ions were computed at the B3LYP/6-31+G(d)//B3LYP/6-31G(d) level in the gas phase and in solution using the polarizable continuum ...

Effect of aromatic aldehydes on the electrodeposition of ZnCo alloy from cyanide-free alkaline-gluconate electrolytes

Abstract: The effects of vanillin and anisaldehyde on electrodeposition of zinc–cobalt alloys onto AISI 1018 carbon steel were studied in an alkaline gluconate zincate electrolyte. The influence of an additive on the metal discharge depends on the structure of the added molecule and on the nature of the substrate. The composition of the deposit varies during the electrodeposition process. Maximum cobalt content is observed close to the steel–ZnCo interface for ZnCo formed with or without vanillin, but the composition profile becomes more uniform when anisaldehyde is added to the bath. The morphology of Zn-rich Co-alloy coatings was evaluated: Cobalt ions produce porous ZnCo alloys; vanillin induces slightly porous deposits, whereas uniform and more compact deposits were observed with anisaldehyde. Furthermore, a crystallographic study showed that the orientation of the lattice planes changes, with highly oriented deposits produced in the presence of anisaldehyde.

Zn Electrodeposition from an Acidic Chloride Bath Containing Polyethyleneglycol (Mw 200) and Benzylideneacetone as Additives

Abstract: The influence of Polyethylene Glycol 200 (PEG200) or a PEG200/benzylideneacetone (BDA) mixture on the mechanism of Zn deposition and nucleation kinetics was studied by voltammetry, chronoamperometry and atomic force microscopy (AFM). The addition of PEG200 or PEG200/BDA to the solution partially inhibited the reduction of Zn(II) at E ¼� 1.135 V vs. SCE. In the presence of PEG200/BDA, an additional reduction process was observed at E ¼� 1.24 V vs. SCE. Analysis of the nucleation processes indicated that, in all systems studied, the initial stage of Zn deposition was dominated by 3D diffusion-controlled nucleation. At E ¼� 1.132 V vs. SCE, the addition of PEG200 caused a reduction in the nucleation rate constant (A) and the number density of active sites (N0) with respect to the values obtained without additives. AFM analysis of coatings obtained at E ¼� 1.132 V vs. SCE, showed the formation of Zn clusters with different sizes distributed randomly on the surface. At E ¼� 1.243 V vs. SCE, both A and N0were higher for the solution containing the PEG200/BDA mixture than for the systems with PEG200 alone or without additives. AFM analysis revealed the formation of similarly sized Zn clusters uniformly distributed on the surface.

Effect of fly ash and hemihydrate gypsum on the properties of unfired compressed clay bricks

Abstract: The effect of fly ash type F and hemihydrate gypsum on the mechanical and thermal properties of unfired compressed clay bricks (UCSB) using a semi-dry mixture was determined. UCSB were molded from two different semi-dry mixtures, the bricks made with dark-brown soil + sand + chemical additives were labeled as DBS-LG while the other bricks made with the mixture dark-brown soil + sand + fly ash + chemical additives were labeled as DBS-FALG. SEM and XRD were used to investigate microstructure and mineralogical composition, respectively. Results showed that the addition of fly ash and hemihydrate gypsum improves the mechanical properties of UCSB compared to those of a clay-polymers system; thermal conductivity was similar to other clay based bricks. These results reinforce the suitability of these mixtures in low cost building bricks with energy conservation. Key words: Carbon footprint, Earth construction, unfired clay bricks, fly ash.

Dynamic Model of a PEM Electrolyzer based on Artificial Neural Networks

Abstract: Hydrogen production by electrolysis is emerging as one of the most promising ways to meet future fuel demand; likewise, the development of models capable of simulating the operation of electrolysis devices is indispensable in the efficient design of power generation systems, reducing manufacturing costs and resources savings. The nonlinear nature of the Artificial Neural Network (ANN) plays a key role at the development of models for predicting the performance of complex systems. The behavior of a Polymer Electrolyte Membrane (PEM) Electrolyzer of three cell stack (100 cm 2 of active area) was modeled successfully using a Multilayer Perceptron Network (MLP). This dynamic model has been trained to learn the internal relationships that govern this electrolysis device and predict its behavior without any physical equations. The electric current supply and the operation temperature were used as input vector able to predict each cell voltage behavior. A reliable accuracy (< 2%) was reached in this work after comparing the single cell performance of the real electrolyzer versus the ANN based model. This predictive model can be used as a virtual device into a more complex energy system.

Intramolecular Conversions of (Aminoferrocenylpenta-1,4-dienyl)-ferrocenylcarbenes: Synthesis of Diferrocenylmono-, bi-, tricycles and Amino(diferrocenyl)hexa-1,3,5-trienes

Abstract: Synthesis of 3,4-diferrocenyltoluene (7), 1-morpholino- and 1-piperidino-2,3-diferrocenylbicyclo[3.1.0]hex-2-enes 8a, 8b, 1-morpholino- and 1-piperidino-7-ferrocenyl-3,4-ferrocenobicyclo[3.2.1]oct-6-enes 9a, 9b, 2- and 3-amino(diferrocenyl)-hexa-1,3,5-trienes 10a,b, 11a,b by reactions of amino(diferrocenyl)cyclopropenylium tetrafluoro-borates with 1-methylprop-2-enylmagnesium chloride at 80 °C is described. The structures of the compounds obtained were determined by IR, 1H- and 13C-NMR spectroscopy and mass spectrometry. X-ray diffraction data for 1-piperidino-7-ferrocenyl-3,4-ferroceno-bicyclo[3.2.1]oct-6-ene (9b), 2-morpholino- and 2-piperidino-1,3-diferrocenyl-4-methyl-hexa-1,3,5-trienes 10a and 10b is presented. The electrochemical behaviour of compounds 7, 8a, 10a and 10b was investigated by means of cyclic voltammetry and square wave voltammetry. For 7 and 8a two electrochemical processes (I-II), attributed to the oxidation of the ferrocene moieties were found. On the other hand for compounds 10a and 10b a single electron transfer for both ferrocene groups and the electrochemical generation of the monocation and dication species were detected.