Search

In this work, the surface of a glassy carbon electrode (GCE) was modified with the polymer of 5-Amino-1-10 phenanthroline (5Aphen), Poly5Aphen, from a deep eutectic solvent (DES). The electrochemical response of the modified electrode (GCE/Poly5Aphen) was established regarding the oxidation of dopamine (DA) in the presence of ascorbic acid (AA) that is one of its major interferents. The results obtained by cyclic voltammetry (CV) showed that it is possible to polymerize 5Aphen on the surface of the GCE when using a DES. On the other hand, the results by CV and differential pulse voltammetry (DPV) showed that, unlike the bare GCE, when using the GCE/Poly5Aphen electrode it is possible to separate the electrochemical signal of the DA and AA as result of their simultaneous oxidation over the modified surface of the electrode.

Alumina-based composites reinforced with titanium were manufactured by powder techniques. Characterizations indicate that titanium content affects densification which in turn causes positive effects on hardness and toughness. Microstructure presents grains of irregular shape and small sizes. Electrochemical impedance spectroscopy indicates that additions of titanium on Al2O3 enhance its corrosion resistance.

In this work, the surface of a glassy carbon electrode (GCE) was modified with gold nanoparticles (AuNPs), by potentiostatic electrodeposition, from Au (III) ions dissolved in a deep eutectic solvent formed by choline chloride and urea (reline) at 70 °C. Using electrochemical techniques, both potentiodynamic and potentiostatic, the mechanism and kinetics of the AuNPs nucleation and growth was determined. It was found that the experimental total current density transients jtotal(t) can be adequately describe by a model that Involves adsorption, jad(t), and 3D nucleation and diffusion-controlled growth, j 3D-dc(t),1 see Figure 1a. Furthermore, the modified electrode (GCE/AuNPs) was used in the evaluation of the electrochemical response of dopamine (DA) by means of cyclic voltammetry (CV) and differential pulse voltammetry (PDV) techniques. The results obtained showed that GCE/AuNPs electrode has a greater catalytic activity towards the electrochemical oxidation of DA, with a sensitivity of 129 , see Figure 1b, which is greater than that shown by the bare GCE and comparable to the performance reported for an ITO/AuNPs electrode.2 As well as the presence of a displacement of the oxidation peak towards lower potentials when using the GCE/AuNPs with respect to the bare GCE, which is indicative that GCE/AuNPs requires less energy for the oxidation of DA. References [1] C. Ramírez, E.M. Arce, M. Romero-Romo, M. Palomar-Pardavé. The effect of temperature on the kinetics and mechanism of silver electrodeposition. Solid State Ionics. 169 (2004) 81–85. [2] J. Aldana-González, M. Palomar-Pardavé, S. Corona-Avendaño, M.G. Montes de Oca, M.T. Ramírez-Silva, M. Romero-Romo, Gold nanoparticles modified-ITO electrode for the selective electrochemical quantification of dopamine in the presence of uric and ascorbic acids, Journal of Electroanalytical Chemistry 706 (2013) 69–75 Figure 1

In this work, the effect of core composition in AuxCuy@Pt/C core@shell catalysts for methanol oxidation is investigated. The catalysts were prepared varying Au:Cu atomic percentage (i.e., 100:0, 75:25, 50:50, 25:75, and 0:100 %) while maintaining Pt constant. The average particle size of every sample was obtained from STEM measurements, while XRD measurements allowed to determining their crystal structure; in all cases, a FCC crystal structure was obtained. From chronoamperometry, it was found that the values of steady-state current density (I ss) increased with the gold content in the core, i.e., I ss values are 2.52, 1.86, 1.18, 0.34, and 0.18 mA cm−2 for Au100Cu0@Pt, Au75Cu25@Pt, Au50Cu50@Pt, Au25Cu75@Pt, and Au0Cu100@Pt, respectively. Similar results were obtained by using cyclic voltammetry, where the value of the peak current density increased as the gold content in the core increased: this behavior is associated to the modified electrochemical activity of Pt shell caused by the core composition (AuxCuy).

Tartrazine (Trz) is one of the most widely used azoic dyes in the alimentary industry; it is added to a great variety of products, for this reason it is necessary to develop analytic methods and materials which allow its detection and quantification. For this purpose ultraviolet-visible spectrophotometry (UV-Vis), high performance liquid chromatography (HPLC), capillary electrophoresis and potentiometric and voltammetric sensors have been used. Potentiometric and voltammetric sensors have many advantages such as simplicity; rapid analysis and cost, besides most recently developed sensors are environmentally friendly and avoid the use of mercury which is toxic. In this regard, carbonaceous electrodes such as carbon paste electrodes have been employed due to its low cost, they are easy to manufacture and can be modified with a great diversity of materials an methods. Nanostructured materials such as bamboo-shaped multiwalled carbon nanotubes (BS-MWCNT) and Pt nanoparticles (Pt/NPs) allow great electrochemical activity and in this work are proposed to modify a CPE in order to detect and quantify Tartrazine samples. The electrochemical experiments were performed in a potentiostat/galvanostat AUTOLAB30, using NOVA 2.1 software, a typical three-electrode electrochemical cell was used. A Pt wire was employed as counter electrode; Ag/AgCl (3M NaCl) in a Luggin capillary as reference electrode, the working electrode was a CPE prepared by mixing graphite powder and mineral oil in a proportion 1:1, the CPE was modified by adding an aliquot of 5mL of BS-MWCNT dispersion and by adding an aliquot of 5mL of Pt/NPs and BS-MWCNT. Cyclic voltammograms obtained in 0.5M NaCl + 2.0x10-5 M Trz (adjusted to a pH=4.0) are shown in Figure 1. In the case of CPE, a peak due to Trz oxidation appears at 0.77V, the oxidation peak is positively shifted (0.15V) when BS-MWCNT are added and now appears at 0.92V, even though the oxidation potential is greater on BS-MWCNT the associated current is also greater. When the experiment is performed on BS-MWCNT + Pt/NPs the oxidation peak appears at 0.99V, the associated current in this last case is greater than in the previous cases, a great current leads to an improvement of some analytical parameters such as sensibility, which may help to detect and quantify Trz more accurately. S Food and Drug Administration Center for Food Safety and Applied Nutrition. (2003) U. S Department of Health and Human Services. López-de-Alba, P. L., López-Martínez, L., De-León-Rodríguez, L. M. Simultaneous Determination of Synthetic Dyes Tartrazine, Allura Red and Sunset Yellow by Differential Pulse Polarography and Partial Least Squares. A Multivariate Calibration Method. (2002). 14(3):197-205. Ramírez-Silva, T., Palomar-Pardavé, M. E. Gónzalez, I., Rojas-Hernández, A. (1995). Carbon Paste Electrodes with Electrolytic Binder: Influence of the Preparation Method. Electroanalysis. 7:184-188. Yu, L., Shi, M., Yue, X., Qu, L. (2016). Detection of Allura Red Based on the Composite of Poly (diallylmethylammonium chloride) Functionalized Graphene and Nickel Nanoparticles Modified Electrode. Sensors and Actuators B: Chemical. 225:398-404. Figure 1

Nanostructured materials have application on different areas such as catalysis which in part is due to the physical properties gained for the nanometric scale. An important application of nanomaterials is as catalysts in fuel cells, for example, in direct methanol fuel cells (DMFC). Since methanol oxidation kinetics is slow Pt is used as catalyst, Pt is generally employed in nanometric size which improves the electrochemical active area and diminishes the amount of Pt employed, lowering the cost. It has been showed that CO (an intermediary generated during methanol oxidation reaction, MOR) adsorbed and poisons Pt surface [1, 2]. In this regard, many investigations have been focused in improving the catalytic activity of Pt nanoparticles, for example, by synthetizing bimetallic catalysts, alloys, core-shell structures, which allow diminishing the amount of Pt even more and promotes COads oxidation on Pt surfaces [3]. Another fact to take into account is that the surface planes of a nanoparticle are associated to its shape [4, 5], also the extend of an oxidation reaction (including methanol oxidation) depend on the crystallographic planes of the electrocatalyst [6]. In this work, three core-shell catalysts for MOR were prepared by using a colloidal method, core nanoparticles consist on Au NPs and Pt shell, additionally Ag+ was added as modifying agent of shape during synthesis. The amount of Ag+ was used to control the final form of core-shell NPs; all NPs were supported in carbon Vulcan XC-72R and evaluated with electrochemical techniques. Pt NPs with spherical shape were synthesized and electrochemically evaluated for comparison purposes. It was found that the activity of core-shell NPs depends on the amount of Ag+ employed during synthesis; the latter is also associated to the final form of the NP. The synthesized catalysts are listed on Table 1. From electrochemical results, it was found that the activity of catalysts is favored for MOR as follows Au@Pt2/C > Au@Pt3/C> Pt/C> Au@Pt1/C, the current response for MOR is affected by the presence of Au which modifies the surface properties of Pt atoms (shell). Additionally Ag+ concentration leads to preferential planes formation during synthesis, the best current response belongs to Au@Pt2/C, the high current is attributed to the presence of (110) planes, which are the most active for MOR. References Bock, C., B. MacDougall, and C.-L. Sun, Catalysis for Direct Methanol Fuel Cells, in Catalysis for Alternative Energy Generation, L. Guczi and A. Erdôhelyi, Editors. 2012, Springer New York: New York, NY. p. 369-412. Rodríguez, J. and O. Savadogo, Celdas de Combustible de Consumo Directo de Moléculas Orgánicas, in Celdas de combustible, F.J.S.O.H.E. Rodríguez, Editor. 2010: Canada. p. 93-123. Xia, X.H., et al., Structural effects and reactivity in methanol oxidation on polycrystalline and single crystal platinum. Electrochimica Acta, 1996. 41(5): p. 711-718. Niu, W. and G. Xu, Crystallographic control of noble metal nanocrystals. Nano Today, 2011. 6(3): p. 265-285. Yiliguma, Y. Tang, and G. Zheng, Colloidal nanocrystals for electrochemical reduction reactions. Journal of Colloid and Interface Science, 2017. 485: p. 308-327. Xia, Y., et al., Shape-Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics? Angewandte Chemie International Edition, 2009. 48(1): p. 60-103. Figure 1

Anode-respiring bacteria (ARB) perform an unusual form of respiration in which their electron acceptor is a solid anode. The focus of this study was to characterize the electrical stress direct evolution of biocatalysts as a way of enriching the community with ARB for microbial fuel cell. The original microbial consortium was sampled from a sodic-saline bottom soil (Texcoco Lake). Interestingly, iron (III) reducing bacteria consortium in the sodic-saline bottom soil was 8500 ± 15 MPN/100 mL by the most probable number method, since microbial reduction of iron (III) is reported to be associated to anode-respiring capabilities. Cyclic voltammetry studies of electrochemical stressed biofilm-ARB were conducted at 28th and 135th days, and an irreversible electron transfer reaction was found possibly related to electron transfer reaction of the cytochrome. The electrochemical impedance spectroscopy results revealed that the resistance of the biofilm-ARB decreased with time (28th day-11.11 ω and 135th day- 5.5 ω ), possibly associated to the adaptability of electroactive biofilm on the graphite electrode surface. Confocal microscopy showed that the biofilms are active in nature and the biofilm-ARB attained ~40 μ m thickness at the 136th day. Electrical stressed-ARB gave a maximum power density of 79.4mW/m2, and unstressed-ARB gave a maximum power density of 41.0mW/m2 in a single-chamber microbial fuel cell (SCMFC). All these electrochemical experiments and evaluation suggest that the electrical-stress directed evolution of ARB community was associated to a more efficient extracellular electron transfer process in SCMFC.

Anode-respiring bacteria (ARB) perform an unusual form of respiration in which their electron acceptor is a solid anode. The focus of this study was to characterize the electrical stress direct evolution of biocatalysts as a way of enriching the community with ARB for microbial fuel cell. We gave the electrical stress continually to the Texcoco bacterial community at -150mV/SCE. The 4th day current started to increase and attained the maximum current of 0.35mA in the 15 th day. The current in this period was associated to biofilm growth. On the 15thday and by using cyclic voltammetery, an irreversible electron transfer reaction of alkaliphilic cytochrome was found, due to the electrode fouling. From the impedance measurement, the biofilm ARB resistance was determined (~250Ω). Further confocal microscopy studies of biofilm ARB revealed ~6µm thickness. In the single chamber microbial fuel cell, the electrochemical stressed biofilm-ARB exhibited a maximum power density of 79mW/m2

A new design of a single chamber MFC-A based on extended electrode surface (larger σ , specific surface or surface area of electrode to cell volume) and the assemblage or ‘sandwich’ arrangement of the a node-proton exchange m embrane- c athode (AMC arrangement) and a standard single chamber MFC-B with separated electrodes were tested with several inocula (sulphate-reducing, SR-In; methanogenic, M-In, and aerobic, Ab-In) in order to determine the effects on the internal resistance R int and other electrical characteristics of the cells. In general, the R int of the new design cell MFC-A was consistently lower than that of the standard MFC-B, for all inocula used in this work. Resistances followed the order R int,SR-In R int,M-In ≪ R int,Ab-In . These results were consistent with reports on reduction of ohmic resistance of cells by decreasing inter-electrode distance. Also, the volumetric power P V output was higher for the MFC-A than for MFC-B; this was congruent with doubling the σ in the MFC-A compared to MFC-B. Yet, power density P An delivered was higher for MFC-A only when operated with SR-In and Ab-In, but not with M-In. The MFC-A loaded with SR-In showed a substantial improvement in P V (ca. 13-fold, probably due to the combined effects of increased σ and decreased of R int ) and a 6.4-fold jump in P An compared to MFC-B. The improvement was higher than the expected improvement factors (or algebraic factors; 6.5 improvement expected for P V due to combined effects of increase of σ and lowering the R int ; 3.25 improvement expected for P An due to lowering the R int ). Our results point out to continuing work using the two-set, sandwich-electrode MFC and sulphate-reducing inoculum as a departing model for further studies on effects of inoculum enrichment and electrode material substitution on cell performance. Also, the MFC-A model seems to hold promise for future studies of bioelectricity generation and pollution abatement processing leachates produced during biohydrogen generation in dark fermentation processes of organic solid wastes.

A study of the oxygen reduction reaction on PdCu electrocatalyst synthesized by a NaBH4 reduction of PdCl2 and CuCl in a THF solution was examined in a 0.5 M H2SO4 electrolyte, at 25 °C. The electrochemical techniques used were cyclic voltammetry (CV) and rotating disc electrode (RDE). The electrocatalyst was characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The physical characterization showed that the method of synthesis allows the formation of spherical agglomerated nanocrystalline particles about 11 nm in size. The PdCu catalyst exhibited high current densities for the ORR compared to that obtained on nanometric Pd catalyst synthesized by the same method.

In this work the oxygen reduction reaction (ORR) on PdCo particles (~ 11 nm) supported in carbon Vulcan XC-72 is analyzed. In 0.5 M H2SO4/O2 the impedance spectra showed one or two time constants, the first time constant was associated to the reduction of O2 to H2O, while the second, to the reduction from H2O2 to H2O. By using electric circuits, the kinetics parameters of ORR were obtained. The values of charge transfer resistance Rct1 obtained from the impedance spectra were used to determine the kinetic parameters (b, α and i0) of ORR. The impedance spectra of PEMFC fed with H2/air and H2/O2 allows determining the values of Rc; with these, the values of b, α, and i0 were calculated. The values of i0, are related to the kinetics of ORR on PdCo/C, the highest value of i0 belongs to the PEMFC fed with H2/O2.

The Oxygen Reduction Reaction (ORR) on synthesized Au nanoparticles was investigated. The reduction of AuCl3 with NaBH4 in THF forms highly crystalline Au particles with a face-centered cubic structure and approximate size of ~5nm. From RDE measurements the kinetic parameters were obtained, i.e. Tafel slope of -0.110 Vdec-1 and charge transfer coefficient, a =0.54. The Nyquist and Bode spectra of Au nanoparticles for E > 0.38 V vs NHE show one loop which may be associated to the reduction process of O2 to generate H2O2. The impedance spectra for E

The catalytic activity of carbon supported PdNi and Pd0.5Ni0.45Se0.05 materials for the oxygen reduction reaction (ORR) in acid media at 25{degree sign}C was studied. The electrocatalysts were synthesized by a chemical from metallic precursors with NaBH4. Thermal treatment in hydrogen atmosphere was performed in a stainless steel reactor, to improve their catalytic properties. The X-Ray diffraction pattern showed an enhancement of the crystallinity as well as a grown of the crystallite size in comparison to those without heat treatment. Displacements of diffraction peaks towards more positive 2θ values were observed and associated to the incorporation of the elements inside a crystalline structure.The catalytic activity was studied by electrochemical hydrodynamic techniques; the mass transfer corrected Tafel plots showed a decreasing in ~50 mV in the overpotential of Pd0.5Ni0.45Se0.05 to reach the same PdNi current density. There is not a significant enhancement of the Pd0.5Ni0.45Se0.05 catalyst associated to the formation of new inactive-ORR phases.

"En este trabajo se presenta el diseño de una celda de combustible con membrana de intercambio de protones (PEMFC) alimentada con oxígeno del aire y una mezcla de hidrógeno y monóxido de carbono. Con este fin se propone la utilización de catalizadores nanoestructurados tipo núcleo-coraza (core-shell) soportados en carbón Vulcan XC-72R, donde el núcleo es un metal noble (Au ), mientras que la coraza es de Pt."

"La fermentación anaerobia por microorganismos es un método prometedor para la producción de hidrógeno. En este trabajoserealizarán una serie de pruebas para investigar el efecto del pH, tiempo de retención hidráulica (TRH) y carga orgánica volumétrica, sobreel rendimiento y velocidad de producción de hidrógeno empleando un reactor UASB. También se establecerá la pertinencia de la ruta metabólica del etanol para la producción de hidrógeno.Se utilizará como sustrato la melaza. Por otra parte, se realizarán experimentos por lotes para establecer el efecto de los parámetros de operación, para luego escalarlos a un reactor en continuo."

In the past decades, direct methanol fuel cell (DMFC) has attracted much interest for their significant advantages in portable and automobile applications, for this technology the anode electrocatalyst is the most important part. The Pt catalyst is widely recognized as the best catalyst for DMFC and one of the key objectives in fuel cell technology is to improve the electrochemical activity and reduce Pt loading of the electrocatalyst. One way to reduce the Pt content in the electrocatlyst is by synthetizing core–shell structural catalysts, in which only surface atoms are active in the catalytic reaction (i.e. Pt as shell). In this work, the modulating effect given by the composition of the core in AuxCuy@Pt/C for the methanol oxidation reaction (MOR) is analyzed. For this purpose, AuxCuy@Pt/C catalysts were prepared varying the Au:Cu percentage (i.e. 100:0%, 75:25%, 50:50%, 25:75%, 0:100%), the catalysts were prepared by a two-step method.

not Available.

not Available.