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Valenzuela-Muniz A.M.,CIMAV | Valenzuela-Muniz A.M.,Ohio University | Alonso-Nunez G.,National Autonomous University of Mexico | Miki-Yoshida M.,CIMAV | And 2 more authors.
International Journal of Hydrogen Energy | Year: 2013

This work presents the synthesis, characterization and electrochemical evaluation of electrocatalysts for PEM fuel cells base on Pt and Pt-Ni nanoparticles over multi-walled carbon nanotubes (MWCNT). The MWCNT were synthesized by spray pyrolysis of toluene, using ferrocene and nickelocene as catalytic agents. The Pt nanoparticles were deposited using the ultrasound assisted aqueous deposition method, followed by either thermal or chemical reduction. The materials were characterized by scanning and transmission electron microscopy, as well as X-ray diffraction. The MWCNT exhibit lengths of 200 μm (using ferrocene) and 30 μm (using nickelocene) and diameters around 50-70 nm. Pt nanoparticles showed sizes between 4 and 8 nm. The electrochemical active area toward the hydrogen oxidation reaction was evaluated by cyclic voltammetry (CV) in a standard three electrodes cell. In addition to corroborate the electrochemical active area, CO stripping tests were done. From both, the CV and CO stripping analyses, it was found that the synthesized electrocatalysts exhibited an electrochemical activity higher (140-230 m 2gr-1) than 10%Pt/Vulcan (Etek). Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Ma J.,CNRS Poitiers Institute of Chemistry: Materials and Natural Resources | Habrioux A.,CNRS Poitiers Institute of Chemistry: Materials and Natural Resources | Morais C.,CNRS Poitiers Institute of Chemistry: Materials and Natural Resources | Lewera A.,University of Warsaw | And 5 more authors.
ACS Catalysis | Year: 2013

This study focuses on clarifying the strong interaction existing between extended graphitic domains of ordered carbonaceous materials such as multiwalled carbon nanotubes and platinum nanoparticles. This interaction results from the heterogeneous nucleation of platinum nanoparticles onto the carbon support. The metal clusters are chemically synthesized by using the carbonyl route. Two different carbon supports are used namely, homemade multiwalled carbon nanotubes, MWCNT-m, and classical Vulcan XC-72. Physicochemical properties of these materials are described by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The effect of the strong interaction on the electronic properties of platinum nanoparticles is electrochemically probed by means of CO stripping experiments coupled with in situ Fourier transform infrared spectroscopy (FTIR). Density functional theory (DFT) is used to evaluate changes to the electronic structure of a platinum cluster interacting with a graphite substrate and their effects on CO adsorption on the cluster. Results are correlated with structural and electronic properties of platinum nanoparticles. The stability of Pt/carbon catalysts under electrochemical potential cycling is correlated with the properties of carbon substrates. © 2013 American Chemical Society.

Escobar B.,Technological Institute of Cancun | Barbosa R.,University of Quintana Roo | Miki Yoshida M.,CIMAV | Verde Gomez Y.,Technological Institute of Cancun
Journal of Power Sources | Year: 2013

Pt colloidal nanoparticles were synthesized by simultaneous chemical reduction of metallic salts in presence of poly (N-vinyl-2-pyrrolidone) as protecting agent. The uniform and highly ordered Pt colloidal nanoparticles were associated to well dispersed particles ranging in particle size distribution around 4.5 ± 1.9 nm. The nanoparticles were deposited onto multiwalled carbon nanotubes (MWCNT). MWCNT were synthesized by chemical vapor deposition (CVD) method. Before the metal impregnation, the MWCNT were treated with HNO3 in reflux. Prepared Pt catalyst were characterized by various physical and electrochemical techniques, that is, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy and cyclic voltammetry (CV). Raman spectroscopy reveals changes intensity ratio IG′/IG in the samples, after the cleaning process and Pt loading, indicating changes in the crystallinity of the materials. HRTEM showed Pt particles between 6.1 ± 0.9 nm and 6.5 ± 1.5 nm are well dispersed along the carbon nanotubes. XRD patterns show characteristics peaks corresponding to graphite and metallic Pt. The electrochemical properties of the MWCNT supported Pt nanoparticles were investigated by analyzing the response of the nanostructured catalyst for cyclic voltammetry and compared with a commercial material. © 2013 Elsevier B.V. All rights reserved.

Alonso-Lemus I.,CIMAV | Verde-Gomez Y.,Technological Institute of Cancun | Alvarez-Contreras L.,CIMAV
International Journal of Electrochemical Science | Year: 2011

Platinum nanoparticles were incorporated in MCM-41 mesoporous support. Two different ways to incorporate metallic nanoparticles were evaluated (i) Pt wetness impregnation in MCM-41 previously synthesized and (ii) Pt incorporated in situ during MCM-41 synthesis in alkaline (iia) and acid (iib) media. Synthesis conditions influence was studied by X-Ray diffraction, nitrogen adsorption analysis and electron microscopy. High surface areas (up to 900 m2/g) were obtained in all methods. However, high Pt loading were observed only in wetness impregnation and in situ incorporation in alkaline media methods. Additionally, composites Pt/MCM-41-black carbon were prepared and their electrocatalytic activity and electrical bulk resistance were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), respectively. An interesting behaviour was observed in the samples where the platinum was in situ incorporated; the samples show structural and textural properties modifications compared to raw MCM-41.Hydrogen oxidation reaction by CV was observed in high Pt loading samples. On the other hands, EIS results indicate that Pt/MCM-41 materials synthesized by in situ incorporation methods have lower electrical bulk resistance than the samples prepared by wetness impregnation method. © 2011 by ESG.

Perez-Hernandez G.,Juarez Autonomous University of Tabasco | Pantoja-Enriquez J.,Research Center y Desarrollo Tecnologico en Energias Renovables | Escobar-Morales B.,Technological Institute of Cancun | Martinez-Hernandez D.,Juarez Autonomous University of Tabasco | And 4 more authors.
Thin Solid Films | Year: 2013

Cadmium sulfide thin-films were deposited on glass slides and SnO 2:F coated glass substrates by chemical bath deposition, sputtering and close-spaced sublimation techniques. The films were studied for the structural and opto-electronic properties after annealing in an ambient identical to that employed in the fabrication of CdTe/CdS devices. Quantum efficiency of the CdTe/CdS solar cells fabricated with CdS buffer films prepared by the three methods were investigated to understand the role of CdS film preparation method on the blue response of the devices. The higher blue response observed for the devices fabricated with chemical bath deposited CdS film is discussed. © 2012 Elsevier B.V.

Barbosa R.,National Autonomous University of Mexico | Andaverde J.,Autonomous University of Mexico State | Escobar B.,Technological Institute of Cancun | Cano U.,Electric Research Institute of Mexico
Journal of Power Sources | Year: 2011

This work uses a method for the stochastic reconstruction of catalyst layers (CLs) proposing a scaling method to determine effective transport properties in proton exchange membrane fuel cell (PEMFC). The algorithm that generates the numerical grid makes use of available information before and after manufacturing the CL. The structures so generated are characterized statistically by two-point correlation functions and by the resultant pore size distribution. As an example of this method, the continuity equation for charge transport is solved directly on the three-dimensional grid of finite control volumes (FCVs), to determine effective electrical and proton conductivities of different structures. The stochastic reconstruction and the electrical and proton conductivity of a 45 μm side size cubic sample of a CL, represented by more than 3.3 × 1012 FVCs were realized in a much shorter time compared with non-scaling methods. Variables studied in an example of CL structure were: (i) volume fraction of dispersed electrolyte, (ii) total CL porosity and (iii) pore size distribution. Results for the conduction efficiency for this example are also presented. © 2010 Elsevier B.V. All rights reserved.

Escobar B.,Technological Institute of Cancun | Hernandez J.,University of Quintana Roo | Barbosa R.,University of Quintana Roo | Verde-Gomez Y.,Technological Institute of Cancun
International Journal of Hydrogen Energy | Year: 2013

The main advantage of the hybrid system compared with separate array solar photovoltaic and stand-alone wind turbine is the possibility of the surplus energy storage by transforming it to hydrogen that can be use in fuel cells. However the design and sizing of this kind of technologies need to meet the local microclimate in order to reach higher efficacies. A tool based on an analytical model to sizing, analyze and assess the feasibility of the hybrid wind/photovoltaic/H2 energy conversion systems using real weather data is presented in this work. The model considers an energy balance analysis and electrical variables of the system components; the tool calculates the subsystems efficacy and proposes the improvements to increase the efficiency of the use in surplus energy produced by the hybrid system. To validate the analytical model, simulation based on wind speed and solar radiation measurements from meteorological monitoring station in a Mexican Caribbean City is discussed. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Guinel M.J.-F.,University of Puerto Rico at San Juan | Brodusch N.,McGill University | Verde-Gomez Y.,Technological Institute of Cancun | Escobar-Morales B.,Technological Institute of Cancun | Gauvin R.,McGill University
Journal of Microscopy | Year: 2013

Carbon nanotubes (CNTs) decorated with platinum (Pt) nanoparticles (NPs) have been characterized using a cold field-emission scanning electron microscope (SEM) and a high resolution field-emission transmission electron microscope (TEM). With this particular composite material, the complementary nature of the two instruments was demonstrated. Although the long CNTs were found to be mostly bent and defective in some parts, the nucleation of Pt occurred randomly and uniformly covered the CNTs. The NPs displayed a large variation in size, were sometimes defective with twins and stacking faults, and were found to be faceted with the presence of surface steps. The shape and size of the NPs and the presence of defects may have significant consequences on the activity of the Pt catalyst material. Also, thin layers of platinum oxide were identified on the surface of some NPs. © 2013 Royal Microscopical Society.

Ben-Youssef C.,Technological Institute of Cancun | Vazquez-Rodriguez G.A.,Autonomous University of the State of Hidalgo
Bioresource Technology | Year: 2011

Microbial degradation of phenol was studied using batch and fedbatch cultures of acclimatized activated sludge under a wide range of phenol (0-793mgl-1) and biomass (0.74-6.7gl-1) initial concentrations. As cell growth continued after total phenol removal, the production and later consumption of a main metabolic intermediate was considered the step governing the biodegradation kinetics. A model that takes explicitly into account the kinetics of the intermediate was developed by introducing a specific growth rate model associated with its consumption and the incorporation of a dual-substrate inhibitory effect on phenol degradation. Biomass growth and phenol removal were adequately predicted in all the cultures. Moreover, the model-based design of the fedbatch feeding strategies allowed driving separately the phenol degradation under substrate-limitation and substrate-inhibition modes. A sensitivity analysis was also performed in order to establish the importance of the parameters in the accuracy of model predictions. © 2010 Elsevier Ltd.

Ben Youssef C.,Technological Institute of Cancun | Zepeda A.,Autonomous University of Yucatán | Gomez J.,Metropolitan Autonomous University
Biochemical Engineering Journal | Year: 2013

The simultaneous oxidation of ammonia, nitrite and toluene using a nitrifying sludge was evaluated and modelled. The experimental data showed that the sole instantaneous inhibition effect due to the presence of toluene was not sufficient to explain the severe decrease in the nitrification activity during the cultures. In addition, prior cell exposure to toluene provoked an important - even complete - inactivation of the nitrifying process. The main contribution was thus to design and integrate an adjustment function in the reaction kinetics to account for the cell inactivation mechanism that occurs during an ongoing culture but is initiated during previous cell exposure to toluene; the use of an adjustment function was a requirement indicated by a previous study using the same nitrifying sludge but in presence of benzene. This inactivation factor varies according to a first-order kinetic model that is time-dependent and enhances the dynamic characteristics of the modelling approach. The model was validated by batch experiments with variable initial toluene concentrations (0 to 20mgCL-1) and additional inactivation batch assays, where cells were first exposed to 0 to 50mg of tolueneCL-1, washed and then reused in a culture medium without toluene. Changes observed in the ammonium, nitrite, nitrate and toluene concentrations agreed well between the model and experimental data with a single set of kinetic parameters in which confidence intervals and sensitivity were also analysed. The proposed model may be used as a predictive tool to avoid critical conditions for nitrification processes where cells are repeatedly or sequentially exposed to hydrocarbons, such as in a SBR system. © 2013 Elsevier B.V.

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