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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. Source


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. Source


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. Source


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. Source


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. Source

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