Browsing by Author "Cespedes, German"

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    Efectos de la membrana de intercambio de protones en el desempeño de una celda de combustible H2 O2
    (Revista Tecnología y Ciencia UTN, 2016) Cespedes, German; Castro Luna, Ana
    Una celda de combustible convierte directamente la energía química de un combustible en electricidad. Su desempeño depende de diferentes parámetros tales como el espesor de la membrana intercambiadora de protones, el contenido de humedad y la temperatura de la celda. Para realizar un estudio sistemático sobre como la variación de estos parámetros afectan la performance de la celda se propone un modelo matemático de poro simple y se aplica en la simulación de las curvas experimentales que muestran la variación del potencial de la celda cuando se drena corriente. Se observa que la variación del contenido de humedad y el espesor de la membrana intercambiadora de protones tienen un efecto tan pronunciado sobre la curva de polarización a diferencia de la temperatura de funcionamiento de la celda.
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    Effect of water content in the gas diffusion layer of H2 O2 PEM fuel cell
    (Journal of Materials Science and Engineering, 2016) Cespedes, German; Asteazaran, Mariano; Castro Luna, Ana
    The heart of a fuel cell is the membrane-electrode assembly consisting of two porous electrodes, where the electrochemical reactions take place, and the ionomer conductive membrane, which allows the proton exchange from the anode to the cathode. The porosity of the electrodes plays an important role in the fuel cell performance. One of the drawbacks presented by the porous electrodes is the accumulation of water in their structure, which implies a hindrance for the reactive gas transport to reach the catalytic reactive sites. In this paper, a mathematical model of a porous electrode, assuming single pores with uniform distribution, is introduced to determine the influence of water accumulation in the electrode on the fuel cell performance under different operating conditions. It is demonstrated that at low current densities, water accumulation has no effect in the fuel cell behavior, whereas at high current densities its performance is severely affected.
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    Research on methanol tolerant catalysts for the oxygen reduction reaction
    (Springer, 2015) Asteazaran, Mariano; Cespedes, German; Bengio, Silvina; Moreno, Mario; Triaca, Walter; Castro Luna, Ana
    Direct methanol fuel cells (DMFCs) generate electricity in a clean and efficient way, so they are a valuable alternative to traditional environmentally harmful technologies. Portable power sources are one of the applications of passive DMFCs. One of the requirements in these devices is the use of high alcohol concentration. Methanol permeation across the polymer electrolyte membrane (methanol crossover) causes a loss of fuel cell efficiency as the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR) occur simultaneously at the cathode. To develop methanol-tolerant catalysts with suitable activity, different PtM/C and PtMRu/C combinations with M = Co or Fe were prepared by a modified impregnation method. The synthesized catalysts were studied to determine the role of the components in enhancing the ORR and simultaneously discouraging the MOR. The materials were characterized by TEM, XPS and EDS. Well-distributed particles for all the catalysts were shown by TEM. XPS spectra revealed that the method produces a great amount of metallic Pt. The electrochemical characterization was carried out by linear sweep voltammetry and cyclic voltammetry, in a three-electrode electrochemical cell with a glassy carbon rotating disk electrode covered with a thin catalytic layer and a Nafion film as the working electrode. Binary and ternary catalysts have a good activity for the ORR. However, the enhanced activity of binary catalysts is lost when the ORR is studied in the presence of methanol. Ternary catalysts containing Ru showed higher methanol-tolerance, regardless of the composition.
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    Searching for suitable catalysts for a passive direct methanol fuel cell cathode
    (Elsevier, 2015) Asteazaran, Mariano; Cespedes, German; Moreno, Mario; Bengio, Silvina; Castro Luna, Ana
    Trimetallic PtMRu/C cathode catalysts with M ¼ Co or Fe obtained by an impregnation procedure using ethylene glycol and NaBH4 as reducing agent, with suitable activity for the oxygen reduction reaction (ORR) and improved tolerance to methanol, have been physically characterized by HRTEM, EDS and XPS. The examined nanoparticles have a small particle size and are well spread on the carbon support. Pt is mainly found as Pt(0) and Co, Fe and Ru are mostly oxidized. To study their durability and performance for ORR and methanol tolerance over time, the catalysts were subjected to an electrochemical accelerated stress test (AST), consisting in cycling the potential 2000 times. Polarization curves for ORR with and without methanol were recorded. After the AST the trimetallic PtMRu/C catalysts are able to keep their performance for ORR in the presence of methanol.