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Escudero-Cid R.,Autonomous University of Madrid | Hernandez-Fernandez P.,Autonomous University of Madrid | Perez-Flores J.C.,University of San Pablo - CEU | Rojas S.,Grupo de Energia y Quimica Sostenibles | And 6 more authors.
International Journal of Hydrogen Energy | Year: 2012

The long-term stability of PtCoRu/C to methanol crossover has been evaluated in a direct methanol fuel cell (DMFC) configuration. The DMFC has been subjected to continuous operation under potential step cycles. The degradation of the DMFC with PtCoRu/C has been followed by comparison of the power density curves recorded after 0, 60 and 312 h of continuous operation, and compared to that recorded for a DMFC with Pt/C. Electrochemical Impedance Spectra (EIS) were recorded directly from the DMFCs and used to identify the main degradation phenomena responsible for the loss of performance of the used fuel cell. AC impedance spectra show that the resistance of the anode reaction increases while resistance associated to the cathode reaction decreases after the long-term stability tests; however, the analysis of the power density curves unequivocally show that the performance of the DMFCs goes down during the stability tests. This apparent contradiction can be explained by taking into account the changes between the fresh and used PtCoRu/C observed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. During the potential step cycles Ru dissolves form PtCoRu/C leading to Pt-enriched catalysts which are more active for the oxygen reduction reaction (lower resistance) but less tolerant to methanol (lower power density). Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights.

Escudero Cid R.,Autonomous University of Madrid | Gomez De La Fuente J.L.,CSIC - Institute of Catalysis | Rojas S.,CSIC - Institute of Catalysis | Rojas S.,Laboratorio Of Electrocatalisis Y Energia Sostenible | And 4 more authors.
ChemCatChem | Year: 2013

The modification of mesoporous carbon black with polypyrrole (C-PP) facilitates the incorporation of homogeneously dispersed nanosized Ru-Pt particles (1-2 nm) onto the support. Polypyrrole-modified carbon supports were prepared by the addition of different amounts of pyrrole, followed by in situ polymerization through oxidative treatments. The Ru-Pt/C-PP electrocatalysts were tested in the oxygen-reduction reaction in methanol-containing acidic electrolytes by using both conventional electrochemical techniques and in a direct methanol single cell. The performance of Ru-Pt/C-PP was far superior to that of Pt/C for the oxygen-reduction reaction in the direct methanol fuel cell. Under severe methanol-crossover conditions, the maximum power density that was delivered by Ru-Pt/C-PP after degradation tests was decreased by 20 %, whereas that of Pt/C decreased by 75 %. Thus, the presence of Ru oxides in the cathode led to more tolerant electrocatalysts towards the presence of methanol in the reaction medium during the oxygen-reduction reaction. With ORR without you: A carbon-supported Ru-Pt electrocatalyst exhibits superior methanol tolerance than Pt/C during the oxygen-reduction reaction, thus leading to more active and durable direct methanol fuel cells. Modification of the carbon support with polypyrrole allows for better dispersion of the Ru-Pt nanoparticles. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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