PdCo Nanoparticles Formation at HOPG and High Surface Area Carbon Support Vulcan XC-72R
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PdCo Nanoparticles Formation at HOPG and High Surface Area Carbon Support Vulcan XC-72R Lisandra Arroyo-Ramírez, Haralampos N. Miras, Raphael G. Raptis and Carlos R. Cabrera Department of Chemistry and Institute for Functional Nanomaterials University of Puerto Rico, Río Piedras Campus, P.O. Box 70377, San Juan, PR 00936-8377 ABSTRACT Thermal reduction of PdCo molecular precursors may lead to the controlled production of nanoparticles on high surface area carbon supports that can be used as methanol tolerant oxygen reduction catalysts for direct methanol fuel cells (DMFC). Following this concept, a single molecular precursor source was used for the synthesis of bimetallic nanoparticles on highly oriented pyrolytic graphite (HOPG) and Vulcan (VC) carbon supports. Nanostructural formation of palladium-cobalt on highly ordered pyrolytic graphite (HOPG) was study by AFM, SEM and voltammetry. The relative humidity during precursor deposition was used to control the rings self-formation on HOPG surfaces. Palladium and palladium-cobalt nanoparticles were also formed on high surface area carbon support (Vulcan XC-72R) by thermal reduction and characterized by TEM. The Pd/VC and PdCo/VC nanoparticles were tested for the oxygen reduction reaction (ORR) with and without methanol. The Pd-based catalysts have ORR activity and high methanol tolerance. INTRODUCTION The nanomaterials development can be done with different techniques or methods. The composition and morphology of the nanomaterials determines its future application in areas such as; catalysis, sensors, electronics, batteries and fuel cells. Nanomaterials are prepared by chemical methods with molecular or ionic precursors as the starting material. These methods allow the control of the size and composition distribution. The particle size distribution also plays an important role with respect to the catalytic performance. The direct methanol fuel cell (DMFC) cathode has a catalyst degradation problem due to methanol crossover through the membrane. Platinum (Pt) is widely used as catalysts for the oxygen reduction reaction (ORR). However, there has been an increase on the synthesis of Pt alloys and non-Pt based ORR electrocatalysts due to Pt high cost and low methanol tolerance. [1,2]. Pd-based electrocatalysts are being used for oxygen reduction due to their high methanol tolerance and lowest cost [3,4]. In this study, we intend to find morphological change for the nanostructure self-formation by controlling the atmosphere used in the deposition process. In addition, the synthesis of palladium-cobalt nanoparticles by thermal reduction on high surface area carbon supports has been done. The nanostructures and nanoparticles on carbon supports were characterized by cyclic and linear sweep voltammetry, atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). EXPERIMENTAL DETAILS The precursors [NH4]2[CoPd2(Me2Ipz)4Cl4] (CoPd2) and Pd3(µ-3-Phpz)6 (Pd) were synthesized following published procedures [5,6]. An
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