Lisandra Arroyo-Ramírez

Synthesis and Characterization of Palladium and Palladium–Cobalt Nanoparticles on Vulcan XC-72R for the Oxygen Reduction Reaction

A single-source approach was used to synthesize bimetallic nanoparticles on a high-surface-area carbon-support surface. The synthesis of palladium and palladium-cobalt nanoparticles on carbon black (Vulcan XC-72R) by chemical and thermal reduction using organometallic complexes as precursors is described. The electrocatalysts studied were Pd/C, Pd2Co/C, and PdCo2/C. The nanoparticles composition and morphology were characterized using inductively coupled plasma mass spectrophotometer (ICP-MS), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray fluorescence spectroscopy (EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques. Electrocatalytic activity towards the oxygen reduction reaction (ORR) and methanol tolerance in oxygen-saturated acid solution were determined. The bimetallic catalyst on carbon support synthetized by thermal reduction of the Pd2Co precursor has ORR electrocatalytic activity and a higher methanol tolerance than a Pt/C catalyst.

Palladium Nanoshell Catalysts Synthesis on Highly Ordered Pyrolytic Graphite for Oxygen Reduction Reaction

A novel approach for the synthesis of palladium (Pd) nanoshells on highly ordered pyrolytic graphite (HOPG) surfaces for the oxygen reduction reaction (ORR) is described. Magnetron sputtering deposition was used to synthesize Pd thin films and nanoshells of different thicknesses on HOPG surfaces. Electrospun polymer fibers mats of poly(ethylene) oxide (PEO) were used as templates for the Pd nanoshells formation. The palladium thicknesses between 25 and 95 nm were deposited by magnetron sputtering. Scanning electron microscopy and energy-dispersive X-ray fluorescence spectroscopy were used to study the morphology and composition of the Pd nanoshells. Electrocatalytic activity toward the ORR and methanol tolerance in oxygen saturated 0.5 M H(2)SO(4) solution was determined. Palladium nanoshells presented higher electrocatalytic activity toward ORR than Pd thin films of similar electrodes thicknesses and geometric area. Since palladium has higher methanol tolerance than platinum, the Pd nanoshells are promising electrode materials for direct methanol fuel cells (DMFC).

Synthesis, Optical Characterization, and Electrochemical Properties of Isomeric Tetraphenylbenzodifurans Containing Electron Acceptor Groups

Isomeric tetraphenylbenzodifuran systems, benzo[1,2-b:5,4]difuran and benzo[1,2-b:4,5]difuran, containing electron acceptor groups (CF(3), CN, and NO(2)) have been synthesized and studied. Their electronic absorption, fluorescence, two-photon absorption cross sections, and electrochemical properties were investigated. The absorption and emission maxima are red-shifted for the linear-conjugated systems in comparison with the corresponding isomer. Dual fluorescence was observed and the existence of a twisted intramolecular charge transfer state was confirmed by low-temperature emission experiments. Wide HOMO-LUMO energy gaps were obtained ranging from 2.53 to 3.28 eV. HOMO levels were found in the energy range of -6.03 to -6.63 eV while LUMO are within -2.55 to -3.52 eV.

Nanostructural Formation of Pd-Co Bimetallic Complex on HOPG Surfaces: XPS and AFM Studies

A new single source approach was developed to synthesize Pd-Co nanoparticles using a bimetallic compound, [Et3NH]2[CoPd2(𝜇-4-I-3,5-Me2pz)4Cl4](CoPd2), as a molecular precursor to obtain dispersed catalyst on highly ordered pyrolytic graphite (HOPG) surface, in view of preparing oxygen reduction catalysts for low temperature fuel cells. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques were employed to characterize the nanostructure formations and to determine the composition and morphology of the complex on the HOPG. Results of high resolution XPS analysis (HR-XPS) revealed the binding energies corresponding to the atomic constituents of the precursor. When the precursor solution was placed on the surface of the HOPG, the bimetallic complex assumes a tubular structure and it appears that the surface of the HOPG offers a ground for the self-organization of nanostructural formations.

Palladium Nanostructures Synthesis by Sputtering Deposition on HOPG Surfaces

The synthesis of palladium thin films and shell nanostructures by dc-magnetron sputtering deposition on highly ordered pyrolytic graphite (HOPG) surfaces is described. Electrospun polymer fibers mats were used as templates for the Pd shell nanostructures formation. The morphology was characterized with atomic force microscopy (AFM) and scanning electron microscopy (SEM). Pd nanostructures were used as catalysts for oxygen reduction reaction (ORR). The ORR activity was evaluated in sulfuric acid and the methanol tolerance in 1 M methanol solutions saturated with oxygen. The Pd shell nanostructures have better ORR activity than Pd thin films.