ABSTRACT
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.
ABSTRACT
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).
ABSTRACT
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.
