Omar Solorza-Feria

Oxygen reduction in acid media at the amorphous Mo-Os-Se carbonyl cluster coated glassy carbon electrodes

An amorphous Mo–Os–Se carbonyl cluster compound has been synthesized in 1,2-dichlorobenzene (b.p.≈180°C) to be tested as an electrocatalyst for molecular oxygen reduction in 0.5 M H2SO4. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) performed for the powder supported on pyrolytic carbon show a distribution of nanometer-scale amorphous particles with agglomerations in cluster forms. The catalytic activity was studied by the rotating disc electrode technique. Kinetic studies show a first-order reaction with a Tafel slope of −0.118 V dec−1 and dα/dT=1.55×10−3 K−1. In the temperature range 298–343 K, an activation energy of 32 kJ mol−1 was determined.

Synthesis of W-Se-Os carbonyl electrocatalyst for oxygen reduction in 0.5 M H2SO4

Abstract Transition metal chalcogenide material based on W-Se-Os(CO)n cluster electrocatalyst were prepared by reacting the transition metal carbonyl compounds OS3 (CO)12 and W(CO)6 , with elemental selenium in 1,2-dichloro- benzene (bp≈180°C). The synthesized material was characterized by FT-IR, 13 C MAS NMR spectroscopy, X-ray diffraction (XRD), SEM and electrochemically. XRD indicated that the powder presents crystalline structure sup- ported on an amorphous surface. The electrocatalytic activity for molecular oxygen reduction was studied by a Rotating Ring-Disc Electrode (rrde) technique in a 0.5 MH2 SO4 . The results showed that the oxygen reduction occurs via multielectron charge transfer (n = 4e- ), to water formation. The yield to water formation is more than 96%.

Remediation of drinking water contaminated with arsenic by the electro-removal process using different metal electrodes

The purification of water by the electro-removal process using different metal electrodes is widely used in different spheres of science and industry. The comparative characteristics under galvanostatic conditions of zinc (Zn), brass (Cu-Zn), copper (Cu) and iron (Fe) anodes for arsenic (As) removal from water by the electro-removal process in laboratory scale experiments were determined at current densities of 1.5, 3 and 12 mA cm(-2) for 60 min, from a solution containing different concentrations of As(v) (from 70 to 130 microg L(-1)). The results at these different current densities indicated that rapid arsenic removal was achieved at higher current densities (12 mA cm(-2)), with the chemical precipitation of arsenate complexes. The removal of As was relatively efficient, with the following tendency (at 1.5 mA cm(-2)): Fe (>93%) congruent with Zn (>93%) > Cu-Zn (>73%) >Cu (>67%), these efficiencies were relatively independent of the removal rate for all the initial arsenic concentrations investigated. This behaviour is attributed to the electrochemical intrinsic properties of the most active metals, and to the chemical precipitation reactions following the electrochemical process, iron being the most attractive metal for arsenic removal for practical applications.

Synthesis and characterization of W0.12Ru2.1Se and W0.013Ru1.27Se electrocatalysts

Nanosized particles of cathodic electrocatalysts were chemically synthesized by reacting transition metal carbonyl compounds and elemental selenium in m-xylene (bp 402 K) and o-dichlorobenzene (bp 443 K). The characterizations of the synthesized materials were performed by neutron activation analysis (NAA), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and infrared spectroscopy (IR). The resulting chemical composition was W0.12Ru2.1Se and W0.013Ru1.27Se for the compounds synthesized in m-xylene and o-dichlorobenzene, respectively. X-ray diffraction spectra (XRD) showed in both cases the formation of amorphous materials and SEM micrographs depict primary particles with almost the same granular morphology. TEM micrographs showed that the particles synthesized in m-xylene were amorphous, dispersed particles and in o-dichlorobenzene were amorphous nanocluster materials of approximately 2 nm in size. The growth of the nanoclusters depends only on the synthesis temperature and not on the nature of the solvents. The synthesized electrocatalysts showed catalytic activity for the molecular oxygen reduction in 0.5 M H2SO4 and could be candidates to be used as cathodes for fuel cells.

Mass spectrometry quantification of hydrogen produced under illumination of p-CuInSe2, and modified surfaces

Hydrogen gas obtained from illuminated p-CuInSe2 (CIS) on 0.5 M sulfuric acid solution was collected in a glass balloon using argon as carrier gas, and quantified with a mass spectrometer. p-CuInSe2 thin films were electrodeposited on SnO2-coated glass plates, according to references already reported. Electrochemical deposition of Se and chemical modifications on the semiconducting surfaces with adsorbed ruthenium were also tested for the hydrogen evolution reaction. The Eg and Efb of the modified p-CuInSe2 were determined. Atomic absorption spectrometry was used to quantify the chemical compositions of the semiconductors before and after the illumination. The modified semiconductors had a composition of CISSe24 and CIS/Se6/(RuO4)0.12, under illumination at 0.8 V in 0.5 M H2SO4 for 4 min, the volumes of evolved hydrogen were 1 cm3 and 2.4 cm3, respectively.

Assessment of BOMD simulations for the ground-state structure determination of transition metal clusters in the nanometer scale

ABSTRACT State-of-the art calculations have been performed for bimetallic transition metal clusters such as Pd19M19 (M=Co and Ni) by employing the linear combination of Gaussian-type orbitals density functional theory (LCGTO-DFT) approach. Structures and energy properties were calculated for these clusters. For each cluster, several dozens of isomers were studied to determine the lowest energy structures. Initial structures for the geometry optimisation were taken along Born–Oppenheimer molecular dynamics (BOMD) trajectories, considering several spin multiplicities. All structures were fully optimised without any symmetry restriction. The optimised structures were characterised by vibrational analysis. Lowest energy structures, relative stability energy, harmonic frequencies, binding energies, vertical ionisation potential, vertical electron affinity and spin density plots are reported. The obtained results are compared with data from the literature. The ground-state structure topology is the same for both clusters. The Pd atoms decorate the surface of the core formed by either Co or Ni atoms. This work demonstrates the importance of using ab initio BOMD simulations to fully explore the potential energy surface of large transition metal clusters. Structure and spin multiplicity of the ground state structure of Pd19M19 (M=Co, Ni) clusters. Dark grey spheres correspond to Pd atoms and light green spheres correspond to either Co or Ni atoms, respectively.

A Combined DFT and Experimental Investigation of Pt-Wrapped CoNi Nanoparticles for the Oxygen Reduction Reaction

AbstractCoNi bimetallic nanoparticles wrapped with Pt were the subject of a theoretical study and experimental validation for the oxygen reduction reaction (ORR). The computational study was carried to evaluate the effect of the core composition of the Pt-wrapped CoNi nanoparticles toward the ORR. For this purpose, Pt44 and ConNi6−n-Pt38 (0≤n≤6) octahedral nanoparticles were employed as models and the O and OH binding energies were taken into account to describe the ORR electrocatalytic activity. The experimental validation of these type of nanoparticles was performed considering two compositions (Co30Ni70-20Pt/C and Co70Ni30-20Pt/C). The ConNi6−n-Pt38 (0≤n≤6) nanoparticles exhibit O and OH adsorption energies weaker than the pure Pt44 nanoparticles, suggesting, therefore, a higher electrocatalytic activity for the CoNi-Pt with respect to one of elemental Pt nanoparticles. The electrochemical results confirm the theoretical prediction, showing that the Co30Ni70-20Pt/C and Co70Ni30-20Pt/C electrocatalysts present higher specific activities, 400% and 300%, above that of Pt/C, respectively, as well as mass activities 50% higher than the commercial Pt/C, taken as reference. Graphical AbstractCorrelation between modeling and experimentation of CoNi bimetallic nanoparticles wrapped with Pt for the oxygen reduction reaction.

A first-principles study of Ni n Pd n (n = 1 − 5) clusters

A first-principle investigation of structures and properties of NinPdn (n=1-5) clusters is presented. For this study, the linear combination of Gaussian-type orbitals auxiliary density functional theory (LCGTO-ADFT) method has been employed. In order to determine the lowest energy structures, several isomers in different spin multiplicities were studied, for each cluster size. Initial structures, for which successive geometry optimization was computed without any constrain, were taken along Born–Oppenheimer molecular dynamics (BOMD) trajectories. To discriminate between minima and transition state structures, harmonic frequency analyses were performed at the optimized structures. Ground state structures, bond lengths, harmonic frequencies, dissociation energy, ionization potential, electron affinity and spin density plots are presented. This work demonstrates, that the Pd atoms prefer to allocate on the surface of the cluster structures whose core is formed by the 3d TM atoms type. Moreover, it has been observed that the ground-state structure spin multiplicity increases as the system size grows. The results of this study contribute to gain insight into how structures and energy properties change with cluster size in bimetallic Pd-based alloys.

Activity and Durability of PEFCs Alloy Core-Shell Catalysts: Role of Surface Oxidation

Low temperature fuel cells are one of the most promising systems for the transformation of fuels into electricity in an efficient, silent, and environmentally friendly manner. In this paper we show the advances accomplished in the synthesis and a theoretical-experimental analysis of the changes induced by the Ni@Pt structure and the presence of the almost unavoidable NiO species. The synthesis of core-shell nanoparticles is described and then physical and electrochemical characterizations confirm the presence of core-shell nanoparticles with a high electrochemical activity towards the Oxygen Reduction Reaction. Periodic density functional theory calculations are used to analyze the shift in the oxidation potential for Pt, Ni@Pt and NiO@Pt with different number of layers in the shell. The changes in the electrochemical activity towards oxygen reduction are evaluated by allowing oxygen to adsorb on the surface of the nanoparticle and alloys. It is found that only the first and second layers of Pt are being affected by the presence of the Ni or NiO core.

Reducing the microcapsule diameter by micro-emulsion to improve the insecticidal activity of Bacillus thuringiensis encapsulated formulations

ABSTRACT The emulsion/internal gelation method is highly effective to produce microcapsules of Bacillus thuringiensis (Bt) in a short time; however, it has the limitation to produce microcapsules within a wide range of diameters (1–1000 µm). The aim of this study was to reduce the range of small microcapsule diameters by using a water/corn-oil (W/CO) micro-emulsion as the dispersing medium and the mixture Tween 80–Span 80 as the surfactant. It involved the development of the W/CO micro-emulsion and the determination of the suitable agitation time to disperse the gelling medium (sodium alginate) through the micro-emulsion. A micro-emulsion formulation that allowed reduction of the microcapsule diameter was composed of 82% corn oil, 12% alginate solution and 6% surfactant mixture Tween80–Span80 (31:69). Evaluation of four dispersing times showed that 45 min was suitable to produce 75% of microcapsules of an average diameter of 3.1 ± 1 µm containing the spore–protein complex (SPC) produced by Bt. Bioassays carried out at low concentrations of microencapsulated formulations of cry proteins allowed determination of how its insecticidal effect increased if the range of microcapsule diameters was reduced in the range 1–9 µm. Furthermore, the SPC formulation in alginate microcapsules showed high resistance to extreme irradiation (2.9 ± 0.5 × 108 erg) of a long wavelength (365 nm), which made the microencapsulated formulation profitable and of high yield since repeated applications of the biopesticide during the same harvest period may not be necessary.