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In this work, copper selenide (Cu3Se2 umangite phase) was synthesized by two routes, using a chemical reaction and the hydrothermal method to obtain CuSe-A and CuSe-H, respectively. The synthesis o...

The present work comprises a study about the synthesis, characterization, and performance evaluation of four Co100-X-NiX (x = 0, 30, 70, and 100) electrocatalysts coated with Pt with potential catalytic activity towards ORR. Electrocatalysts were prepared through a two-stage process combining the versatile high-energy ball milling synthesis and the galvanic displacement method. On a first stage, high-energy ball milling was used to produce nanoparticles of non-noble transition metals, (M = Co100 and Ni100) and (BM = Co30Ni70 and Co70Ni30). On a second stage, galvanic displacement reactions via chemical reflux treatment were employed to promote a Pt coating over the milled nanoparticles. The four electrocatalysts were dispersed on Vulcan carbon maintaining a metal:carbon (wt.%) ratio of 50:50 each one. The result was two type of systems: (M-Pt/C = Co100–Pt/C and Ni100–Pt/C) and (BM-Pt/C = Co30Ni70–Pt/C and Co70Ni30–Pt/C). All the electrocatalysts presented a final composition: ~10 wt%. of Pt, ~40 wt% of Co100-xNix, and ~50 wt% of Vulcan carbon. Physical characterization of the synthesized electrocatalysts involved XRD, STEM, AAS-ICP-MS and EDS-SEM studies confirming the formation of homogeneously-distributed metallic nanoparticles on the carbon. The electrochemical evaluation, through cyclic voltammetry and steady-state polarization curves using rotating disk electrode technique, was performed for the four synthesized electrocatalysts and for a commercial platinum-loaded carbon black (Pt Etek 20 wt%) catalysts. All four synthesized electrocatalysts were electroactive for ORR. Moreover, the Ni100–Pt/C electrocatalyst presented the highest mass activity whereas Co30Ni70–Pt/C electrocatalyst showed the major stability after 3000 cycles of accelerated degradation test than the others. Two membrane electrode assemblies (MEAs) for PEM fuel cell were fabricated with the synthesized Ni100–Pt/C and Co30Ni70–Pt/C electrocatalysts used as cathodes. Results under single-fuel cell operation showed the same performance trend for those materials that observed under electrochemical glass cell conditions.

The design and manufacture of highly efficient nanocatalysts for the oxygen reduction reaction (ORR) is key to achieve the massive use of proton exchange membrane fuel cells. Up to date, Pt nanocatalysts are widely used for the ORR, but they have various disadvantages such as high cost, limited activity and partial stability. Therefore, different strategies have been implemented to eliminate or reduce the use of Pt in the nanocatalysts for the ORR. Among these, Pt-free metal nanocatalysts have received considerable relevance due to their good catalytic activity and slightly lower cost with respect to Pt. Consequently, nowadays, there are outstanding advances in the design of novel Pt-free metal nanocatalysts for the ORR. In this direction, combining experimental findings and theoretical insights is a low-cost methodology—in terms of both computational cost and laboratory resources—for the design of Pt-free metal nanocatalysts for the ORR in acid media. Therefore, coupled experimental and theoretical investigations are revised and discussed in detail in this review article.

The synthesis of catalysts in the lab is typically limited to low mass quantities, and it makes the large quantity production of catalysts a challenge. The High Energy Ball Milling technique allows for the processing of more massive amounts. In this work, we prepared CuPt nanoparticles, and their oxygen reduction catalytic activity was evaluated. The nanoparticles were prepared by galvanic displacement of Cu coming from a High Energy Ball Milling process. Alumina from the wear of the milling vials was present in the catalyst. Hydrodynamic curves from rotating-disk electrode measurements showed a catalytic activity seven times higher on the alloy than that observed on platinum-loaded carbon black. The catalytic activity was not negatively affected by the presence of the Al2O3 impurities.

CoNi 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.

The aim of this work was to synthesize and characterize nanoscale zero-valent iron (NZVI) supported on diatomaceous earth (DE) at two different molar concentration 3 M and 4M (nZVI-DE-1 nZVI-DE-2), to test the decolorization treatment of acid blue dye (AB) and perform a toxicological test using zebrafish. The synthesis of the nanoparticles was obtained using the chemical reduction method and the material was characterized by X-ray diffraction, Scanning Electron Microscopy (SEM), Energy-Dispersive X-Ray (EDX), and transmission electron microscopy and Specific Surface Area (BET). The results showed spherical forms in clusters between 20 to 40 nm of zero valent iron supported on diatomaceous earth. The removal of 1 g/l of AB from water treated with NZVI-DE-1 and NZVI-DE-2 reached the decolorization of 90% and 98% of all dye. While controls like NZVI and DE-1 and DE-2 achieved the removal of 40, 37 and 24 % of the dye. Toxicological analysis using zebrafish showed that AB causes a severe defect in development and embryos die after exposure. However, the water samples treated with NZVI-DE-1 and NZVI-DE-2 are not harmful for the zebrafish embryos during the first 24 hours. We conclude that the use of NZVI-DE-1 and NZVI-DE-2 is a promising treatment for dye pollution.

A CoNi-decorated-Pt (40:40:20 wt%) electrocatalyst was theoretically studied and experimentally validated for the oxygen reduction reaction (ORR) in acid media. To predict the activity of the electrocatalyst a Co 16 Ni 16 -decorated-Pt 3 cluster was employed. The O and O 2 adsorption energies were used as descriptors of the catalytic activity for the ORR. All calculations were performed using the density functional theory approach as implemented in the deMon2k code. A combined synthesis of high energy milling-galvanic displacement was performed to produce the CoNi-decorated-Pt electrocatalyst. The physical characterization of the electrocatalyst was developed using X-ray diffraction (XRD) for the phases identification, energy disperse X-ray spectroscopy (EDX) for compositional analysis and scanning transmission electron microscopy (STEM) to determine morphology and particle size of the synthesized electrocatalyst. Cyclic voltammetry and rotating disk electrode techniques were used for the electrochemical characterization of the synthesized electrocatalyst. The O and O 2 adsorption energies showed that CoNi-decorated-Pt (Co 16 Ni 16 –Pt 3 cluster) electrocatalyst represents an attractive candidate for the ORR. STEM micrographs showed homogeneous nanocrystalline particles of 5–10 nm size. The CoNi-decorated-Pt nanoparticles presented high specific activity, 40% above of the determined from Pt/C and similar mass activity from the same commercial Pt/C, used as comparison. Electrochemical results confirm the feasibility of a combined synthesis method to produce nanocatalysts which exhibit similar catalytic activity than that of commercially available Pt/C electrocatalyst.

High energy milling in combination with galvanic displacement were used for the preparation of bimetallic nanocatalysts. Co and Ni monometallic powders milled for 30 and 20 h, respectively were both produced in air atmosphere and used as precursors for the preparation of M-Pt (M = Co,Ni) compounds. Nanosized monometallic powders were physically supported on Vulcan carbon, and covered with 20 wt%Pt through a Galvanic Displacement Reaction (GDR) to produce Co-20Pt/C and Ni-20Pt/C electrocatalysts. XRD was used for phase identification on milled powders and for demonstrating structural transformations of Co powders during milling. Results on unmilled metallic Co powder show a predominant HCP structure modifying to a FCC structure after milling. Ni powders maintain their same FCC structure. Energy Dispersive X-Ray Spectometry (EDX) was used for chemical composition analysis on milled powders at several milling times. Scanning Transmission Electron Microscopy (STEM) show the formation of heterogeneous particle with ∼10 nm in size for both electrocatalysts. The electrocatalytic activity was evaluated by Cyclic Voltammetry (CV) and steady state Rotating Disk Electrode (RDE) for the Oxygen Reduction Reaction (ORR) in 0.1 M HClO 4 . The kinetic parameters on Co-20Pt/C conducted to the highest mass activity for the cathodic reaction.

The mechanochemical synthesis of PbTe nanostructures via the high-energy milling (HEM) process is proposed, as a synergistic approach, to minimize the thermal conductivity of this semiconductor material at room temperature. In this study, the effect of process control agent (PCA) addition on the microstructure and thermal properties of the as-milled PbTe nanostructures was also investigated. The synthesis design is based on a solid-state technique which allows enhancing the grain boundary scattering and consequently, decreases the thermal conductivity in the PbTe nanostructures. Moreover, the challenging part is the formation of coarse particles with embedded quantum dots and nanoparticles, which are expected to scatter long- and mid-wavelength phonons. In this sense, via the HEM-process, it is feasible to activate other phonon scattering modes by introducing rough-surfaced grains and nanoroughness to the particle surfaces. Overall, the thermal conductivity is decreased in the PbTe nanostructures by two means; namely, adding scattering processes and phonon group velocity, which were heightened due to the PCA added during milling. To elucidate the role of these components of the phonon thermal conductivity, atomic force microscopy and high-resolution transmission electron microscopy were used. On the other hand, photoacoustic (PA) and photopyroelectric (PP) techniques were applied to study the thermal properties of the PbTe nanostructures obtained by the HEM-process. The total thermal conductivity values of the PbTe nanostructures obtained by the PA and PP techniques were at least a half lower (1.06 W m−1 K−1) than that of bulk PbTe value counterpart (∼2.13 W m−1 K−1) and lower than those from PbTe nanomaterials (ranging from 1.5 to 2.2 W m−1 K−1) obtained via other means. The thermal conductivity values of the as-milled PbTe nanostructures were closely related to the carrier concentration experimental findings. We inferred that this strategy can be widely applicable to enhance existing thermoelectric compounds into their nanoforms by a scalable and a simple low-cost route.

A fundamental understanding of the Ostwald ripening effect (ORE) during the mechanochemical synthesis of PbTe nanostructures is presented. The ripening process involves the coarsening of larger particles from those of smaller size; this phenomenon was systematically evaluated at different stages of milling by microscopy analyses (AFM, TEM, STEM and HRTEM). At the early stage of milling, smaller particles and quantum dots are eventually dissolved to lower the total energy assciated with their surfaces. The ripening process – during milling – involves short-range mass transfer among particles. HRTEM analyses allowed us to identify that coarsening occurs by thermo-mechanically activated cooperative mechanisms. The detachment of the atoms from smaller particles to form bigger ones plays a major role in the particle coarsening. It was found that the coarsening process was not limited to crystalline nanostructures; so grain boundaries, edge dislocations and boundaries among crystalline and amorphous phases also play an important role to determine how species migration contributes to generate coarse particles. Those serve as sites for inducing coarsening in an equivalent way as surfaces do. Secondary ion mass spectrometry and elemental chemical mapping (EDX-STEM) revealed that both the purity and the chemical homogeneity of the PbTe nanostructures are prominent features of this material. Additionally, a direct band gap enhancement (780 nm) compared to bulk PbTe (3859 nm) was detected. It occurred due to the quantum confinement effect, lattice imperfections and even surface properties of the nanostructures. It is important to point out that the whole optical behaviour of the PbTe nanostructures was dependent upon the embedded nanoparticles and quantum dots in the clusters and coarse particles ranging from 15 nm to 35 nm.

Un espécimen de Eumops perotis se recolectó en Sierra Juárez, Baja California, México. Este registro representa el primero de esta especie para el estado y para la península de Baja California.