Chalcogenides and Carbon Nanostructures: Great Applications for PEM Fuel Cells

Nanostructured metal chalcogenides (NMCs) and carbon nanostructures (CNS) are attracting significant attention due to their features such as high stability in an acidic environment, especially if they have a significant oxygen reduction activity and remarkable superconducting properties. The broad range of CNS exhibits novel physicochemical properties, and thus it is triggering intense research about carbon nanoscience with numerous applications. In this context, new synthesis routes are designed under moderate conditions, which are definitely needed in order to simplify the process, reduce costs, and allow the production of NMCs at lower temperatures and CNS whose size and shape can be controlled. Some related studies about Pt based on sulfides and selenides, transition metal chalcogenides (TMCs), and carbon nanostructures (nanotubes and graphene) are revealed here; however, they show promise for fuel cells that these NMCs, CNS, or even NMC-CNS materials have been applied for other energy devices. Until now, a good response for cathodic reactions is employing TMCs based on tungsten and CNS without metal. According to experimental results and in terms of catalytic activity, durability, and chemical/electrochemical stability, much more research is required to produce commercially valid non-noble catalysts, electrocatalysts, or supports; however, one approach on this field is metal-free CNS

Síntesis y caracterización de películas ZrO2:Sm3+ preparadas por la técnica de rocío pirolítico ultrasónico

Se presenta el estudio de Fotoluminiscencia en películas delgadas de ZrO2:Sm3+, preparadas por la técnica de Rocío Pirolítico ultrasónico, interpretando las principales bandas del espectro fotoluminiscente y determinando la relación existente entre ellas. La Fotoluminiscencia y los espectros de excitación de ZrO2 :Sm3+ fueron investigados. Bajo un bombeo de excitación óptica en longitud de onda de 231 nm, las películas delgadas de ZrO2:Sm3+ muestran bandas dominantes centradas en 569, 619, 659 y 718 nm asociadas a las transiciones electrónicas 4G5/2→6H5/2, 4G5/2→6H7/2, 4G5/2→6H9/2 y 4G5/2→6H11/2. La luminiscencia presenta una fuerte emisión a 619 nm, además de observar un “apagamiento” con el aumento de la concentración del dopaje. Los estudios de difracción de rayos X, presentan una estructura cristalina tetragonal y cúbica del circonio cuando se aumenta la temperatura del substrato

Síntesis y caracterización de electrocatalizadores basados en calcogenuros nanoestructurados de Ru-WS:zfC y Ru-WS~TC

En este trabajo se llevó a cabo una reacción química entre metales de transición, específicamente tiosales de tungsteno y rutenio para sintetizar dos precursores catalíticos soportados en carbón Vulcan y un precursor catalítico soportado en nanotubos de carbono (NTC). Los materiales se caracterizaron por difracción de rayos X (DRX), microscopía electrónica de barrido (MEB) y microscopía electrónica de transmisión (MET). El electrocata1izador comercial de Pt/C al 20 % en peso metálico se utilizó para comparar el desempeño catódico de los electrocatalizadores sintetizados y basados en calcogenuros de Ru-WS2• Los electrocatalizadores obtenidos se analizaron mediante técnicas voltamperométricas para la reacción de reducción de oxígeno (RRO) en medio ácido. El electrocatalizador RuxWySz /C resultó 38 % más eficiente para la geoeración de corriente como cátodo respecto al electrocata1izador RuxWyS2z /C. Este resultado se atribuye a la alta dispersión y homogeneidad en el tamaño nanométrico de las partículas metálicas de la fase activa

Preparación de materiales funcionalmente graduados por deposición electroforética

The objective of this work is to develop a superhydrophobic and self-healing coating with the ability to protect metal surfaces and extend the useful life of both metal and coating. By means of the electrophoretic deposition technique, titanium dioxide coatings with variable morphology and composition were created. So far two techniques have been used for the manufacture of superhydrophobic coatings: 1) Functionalization of TiO2 nanoparticles (anatase) with polydimethylsiloxane by UV irradiation and 2) Functionalization of electrophoretic deposits with polydimethylsiloxane by UV irradiation. The electrophoretic deposits vary the applied potential and the deposition times, they are observed that they are used, they are eliminated, the uniforms are uniform and homogeneous, they are minimized, they are reduced, they are diminished, they are diminished, they are diminished, they are increased, they are they increase, they increase, they increase, they decrease, they increase, they are deposited first, thus generating a homogeneous arrangement on the surface of the highly rough metal.  All deposits were characterized by FTIR, RAMAN, DLS, UV-vis- Diffuse Reflectance, AFM y FESEM.El objetivo de este trabajo es desarrollar un recubrimiento superhidrofóbico y autoregenerable con la capacidad de proteger superficies de titanio y extender la vida útil tanto del metal como del recubrimiento. Mediante la técnica de deposición electroforética se crearon recubrimientos de dióxido de titanio con morfología y composición variable. Hasta el momento se han empleados dos técnicas para la fabricación de los recubrimientos superhidrofobicos: 1) Funcionalización de nanopartículas de TiO2 (anatasa) con polidimetilsiloxano por irradiación UV y 2) Funcionalización de los depósitos electroforéticos con polidimetilsiloxano por UV. Los depósitos electroforéticos se prepararon variando el potencial aplicado y los tiempos de deposición, se observa que al utilizar potenciales menores los depósitos son más uniformes y homogéneos, se logra observar también que las grietas disminuyen significativamente con la disminución del potencial aplicado debido a que las partículas más pequeñas se depositan primero generando así un arreglo homogéneo en la superficie del metal altamente rugoso. Los depósitos fueron caracterizados por diferentes técnicas: FTIR, RAMAN, DLS, UV-vis de reflectancia difusa, AFM y FESEM

The use of sugarcane bagasse ash and lime to imporve

This study analyzes the use of lime and sugar cane bagasse ash (SCBA) as chemical stabilizers in compacted soil blocks. The blocks were tested for flexure and compression in a dry and a saturated state. The tests were performed at 7, 14 and 28 days of age in order to evaluate the effects of the addition of lime and SCBA on the mechanical properties of the compacted soil blocks. The results indicate that blocks manufactured with 10% of lime in combination with 10% of SCBA showed better performance than those containing only lime. Nevertheless, the addition of lime improved the strength of the blocks when compared with blocks fabricated with plain soil. According to SEM and DRX analyses, considerable improvement of the matrix was observed due to the formation of strong phases, such as CSH and CAH for the mixtures with additives. It was also concluded that the combination of SCBA and lime as a replacement for cement in the stabilization of compacted soil blocks seems to be a promising alternative when considering issues of energy consumption and pollution

Evaluation of cobalt nanoparticle deposited graphene oxide and carbon nanotube supports as supercapacitor electrodes

Cobalt nanoparticles were deposited on multi-wall carbon nanotubes (CNT) and graphene oxide (GO) carbon supports and evaluated as a potential supercapacitor electrodes. The structure and morphology of the cobalt nanoparticles deposited on carbon supports were studied using XRD, TGA, and Raman spectroscopy. Cyclic voltammetry was used to measure the electrical charge of the electrode based on the materials and their specific capacitance (Csp) were calculated. GO based electrode showed a higher Csp than CNT electrode which is attributed to a larger surface area of the GO carbon support. Interestingly, the deposition of Co nanoparticles promoted an enhanced Csp in the both GO and multi-wall CNT supports.Las nanopartículas de cobalto se depositaron en soportes de carbono, nanotubos de carbono de pared múltiple (CNT) y óxido de grafeno (GO), y se evaluaron como potenciales electrodos de supercondensadores. La estructura y la morfología de las nanopartículas de cobalto depositadas sobre los soportes de carbono se estudiaron mediante XRD, TGA y espectroscopía Raman. La voltametría cíclica se utilizó para medir la carga eléctrica del electrodo en función de los materiales y se calculó su capacitancia específica (Csp). El electrodo basado en GO mostró un Csp mayor que el electrodo CNT, lo cual se atribuye a un área de superficie mayor del soporte de carbono GO. Curiosamente, el depósito de nanopartículas de Co promovió una Csp mejorada en los soportes GO y en los CNT de pared múltiple

A green synthesis of copper nanoparticles using native cyclodextrins as stabilizing agents

In this work, a comparative study of the effect of the NCD size as a stabilizing agent, on the synthesis of copper nanoparticles (Cu-NPs) by an easy green method was reported. The nanoparticles were synthesized through the chemical reduction of aqueous solutions of copper (II) sulfate with ascorbic acid, using different native cyclodextrins (NCDs) (α-, β-, or γ-NCD) as stabilizing agents. Cu-NPs were characterized by scanning electron microscopy–energy dispersive spectroscopy (SEM–EDX), powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The pattern showed in the typical selected area electron diffraction (SAED) and lattice fringes, evidence that the crystalline structure of Cu-NPs is face-centered cubic (FCC) with a (111), (200) and (220) lattice planes of Cu. The analysis of the TEM images show that the size of the Cu-NPs depends on the type of native cyclodextrin (NCD), also it was observed that the nanoparticles are spherical and with a size between ∼2 and 33 nm. The smaller Cu-NPs were obtained with α-NCD (mode 4 nm), while the nanoparticles obtained with β-NCD show the narrow size distribution (mode 6.5 nm). The average particle size and particle size distribution of Cu-NPs depend upon the type of CDs

Tolerant Chalcogenide Cathodes of Membraneless Micro Fuel Cells.

International audienceThe most critical issues to overcome in micro direct methanol fuel cells (μDMFCs) are the lack of tolerance of the platinum cathode and fuel crossover through the polymer membrane. Thus, two novel tolerant cathodes of a membraneless microlaminar-flow fuel cell (μLFFC), Pt(x) S(y) and CoSe(2) , were developed. The multichannel structure of the system was microfabricated in SU-8 polymer. A commercial platinum cathode served for comparison. When using 5 M CH(3) OH as the fuel, maximum power densities of 6.5, 4, and 0.23 mW cm(-2) were achieved for the μLFFC with Pt, Pt(x) S(y) , and CoSe(2) cathodes, respectively. The Pt(x) S(y) cathode outperformed Pt in the same fuel cell when using CH(3) OH at concentrations above 10 M. In a situation where fuel crossover is 100 %, that is, mixing the fuel with the reactant, the maximum power density of the micro fuel cell with Pt decreased by 80 %. However, for Pt(x) S(y) this decrease corresponded to 35 % and for CoSe(2) there was no change in performance. This result is the consequence of the high tolerance of the chalcogenide-based cathodes. When using 10 M HCOOH and a palladium-based anode, the μLFFC with a CoSe(2) cathode achieved a maxiumum power density of 1.04 mW cm(-2) . This micro fuel cell does not contain either Nafion membrane or platinum. We report, for the first time, the evaluation of Pt(x) S(y) - and CoSe(2) -based cathodes in membraneless micro fuel cells. The results suggest the development of a novel system that is not size restricted and its operation is mainly based on the selectivity of its electrodes

Polylactic acid/multi walled carbon nanotubes (PLA/MWCNT) nanocomposite for 3D printing of medical devices

In recent years, the composite nanomaterials area has had a great development impact in health sciences. Biomaterials depict as one of the most promising since they are compatible with additive manufacturing (AM) techniques. It is also possible to use them to mold specific medical parts. Composite nanomaterials have shown good biocompatibility and low toxicity to have benefits equal to or greater than metals (i.e., Co-Cr alloy). The purpose of this study is to develop a nanocomposite biomaterial (PLA/MWCNTf) from Polylactic Acid (PLA) and functionalized Multi Walled Carbon Nanotubes (MWCNTf) to evidence its potential application in 3D printing of orthopedic fixation devices. PLA/MWCNTf nanocomposite was prepared by solution blending technique, incorporating a proportion of 0.5 wt% of MWCNTf to the PLA matrix. TGA analysis of the PLA/MWCNTf was used to determine the thermal stability, a slight increase was found compared to the PLA.  FTIR spectroscopy confirmed the presence of carboxylic acid groups in the MWCNTf which improves good incorporation of the nanotubes in the PLA matrix. Additionally, Raman spectroscopy, SEM, and AFM micrographs were used to verify MWCNTf reached the PLA surface homogeneously. Additive manufacturing preparation was done by extrusion molding of PLA/MWCNTf as well as its 3D printing.