Se presentan resultados de la evaluación del comportamiento en operación de una celda de combustible unitaria PEM de hidrógeno/oxígeno a escala prototipo construida con electrodos porosos de difusión de gas desarrollados en el laboratorio con incorporación de nanopartículas de Pt policristalinas soportadas sobre Vulcan XC-72. Las curvas de polarización muestran los perfiles típicos donde se distinguen las diferentes zonas de pérdidas de energía asociadas a los fenómenos limitantes. Se estudia la influencia de la variación de la temperatura de operación de la celda de combustible y de la humidificación de los gases de alimentación sobre su desempeño y se propone un método de activación de los electrodos porosos de difusión de gas utilizados en la celda de combustible prototipo

The performance of a hydrogen storage prototype loaded with AB5H6 hydride, whose equilibrium pressure makes it suitable for both feeding a H2/air proton exchange membrane (PEM) fuel cell and being charged directly from a low-pressure water electrolyzer, interacting thermally with the fuel cell exhaust air, is reported. The nominal 70 L hydrogen storage capacity of the prototype suffices for hydrogen delivery at 0.5 L min−1, which allows a power supply of 50 W for 140 min from the H2/air fuel cell in the absence of thermal interaction. The storage prototype was characterized by monitoring the internal pressure and the temperatures of the external wall and at the center inside the container at different hydrogen discharge conditions. The responses of the integrated system after either immersing the metal hydride container in air or exposing it to the fuel cell hot exhaust air stream under forced convection were compared. The system shows the best performance when the heat generated at the fuel cell is used to increase the metal hydride container temperature, allowing the operation of the fuel cell at 280 W for 16 min at a high hydrogen flow rate of 4 L min−1.

Direct methanol fuel cells (DMFCs) generate electricity in a clean and efficient way, so they are a valuable alternative to traditional environmentally harmful technologies. Portable power sources are one of the applications of passive DMFCs. One of the requirements in these devices is the use of high alcohol concentration. Methanol permeation across the polymer electrolyte membrane (methanol crossover) causes a loss of fuel cell efficiency as the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR) occur simultaneously at the cathode. To develop methanol-tolerant catalysts with suitable activity, different PtM/C and PtMRu/C combinations with M = Co or Fe were prepared by a modified impregnation method. The synthesized catalysts were studied to determine the role of the components in enhancing the ORR and simultaneously discouraging the MOR. The materials were characterized by TEM, XPS and EDS. Well-distributed particles for all the catalysts were shown by TEM. XPS spectra revealed that the method produces a great amount of metallic Pt. The electrochemical characterization was carried out by linear sweep voltammetry and cyclic voltammetry, in a three-electrode electrochemical cell with a glassy carbon rotating disk electrode covered with a thin catalytic layer and a Nafion ® film as the working electrode. Binary and ternary catalysts have a good activity for the ORR. However, the enhanced activity of binary catalysts is lost when the ORR is studied in the presence of methanol. Ternary catalysts containing Ru showed higher methanol-tolerance, regardless of the composition.

An improvement in ethanol oxidation electrocatalysis is possible with multifunctional Pt-based combinations. Thus, the addition to Pt of Sn, Ir or Ni enhances the ethanol oxidation reaction (EO) and shifts the onset oxidation potential to lower values. It has been suggested that metallic oxides in the vicinity of Pt have the capacity of promoting the oxidation of residues coming from alcohol oxidative adsorption. In order to get a deeper knowledge on the ethanol oxidation catalysis, supported catalysts prepared either by thermal decomposition of polymeric precursors (PP) or by microwave assisted poliol reduction (MW) methodology are studied to determine the role of the catalyst components and its oxides on the improvement of ethanol oxidation. The catalysts are physically and electrochemically characterized. According to the synthesis method, the amount of SnO2 in the catalyst varies. Faceted particle structures for the microwave-synthesized catalysts are observed. By employing electrochemical techniques it is concluded that the catalyst with the highest amount of SnO2 has the best catalytic behaviour for EO.

Direct methanol fuel cells (DMFCs) represent an interesting alternative in obtaining electricity in a clean and efficient way. Portable power sources are one of the most promising applications of passive DMFCs. One of the requirements in these devices is to use high alcohol concentration, which due to methanol crossover causes a considerable loss of fuel cell efficiency. In order to develop methanol tolerant cathodes with suitable activity, different supported catalysts namely PtCo/C and PtCoRu/C, were prepared either via ethylene glycol reduction (EG) with or without microwave heating assistance (MW) or via the alloy method, the latter followed by a thermal treatment in a reducing atmosphere (N2/H2). All cathode-catalysts were tested to determine the role of the components in simultaneously enhancing the oxygen reduction reaction (ORR) and discouraging the methanol oxidation reaction. According to the synthesis methodology, X-ray photoelectron spectra showed that the amount of metal oxides on the surface varies, being higher on the PtCo/C EG and PtCoRu/C EG catalysts. The electrochemical characterization of the catalysts was accomplished in a three electrodes electrochemical cell with a glassy carbon rotating disk electrode covered with a thin catalytic film as working electrode. To study the ORR and the influence of different methanol concentrations, linear sweep voltammetry and cyclic voltammetry were employed. The PtCo/C EG, with an important metal oxide amount on the surface, and the PtCoRu/C MW and EG electrodes, both with RuO2 on their surfaces, were the most tolerant to methanol presence.

Las celdas de combustibles de tecnologia PEM se encuentran dentro de los recursos tecnologicos cuyo desarrollo impulsara la transicion hacia una economia del hidrogeno. Las celdas de combustible de tecnologia PEM son dispositivos que convierten, a traves de procesos electroquimicos, la energia quimica del hidrogeno directamente en energia electrica y termica. Estos dispositivos trabajan a bajas temperaturas de operacion, con un tiempo rapido de arranque y con una alta densidad de potencia y alta eficiencia de conversion, lo que los hace fuertes candidatos para la generacion de energia. La mayor brecha que debe superarse para la comercializacion de estos dispositivos es el costo y tiempo de vida de los mismos, lo que implica, entre otras cosas, la optimizacion de los materiales que los componen y el estudio de los fenomenos multifisicos, de transporte y electroquimicos que toman lugar durante su operacion. En este trabajo se presenta la evaluacion de dos prototipos de celdas de combustible de tecnologia PEM que difieren, principalmente, en el area y diseno de los canales de flujo. Uno de los prototipos es de diseno comercial, con canales de flujo que representan 25 cm2 de area, en serpentin, lineal, tipo U (prototipo I) y, el otro, de fabricacion endogena (en colaboracion con el Laboratorio de Mecanica de la UTN), posee canales de flujo que representan un area de 9 cm2, en serpentin, no lineal, tipo Z (prototipo II). Para la prueba de los prototipos se construyeron ensambles MEA, mediante una tecnica de pincelado desarrollada en nuestros laboratorios, utilizando como membrana polimerica Nafion 117, tela de carbono como medio de difusion de gases, y platino soportado sobre carbono grafitizado Vulcan XC-72, al 20%, marca E-TEK, como catalizador soportado. Los prototipos se sometieron a distintas condiciones operativas de presion, temperatura, humidificacion y caudal. El mejor desempeno se logro con el prototipo I a una temperatura de celda de 40 oC y temperatura de humidificacion de H2 de 60 oC (Figura 1). El prototipo II presento altas corrientes de crossover comparadas con las reportadas en la literatura para membranas de Nafion 117, presentando un OPC por debajo del esperado para este tipo de celdas PEM y afectando el rendimiento de la misma (Figuras 2 y 3). Es posible que esta alta corriente de crossover se deba al pre- tratamiento aplicado a la membrana para la construccion de los electrodos utilizados en la evaluacion de este prototipo. Esto aun se encuentra en estudio.

The desorption behavior of a hydrogen storage prototype loaded with AB(5)H(6) hydride, whose equilibrium pressure makes it suitable for both feeding a PEM fuel cell and being charged directly from a low pressure water electrolyzer without need of additional compression, was studied. The nominal 70 L hydrogen storage capacity of the container (T = 20 degrees C, P = 101.3 kPa) suffices for ca. 2.5 h operation of a 50 W hydrogen/oxygen fuel cell stack. The hydride container is provided with aluminum extended surfaces to enhance heat exchange with the surrounding medium. These surfaces consist of internal disk-shaped metal foils and external axial fins. The characterization of the storage prototype at different hydrogen discharge flow rates was made by monitoring the internal pressure and the temperatures of the external wall and at the center inside the container.The response of the storage device was tested at room temperature under different conditions such as natural convection in air and forced air ventilation, and at different temperatures in a thermostated water bath, representing possible real situations to feed hydrogen/oxygen fuel cells. Current results are discussed and correlated with each particular environmental condition and hydrogen flow rate. It is found that for some environmental conditions the flow rate discharge behavior improves significantly. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Supported PtSnIr/C, PtSn/C, and IrSn/C catalysts with potential application in a direct alcohol fuel cell were prepared by chemical reduction employing Pechini methodology. The catalyst particles were characterized by high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy (XPS). Linear sweep voltammetry (LV), chronoamperometry, and electrochemical impedance spectroscopy (EIS) measurements were performed by using a glassy carbon working electrode covered with the catalyst in a 1 M ethanol + 0.5 M H 2 SO 4 solution at 60 °C. It was demonstrated through XPS that PtSnIr/C and IrSn/C contain both IrO 2 and SnO 2 . LV and chronoamperometry show a better catalytic behavior for ethanol oxidation on PtSnIr/C in the low-potential region and the improvement is attributed to the presence of both Sn and Ir oxides. The EIS accurately established that PtSnIr/C improved ethanol oxidation at lower potentials than PtSn/C.

Supported Pt-Sn-Ir/C (P), Pt-Sn/C (PO) and PtRu/C (BH) catalysts with potential application in a direct alcohol fuel cell (DAFC) were prepared by chemical reduction employing Pechini (P), Polyol (PO) and NaBH4 (BH) methodology. The catalyst particles were characterized by high resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV), chronoamperometry and electrochemical impedance spectroscopy (EIS) measurements were performed by using a glassy carbon working electrode covered with the catalyst in a 1 M (ethanol or methanol) + 0.5 M H2SO4 solution in the 25 to 60 degrees C temperature range. In all electrochemical measurements it was demonstrated that PtSnIr shows the best catalytic activity for both alcohols oxidation. The improvement is attributed to the presence of both SnO2 and IrO2 oxide in the Pt composite, though influence of particle size can not be discarded. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

The great challenge of our times is to replace polluting oil energy sources with renewable and clean energies that are ready to be used, which requires addressing the need for proper storage solutions. Electric energy storage should be clean, economical, efficient, safe, have long useful life and high specific capacity ( mass and volume). The lithium-ion batteries fulfill most of these requirements. To expand the scope of application of these batteries, which are currently used in electric cars, we are working on the development of techniques to construct electrodes with a good response to high discharge currents. Results on the development of lithium iron phosphates with olivine structures to be used as cathodes in advanced batteries are presented.

The analysis of telemetry data of the Argentine electricity storage system SAC-C satellite is presented.Diagnostic indicators were established in order to evaluate the in-flight performance of the satellite nickel-hydrogen batteries.The state of charge of the batteries was related to the hydrogen pressure.A predictive analysis allowed us to detect early failure of the electricity storage system.

Three Pt-based anode catalysts supported on Vulcan XC-72R (VC) were prepared by using a modified polyol process. These materials were characterized and tested by X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF) and Transmission Electron Microscopy (TEM). XRD and TEM analysis indicated that especially the ternary anode catalysts consisted of uniform nanosized particles with sharp distribution. The Pt lattice parameter was smaller, in the ternary PtSnIr catalyst whereas it increased with the addition of Sn and Rh, in the corresponding binary and ternary catalysts. Cyclic voltammetry (CV) measurements showed that Sn, Ir and Rh may act as promoter of Pt enhancing ethanol electro- oxidation activity. It was found that the direct ethanol fuel cell (DEFC) performances were significantly improved with these modified anode catalysts. This effect on the DEFC performance is attributed to the so-called bi-tri-functional mechanism and to the electronic interaction between Pt and additives. The performance increased significantly with the temperature. However, it was also possible to observe some decay with time for all catalysts due to the formation of surface poisons, probably consisting in CO-like species. At 60 °C, the PtSnIr catalyst showed the best performance, as a result of a proper morphology and promoting effect.

The effect of the addition of Pt on the electrochemical characteristics of AB(2) type ZrCrNi alloys as negative electrode materials for nickel metal-hydride (Ni-MH) batteries is studied. Electrochemical characteristics of the alloys like as discharge capacity, activation behavior, high rate dischargeability (HRD) and electrochemical impedance spectroscopy (EIS) were analyzed. The resulting ZrCrNiPtx alloys (x = 0.05 and 0.1 corresponding to 5 wt. % and 10 wt. % respectively) retain the crystalline structure related to hexagonal C14 Laves phases, on both as-melted and annealed samples. Alloy samples containing Pt are found to have a similar activation behavior to the as-melted alloy without Pt. However, this characteristic is improved in annealed samples containing Pt. The discharge capacity of the ZrCrNiPtx alloys is higher than the discharge capacity corresponding to ZrCrNi alloys, except in the case of as-melted ZrCrNiPt0.1 alloy. The addition of Pt also improves significantly the high rate dischargeability, maintaining the capacity values in a wide range of discharge current. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Pt-Sn-Ni/C and the Pt-Sn/C supported catalysts with potential application in a direct ethanol fuel cell (DEFC) were prepared by a chemical reduction method.The Vulcan XC-72R (Vu) used as carbon support was chemically treated with concentrated HNO3 (Vu(t)) and then analyzed by thermal programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). The catalyst particles were characterized by high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD).Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements were performed by using a glassy carbon working electrode covered with the catalyst powder in a 1M ethanol + 0.5M H2SO4 solution at 60 degrees C. EIS shows that ethanol oxidation (EO) on the Pt-Sn-Ni/Vu(t) catalyst at various potentials exhibits different impedance behaviors. The catalytic activity of the Pt-Sn-Ni/Vu(t) catalyst for EO is higher than that of the Pt-Sn/Vu(t) catalyst. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

The preparation and characterisation of Pt nanoparticles electrodeposited on carbon substrates by pulsating electrolysis are presented. The characterisation studies of metal electrodeposits by using SEM, TEM, XRD and cyclic voltammetry revealed the presence of facetted Pt nanoparticles having a predominant (111) preferential crystal orientation. The amount of electrodeposited Pt was determined by means of a spectrophotometric technique. An improvement in performance of the hydrogen/oxygen PEM fuel cell with (111)-type Pt nanoparticles incorporated in the cathode was observed, which was assigned to the decrease of the blocking effect of the cathode electrode surface by intermediate peroxide species produced during the overall oxygen electroreduction process.

Multiwalled carbon nanotubes were obtained by chemical vapor deposition of xylene ferrocene and employed as supports for PtSn alloy nanoparticles synthesized by the polyol method. The same metal alloy catalyst was also supported on Vulcan XC-72R to compare the influence of the substrate on the catalyst behavior for ethanol oxidation. The physical characterization of the carbon samples and supported alloy catalysts was performed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Ethanol oxidation was chosen as a reaction model to study the electrocatalytic behavior of the supported PtSn nanoparticles. Cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy were used for the electrochemical characterization. The PtSn/MWNT electrodes show a better catalytic behavior for ethanol oxidation than PtSn/Vulcan XC-72R electrodes. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Three cathode catalysts (60% Pt/C, 30% Pt/C and 60% Pt–Fe/C), with a particle size of about 2–3 nm, were prepared to investigate the effect of ethanol cross-over on cathode surfaces. All samples were studied in terms of structure and morphology by using X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. Their electrocatalytic behavior in terms of oxygen reduction reaction (ORR) was investigated and compared using a rotating disk electrode (RDE). The tolerance of cathode catalysts in the presence of ethanol was evaluated. The Pt–Fe/C catalyst showed both higher ORR activity and tolerance to ethanol cross-over than Pt/C catalysts. Moreover, the more promising catalysts were tested in 5 cm 2 DEFC single cells at 60 and 80 °C. An improvement in single cell performance was observed in the presence of the Pt–Fe catalyst, due to an enhancement in the oxygen reduction kinetics. The maximum power density was 53 mW cm −2 at 2 bar rel. cathode pressure and 80 °C.

Carbon-supported binary PtSn/C and ternary PtSnNi/C catalysts were prepared for the electro-oxidation of ethanol. The carbon-supported nanoparticles were synthesised by employing a modified polyol methodology and characterised in terms of structure, morphology and composition by using XRD, EDX and TEM techniques. Their electrocatalytic behaviour for ethanol oxidation (EO) was investigated by employing a disccomposite electrode covered by a thin layer of catalyst imbedded in a Nafion polymer electrolyte film. An enhancement of the EO through a negative shift of the onset oxidation potential and higher current density at constant potentials were observed on the PtSnNi/C electrodes as compared to those for PtSn/C electrodes. The temperature was changed in the range 40 degrees C <= t <= 80 degrees C, and the variation of the activation energy calculated by linear regression of the Arrhenius plots.

Recent advances in the design and construction of a hydrogen/oxygen PEM fuel cell stack are presented. A test bench including measurement and control devices to monitor the fuel cell operating parameters was mounted. The influence of the characteristics of the membrane electrode assembly, bipolar plates, etc., on the performance of the fuel cell stack was studied. The behavior of the fuel cell stack with a different number of cells in series was evaluated. In order to identify and minimize the energy losses a critical analysis of the results was done.