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In this work, graphitized ordered mesoporous carbons (gCMK-3) were employed as support for Pt and Pt–Ru nanoparticles synthesized by different reduction methods. The catalysts displayed metal contents and Pt:Ru atomic ratios close to 20 wt % and 1:1, respectively. A comparison of the physical parameters of Pt and Pt–Ru catalysts demonstrated that Ru enters into the Pt crystal structure, with well-dispersed nanoparticles on the carbon support. The Pt catalysts exhibited similar surface oxide composition, whereas a variable content of surface Pt and Ru oxides was found for the Pt–Ru catalysts. As expected, the Pt–Ru catalysts showed low CO oxidation onset and peak potentials, which were attributed to the high relative abundances of both metallic Pt and Ru oxides. All the studied catalysts exhibited higher maximum current densities than those observed for the commercial Pt and Pt–Ru catalysts, although the current–time curves at 0.6 V vs. reversible hydrogen electrode (RHE) demonstrated a slightly higher stationary current density in the case of the Pt/C commercial catalyst compared with Pt nanoparticles supported on gCMK-3s. However, the stationary currents obtained from the Pt–Ru/gCMK-3 catalysts surpassed those of the commercial Pt–Ru material, suggesting the suitability of the prepared catalysts as anodes for these devices.

The graphitisation of ordered mesoporous carbons (CMK-3) was carried out by thermal treatments under different conditions of temperature and heating rate. The electrochemical characterization in acidic medium of the graphitised CMK-3 showed that such a thermal treatment is effective to decrease the carbon oxidation rate (corrosion) while preserving a good porosity in terms of capacitance. Besides, the graphitisation degree and, in consequence the electrochemical corrosion resistance, can be modulated by an appropriate choice of thermal treatment conditions, where the heating rate and temperature appear as critical parameters. Under certain graphitisation conditions, the carbon corrosion of CMK-3 can be minimized showing lower rates compared to a commercial carbon black (Vulcan XC-72R). Palladium nanoparticles were supported on the most promising graphitised CMK-3 and Vulcan using a method based on impregnation and reduction with borohydride, resulting in suitable metal crystallite sizes. The electrocatalytic activity towards the oxidation of carbon monoxide and formic acid were assessed in aqueous sulphuric acid electrolyte for application at the anode of direct formic acid fuel cells (DFAFCs). The best activity results were obtained for the Pd catalyst supported on a graphitised CMK-3.

Carbon nanocoils (CNCs) were synthesized using resorcinol–formaldehyde gel as carbon precursor and a mixture of cobalt and nickel salts as the graphitization catalysts. The last step of the synthesis process involves the elimination of the metals using an oxidative treatment, commonly HNO3 treatment. However, during this treatment not only the metals are eliminated, but also the amorphous and graphitic carbon. On the other hand, this treatment can create surface oxygen groups, modifying the surface chemistry of CNCs. The aim of this work is to study the effect of different oxidative treatments on the final properties of carbon nanocoils in order to obtain materials with high graphitic character. The effect of liquid phase oxidation treatments on the texture, surface chemistry and structure of carbon nanocoils was studied by means of different analytical techniques as N2-physisorption, X-ray diffraction (XRD), temperature programmed oxidation (TPO) and temperature programmed desorption (TPD). During these treatments, surface oxygen groups were created and their number was function of the concentration of the oxidizing agent used and the treatment time.

Pt-Ru nanoparticles supported on carbon nanofibers (CNF) were synthesized by the sodium borohydride reduction method, using different generation dendrimers (zero, one, two and three generations). After the synthesis process, these materials were submitted to a heat treatment at 350 °C, in order to clean the nanoparticle surface of organic residues. TEM characterization showed that the Pt-Ru nanoparticles size ranged between 1.9 and 5.5 nm. The use of dendrimers did not totally avoid the formation of aggregates, although monodisperse sizes were observed. The heat treatment produces the desired surface cleaning, although promoted the formation of agglomerates and crystalline Ru oxides. The study of the electrochemical activity towards the methanol oxidation displayed some clues about the influence of both the dendrimer generation and the presence of Ru oxides. Moreover, the apparent activation energy Eap for this reaction was determined. The results showed a beneficial effect of the heat treatment on the methanol oxidation current densities for the materials synthesized with the biggest dendrimers, being the methanol deprotonation and COad diffusion the predominant rate determining steps (rds).

Carbon nanocoils (CNCs) were used to prepare Pt and Pt-Ru catalysts by the sodium borohydride (BM), methanol (MM) and polyol (EGM) solution reduction methods. Their physicochemical properties were studied by means of energy dispersive X-ray analysis, X-ray diffraction and transmission electron microscopy, whereas the electrochemical activity towards carbon monoxide and methanol oxidations was studied using cyclic voltammetry and chronoamperometry. Furthermore, differential electrochemical mass spectrometry experiments were carried out to study the reaction mechanisms. Results were compared with those obtained for the commercial Pt/C and PtRu/C catalysts from E-TEK. It is shown that choosing an adequate synthesis procedure, better electrocatalytic behaviours towards CO and methanol oxidation can be obtained by using carbon nanocoils as support material.

Different carbon materials with high electrical conductivity have been studied as electrocatalyst support for direct alcohol fuel cells (DAFCs). The aim of the work was to establish the influence of the support on the catalyst properties and to improve their efficiency in the fuel cell. Carbon nanofibers (CNFs), carbon nanocoils (CNCs) and ordered mesoporous carbons (gCMK-3) have been used for synthesizing platinum catalysts by the polyol method. Results have been compared with those obtained for a platinum catalyst supported on Vulcan XC-72R, prepared by the same method, and for the commercial Pt/C catalyst from E-TEK. It has been demonstrated that novel carbon supports could help to oxidize CO adsorbed on platinum particles more easily than the commercial carbon support and improve the alcohol oxidation reaction, both in terms of onset potential and current density. The catalyst supported on gCMK-3 carbon resulted to be the most effective in both the methanol and ethanol oxidation, which can be attributed to its ordered structure and high electrical conductivity. © 2013 Elsevier Ltd. All rights reserved.

The use of liquid organic hydrides as hydrogen carriers is a promising storage and delivery system due to the advantages of using liquid-based infrastructures and its economic feasibility compared to other conventional systems. The reversible dehydrogenation/hydrogenation of liquid organic hydrides is a key point for the development of highly performance reactors. In this study different carbon materials have been investigated as platinum supports, including carbon nanofibers, carbon black, carbon xerogel, activated carbon and ordered mesoporous carbon. To individuate the effect of the carbon support on the catalytic activity, platinum particles were synthesized by a microemulsion procedure. The analysis of the hydrogen evolution curves indicate that the support BET surface area plays a very important role on the initial catalytic activity, obtaining a maximum rate of 220 mmol gPt -1 min-1 when using an ordered mesoporous carbon with a surface area of 930 m2 g-1. Nevertheless, the analysis of catalytic activity at prolonged duration indicates a better behavior towards deactivation for supports characterized by wide pores and low graphitization degree like carbon black or carbon xerogel, despite their lower initial dehydrogenation rate (100-140 mmol gPt -1 min-1). The ultimate use in the dehydrogenation reactor as well as the operation conditions will define the best catalyst structure from the point of view of the carbon support.

La presente invención se refiere a un procedimiento para incrementar la conductividad eléctrica de un material de carbono mesoporoso ordenado (CMK-3) obtenido mediante la técnica de nanomoldeo, donde dicho procedimiento comprende tratar térmicamente en atmósfera inerte dicho material de carbono mesoporoso ordenado. Asimismo, es objeto de la invención el material obtenible a partir de dicho procedimiento, un procedimiento para la obtención de un electrocatalizador a partir de dicho material y su uso para la obtención de un ensamblaje membrana-electrodo.

Different advanced nanostructured carbon materials, such as carbon nanocoils, carbon nanofibers, graphitized ordered mesoporous carbons and carbon xerogels, presenting interesting features such as high electrical conductivity and extensively developed porous structure were synthesized and used as supports in the preparation of electrocatalysts for direct methanol fuel cells (DMFCs). The main advantage of these supports is that their physical properties and surface chemistry can be tailored to adapt the carbonaceous material to the catalytic requirements. Moreover, all of them present a highly mesoporous structure, diminishing diffusion problems, and both graphitic character and surface area can be conveniently modified. In the present work, the influence of the particular features of each material on the catalytic activity and stability was analyzed. Results have been compared with those obtained for commercial catalysts supported on Vulcan XC-72R, Pt/C and PtRu/C (ETEK). Both a highly ordered graphitic and mesopore-enriched structure of these advanced nanostructured materials resulted in an improved electrochemical performance in comparison to the commercial catalysts assayed, both towards CO and alcohol oxidation.

La presente invención proporciona un procedimiento para preparar nanoespirales de carbono las cuales son usadas para la fabricación de un electrocatalizador soportado sobre dichas nanoespirales de carbono (CNC), a su vez dicho electrocatalizador se usa para la fabricación de celdas de combustible de baja temperatura (pilas de combustible de electrolito polimérico o de alcohol directo). El carácter grafítico de este tipo de materiales les proporciona unas propiedades electrónicas que lo hacen adecuado para su uso como soporte de catalizadores metálicos.

Electrocatalizadores para pilas de combustible de membrana de intercambio protónico. Procedimiento de obtención de un material de carbono mesoporoso (SMC) que comprende: la adición de sílice coloidal a un precursor polimérico de carbono; el curado térmico; el carbonizado del compuesto obtenido; lavado del compuesto carbonizado con ácido fluorhídrico (HF) o NaOH; y la oxidación del material lavado. Además la invención se refiere a un catalizador para pilas de combustible de electrolito polimérico basado en la utilización del nuevo soporte carbonoso mesoporoso.

Electrocatalizadores para pilas de combustible de membrana de intercambio protónico. Procedimiento de obtención de un material de carbono mesoporoso (SMC) que comprende: la adición de sílice coloidal a un precursor polimérico de carbono; el curado térmico; el carbonizado del compuesto obtenido; lavado del compuesto carbonizado con ácido fluorhídrico (HF) o NaOH; y la oxidación del material lavado. Además la invención se refiere a un catalizador para pilas de combustible de electrolito polimérico basado en la utilización del nuevo soporte carbonoso mesoporoso.