César Merino

Selective suspension of single layer graphene mechanochemically exfoliated from carbon nanofibres

This paper presents the first report of the successful ball-milling exfoliation of graphitic filaments (GANF® carbon nanofibres) into single layer graphene. The addition of small amounts of solvent during the milling process makes it possible to enhance the intercalation of the exfoliating agent (melamine) between the graphene layers, thus promoting exceptional exfoliation. Advantage has also been taken of the fact that the Hansen solubility parameters of graphene are different from those of carbon fibres, which allows single and few-layer graphene to be suspended in a particular solvent, thus discriminating them from poorly exfoliated carbon nanofibres.

Study of the Silanization Process in CNFs: Time, Temperature, Silane Type and Concentration Influence

Functionalization of CNFs with silane coupling agents (SCAs) has been studied in this work. APS silane has been used in order to study the influence of temperature and reaction time on the silanization process. Thermal analysis and surface area measurements have revealed that reaction times higher than 1 min. and temperature reaction higher than 25°C do not increase the amount of adsorbed silane on CNFs surface. Silanization process carried with different SCAs (APS, AMO, DMO and GMO) has allowed the study of the concentration and silane structure influence. It has been observed that differences in SCA adsorption are related to the silane structure. Aminosilanes APS and AMO show a very similar behaviour because they have the same functional group. However, the diaminosilane DMO shows lower interaction with CNFs surface due to the length of the diamine chain, that avoid further silane adsorption on the coated CNFs surface. The epoxysilane GMO shows a similar behaviour to other SCAs at low concentrations, while for high silane concentrations epoxysilane GMO forms multilayers.

Conductive CNF-doped laminates processing and characterization

In this study, carbon nanofiber (CNF)/glass fiber/polyester resin laminated composites were prepared using two different manufacturing methods: Hand lay-up method and vacuum bagging. These techniques were used in order to compare their influence in the final properties of the composite. Every kind of laminate was loaded with CNF between 0 and 2 wt% with respect to the resin weight. It was found that the presence of CNF produced a reinforcement of the composites in both flexural and tensile strengths regardless of the manufacturing method. On the other hand, composites prepared by the vacuum bag technique showed an important increase in their mechanical properties due to the preparation method. Finally, the CNF-loaded laminates were found to be conductive with only 0.5 wt% CNF loading.

A cost-effective PEM fuel cell test system based on hydraulic compression with optimized platinum catalyst loading

For this study gas diffusion electrodes (GDE) with low platinum loading are prepared for the application as anode in polymer electrolyte membrane fuel cell (PEMFC) systems based on hydraulic compression. As catalyst support material, carbon nanofibers (CNF) are investigated because of their high specific surface area and high graphitization degree. The electrode preparation is optimized by an economic and environmental friendly pre-treatment process in oxygen plasma. For GDE manufacture an ink containing oxygen plasma activated CNFs as well as hydrophilic polymer is used. After spray coating of this CNF ink on a graphitic substrate, platinum is deposited using the pulse plating technique. Preliminary results showed a considerable improvement of CNF dispersibility as well as an increased amount and an optimized morphology of the deposited platinum. Morphology and microstructure are observed by scanning electron microscopy as well as transmission electron microscopy. Platinum loading is determined by thermogravimetric analysis to be in the range of 0.01 mg cm-2 to 0.017 mg cm-2. Furthermore, MEAs are prepared from these GDEs and testing is performed in a novel modular fuel cell test stack based on hydraulic compression. Technical information about stack design and functions is given in this work.