Synthesis of Ca Decorated Carbon Nanostructures for Hydrogen Storage
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Synthesis of Ca Decorated Carbon Nanostructures for Hydrogen Storage D. Mirabile Gattia1, M. Vittori Antisari1, R. Marazzi1, A. Montone1, E. Piscopiello2, C. Mingazzini3 1 ENEA, MAT-COMP, Research Centre of Casaccia, Via Anguillarese 301, 00123 Rome, Italy. 2 ENEA, MAT-COMP, Research Centre of Brindisi, SS.7, Appia, km 706, 72100 Brindisi, Italy. 3 ENEA, MAT-ING, Research Centre of Faenza, Via Ravegnana 186, 48018 Faenza, Italy. ABSTRACT The AC powered electric arc has been used to synthesize single wall carbon nanohorns aggregates with Ca dispersed inside. To this purpose the electric arc has been ignited between two electrodes, one of which was constituted by a mixture of graphite and CaCO3. The experimental evidence on the microstructure and on the chemical composition has been obtained by observation with a transmission electron microscope equipped with X-ray microanalysis. Xray diffraction revealed the presence of residual CaCO3 indicating that the process has still to be optimized. The experiment represents a first attempt to decorate carbon nanostructures with alkaline earth metals, in particular Ca, by this relatively simple method. These composites are theorized to adsorb relevant amounts of hydrogen. Further work will be focused to optimize the dispersion of Ca atoms in the carbon nanostructure. INTRODUCTION Lightweight materials for solid state hydrogen storage can play a critical role for a widespread diffusion of hydrogen as energy carrier. Among others, carbon nanostructures have been studied to this purpose and in particular carbon nanotubes, carbon nanofibers, single-wall carbon nanohorns have displayed some hydrogen adsorption due to their large surface area and high reactivity showing also the possibility of tailoring nanosized porosity. On the other hand, nowadays, several carbon based nanomaterials have been synthesized and characterized since the discovery of fullerenes in 1985 [1]. In particular several new forms of carbon nanostructures based on the organization of graphene layers have been discovered and analyzed both from the fundamental point of view and also considering possible technological applications. However, considering the application as support for hydrogen storage, the large variety of carbon nanostructures show generally a similar behavior despite the differences among them in terms of microstructure and no material suitable for practical hydrogen storage is presently available. Generally speaking hydrogen on nanocarbon shows two bonding conditions, none of which appears suitable for hydrogen storage application. In fact physisorption of H2 molecules is characterized by a weak bonding so that high pressure and cryogenic temperatures are required for a detectable hydrogen adsorption. On the contrary chemisorption of atomic H shows a strong bonding so that temperatures too high for practical applications are required for H release. Recently it has been reported that carbon materials coated with alkaline earth metals, like Ca, could theoretically adsorb relevant amount
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