The use of a novel three-dimensional graphene structure allows circumventing the limitations of the two-dimensional nature of graphene and its application in hydrogen absorption. Here we investigate hydrogen -bonding on monolayer graphene conformally grown via the epitaxial growth method on the (0001) face of a porousified 4H-SiC wafer. Hydrogen absorption is studied via Thermal Desorption Spectroscopy (TDS), exposing the samples to either atomic (D) or molecular (D2) deuterium. The graphene growth temperature, hydrogen exposure temperature, and the morphology of the structure are investigated and related to their effect on hydrogen absorption. The three-dimensional graphene structures chemically bind atomic deuterium when exposed to D2. This is the first report of such an event in unfunctionalized graphene-based materials and implies the presence of a catalytic splitting mechanism. It is further shown that the three-dimensional dendritic structure of the porous material temporarily retains the desorbed molecules and causes delayed emission. The capability of chemisorbing atoms after a catalytic splitting of hydrogen, coupled to its large surface-to-volume ratio, make these structures a promising substrate for hydrogen storage devices.

The use of Mg as hydrogen storage material is hampered by slow sorption kinetics and high thermodynamic stability. This work reports on biphasic Mg-Ti-H nanoparticles that outperform known Mg-based materials in both respects. By exploiting gas-phase condensation of Mg and Ti vapors under He/H-2 atmosphere, biphasic nanoparticles are grown, in which the bulk-immiscible MgH2 and TiH2 phases are mixed at the nanoscale. TiH2 conveys catalytic activity for H-2 dissociation/recombination and accelerated hydrogen diffusion, while MgH2 provides reversible hydrogen storage. At the remarkably low temperature of 150 degrees C, hydrogen absorption and desorption are completed in less than 100 s and 1000 s, respectively. Moreover, the equilibrium pressure for hydrogen sorption exhibits a composition-dependent upward shift compared to bulk Mg, resulting in a pressure increase by a factor of about 4.5 in the Ti-richest samples at 100 degrees C. The enthalpy and entropy of the metal-hydride transformation are both lower in magnitude with respect to the bulk values, suggesting opposite contributions to the free energy change. The results are analyzed by an interface-induced hydride destabilization model, determining an interfacial free energy difference Delta gamma = (0.38 +/- 0.04) Jm(-2) between hydride and metal phases at T = 100 degrees C. These unique composite nanoparticles significantly extend the temperature/pressure window of hydrogen storage applications using Mg-based materials compatible with up-scaling.

The hydrogen storage is one of the main problems to be solved because hydrogen is going to be the energy vector of the future. Among all developed methods, the H2 storage on solid materials (by chemical or physical sorption) is the most studied. For this aim, in the last years, the carbonaceous materials classes, such as carbon-based matrices, are analysed. Particular study is aimed at new carbon precursors, easy to prepare, cheap and environmentally friendly. All these materials show a direct correlation between the H2 adsorption capacity (77 K) and their surface area. Some of these carbonised organic materials, such as furfural, glucose, starch, cellulose and eucalyptus sawdust, are used as precursors to produce activated carbons (ACs) having a high surface area (up to 2700 m2 g-1) and a narrow size distribution pores in the range of 0,7-2 nm. Among the studied precursor a lot of these coming from different animal and vegetable wastes and interesting H2 storage values were obtained: chicken feather fibers (1,5 wt% at 77 K / 2 MPa), coffee beans (0,6 wt% at 298 K and 4 wt% at 77 K), cannabis roots (3,28 wt% at 77 K / 0,1 MPa), coconut shells (8 wt% at 77 K and 2,3 wt% at 298 K / 7 MPa), rice straw and mulberry paper (4,35 wt% at 77 K / 1 MPa), jute fibers (1,2 wt% at 303 K / 4 MPa). In this work, in addition to the above-mentioned materials, other classes will be considered, correlating their morphology and porosity with the H2 storage capacity.

Hydrogen, the most abundant element in the universe, could solve problems related to environmental pollution impact. But it is difficult to store it at room temperature due to its low density. Usually, hydrogen is stored in the gas compressed form or in liquid state. During last years, research has dealt with new materials that adsorb and release hydrogen under certain temperature and pressure conditions, occupying a reduced volume. These conditions are very important, in particular, in the transport sector. At CNR-ITAE, the hydrogen storage activity is focused on different materials having promising hydrogen sorption capability. Some of these have natural origins, other ones are designed and synthetized in laboratory: Lava Etna powders, banana peels, polymeric coverage for metal alanates, composite polymers containing metal oxide. Two kinds of volcanic powders, coming from Etna eruptions (1880 and 2006), are studied and characterised. Their slight different compositions are probably responsible of their different hydrogen sorption degrees: after activation, powder of 2006 is more efficient than one of 1880. Inspired by storage literature on activated carbon obtained from vegetal matrix, a study on carbonized banana peels, focusing the attention on activation methods and porosity, fundamental points for this scope, was carried out. Hydrogen sorption properties of alanates are known, but their high reactivity with air exposition is a big limit. So, a method to cover alanates with a particular polymeric capsule (Polysulphone, Polyetilene, etc) with high selective permeability for hydrogen is studied. Previous results, demonstrated that Mn oxides are promising for H2 sorption systems. To improve their storage capabilities (3wt% at 40bar/50°C after 300 hrs), a study on the steps of synthesis is carried out. Particularly, the precipitant solvent, chlorosulphonic acid and PEEK molar ratio, Mn oxide precursor concentration, reaction time, catalysts utilisation (to improve H2 sorption kinetic reaction) were investigated.

Prefazione al volume e presentazione della congferenza

Il volume contiene gli abstract dei lavori accettati per i contributi orali e i poster presentati a HYPOTHESIS XII

The dynamics and energetics related to the release of chemisorbed hydrogen from small-diameter single-walled carbon nanotubes is investigated by first-principles molecular dynamics simulations. Our results suggest a possible route for thermally-activated desorption of hydrogen from the nanotube sidewall, leading to formation of molecular H2, and shed light on the basic mechanisms of the reversible storage of hydrogen in carbon nanotubes. In agreement with recent experiments, simulations indicate carbon nanotubes as suitable materials for the reversible storage of hydrogen. Moreover, calculations point to the restoration of the ? bond patterning of the sidewall as the driving force for the desorption of hydrogen from carbon nanotubes.

A mixture of MgH2 and Mg2FeH6 was synthesized by reactive ball milling of magnesium hydride and iron in hydrogen atmosphere. The material is highly nanocrystalline, with typical dimensions of the order of 10 nm; after hydrogen cycling at ~400 °C, well defined XRD peaks of Mg2FeH6 can be observed. Volumetric measurements of hydrogenation/dehydrogenation provide clear evidence of the presence of both hydrides even at lower temperatures. The relative content of magnesium-iron hydride increases on increasing H2 cycling temperature, passing from ~44% at 335 °C to ~54% at 390 °C. Already at 250 °C the composite releases ~3wt% H2 in ~1000 s, while above 340 °C, more than 4wt% H2 can be discharged in less than 100s, following the Johnson-Mehl-Avrami-Kolmogorov equation, with an exponent n = 1, compatible with a reaction controlled transformation. Finally, also the electrochemical performances in a lithium cell have been investigated: the material is able to undergo a conversion reaction and gives on the first discharge more than 1400 mAhg-1. The overpotentials decrease after materials activation by H2 sorption treatments. Moreover, for the first time, the partial reversibility of the conversion reaction for materials containing magnesium iron hydride is here reported. © 2017 Hydrogen Energy Publications LLC

Composite material synthesis, based on Manganese oxide (MnO2) anchored to a functionalized polymeric matrix, was optimized. For this investigation two different MnO2 loadings were selected (16 and 80wt%) in order to understand the relation between the oxide content, chemical-physical characteristic and the H2 sorption properties. SEM, XRD were carried out and the obtained results were correlated to the H2 sorption/desorption characterizations by Sievert apparatus. From these measurements at 50°C/40bar, the sample containing 16wt% of metal oxide content has revealed a low H2 sorption capability (0,04 wt%) instead of the 80wt% sample that showed a very high H2 storage value (3 wt%). A short sorption/desorption cycles were carried out and a good reversibility was revealed. A modelling study, ab-initio Density Functional Theory (DFT) calculations, was carried out. The starting unit cell was MnO2 while Mn24O48 was considered as a supercell. The number of H atoms was gradually increased and desorption energy was calculated. Desorption energy starts from 366 kJ/mol and decreases by increasing the number of H atoms. For the experimental H2 sorption value (1,7wt%) it was calculated the number of the respective H atoms (36) and the corresponding desorption energy (150kJ/mol).

Chemical hydrogen storage with small lightweight and hydrogen-rich molecules like ammonia-borane (NH3?BH3, AB, 19.3 wt.% H2) or amino boranes of general formula RNH2?BH3 (R = alifatic chain or cycle) is a topic of great interest, as witnessed by the exponential growth of the number of papers published in the recent literature. Transitionmetal complexes can catalyze H2 release from these species under mild conditions and offer great potential as H-storage materials. The reactions of assorted Ir(I), Pd(II) and Ru(II) polyphosphine and pincer type complexes with AB and amine boranes have been analyzed experimentally through variable-temperaure multinuclear (11B, 31P, 1H) NMR spectroscopy, kinetic rate measurements and kinetic isotope effect (KIE) determination with deuterated isotopologues. At the same time, a DFT modeling of the reaction mechanisms has been carried out, starting from the experimental data available. The results will be presented.

A simple thermodynamical model taking into account non-ideality and inhomogeneity of absorbed hydrogen molecular gas has been proposed to calculate hydrogen storage capacity in carbon nanostructures as a function of temperature and pressure. The model utilizing the effective interaction potential of the hydrogen molecule with the atoms of the considered material, is based on the experimental equation of state and a local density approximation for molecular hydrogen. We have applied the model for the search of the optimal geometry for hydrogen storage of such promising carbon materials as a set of graphene layers and bundles of carbon nanotubes. We demonstrate that the hydrogen storage capacity depends on the geometry of material and discuss the origin of this effect.

The combined power of the maximum entropy method (MEM) and synchrotron powder X-ray diffraction (SPXRD) is exerted to accurately reconstruct the electron density distribution (EDD) of the hydrogen storage material, KBH4. Its crystal structure features thermally activated disorder among the BH 4 - moieties, and weak secondary bonding effects occupy a key role in determining the energetic barrier for this dynamical effect. The MEM reconstruction is meticulously optimised and inspected for errors, in what may be envisaged as a general manual for this kind of studies. The successful outcome constitutes an experimental EDD of cutting-edge quality, from which atomic charges and the complete bonding network are mapped by topological descriptors. Remarkably, the chemical insights even extend to the delicate interplay of closed-shell bonding in excellent correspondence with ab initio and two-channel MEM calculations. For the current class of functional materials, access to such subtle electronic features is essential for the fundamental understanding of hydrogen desorption pathways.

Hydrogen storage in composite materials is a feasible way to overcome the main drawbacks of the metal hydride systems. In the present paper, we report on the hydrogenation properties of three polydimethylsiloxane (PDMS)-palladium composite samples with different content of metallic fraction (5, 15, 50 in wt.%). Hydrogenation tests in different conditions of temperature and pressure were performed using a Sievert's type apparatus, while the microstructure of the samples was characterised by means of scanning electron microscopy observations and X-ray diffraction measurements. Results show that the hydrogen storage capacity is inversely proportional to the metallic content in the composite samples. Copyright © 2014 Inderscience Enterprises Ltd.

We report an innovative synthetic strategy based on the solid state reaction of fullerene C60 with lithium-transition metals alloys (platinum and palladium), which provides transition metal-decorated lithium intercalated fullerides, with improved hydrogen storage properties. Compounds with Li6Pt0.11C60 and Li6Pd0.07C60 stoichiometry were obtained and investigated with manometric/calorimetric techniques which showed an 18% increase of the final H2 absorbed amount with respect to pure Li6C60 (5.9 wt% H2) and an improved absorption process kinetic. The absorption mechanism was investigated with X-rays diffraction which allowed to identify the formation of the hydrofullerides. Scanning Electron Microscopy was applied to gain information on transition metal distribution and detected the presence of platinum and palladium aggregates which are shown to perform a surface catalytic activity towards hydrogen molecule dissociation process.

We set up and validated a volumetric method to quantify the amount of hydrogen "delivered" after saturation of a solid material as adsorber at different pressures (up to 100 kgf/cm2) and temperatures (down to 77 K). This is the practically most relevant datum to quantify the effectiveness of an adsorbent for the present application. A complementary dynamic method has been also developed to take into account the reversibility of adsorption and to assess in at least a semi-quantitative way the strength of interaction between H2 and the adsorbent. The method has been applied to compare the hydrogen storage capacity of some significant different carbon-based materials (two active carbons and one graphite), as supplied or after thermal treatments under oxidising or reducing conditions. The best results, ca. 7 wt% H2 "delivered", were achieved after saturation at 77 K, 20 kgf/cm2 with an active carbon with ca. 3000 m2/g of apparent specific surface area. The thermal treatments, almost always inducing a drop in surface area, showed effective only for saturation at 273 K, in particular the oxidising procedure. This was correlated to the formation of surface oxidised species, likely carboxylic groups, which improved the interaction strength between H2 and the adsorbent.

A thermo-mechanical model describing hydrogen storage by use of metal hydrides has been recently proposed in Bonetti et al. (2007) describing the formation of hydrides using the phase transition approach. The model is derived within the framework of phase transitions and it is written in terms of three state variables: the temperature, the phase parameter (representing the fraction of one solid phase), and the pressure. The equations come from the laws of thermo-mechanics, by use of a generalized principle of virtual powers that has been proposed by Frémond (2002). In particular, the whole energy balance of the system accounts for micro-forces, which are responsible for the phase transition. Three coupled nonlinear partial differential equations combined with initial and boundary conditions have to be solved. The main difficulty in investigating the resulting system of partial differential equations relies on the presence of the squared time derivative of the order parameter in the energy balance equation, and actually this term was neglected in the analysis performed in Bonetti et al. (2007). Here, the global existence of a solution to the full problem is proved by exploiting known and sharp estimates on parabolic equations with the right hand side in L1L1. Some complementary results on stability and steady state solutions are also given.

Incoherent inelastic neutron scattering measurements on four impregnated/infiltrated composites of hydrides (namely, NaAlH_4,NH_3BH_3, LiBH_4 + Mg(BH_4)_2, and MgH_2) plus nanoporous scaffolds (active carbon fibers or silica-based MCM41) have been performed at low temperature. After a careful data analysis, the present experimental results have been compared to the corresponding spectroscopic data of bulk hydrides. Evident signatures induced by infiltration process on the NaAlH_4 phonon bands have been detected, showing up as a strong peak broadening and smoothing together with, in some cases, an energy shift. Less pronounced phonon spectrum modifications have been found in MgH_2 and NH_3BH_3, mainly concentrated in the low-energy acoustic region. Finally, no relevant effect has been observed for LiBH_4 + Mg(BH_4)_2.