The development of effective methods for hydrogen storage is of paramount importance in using hydrogen as a transportation fuel for on-board applications. The rate at which the hydrogen is adsorbed/desorbed on porous materials in compressed pellets is directly related to the thermal conductivity of the adsorbent. This work aims to increase the hydrogen adsorption rate in MIL-101(Cr) and MIL-100(Fe) compressed pellets by using reduced graphene oxide (rGO) as an additive, in order to get an increased thermal conductivity and thus a more efficient heat transport through the pellets. To achieve this goal, a complex study was undertaken using different techniques, namely photothermal radiometry (PTR) for thermal conductivity investigation, a volumetric home-made device for kinetic measurements and other techniques (XRD, SEM, TEM, BET, TG-DTA) for structural and morphological characterization of the samples. It has been found that the thermal conductivity of the pellets increases with the graphene addition. A significant enhancement in thermal conductivity (by factors of 4 compared to pellets without additives) is obtained and reaches a maximum of 0.58 W/mK for MIL-100(Fe) pellet (p = 0.65 g/cm(3)). The hydrogen adsorption equilibrium time in neat samples is reached in about 180 s. The presence of 10 wt% rGO in both MIL-100 and MIL-101 pellets improves the hydrogen adsorption kinetics and favors the equilibrium in shorter times, respectively 20 and 40 s, than in neat samples. The experimental data are in very good agreement with the Linear Driving Force Model (LDF) for gas adsorption kinetics. (C) 2019 Elsevier Ltd. All rights reserved.

Hydrogen adsorption isotherms for MIL-101 metal-organic framework are reported within a wide pressure range for temperatures between 77 and 295 K. Data modeling with the modified Dubinin-Astakhov equation shows a good fitting with the experimental results. The calculated absolute adsorption allowed the evaluation of the total hydrogen storage capacity for high pressure storage tank filled with MIL-101 as sorbent. The results show that the gravimetric and volumetric storage capacities at 198 K and 70 MPa are within the presentday accepted DOE targets, even if the storage capacity is slightly decreased by 3-6% as compared to the tank without sorbent. Moreover, the calculations reveal that the dormancy time is much increased, as compared to a tank without sorbent, exceeding the ultimate DOE target of 14 days. The MIL-101 assisted cold high-pressure hydrogen storage at -200 K and 70 MPa, brings about an additional advantage and seems promising for both mobile and stationary applications. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

We report here the unprecedented modification of the hydrogen absorption/desorption properties of 1 nm Pd clusters relative to the bulk and nanoparticles down to 2-3 nm. These metal clusters have been synthesized by a facile double solvent impregnation method. They contain on average 33 atoms and are confined/stabilized into a metal-organic-framework with different metal loadings (5-20 wt%). This is the first time, to the best of our knowledge, that 1 nm Pd clusters are effectively confined into a MOF for high metal loadings. Such ultra-small nanoparticles are crystalline with the archetypical fcc structure of the bulk metal, as confirmed by both HR-TEM and in situ EXAFS. Hydrogen absorption/desorption properties of 1 nm Pd clusters have been characterized by both laboratory and synchrotron facilities. Under ambient conditions, 1 nm Pd clusters absorb hydrogen forming solid solutions instead of a hydride phase, as usually encountered for the bulk and Pd nanoparticles down to 2-3 nm. This can be understood by a decrease of the critical temperature of the two-phase region in the Pd-H phase diagram below room temperature. Moreover, the activation energy of hydrogen desorption from Pd clusters strongly decreases relative to bulk Pd. This suggests a change in the rate limiting step from surface recombination or beta -> alpha phase transformation usually encountered in bulk Pd to hydrogen diffusion into alpha and beta phases in 1 nm clusters.

A new type of MIL-101: aluminum composites with improved thermal conductivity is reported and their hydrogen adsorption rate investigated in a systematic study of hydrogen adsorption/desorption kinetics of MIL-101 single pellets, filling the gap of data on hydrogen sorption kinetics by compressed monoliths in the cryo-adsorption storage conditions.Kinetic curves were measured within a wide range of pressure in the temperature range 77-159 K and the hydrogen diffusivity were estimated from the rate constants obtained by fitting the fractional uptake with the kinetic equations. In order to compare MIL-101 with other metal-organic frameworks (MOFs), measurements on pellets of MIL-100(Fe) and HKUST-1 were also performed. As expected, the results, together with some data available in literature, reveal that the hydrogen diffusivity obtained from kinetic studies is strongly related to the pore diameter. The activation energy of hydrogen diffusion in MIL-101, calculated from the rate constants, is 1.6 kJ mol(-1), close to the literature values reported for other MOFs. Kinetic studies on composite pellets of MIL-101 with Al tapes (8-10%) with improved thermal conductivity (similar to 0.5 W m(-1)K(-1)) are also reported. They show indeed higher uptake rates, consistent with the requirement of fast filling time (less than 3 min) required for applications. The adsorption/desorption rate at 77 K allows similar to 90% fractional uptake in about 40 s, promising for applications of cryo-adsorption storage. The results show that the time required to reach saturation and thermal equilibrium depends on pellet geometry and hydrogen diffusivity. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

A new method for the preparation of HKUST-1 using a microwave-assisted non-solvothermal synthesis is presented. The influence of the reaction parameters (concentration of reactant mixtures, solvent, temperature, reaction time and microwave power) on the material's textural properties and yields has been investigated and the synthetic method was optimized. By exposing the reaction mixture to microwaves for up to 10 minutes HKUST-1 with a surface area and pore volume close to the theoretical values and a yield of about 70% was obtained. In addition, yields could reach around 90% if the product formed in the mother liquor is counted.

Hexagonal prism shaped monoliths of envelope density 0.40-0.467 g/cm3 and remarkable mechanical stability were obtained from MIL-101 powder. The hydrogen adsorption isotherms within an extended pressure range show that the excess adsorption decreases with the increasing density of the pellets. At 77 K and 150 bar, the total volumetric capacity is 46.5 g/L; the discharge to 159 K and 5 bar leads to 45 g/L (38.8 g/L referring to the outer tank volume) supporting MIL-101 as a promising candidate for applications in the 77-160 K range of interest for cryo-adsorption hydrogen storage method. The isosteric adsorption enthalpy evaluated from the experimental data with the van't Hoff equation, using fugacity, is in agreement with the calorimetric heat of adsorption reported in literature. Monoliths of this shape allow the best possible packing density of any sorbent in a container and the primary data reported here on MIL-101 could serve as material engineering properties required for modeling hydrogen storage tanks. Copyright (c) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

The physical upper limit of hydrogen uptake for powder and compressed pellet MIL-101 has been experimentally investigated. Maximum uptake in pellets at 20 K achieves 9.6 wt% and 42 g L−1. Moreover, cryo-adsorption of hydrogen on pellets compared to liquid H2 possesses a larger temperature window for operation without boil-off loss, which will be beneficial for industrial applications.

The effect of ball milling energy on hydrogen adsorption on metal-organic framework:Pt/AC mixtures (HKUST-1:Pt/AC, AC - activated carbon) is reported. Experiments within a wide range of ball milling energies show a decrease of hydrogen adsorption with the increasing energy transferred to the sample. The results correlate well with the decrease of surface area and pore volume. The infrared spectra reveal that the mechanical energy transferred to the sample induces modifications in the metal coordination environment, the most compliant to compression part in the structure of the metal-organic frameworks. A comparison with the results on compressed pellets of the mixture reveals that both the ball milling and compression lead to similar effects, originating in mechanical energy transferred to the sample. (C) 2014 Elsevier Inc. All rights reserved.

The hydrogen adsorption isotherms of MIL-101 compressed pellets at 77.3 K are reported. The specific surface area and micropore volume decrease rather sharply when the pellet density approaches the crystal density. Optimum volumetric storage capacity of 40 g L-1 is obtained for monoliths of remarkable mechanical integrity. The X-ray diffraction patterns do not exhibit notable changes with,compression up to densities close to the crystal density. However, the infrared spectra show significant modification of the band structure in the range of vibration frequencies characteristic to the carboxylate and phenylene groups, due to the pressure-induced changes in the coordination environment of the metal, close to the adsorption sites. The compression effect on hydrogen adsorption can be correlated with the changes in the nitrogen adsorption isotherms. The results are discussed and compared with the literature results on volumetric hydrogen storage capacity of MOF-5 and MOF-177 monoliths. Copyright (c) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

High-quality multi-walled carbon nanotubes (MWCNTs) were efficiently synthesized on the CaCO3 supported Fe-Co catalyst with catalytic chemical vapor deposition method using acetylene as carbon source. The relationship between the catalyst structure and the carbon nanotube growth was systematically studied by using multiple techniques including SEM, TEM, TGA, Raman spectroscopy, and XRD. It was found that the MWCNT product demonstrates two groups in the outer diameter distribution, which is associated with the partial decomposition of CaCO3. This thermal decomposition was found to have as a result the coexistence of two catalytic systems throughout the entire synthesis process: Fe-Co/CaCO3 and Fe-Co/CaO. It was also found that the smaller diameter nanotubes grow on the Fe-Co/CaO system, while Fe-Co/CaCO3 produces larger diameter tubes.

IRMOF-8 bridged and un-bridged composites with Pt on activated carbon catalyst were synthesized with the aim to reproduce the considerable enhancement of hydrogen storage at ambient temperature reported in literature. X-ray powder diffraction patterns, surface areas and pore volumes of the synthesized materials are comparable with the literature data. However, the hydrogen sorption isotherms at room temperature do not exhibit any significant enhancement of hydrogen uptake as compared to the pristine materials.

The paper analyzes heat and mass transfer process in metal hydride hydrogen storage systems as key element in the development of a solar powered pump system. Hydrogen storage and compression performance of the developed reactors are investigated according to the type of metal alloys, the metal hydride bed parameters and system operating conditions. To reach the desired goal, some metal hydride from groups AB(5) and AB(2) were synthesized and characterized using elements substitution for tailoring their properties: reversible hydrogen absorption capacity between the hydrogen absorption and desorption pressures at equilibrium at small temperature differences. For the designed hydrogen storage reactors, a new technical solution which combines the effective increase of the thermal conductivity of MH bed and good permeability to hydrogen gas circulation, was implemented and tested. The results permitted us to develop a heat engine with metal hydride, the main element of the functional model of a heat operated metal hydride based water pumping system using solar energy. This is a free energy system able to deliver water, at a convenience flow and pressure, in remote places without conventional energy access.

Multiwalled carbon nanotubes were synthesized by catalytic chemical vapor deposition using two different methods of heating. By one method, an external resistive tube furnace was used, whereas the other method involved heating with radio frequency excitation by induction coil. A comprehensive comparison was made between these two methods with regards to feed gas utilization, nanotube growth efficiency, nanotube product characterization and morphology, and the formation of amorphous carbon and gaseous byproducts. The carbon nanotubes synthesized using radio frequency excitation exhibited smaller outer diameters, fewer carbon layers, less amorphous carbon, and superior crystalline properties than those produced by external tube furnace. The radio frequency process resulted in more rapid and sustained growth rates of the nanotubes and more efficient use of the carbon source. The reason for these enhanced effects by inductive heating may be due not only to the internally produced thermodynamic heat flow characteristics but perhaps also to induced electron currents generated within the magnetic and metallic catalytic clusters due to RF.

A new metal-organic framework [Fe3O(OOC-C6H4-COO)(3)(H2O)(3)]Cl center dot(H2O)(x) was synthesized with a specific surface area of 2823 m(2)/g and a lattice parameter of 88.61 angstrom. Isostructural with MIL-101, this compound exhibits similar hydrogen adsorption properties, with maximum adsorption capacity of 5.1wt.% H at 77 K. The adsorption enthalpy of hydrogen for MIL-101 and ITIM-1 (MIL-101Fe) at zero coverage was calculated for a wide temperature range of 77 K divided by 324 K, considering corrections for the variation of hydrogen gas entropy with the temperature. The resulted adsorption enthalpy is 9.4 kJ/mol for MIL-101, in excellent agreement with the value reported in literature from microcalorimetric measurements, and a value of 10.4 kJ/mol at zero coverage was obtained for ITIM-1 (MIL-101Fe). Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Hydrogen adsorption in Metal-Organic Frameworks is improved by using platinum and palladium on different carbon support: activated carbon or carbon nanofibres. Although, hydrogen adsorption is directly dependent of the specific surface area of the material, it is not the only factor contributing to the hydrogen adsorption, as presented in this work. Direct synthesis of metal-organic frameworks on supported Pt and Pd catalysts, reduces the surface area significantly, but the presence of the catalysts overcomes this drawback by improving hydrogen adsorption by a factor of 2.2, in case of platinum and by a factor of 1.4 in the case of palladium, compared to the metal-organic framework without catalysts.

We report the photo-thermal properties of single and double wall carbon nanotubes (CNT) dispersed in various solvents with different concentrations when exposed to near infrared nm laser irradiations. All these studies were correlated to the dispersivity of CNT in various solvents. The observed temperature increase of the various nanotube solutions was found to be determined by the concentration of the optically active nanotubes, as determined from their Raman scattering spectra, which are resonant in the spectral range of the laser excitation. Such findings could significantly improve the understanding of the optically active CNT species, their overall laser induced-heating levels, and thus reducing the amount of the CNT required for bio-medical photothermal applications to limit the possible undesired cytotoxic effects that occur at high nanotube concentrations. Our studies open up the possibility of using selective species of CNT as effective low-toxic photo thermal agents for cancer targeting and ablation.

MOF-5 was efficiently and quickly synthesized by a new method: microwave-assisted synthesis under atmospheric pressure, affording a microporous material with large surface areas. Its physicochemical and textural properties are similar to those synthesized by convective solvothermal synthesis.

The paper presents a comparative study between multiwall carbon nanotubcs (MWCNT) grown by the two different versions of catalytic chemical vapor deposition (CCVD) method, namely: the classic method when the heating is performed by an external electrical furnace (EF-CCVD) and an original version of CCVD method based on induction heating and radio frequency (RF-CCVD) excitation of the catalyst system. Distinctive differences were observed in the MWCNTs grown by these two methods. RF-CCVD was also led to high quality single wall carbon nanotubes (SWCNT). Thermogravimetric analyses (TGA) and Raman spectra performed presented the differences among these methods.

High quality singlewall carbon nanotubes (SWCNTs) with a diameter variation ranging between 0.8 and 1.4nm were synthesized over a novel catalytic system Fe:Mo:MgO obtained by co-precipitation by Radio-Frequency-Catalytic Chemical Vapor Deposition. It was found that during the first three minutes of reaction time, the catalyst presented a high yield towards the synthesis of SWCNTs without the generation of other types of carbonaceous species. The corresponding nanotubes were analyzed structurally by electron microscopy, Raman and fluorescence spectroscopy and were found to have high purity and crystalline properties. Very little impurities were present in the samples after the purification process indicating the possibility of obtaining single walled carbon nanotubes with extremely high purity.