Eric Poirier

Hydrogen adsorption in carbon nanostructures

Abstract Hydrogen adsorption, (BET) specific surface area and X-ray diffraction (XRD) measurements have been performed on carbon nanofibers, intercalated and exfoliated carbon materials. Excess adsorption capacity was evaluated at equilibrium pressures and temperatures ranging from 0.1 to 10.5MPa and 77 to 295K, respectively. We find that at room temperature, carbon nanofibers can adsorb up to 0.7wt% at 10.5MPa. We observed that the presence of different nickel–copper ratios in the catalyst particles leads to change in crystalline structure and specific surface area. Furthermore, we noted that the latter can be increased by the addition of hydrogen in the organic gas during the synthesis of the nanofibers. Finally, we will discuss the hydrogen coverage per unit surface area which is substantially larger on nanostructures than on activated carbon.

A mesoporous metal–organic framework constructed from a nanosized C3-symmetric linker and [Cu24(isophthalate)24] cuboctahedra

The mesoporous framework [Cu(3)(L)(H(2)O)(3)]·(DMF)(35)·(H(2)O)(35) (NOTT-119) shows on desolvation a BET surface area of 4118(200) m(2) g(-1), a pore volume of 2.35 cm(3) g(-1), a total H(2) uptake of 101 mg g(-1) at 60 bar, 77 K and a total CH(4) uptake of 327 mg g(-1) at 80 bar, 298 K.

Inspired by nature: investigating tetrataenite for permanent magnet applications

Chemically ordered L10-type FeNi, also known as tetrataenite, is under investigation as a rare-earth-free advanced permanent magnet. Correlations between crystal structure, microstructure and magnetic properties of naturally occurring tetrataenite with a slightly Fe-rich composition (~ Fe55Ni44) obtained from the meteorite NWA 6259 are reported and augmented with computationally derived results. The tetrataenite microstructure exhibits three mutually orthogonal crystallographic variants of the L10 structure that reduce its remanence; nonetheless, even in its highly unoptimized state tetrataenite provides a room-temperature coercivity of 95.5 kA m(-1) (1200 Oe), a Curie temperature of at least 830 K and a largely temperature-independent anisotropy that preliminarily point to a theoretical magnetic energy product exceeding (BH)max = 335 kJ m(-3) (42 MG Oe) and approaching those found in todays best rare-earth-based magnets.

Evaluation of an industrial pilot scale densified MOF-177 adsorbent as an on-board hydrogen storage medium

Exploring and evaluating on-board solid state hydrogen storage systems performance are of great interest for fuel cell electric vehicles development. In this report, we present gravimetric and volumetric capacities of a hydrogen storage system based on a densified MOF-177 adsorbent. This is, to our knowledge, the first thorough study of an engineered industrial scale MOFs for hydrogen storage application. The measurements were performed over the 50–120 K and 0–40 bar ranges, and modeled using micropore filling approaches. The performances of a potential 100 L vessel filled with the densified MOF-177 are inferred from the modeling parameters. A comparison of this technology with the 70 MPa compressed gas hydrogen system shows under which conditions the adsorbent offer advantages in terms of volumetric and gravimetric capacities. Further comparison with AX-21 activated carbon pellets reveals that densified MOF-177 stores about 40% more at 77 K and 35 bar. In order to get a physically sound modeling analysis, we introduced an approach to establish effective saturation pressures for supercritical adsorption. This approach insures a consistency between key model parameters and the observed liquid properties of the adsorbed phase at the lowest temperatures. We show that modeling using temperature-dependent saturation pressures and adsorbed phase densities leads to important differences in the projected usable storage capacities. Such differences can be as much as 25% at 50 K in the high pressure limit, revealing the importance of physical insights in the modeling approach.

Gravimetric and volumetric approaches adapted for hydrogen sorption measurements with in situ conditioning on small sorbent samples

We present high sensitivity (0 to 1 bar, 295 K) gravimetric and volumetric hydrogen sorption measurement systems adapted for in situ sample conditioning at high temperature and high vacuum. These systems are designed especially for experiments on sorbents available in small masses (mg) and requiring thorough degassing prior to sorption measurements. Uncertainty analysis from instrumental specifications and hydrogen absorption measurements on palladium are presented. The gravimetric and volumetric systems yield cross-checkable results within about 0.05 wt % on samples weighing from (3 to 25) mg. Hydrogen storage capacities of single-walled carbon nanotubes measured at 1 bar and 295 K with both systems are presented.

Thermodynamics of hydrogen adsorption in MOF-177 at low temperatures: measurements and modelling

Hydrogen adsorption measurements and modelling for the Zn-based microporous metal-organic framework (MOF) Zn4O(1,3,5-benzenetribenzoate)2, MOF-177, were performed over the 50-77 K and 0-40 bar ranges. The maximum excess adsorption measured under these conditions varies over about 105-70 mg g(-1). An analysis of the isotherms near saturation shows that hydrogen is ultimately adsorbed in an incompressible phase whose density is comparable to that of the bulk liquid. These liquid state properties observed under supercritical conditions reveal a remarkable effect of nanoscale confinement. The entire set of adsorption isotherms can be well described using a micropore filling model. The latter is used, in particular, to determine the absolute amounts adsorbed and the adsorption enthalpy. When expressed in terms of absolute adsorption, the isotherms show considerable hydrogen storage capacities, reaching up to 125 mg g(-1) at 50 K and 25 bar. The adsorption enthalpies are calculated as a function of fractional filling and range from 3 to 5 kJ mol(-1) in magnitude, in accordance with physisorption. These results are discussed with respect to a similar analysis performed on another Zn-based MOF, Zn4O(1,4-benzenedicarboxylate)3, IRMOF-1, presented recently. It is found that both materials adsorb hydrogen by similar mechanisms.

Thermodynamic study of the adsorbed hydrogen phase in Cu-based metal-organic frameworks at cryogenic temperatures

The hydrogen adsorption properties of two isostructural copper-based microporous metal-organic frameworks (MOFs) materials which differ in the length of the bridging ligands were investigated over the 50–100 K and 0–40 bar ranges. The measured excess adsorption isotherms were analyzed in terms of adsorption enthalpies, adsorbed phase densities and volumes. The characteristic excess maximum was found to be displaced to lower pressures and to vary less as a function of temperature on the material with the shorter ligand. This behaviour could be explained, on the basis of enthalpy calculations, by an enhanced hydrogen affinity in smaller pores. On the other hand, it was also found that the material with the shorter ligand has a reduced storage capacity. This observation could be explained, from measurements near saturation, by a reduction of both adsorbed phase density and volume. Despite their structural difference, both MOFs adsorbed hydrogen near saturation under an incompressible phase reaching bulk liquid densities. These properties suggest that repulsive forces may ultimately limit the packing of supercritical molecules in small pores despite apparently stronger solid–gas interactions.

De Magnete et Meteorite: Cosmically Motivated Materials

Meteorites, likely the oldest source of magnetic material known to mankind, are attracting renewed interest in the science and engineering community. Worldwide focus is on tetrataenite, a uniaxial ferromagnetic compound with the tetragonal L1 0 crystal structure comprised of nominally equiatomic Fe-Ni that is found naturally in meteorites subjected to extraordinarily slow cooling rates, as low as 0.3 K per million years. Here, the favorable permanent magnetic properties of bulk tetrataenite derived from the meteorite NWA 6259 are quantified. The measured magnetization approaches that of Nd-Fe-B (1.42 T) and is coupled with substantial anisotropy (1.0-1.3 MJ/m 3) that implies the prospect for realization of technologically useful coercivity. A highly robust temperature dependence of the technical magnetic properties at an elevated temperature (20-200 °C) is confirmed, with a measured temperature coefficient of coercivity of -0.005%/K, over one hundred times smaller than that of Nd-Fe-B in the same temperature range. These results quantify the extrinsic magnetic behavior of chemically ordered tetrataenite and are technologically and industrially significant in the current context of global supply chain limitations of rare-earth metals required for present-day high-performance permanent magnets that enable operation of a myriad of advanced devices and machines.

Intrinsic magnetic properties of L10 FeNi obtained from meteorite NWA 6259

FeNi having the tetragonal L10 crystal structure is a promising new rare-earth-free permanent magnet material. Laboratory synthesis is challenging, however, tetragonal L10 FeNi—the mineral “tetrataenite”—has been characterized using specimens found in nickel-iron meteorites. Most notably, the meteorite NWA 6259 recovered from Northwest Africa is 95 vol. % tetrataenite with a composition of 43 at. % Ni. Hysteresis loops were measured as a function of sample orientation on a specimen cut from NWA 6259 in order to rigorously deduce the intrinsic hard magnetic properties of its L10 phase. Electron backscatter diffraction showed that NWA 6259 is strongly textured, containing L10 grains oriented along any one of the three equivalent cubic directions of the parent fcc structure. The magnetic structure was modeled as a superposition of the three orthonormal uniaxial variants. By simultaneously fitting first-quadrant magnetization data for 13 different orientations of the sample with respect to the applied field d...

Ultimate H2 and CH4 adsorption in slit-like carbon nanopores at 298 K: a molecular dynamics study

Hydrogen and methane adsorption is studied on a range of nanoscale carbon slit pores up to 1000 bar at 298 K using molecular dynamics. Past about 200 bar, the calculated adsorbed hydrogen density increases as a function of pressure at the same rate as the highly compressed bulk liquid and thus no saturation plateau is predicted under these conditions. This behaviour implies a continuous increase of the adsorbed hydrogen density past the normal boiling point value and explains high pressure experimental hydrogen adsorption data at 298 K on porous carbons, such as AX-21 activated carbon. This result is put into perspective by comparing with the adsorbed hydrogen phase measured at 50 K on AX-21, which exhibits an ideal incompressible liquid behaviour and a maximum density of only 0.06 g mL−1. These findings therefore suggest the existence of two distinct temperature dependent saturation regimes, most likely of quantum origin. The volumetric capacities show that the adsorbents provide no gains over compression past 600 bar at about 0.04 g mL−1. Conversely, gravimetric capacities inferior to 0.03 g g−1 found below 200 bar indicate large mass penalties when significant gains over compression are achieved. The calculated adsorbed methane density reaches at about 50 bar a true saturation plateau comparable to the pressurized bulk liquid at lower temperatures. Large volumetric and gravimetric capacities of about 365 v v−1 and 0.21 g g−1, respectively, are found in these conditions. These results therefore indicate an interesting 10 fold improvement over compression and a small mass penalty for methane adsorbed on well compacted engineered materials.