We have studied structural change and lattice strain formation during absorption and desorption of hydrogen (deuterium) by high purity LaNi5-x Snx alloys (x = 0.22, 0.25) using in situ X-ray and neutron diffraction along with simultaneously measuring the P-C isotherms. From profile analysis of the X-ray diffraction data, lattice parameter and lattice strain in each hydriding state are evaluated. In situ neutron diffraction data provided hydrogen occupation changing with hydrogen content. Significant lattice contract and strain formation were observed in the hydride phase in desorption. This behavior was related with decrease in hydrogen occupation in the hydride phase revealed from the neutron diffraction data.

Hydrogen adsorption has been observed with a binding energy of ∼ 50 kJ /mol on as-synthesized carbon multi-wall nanotubes (MWNTs). The MWNTs are virtually free of non-nanotube carbon impurities but contain residual iron catalyst particles. The MWNTs are also highly graphitic. No hydrogen adsorption is observed at near ambient temperatures for purified MWNTs that are free of iron particles. However, hydrogen adsorption is also not observed on bare iron particles even following reduction in the presence of hydrogen at 775 K. These results imply that a special synergy occurs when small iron particles or atoms are in intimate contact with sp2-hybridized aromatic carbon. Interestingly, reducing the as-synthesized MWNTs in H2 at 573 K results in an increased hydrogen capacity. Understanding this hydrogen storage mechanism could facilitate the economical engineering of a hydrogen storage material that meets the United States Department of Energy targets for vehicular fuel cell applications. Recent theoretical studies have shown that an iron ad atom forms a complex with a C36 fullerene and shares charge with four carbon atoms of a bent five-membered ring. Three H2 ligands then coordinate with the iron forming a stable 18-electron organometallic complex. Here the binding energy of the molecular hydrogen ligands is ∼43 kJ /mol. These theoretical results could possibly explain the unique hydrogen storage properties of MWNTs that are grown with an iron catalyst.

Sodium alanate was milled with and without TiCl3. The hydrogen release and uptake was measured during temperature-programmed absorption and desorption, as well as by isothermal charging and discharging, using a Sieverts' type apparatus. These data were supplemented by in-situ X-ray diffraction studies of hydrogen desorption. Rate constants derived from XRD were slower than those derived from volumetric H2 measurements. Al formation observed in XRD exceeded that expected from the observed decomposition of NaAlH4 and Na3AlH6.

We report on non-particulate titania photoelectrodes with a unique highly-ordered nanotube-array architecture prepared by an anodization process that enables precise control over array dimensions. Under 320–400 nm illumination titania nanotube-array photoanodes, pore size 110 nm, wall thickness 20 nm, and 6 μm length, generate hydrogen by water photoelectrolysis at a normalized rate of 80 mL/W•hr, to date the most efficient titania-based photoelectrochemical device, with a conversion efficiency of 12.25%. The highly-ordered nanotubular architecture allows for superior charge separation and charge transport, with a calculated quantum efficiency of nearly 100% for incident photons with energies larger than the titania bandgap.

Multiwalled carbon nanotubes (MWNTs) were continuously synthesized by hot wire chemical vapor deposition (HWCVD) using a methane source catalyzed by metal-organic ferrocene. The microstructure of the MWNTs and the catalyst particles were subsequently characterized with transmission electron microscopy which identified three different phases, i.e., bcc α-Fe, fcc γ-Fe and orthorhombic Fe3C. The hydrogen storage capacity of MWNTs was determined with temperature-programmed desorption (TPD) technique. Hydrogen adsorption at near ambient conditions was observed only in as-synthesized MWNTs containing iron particles and was dramatically increased after hydrogen reducing treatment. Possible adsorption mechanism was also discussed.

The development of light weight hydrogen storage systems with high volumetric and gravimetric hydrogen densities is indeed essential for the on-board fuel cell vehicular applications. Titanium doped NaAlH4 is right now considered as the potential hydrogen storage system, which satisfies the said criteria. The dehydrogenation of NaAlH4 consists of two consecutive steps of decomposition at 220 and 250° C with the total hydrogen release of 5.6 wt.%. However, doping a few mole concentrations of selected transition metal complexes to the host hydride reduces significantly the decomposition temperatures to 100 and 185° C (equilibrium H2 pressure ∼1 MPa) respectively. This breakthrough has been followed by a great deal of effort to develop NaAlH4 as a practical hydrogen storage material. For an ideal hydrogen storage material, the dehydrogenation kinetics and the cycling stability are important properties to be evaluated. Keeping these points to ponder, we have studied the dehydriding kinetics of the Ti-doped NaAlH4 over a number of dehydrogenation and rehydrogenation cycles. Besides, the Ti-doped NaAlH4 has been prepared from the hydrogenation of NaH and Al using the solvent mediated milling method. Comparing the initial and final cycling stages of Ti doped (NaH + Al), the synchrotron powder x-ray diffraction profiles exhibit, a growing resistance to the hydrogenation of Na3AlH6 to NaAlH4.

Electrospun PAN nanofibers were carbonized with or without iron(III) acetylacetonate to induce catalytic graphitization within the range of 900–1500°C, resulting in ultrafine carbon fibers with the diameter of about 90–300 nm. The structural properties and morphologies of the resulting carbon nanofibers were investigated using XRD, Raman IR, SEM, TEM, and surface area/pore analysis. The PAN-based carbon nanofibers carbonized without a catalyst had amorphous structures, with d002 = 0.37 nm, and smooth surfaces with very low surface areas of 22–31 m2/g. The carbonization of PAN-based nanofibers in the presence of the catalyst produced the graphite nanofibers (GNF) with d002 = 0.341 nm, indicating turbostrate structures. The graphite structures were grown by increasing the catalyst contents and the carbonization temperature. The hydrogen storage capacities of the aforementioned carbon nanofiber materials were evaluated through the gravimetric method using Magnetic Suspension Balance (MSB) at room temperature and at 100 bars. The storage data were obtained after the buoyancy correction. The CNFs showed hydrogen storage capacities of 0.16–0.50 wt.%, increasing with the increase of carbonization temperature, but that of the CNF at 1500°C was lowest. The hydrogen storage capacities of the GNFs with low surface areas of 100–250m2/g were 0.14–1.01 wt%.

MgH2 was mechanically milled with nano-Ni (nano-Ni/Al2O3/C) and Ni catalysts (Ni), yielding Mg-based nano-composite materials. X-ray and TEM measurements revealed that nano-Ni particles, which are 6–20 nm size, were dispersed in the MgH2 matrix. The nano-composite material with nano-Ni/Al2O3/C showed excellent properties as compared to that with Ni, a ball-milled MgH2 and the mixture of MgH2 and nano-Ni/Al2O3/C in terms of the H2 desorption and absorption. The nano-composite material with nano-Ni/Al2O3/C desorbed H2 of 4.9–5.8 wt% at 423–473 K, while the mixture could not desorb H2 at the temperature. The H2 absorption capacity at 9 MPa and room temperature in 6 hr. increased from below 0.1 wt% for the mixture to 5.0 wt % for the nano-composite material, approaching a maximum of 6.5 wt% in 70 hr. The catalyst activity was improved with decreasing Ni size. The improved kinetics is indicated by the small activation barrier, the short diffusion path length and the high driving force.

Ti K -edge x-ray absorption spectroscopy was used to explore the local titanium environment and valence in 2–4 mol% Ti-doped sodium alanate. An estimate of the oxidation state of the dopant, based upon known standards, revealed a zero-valent titanium atom. An analysis of the near-edge and extended fine structures indicates that the Ti does not enter substitutional or interstitial sites in the NaAlH4 lattice. Rather, the Ti is located on/near the surface and is coordinated by 10.2±1 aluminum atoms with an interatomic distance of 2.82±0.01 Å, similar to that of TiAl3. The Fourier transformed EXAFS spectra reveal a lack of long-range order around the Ti dopant indicating that the Ti forms nano-clusters of TiAl3. The similarity of the spectra in the hydrided and dehydrided samples suggests that the local Ti environment is nearly invariant during hydrogen cycling.

We propose that generalized Kubas complexes of molecular hydrogen with light metal elements, such as B and Be embedded in carbon nanostructures, or related Be and B materials, could offer breakthrough performance in room temperature hydrogen storage. First-principles local-density functional calculations show that hydrogen bound to these materials are intact, in similarity to physisorbed H2, but with a greatly enhanced adsorption energy in the range of 0.2–0.7 eV. The metal-H2 binding is attributed to the Coulombic interaction between holes created at the metal sites and Σ electrons of the H2. Management of the hole density and electron-hole orbital overlap thus enables us to control the binding strength of H2 for optimal storage properties.

In this paper systematic approach to study the structural stability of the complex hydride, LiBH4 is presented. The ground state energies of various symmetry structures are determined by means of Density Functional Theory. Simulated annealing method is used to confirm if ground state structures represent real energy minima. The vibrational spectrum and temperature dependence of the free energy of the structures with the lowest energies is determined. Calculated Raman active modes for three symmetries are presented. We show that at high temperatures LiBH4 possesses monoclinic symmetry and some of the low energy structures are unstable with respect to atomic vibrations. Our studies point to the necessity of calculation of the phonon spectra for complex metal hydrides that contain covalently bounded hydrogen.

Electrodes which are resistant to chemical poisoning by CO, S, and other fuel impurities are needed to replace Pt in proton exchange membrane (PEM) fuel cells. We have designed composite electrodes comprised of single walled carbon nanotubes (CNTs) within a conducting polymer matrix. A method for solubilizing single-walled carbon nanotubes (CNTs) in aqueous media using polyelectrolyte layer-by-layer (LbL) nanoassembly of polystyrene sulfonate (PSS) and polyallylamine (PAH) at the CNT surface is elucidated. Once soluble, the CNTs were assembled onto planar substrates using alternate LbL nanoassembly to form nanocomposite films. These films will later be tested for their potential as alternative anodes in proton exchange membrane fuel cells.

The local bonding environment of Ti3+-dopant atoms in NaAlH4 after decomposition to release H2 has been studied using x-ray absorption fine structure (XAFS). The titanium K-edge spectra from doped hydride samples and the standard materials TiCl3 and TiO2 were collected in ambient atmosphere at the synchrotron source at the Center for Advanced Microstructures and Devices (CAMD). Titanium valence states present in the spectra collected from Ti-doped NaAlH4 after decomposition in air are Ti3+ and Ti4+. The Ti3+ is attributed to unreacted TiCl3. The Ti4+ present in the sample is attributed to TiO2 occurring after air oxidation. Coupled with studies of the kinetics of hydrogen desorption reactions, examination of dopant ion valence states after entry into the lattice may lead to better understanding of the interrelationship between lattice doping and desorption kinetics.

First principles calculations based on gradient corrected density functional theory are carried out to understand the electronic structure and mechanisms responsible for desorption of hydrogen from Ti doped and vacancy containing sodium-alanate (NaAlH4). The energy necessary to remove a hydrogen atom from Ti doped NaAlH4 is significantly smaller than that from pristine NaAlH4 irrespective of whether Ti substitutes the Na or the Al site. However, the presence of Na and Al vacancies is shown to play an even more important role: The removal of hydrogen associated with both Na and Al vacancies is found to be exothermic. It is suggested that this role of vacancies can be exploited in the design and synthesis of complex light metal hydrides suitable for hydrogen storage.

Poly(vinylidene fluoride) (PVdF) fine fiber of 200–300 nm in diameter was prepared through the electrospinning process. Dehydrofluorination of PVdF-based fibers for making infusible fiber was carried out using DBU, and the infusible PVdF-based nanofibers were then carbonized at 900–1800°C. The structural properties and morphologies of the resulting carbon nanofibers were investigated using XRD, Raman IR, SEM, TEM, and surface area & pore analysis. The PVdF-based carbon nanofibers had rough surfaces composed of 20-to 30-nm granular carbons, indicating their high surface area in the range of 400–970 m2/g. They showed amorphous structures. In the case of the highly ehydrofluorinated PVdF fiber, the resulting carbon fiber had a smoother surface, with d002 = 0.34–0.36 nm, and a very low surface area of 16–33 m2/g. The hydrogen storage capacities of the above carbon nano-fibers were measured, using the gravimetric method, by magnetic suspension balance (MSB), at room temperature and at 100 bars. The storage data were obtained after the buoyancy correction. The PVdF-based microporous carbon nanofibers showed a hydrogen storage capacity of 0.04–0.4 wt%. The hydrogen storage capacity depended on the dehydrofluorination of the PVdF nanofiber precursor, and on the carbonization temperatures.

Hydrogen absorption and desorption isotherms have been measured on ballmilled mixtures of LiH+Si powders to evaluate the thermodynamic parameters of these reversible reactions. The phase compositions at the various stages of reaction have been examined by Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR) of the 7Li, 1H, and 29Si nuclei and powder x-ray diffraction (XRD). The initial mixtures of LiH and Si were found to convert into known Li-Si silicide intermetallics (i.e., Li12Si7, Li7Si3, and Li13Si4) as well as providing evidence for a previously unknown ternary Li-Si-H phase as hydrogen was first desorbed and then absorbed. While the absorption reactions are reversible over portions of the Li-Si-H composition range, incomplete recovery of the original LiH + Si phases was also observed under some test conditions.

The hydrogen storage properties of nanostructured Mg and MgH2 thin films were studied as created by Ar and Ar+H2 plasma sputter deposition. Columnar structures with typical widths of ∼120 nm are observed with their long columnar axis extending throughout the thickness of the films. Applying substrate bias voltages during deposition results in narrower columns. A concomitant reduction in hydrogen desorption temperature from 400 °C to 360 °C is observed. Capping the Mg films with a ∼100 nm thin Pd layer leads to significantly reduced hydrogen desorption temperatures of ∼200 °C induced by the catalytic activity of the Pd cap layer. Also, hydrogen permeation of the films is strongly improved. The rate-determining factor is found to be the dissociation of the hydrogen molecules. Optimum hydrogen loading conditions of the Pd/Mg films were obtained just above ∼200 °C at hydrogen pressures of 0.25–1.0 MPa, resulting in hydrogen storage capacities in the range of 4–7 wt%.

In order to explore rational designs and synthetic strategies toward efficient hydrogen storage materials, quantum mechanical calculations and grand canonical Monte Carlo simulations have been carried out on a series of the Metal-Organic Frameworks containing various organic linkers. The calculations for specific surface areas and the shape of frontier orbitals for various frameworks indicate that the hydrogen storage capacity is largely dependent on the effective surface area of the material, rather than the free volume. Based on the iso-electrostatic potential surface from density functional calculations and the theoretical amount of adsorbed hydrogen from the grand canonical Monte Carlo calculations, it was also found that the electron localization around the organic linker plays an important role in the hydrogen storage capacity of Metal-Organic Frameworks. The prediction of the modeling study is supported by the hydrogen adsorption experiments with IRMOF-1 and -3, revealing the more enhanced hydrogen storage capacity of IRMOF-3 compared with that of IRMOF-1 at 77 K and H2 1 atm.

Self-assembled sheets of single wall carbon nanotubes (SWNTs) were used as the working electrode for electrochemical hydrogen adsorption/storage in a three-electrode cell in 6M aqueous KOH or HNO3 solution. Hydrogen adsorption studies on pristine SWNTs, as well as SWNTs functionalized with electrodeposited nanoparticles of magnesium (Mg) and cobalt (Co), have been performed. The adsorbed hydrogen (uncorrected for possible water uptake via nanocapillarity) was measured to be 2.5 weight percent by thermogravimetric analysis (TGA) on a Mg-functionalized sample and 3.2 weight percent by Prompt-Gamma Activation Analysis (PGAA) for a pristine sample charged for 20 hrs. Weight loss occurs in the 105° to 125°C temperature range for both sample types. Hydrogen in Co-functionalized SWNTs and 6M HNO3 electrolyte appears to be strongly chemisorbed as indicated by the appearance of a C-H stretching line in the Fourier-transform infrared spectrum (FTIR) and absence of a desorption peak in the TGA data in the 25° to 600°C temperature range. Thermopower measurements scale with the TGA data and suggest that hydrogen uptake is associated with partial charge transfer. Ex-situ Raman spectroscopy shows a reproducible downshift of the SWNT tangential stretching mode consistent with charge transfer or chemisorption on electrochemical charging, and a substantial decrease under some conditions in resonance-enhanced intensity with increasing charging time. A SWNT sheet electrochemically coated with the conducting polymer polyaniline and then charged in 6M KOH shows possible hydrogen uptake of 1.5 weight % that desorbs at 70°C.

Kinetics of the lithium amide (LiNH2) decomposition reaction 2 LiNH2 → Li2NH + NH3 were determined using thermogravimetric analysis (TGA). LiNH2 is a primary component of the hydrided state of Li3N- and Li2NH-based storage materials. Its decomposition by ammonia release, and the resulting degradation of hydrogen storage capacity, has important implications for the durability of Li-N-H storage systems. Fine powders of LiNH2 were prepared by ball milling for 20 min. Kinetic parameters were extracted from a set of TGA weight loss curves taken at different heating rates between 1 and 20°C/min, and the activation energy Ea was determined to be 124 kJ/mole. Although decomposition occurs slowly below 300°C, isothermal TGA measurements on Li3N demonstrate that its cumulative effect is large in real Li-N-H systems, where LiNH2-containing hydrided material is held at elevated temperature under dynamic gas flow.