Real Space Observations of Magnesium Hydride Formation and Decomposition

The mechanisms of magnesium hydride formation and thermal decomposition are directly examined using in-situ imaging.Comment: 3 pages, 4 figure

Surface and Particle-Size Effects on Hydrogen Desorption from Catalyst-Doped MgH2

With their high capacity, light-metal hydrides like MgH2 remain under scrutiny as reversible H-storage materials, especially to develop control of H-desorption properties by decreasing size (ball-milling) and/or adding catalysts. By employing density functional theory and simulated annealing, we study initial H2 desorption from semi-infinite stepped rutile (110) surface and Mg31H62 nanoclusters, with(out) transition-metal catalyst dopants (Ti or Fe). While Mg31H62structures are disordered (amorphous), the semi-infinite surfaces and nanoclusters have similar single, double, and triple H-to-metal bond configurations that yield similar H-desorption energies. Hence, there is no size effect on desorption energetics with reduction in sample size, but dopants do reduce the H-desorption energy. All desorption energies are endothermic, in contrast to a recent report

Stabilization of Nanosized Borohydrides for Hydrogen Storage: Suppressing the Melting with TiCl 3 Doping

Lightweight complex hydrides, M(BH4)n (M = Li, Na, Mg, and Ca; n = 1 for Li and Na, n = 2 for Mg and Ca), are believed to be promising hydrogen storage materials with extreme high hydrogen density up to 18.5 mass %. However, these materials suffer high dehydrogenation temperature, melting, and reversibility problems, which exclude them from the list of practical hydrogen storage systems. Herein, borohydrides (M(BH4)n-Ti, with M = M1 or M2 and n = 1 or 2), were modified with TiCl3 via a wet chemistry approach, and in some cases this led to the formation of solvent-stabilized nanoparticles. As a result of TiCl3 modification, the melting before hydrogen release was suppressed as evidenced by DSC and thermal microscopy observations. Furthermore, the hydrogen release temperature of M(BH4)n-Ti was significantly reduced. For example, the dehydrogenation temperature of NaBH4-Ti was reduced from 570 to 120 °C. Ti modification was also found to improve to some extent the reversibility of the doped materials. In particular, up to 2 mass% H2 was reversibly cycled for Ca(BH4)2-Ti at 300 °C and 9 MPa H2 pressure, in comparison to 400 °C and 70 MPa for pristine Ca(BH4)2. This study demonstrates a simple method to synthesize surfactant-free Ti-doped nanosized borohydrides, and by removing the melting of these materials, it provides a new path toward the stabilization of borohydride particles at the nanoscale

CO oxidation and the inhibition effects of carboxyl-modification and copper-clusters on multi-walled carbon nanotubes

An inhibition of CO oxidation on catalytically active pristine multi-walled carbon nanotubes (MWCNT) in the presence of selected pollutant constituents in flue gas streams was studied. We simulated an interaction between the active MWCNT and the contaminants in an O₂-rich CO oxidation atmosphere of: (i) an acidic wet flue gas environment modelled by using MWCNT grafted with carboxyl (–COOH) groups; and (ii) a polluted environment formed by trace metal copper particles and other contaminant constituents such as polycyclic aromatic hydrocarbons (PAH), volatile organic compounds (VOC), and phosphorous (P), by using a 2 copper cluster as a model pollutant. The model copper pollutant was in the form of a copper cluster species of chemical formulae [(PPh3)CuH]6·0.75THF, and its simulated modification of the active MWCNT was modelled by using MWCNT doped with these cluster species. In the case of pristine, unmodified MWCNT exposed to reaction gas mixture, MWCNT were catalytically active from ~150 °C, achieving close to complete CO oxidation from approximately 230 °C. In an acidic environment where the MWCNT’s surface was modified with –COOH groups, the material behaved as an adsorbent of CO molecules without converting them into CO₂ in the presence of O₂. Low concentrations of dispersed Cu particles by themselves (not in the form of copper cluster species) doped on the carboxyl-modified MWCNT prepared by conventional method demonstrated activity in the CO oxidation. In the case of copper cluster species pollutant, the model copper cluster was found to have formed CuCO₃ during the CO oxidation reaction at temperatures below 330 °C but decomposed above 400 °C to release CO₂ product

Carbon nanostructures/Mg hybrid materials for hydrogen storage

For achieving an economy based on renewable energy sources, effective solutions toward energy storage remain the main challenge. To date, there is no efficient systems to store electricity in large amounts. A promising solution is to accumulate energy in the form of hydrogen, which can then be conveniently stored and transported. However, compared to the volumetric energy density of fossil fuels, current technologies relying on hydrogen compression or liquefaction have major disadvantages, including low energy density and safety issues. The use of light materials forming hydrides could provide an alternative way to stock hydrogen with high volumetric energy densities. Herein, we present recent developments in the research for magnesium/graphene hybrid materials and their hydrogen-storage properties

Ultrahigh hydrogen storage using metal-decorated defected biphenylene

Hydrogen (H2) energy has emerged as a principal contender for renewable green energy applications because of the ultra-high energy density and natural abundance. The implementation of this prospective technology necessitates the ultra-high capacity of H2 storage mediums. This work reports the exceptional H2 storage capacities of two-dimensional (2D) carbon allotrope biphenylene (BPL) functionalized by Li, Na, K, and Ca. The combined theoretical approaches including the density functional theory (DFT), ab-initio molecular dynamics (AIMD), maximally localized Wannier functions (MLWFs), and thermodynamic analysis were employed to elucidate the storage efficiencies at operationally practical conditions. The findings reveal that pristine BPL decorated by the selected metals are all inefficient for H2 storage because of the sensitive crystal instability caused by the energetic aggregation of the metallic dopants. On the other hand, point-defected BPL resolves this issue because it adequately magnifies the binding energies with all the decorated metals via the highly ionic bonds. Crucially, these binding energies exceed the cohesive counterparts of the parental metal bulks, consequently stabilizing the crystal integrity. Intriguingly, the Li- and Na-decorated divacancy BPL retain the ultimate H2 storage capacities of 6.76 wt% and 6.66 wt% at the practical temperature and pressure, respectively, surpassing the goal value of 5.50 wt% to be achieved by 2025. Hence, metal-functionalized BPL are conclusively the promising carbon materials for the H2 storage functionality