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

Synergistic ultraviolet and visible light photo-activation enables intensified low-temperature methanol synthesis over copper/zinc oxide/alumina

Although photoexcitation has been employed to unlock the low-temperature equilibrium regimes of thermal catalysis, mechanism underlining potential interplay between electron excitations and surface chemical processes remains elusive. Here, we report an associative zinc oxide band-gap excitation and copper plasmonic excitation that can cooperatively promote methanol-production at the copper-zinc oxide interfacial perimeter of copper/zinc oxide/alumina (CZA) catalyst. Conversely, selective excitation of individual components only leads to the promotion of carbon monoxide production. Accompanied by the variation in surface copper oxidation state and local electronic structure of zinc, electrons originating from the zinc oxide excitation and copper plasmonic excitation serve to activate surface adsorbates, catalysing key elementary processes (namely formate conversion and hydrogen molecule activation), thus providing one explanation for the observed photothermal activity. These observations give valuable insights into the key elementary processes occurring on the surface of the CZA catalyst under light-heat dual activation

Metal hydrides for concentrating solar thermal power energy storage

The development of alternative methods for thermal energy storage is important for improving the efficiency and decreasing the cost for Concentrating Solar-thermal Power (CSP). We focus on the underlying technology that allows metal hydrides to function as Thermal Energy Storage (TES) systems and highlight the current state-of-the-art materials that can operate at temperatures as low as room-temperature and as high as 1100 oC. The potential of metal hydrides for thermal storage is explored while current knowledge gaps about hydride properties, such as hydride thermodynamics, intrinsic kinetics and cyclic stability, are identified. The engineering challenges associated with utilising metal hydrides for high-temperature thermal energy storage are also addressed

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

Ni coated LiH nanoparticles for reversible hydrogen storage

Lithium is a material of choice for batteries, but it has also the potential to store energy with high density as a hydrogen storage material, i.e. via the formation of its hydride (LiH). However, the high thermodynamic stability of LiH has so far precluded the use of lithium as an effective hydrogen storage material owing the high temperature 700 °C for hydrogen release. Herein, we report on a novel method to enable the reversible storage of hydrogen with lithium under mild conditions of pressure (6 MPa) and temperature (350 °C). Through the catalytic hydrogenation of lithium, LiH particles were restricted to a few nanometres (<4 nm). Further coating with nickel chloride enabled the formation of a Ni shell at the surface of the LiH nanoparticles leading to their effective stabilization for hydrogen release and uptake with fast kinetics - full hydrogen release/uptake was achieved in less than 50 min at 350 °C. This demonstrates that the properties of LiH are particle size dependent and thus offers new avenues to achieve high energy storage lithium based devices. Copyright © 2016, Hydrogen Energy Publications, LLC

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

Nanoconfined lithium aluminium hydride (LiAlH4) and hydrogen reversibility

Lithium aluminium hydride (LiAlH4) is a promising hydrogen storage material with a storage capacity of 10.6 mass % H2. However, its practical use is hampered by the lack of direct rehydrogenation routes. In this study, we report on the confinement of LiAlH4into the nanoporosity of a high surface area graphite resulting in a remarkable improvement of its hydrogen storage properties. Nanoconfined LiAlH4started hydrogen desorption near 135 °C and after full dehydrogenation at 300 °C limited rehydrogenation was observed at the same temperature and 7 MPa of hydrogen pressure. Rehydrogenation took place through the formation of Li3AlH6with some limited rehydrogenation back to LiAlH4indicating the existence of different (de)hydrogenation paths upon nanoconfinement as compared to the known dehydrogenation path of bulk LiAlH4

Formation of aluminium hydride (AlH3) via the decomposition of organoaluminium and hydrogen storage properties

© 2017 Hydrogen Energy Publications LLC. Aluminium hydride (AlH3) is a promising hydrogen storage material due to its competitive hydrogen storage density and moderate decomposition temperature. However, there is no convenient way to prepare/regenerate AlH3from (spent) Al by direct hydrogenation. Herein, we report on a novel approach to generate AlH3from the decomposition of triethylaluminium (Et3Al) under mild hydrogen pressures (10 MPa) with the use of surfactants. With tetraoctylammonium bromide (TOAB), the synthesis led to the formation of nanosized AlH3with the known a phase, and these nanoparticles released hydrogen from 40 °C instead of the 125 °C observed with bulk a-AlH3. However, when tetrabutylammonium bromide (TBAB) was used instead of TOAB, larger nanoparticles believed to be related to the formation of ß-AlH3were obtained, and these decomposed through a single exothermic process. Despite the possibility to form a-AlH3under low conditions of temperature (180 °C) and pressure (10 MPa), TOAB stabilised AlH3was found to be irreversible when subjected to hydrogen cycling at 150 °C and 7 MPa hydrogen pressure