Hydrogen absorption kinetics of the transition-metal-chloride-enhanced NaAlH4 system
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This study elucidates the role of transition metal (TM) additives in enhancing hydrogen (H) reversibility and hydrogenation kinetics for the NaAlH4 system. The isothermal hydrogen absorption kinetics of the planetary milled (PM) NaAlH4 + xTMCln (TM row 1 = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu; row 2 = Zn, Y, Zr, Nb, Mo, Ru, Rh Pd; row 3 = Pt; 2 < n < 5) and cryo-milled (CM) NaAlH4 + xTMCln (TM row 1 = Ti, V, Cr, Fe, Co, Ni, Cu; 2 < n < 3) systems have been measured at 140 °C and 150 bar system pressure. The variation in hydrogenation kinetics across the TM series for NaAlH4 + xTMCln is strongly dependent on the TM species and additive level, milling technique, and the type, structure, and morphological arrangement of nanoscopic Al1−xTMx phases that are embedded on the NaAlH4 surface. In the most interesting case, the surface-embedded Al1−xTix phases in the TiCl3-enhanced NaAlH4 system perform a dual catalytic function, where the outer Al1−xTix surface performs dissociation/recombination of molecular H2 and the inner Al1−xTix surface allows the distortion of a minor number of Al−H bonds from AlH4 − tetrahedra in the vicinity of the subsurface Al1−xTix/NaAlH4 interface. The density of Ti atoms in the subsurface interface (which is Al:Ti composition- and H cycling temperature-dependent) shows the strongest effects on hydrogenation kinetics.
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Hydrogen absorption kinetics and structural features of NaA1H4 enhanced with transition meal-and Ti-based nanoparticlesPitt, M.; Vullum, P.; Sorby, M.; Emerich, H.; Paskevicius, Mark; Webb, C.; Gray, E.; Buckley, Craig; Walmsley, J.; Holmestad, R.; Hauback, B. (2012)The hydrogen cycled (H) planetary milled (PM) NaAlH4 + xM (x < 0.1) system (M = 30 nm Ag, 80 nm Al, 2–3 nm C, 30 nm Cr, 25 nm Fe, 30 nm Ni, 25 nm Pd, 65 nm Ti) has been studied by high resolution synchrotron powder X-ray ...
Pitt, M; Vullum, P; Sorby, M; Emerich, H; Paskevicius, Mark; Buckley, Craig; Gray, E; Walmsley, J; Holmestad, R; Hauback, B (2012)The hydrogen (H) cycled planetary milled (PM) NaAlH4 + 0.02TiCl3 system has been studied by high resolution synchrotron X-ray diffraction and transmission electron microscopy during the first 10 H cycles. After the first ...
Functionality of the nanoscopic crystalline Al/amorphous Al50Ti50 surface embedded composite observed in the NaAlH4 + xTiCl3 system after millingPitt, M.; Vullum, P.; Sørby, M.; Sulic, M.; Emerich, H.; Paskevicius, Mark; Buckley, Craig; Walmsley, J.; Holmestad, R.; Hauback, B. (2012)The NaAlH4 + xTiCl3 (x < 0.1) system has been studied by a combination of X-ray synchrotron and neutron diffraction, and isotopic H2/D2 scrambling after the completion of the milling process, and the first thermal release ...