Final Report: DE- FC36-05GO15063, Fundamental Studies of Advanced High-Capacity, Reversible Metal Hydrides
- Univ. of Hawaii, Honolulu, HI (United States)
- Univ. of New Brunswick, Fredericton NB (Canada)
The project was component of the US DOE, Metal Hydride Center of Excellence (MHCoE). The Sandia National Laboratory led center was established to conduct highly collaborative and multi-disciplinary applied R&D to develop new reversible hydrogen storage materials that meet or exceed DOE/FreedomCAR 2010 and 2015 system targets for hydrogen storage materials. Our approach entailed a wide variety of activities ranging from synthesis, characterization, and evaluation of new candidate hydrogen storage materials; screening of catalysts for high capacity materials requiring kinetics enhancement; development of low temperature methods for nano-confinement of hydrides and determining its effects on the kinetics and thermodynamics of hydrides; and development of novel processes for the direct re-hydrogenation of materials. These efforts have resulted in several advancements the development of hydrogen storage materials. We have greatly extended the fundamental knowledge about the highly promising hydrogen storage carrier, alane (AlH3), by carrying out the first crystal structure determinations and the first determination of the heats of dehydrogenation of β–AlH3 and γ-AlD3. A low-temperature homogenous organometallic approach to incorporation of Al and Mg based hydrides into carbon aerogels has been developed that that allows high loadings without degradation of the nano-porous scaffold. Nano-confinement was found to significantly improve the dehydrogenation kinetics but not effect the enthalpy of dehydrogenation. We conceived, characterized, and synthesized a novel class of potential hydrogen storage materials, bimetallic borohydrides. These novel compounds were found to have many favorable properties including release of significant amounts of hydrogen at moderate temperatures (75-190 º C). However, in situ IR studies in tandem with thermal gravimetric analysis have shown that about 0.5 equivalents of diborane are released during the dehydrogenation making re-hydrogenation effectively impossible and precluding these compounds from further consideration as hydrogen storage materials. The hydrogen cycling of >11 wt % between MgB2 to Mg(BH4)2 was achieved but required very forcing conditions. Under moderate conditions (dehydrogenation 200°C; re-hydrogenation 250°C, 120 atm H2), Mg(BH4)2 undergoes reversible dehydrogenation to Mg(B3H8)2. Although the 2.5 wt% cycling capacity does not meet current on-board storage targets, this result provides first example of direct hydrogen cycling of a borohydride under moderate conditions and demonstrates the plausibility of finding mild, PEM fuel cell relevant conditions for the high capacity, reversible dehydrogenation of borohydrides. A method was developed for the room temperature, direct hydrogenation of Ti-doped LiH/Al in liquefied dimethyl ether under 100 atm of H2. The process has been optimized such that Ti-doped LiAlH4 is obtained in >95% yield. The WTT energy efficiency our direct synthesis process has been estimated to approach the 60% U.S. DOE target. Thus our simplification of the hydrogenation half-cycle may provide the key to harnessing the long-recognized potential of this lightweight, high capacity material as a practical hydrogen carrier. Finally, we have gained insight into the fundamental basis of the enhanced hydrogen cycling kinetics of Ti-doped NaAlH4 through studies by solid state 1H NMR, anelastic spectroscopy; muon spin rotation; and positron annihilation.
- Research Organization:
- Univ. of Hawaii, Honolulu, HI (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Fuel Cell Technologies Office (EE-3V)
- DOE Contract Number:
- FC36-05GO15063
- OSTI ID:
- 1169445
- Report Number(s):
- DE-FC36-05GO15063
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
77 NANOSCIENCE AND NANOTECHNOLOGY
Hydrogen
borohydride
alanates
alane
borane
lithium
aluminum
boron
magnesium
sodium
titanium
bimetallic
direct hydrogenation
hydrogen storage
reversible
catalysts
kinetics
nano-confinement
hydrides
organometallic
carbon aerogels
in situ
infra red
diborane
triborane
dimethyl ether
lightweight
high capacity
NMR
anelastic spectroscopy
muon spin rotation
positron annihilation