C. Metal Hydrides
1. Storage Materials
Goals: Storage/Release Temperature (< 90°C), Weight Density (> 6 wt%), Cost, Reversibility, On-Board Regeneration
a) Light-metal hydrides
Description: Use combinatorial analysis to identify promising compounds.
i. Alanates
Description: Alanates generally regenerate at medium temperatures.
a. Sodium alanate (NaAlH4)
b. Other alanates (e.g., LiAlH4)
ii. Other compound hydrides
a. Magnesium hydrides (e.g., Mg2NiH4)
Description: Magnesium hydrides require high temperature for regeneration.
b. Transitional-metal-based compounds
b) Metal nitrides and imides
i. Lithium nitride
c) Novel materials
d) Synthetic metals
Description: Polymer-dispersed metal hydrides (“synthetic metals”) such as polyaniline and polypyrrole have achieved densities of 8 wt% (reported) by incorporating a low-density polymer. The polymer interacts with the metal hydride on a molecular level and also stores H2 within the polymer structure.
2. Complex Structures
a) Nanostructures
i. Nanophase materials
ii. Nanocluster composites
iii. Develop methods to control particle size and grain size by thermal management.
iv. Theory and modeling
v. Surface modification with organic molecules
b) Microstructures
i. Multiphase intermetallics
c) Thin films
i. Multilayer film structures
ii. Amorphous film structures
3. Characterization of Physical Mechanisms
a) Hydrogen bonding
Description: Understand the fundamental atomic processes in absorption and desorption of hydrogen.
b) Lifetime degradation issues
c) Kinetics
Description: Determine the effect of the following factors on kinetics and cycling characteristics.
i. Processing
ii. Dopants
iii. Catalysts
iv. Decomposition products and chemical pathways
v. Particle size
vi. Defect sites (atomic scale)
d) Surfaces
Description: Investigate the effect of surface barriers and surface catalysts on hydrogen storage.
e) Mass transport issues
Description: Investigate the role of hydrogen-promoted mass transport on phase transformations.
f) Thermophysical properties
Description: Adjusting the lattice parameters and strains, grain structure, Fermi level, polarization, and charge distribution of the absorbents should allow tuning of the absorption potential and hence the thermodynamics of absorption. Combine experimental data with state-of-the-art characterization tools and establishment of standards for comparison.
i. Structural
ii. Thermodynamic
iii. Physical
iv. Chemical
g) Non-thermal discharge mechanisms
i. Mechanical
ii. Chemical
iii. Electrical
4. Containment Materials
Goal: Cost, Durability, Compatibility with storage material
a) Composite wall containers
5. System Analysis
a) Cost estimates
i. Hydrogen storage materials
ii. Cryo-coolers for metal hydrides
b) Data collection
i. Compile a consistent database of test results for the charge/discharge behavior of potential hydrogen storage compounds (over 2,000 compounds listed in the Sandia Hydride Information Center).
c) Magnetic detection of diffusible hydrogen
Description: Magnetic and electronic measurements to quantify hydrogen availability, absorption, and desorption in various materials.
d) Neutron scattering diagnostics
Description: Neutron radiation is the ideal penetrating probe for measurement and visualization of the 3-D chemical kinetics of hydrogen uptake in materials. The range of size resolutions (50 um – 1 m) and time resolutions (100 ns – 10 fs) are sufficient for most structural and dynamic processes in hydrogen storage media. (NIST Center for Neutron Research)
Goal: Characterization of new hydrogen storage hydrides in terms of structure, recyclability, and storage capacity.
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