Hydrogen Storage in Ti-doped NaAlH4

1
Hydrogen Storagein Ti-doped NaAlH4

• William Gempel

2
National Hydrogen Initiative

• President Bush has proposed
• 1.2 billion over the next five years
• to support a new Hydrogen Fuel Initiative.

3
Elements of a Hydrogen Energy Infrastructure

• Production
• Delivery
• Storage
• Conversion
• Applications

4
Hydrogen Storage Methods

• High Pressure Tanks
• Liquid Hydrogen
• Carbon Nanotube Surface Absorbtion
• MgH2
• NaAlH4

5
Comparison of Methods
Method Weight H Volume 1kg H
H Gas 200 bar 100 .06m3
H Liquid 100 .014m3
C-Nanotube 6-8 .02m3
MgH2 7.6 .009m3
NaAlH4 7.5 (5.6) .010m3
6
Reversible Hydrogen Exchange in Metal Hydrides

• H2 absorbed under pressure
• H atoms bond to metal
• H2 released at elevated temperature

7
Sodium Alanate

• 3NaAlH4 -gt Na3AlH6 2Al 3H2
• Na3AlH6 -gt 3NaH Al 3/2H2
• 5.6 Hydrogen by Weight
• 50 per kg
• Slow Kinetics
• Reversible only at 600 K

8
Ti-Doped Sodium Alanate

• Reversible at 450 K
• Kinetics 2-4 times faster
• Still unsatisfactory, but
• Working model for possibility of catalytic
  improvement

9
Sodium Alanate Structure

• Body Centered Tetragonal
• Space Group IA/4
• Lattice 5x11 Ang.

10
First Principle Calculations forSodium Alanate

• Geometry
• Electronic Structure
• Energy of Formation

11
First Principles Calculationsfor Ti-Doping

• Structurally Stable
• Ti Prefers to Substitute for Na
• Ti Softens Al-H bonds
• It is energetically favorable for Ti to drag
  extra H into the system

12
First Principle Studies of Analogous Systems

• MxH
• Electronic Structure
• Energy of Formation
• Cohesive Energy
• Metal-Hydrogen Bond Strength

13
Local Projects

• Comparing CASTEP to VASP
• Reproducing Calculations in Literature
• Sodium Alanate Structure (In Progress)
• Energy of Formation
• Titanium Valence (Population Analysis)?

14
Conclusion

• Ti Doped Sodium Alanate Experiments show that
  Catalytic methods can be used to improve
  operation of Metal Hydrides
• First Principle Calculations may lead to
  understanding of mechanism that will allow
  improved Catalytic Methods