This document outlines Kyle D. Crosby's M.S. defense presentation on hydrogen storage research using LiBH4. The presentation covers hydrogen storage background and challenges, research objectives to improve LiBH4 properties through nanoengineering, mechanical activation and additive effects. Major findings showed ball milling factors like time and temperature improved properties. Additives like graphite and transition metals enhanced hydrogenation/dehydrogenation kinetics and capacities. In conclusion, the research demonstrated diffusion-controlled kinetics and capacity improvements through destabilization, nanostructuring and additive effects.

1. Kyle D. Crosby
University of Connecticut
M.S. Defense
December 18, 2009

2. Outline
 H2 storage background – Motivation
 Freedom CAR targets
 Research objectives using LiBH4
 Thermodynamic destabilization
 Nanoengineering
 Mechanical activation
 Transition metal addition
 Major findings
 Ball milling factors
 Effects of milling additives
 Concluding Remarks

3. Why H2 Energy?
 Fossil Fuel issues
 Pollution (CO2 & CO)
 Limited resource
○ Destructive drilling/mining to obtain
 Fuel cell technology, H2
 Byproduct of energy is merely H2O
 Economic benefit of domestic production
 Limitations/Dangers
○ Pressure (700 bar gas cylinder)
○ Temperature (>350°C)
○ Volumetric (<1/3 volumetric density of gasoline)
○ High cost/pollution of H2 production
○ Explosive when oxygen (air) and ignition (electronics of car)
source present

4. Fossil Fuel Issues
 Transportation sector = 17.6% of energy
 Gasoline internal combustion engine
 “dirty” fuel
 1/3 the energy content of H2 on a weight basis
○ (48.6 MJ/kg vs. 140.4 MJ/kg)
Rohde, R. Global Warming Art. National Oceanic and Atmospheric Administration.
http://www.globalwarmingart.com/wiki/File:Mauna_Loa_Carbon_Dioxide_png

5. PEMFC
•High energy density
•Low operating temperature
•Only byproduct is water
•Could recycled and used for
onboard H2 production
•Requires highly purified H2 fuel
•Impurities in fuel are deposited in
the hydride pores = loss in storage
capacity as sites for H bonding are FCtec. Proton Exchange Membrane Fuel Cells.
blocked Concurrent Technologies Corporation. 2001 - 2009.
Anode Reactions: 2H2 => 4H+ + 4e-
Cathode Reactions: O2 + 4H+ + 4e- => 2 H2O
Overall Cell Reactions: 2H2 + O2 => 2 H2O

6. H2 Storage
 Compressed gas hydrogen
 Liquefied hydrogen
 Solid state materials
U.S. DOE. Energy Efficiency and Renewable Energy. Fuel Cell Technologies Program. 2008.
http://www1.eere.energy.gov/hydrogenandfuelcells/storage/basics.html

7. Metal Hydride Storage Physics
 H2 is physisorbed on surface of metal
particle
 H2 dissociates on surface of metal before
absorption
 Host metal dissolves H as a solid solution
(α-phase)
 H atoms locate at interstitials of host metal
 As H concentration increases, local H-H
interaction dominates
 (β-phase) nucleates to saturation

8. Honda FCX Clarity – 1st consumer FC Vehicle
American Honda Motor Co., Inc. Honda FCX Clarity. 2009. http://automobiles.honda.com/fcx-clarity/how-fcx-works.aspx
61 mpg, 240 mile range, 100 kW peak output
3.92 kg H2 @ 5000 psi (~350 bar)
$600/month lease in isolated markets

9. 5.5. wt% 7.5 wt%
Freedom CAR targets
• Ford
• GM
• DaimlerChrysler
• BP
• Chevron
• ConocoPhillips
• Exxon Mobile
• Shell

10. Research Objectives
 To reduce hydrogenation/dehydrogenation temperature while
simultaneously improving the hydrogen sorption/desorption kinetics in
the LiBH4-based hydrogen storage system via.....
 Kinetic = Nanoengineering and mechanical activation
○ Long time ball milling
○ Ball milling at liquid nitrogen temperature (LN2)
 Thermodynamic = MgH2 destabilization
○ MgH2 decomposes into Mg and H2
○ Mg catalyzes dehydrogenation of LiBH4
 Processing agent = graphite addition
○ Graphite occludes the hydride particle, protecting freshly created surfaces from
oxidation
○ Graphite allows small particles to slide past balls easily (solid lubricant) while forcing
large particles to be refined further, resulting in a highly homogeneous product
 Lattice distortion = transition metal addition (Mn & V)

11. Research Approach
 Nanoengineering
○ Reduce diffusion distance by reducing particle and
crystallite sizes
 Diffusion kinetics are exponentially dependent on distance
 Reduction in size of 100x = 10,000x times faster reaction
 Kinetic modeling reveals diffusion controlled rate limiting
 Mechanical activation
○ Introduce a large number of defects and create fresh
surfaces
 Increase # of sites for H2 sorption = increased capacity
 Create fresh surfaces = increases reactivity, reduces
sorption/desorption temperature
Dfree surface >> Dg.b. >> Dbulk

12. Research Approach
 Thermodynamic destabilization
○ Introduce alternate lower energy reaction pathway
into system
 Lowers thermodynamic driving force necessary to react
= lowers sorption/desorption temperature
 G = H – TS
ΔHLiBH4 = 67 kJ/mol ΔHLiBH4 + MgH2 = 44 kJ/mol
 Transition metal additive enhancement (Mn/V)
○ Disperse additional elements to decrease the
activation energy, Q, for diffusion of the rate
limiting species
D = D0e(-Q/RT)

13. Effect of ball milling time
2LiH + MgB2
10
8
6
Hydrogen (wt%)
3 hr as milled
4
24 hr as milled
24 hr as milled
2
120 hr as milled
120 hr as milled
0
0 1 2 3 4 5 6 7 8
-2
-4
Time (hr)

14. (Mg1-xLi2x)B2 Formation
2LiBH4 (s) + MgH2 (s)  2LiH (s) + MgB2 (s) + 4H2 (g)
Direct, reversible reaction
Actually proceeds through (Mg1-xLi2x)B2 before forming LiBH4
Hu, J. Z.; Kwak, J. H.; Yang, Z.; Wan, X.; Shaw, L. “Direct observation of ion exchange in mechanically activated LiH+MgB2 system using ultra-high field
nuclear magnetic resonance spectroscopy,” Appl. Phys. Lett. 2009, 94, 141905.

15. Effect of Ball Milling Temperature
 Rise in local temp. at ball collision site can be
>300°C
 Tm = 280°C for LiBH4
 Ball milling at room temp. (25°C) leads to >325°C
indicating melting, agglomeration, and sintering
 Ball milling at LN2 (-196°C) leads to >104°C
indicating no melting and a decrease in cold welding,
agglomeration still witnessed however

16. Effect of processing agent, C
w/o C
2LiBH4 + MgH2
with 5 vol% C 3 hr LN2 ball milling
2°C/min ramp to 265°C
35
Si MgH2 LiBH4
30
2LiBH4 + MgH2
25 ball milled 3 hr @ LN2
Cu Kα
Relative Intensity
20
2LiBH4 + MgH2 + 5 vol% C
15 hand mixed
10
2LiBH4 + MgH2 + 5 vol% C
ball milled 3 hr @ LN2
5
0
10 20 30 40 50 60 70 80
2 Theta

17. Dehydrogenation Products
1.E-06
1.E-07
Intensity (Torr)
1.E-08
1.E-09
1.E-10
1.E-11
1.E-12
0 50 100 150 200 250 300 350 400 450
Temperature (oC)

18. Dehydrogenation Products
MgH
LiBH4 2
MgH 2
LiBH4

19. Dehydrogenation Products
950
D band = 1349 cm-1
Breadth = 328 cm-1
850 G band = 1595 cm-1
Breadth = 297 cm-1
750
Intensity (a.u.)
650
550
G band = 1594 cm-1
450 Breadth = 166 cm-1
D band = 1351 cm-1
350
Breadth = 139 cm-1
250
1000 1200 1400 1600 1800 2000
Raman Shift (cm-1)

20. Dehydrogenation under Different
Conditions

21. XRD of Different Conditions
60 Si MgH2 LiBH4 Mg MgO
50
3 hr LN2 milled
40
Relative Intensity
Release vac ,
280°C 30
Release vac,
275°C
20
Release 4-bar,
265°C
10
Cycled vac,
265°C 0
10 20 30 40 50 60 70
2 Theta

22. XRD Analysis

23. Kinetic Modeling
 Diffusion Control
 Moving Interface Control
 Gas Adsorption Control
 Nucleation and Growth
Control
[Wan, X.; Markmaitree, T.; Osborn, W.; Shaw, L. “Nanoengineering-enabled solid-state hydrogen uptake and release in the LiBH4 plus MgH2 system,”
J. Phys. Chem. C 2008, 112, 18232-18243 .

24. Kinetic Modeling - Solid State (T = 265°C)
Nucleation and Growth Control
ln{ln(1/1-f’f)} = -13.355 + 1.3002lnt
with R2 = 0.6724
Gas Desorption Control
(f’f) = 0.0853 + 0.00002(t + Δt)
with R² = 0.7652
Moving Interface Control
(1-f’f)1/3 = 0.9727 - 0.000007(t + Δt)
with R² = 0.7984
Diffusion control
(1- f’f)1/3 = 1.0041 - 0.0012(t + Δt)1/2
with R² = 0.9143

25. Kinetic Modeling – Solid State (T = 265°C)
Release under 4-bar backpressure results in unambiguous diffusion controlled
reaction because H2 suppresses formation of elemental Mg, thus MgH2 does
not contribute to diffusion, thus a single species mechanism is accurate (R2 ↑).

26. Kinetic Modeling – Liquid State
Gas Desorption Control
(f’f) = -0.0034 + 0.00008t
with R² = 0.9952
T = 280°C
Gas Desorption Control
(f’f) = -0.0068 + 0.00006t
with R² = 0.9986
T = 275°C
Diffusion Control
(1-f’f)1/3 = 0.9913 - 0.0008(t + Δt)1/2
with R² = 0.849
T = 275°C

27. Dehydrogenation/Hydrogenation
Cycling Properties
Loss of cycling capacity due to grain growth
and formation of metallic Mg
G.B. area decreases, bulk diffusion takes over

28. Effect of Mn/V addition
7
6
5
4 No Addition
2LiH + MgB2
Hydrogen (wt%)
3 No Addition 24 hr R.T. ball milling
2 With Mn 2°C/min ramp to 265°C
1 With Mn
With V
0
0 2 4 6 8 With V
-1
-2 35
-3
Time (hr) 30
Relative Intensity 25
20
Unmilled
15 3 hr as milled
Cu Kα 10 24 hr as milled
5
0
35 40 45 50 55
2 Theta

29. Concluding Remarks
 Increasing ball milling duration results in more favorable hydrogenation/dehydrogenation attributes because of the
mechanical activation and nanoengineering effects (i.e. ball milling produces particles with refined crystallites,
increased defect concentrations, increased grain boundary area, fresh reactive particle surfaces, and homogeneous
mixtures of the metal hydride reactants)
 Ball milling at LN2 temperature further enhances the mechanical activation and nanoengineering processes
because the equivalent energy transfer is applied to a particle that is now more brittle than for identical mixtures ball
milled at room temperature (i.e. brittle particles experience more efficient fracture with less cold welding)
 MgH2 destabilization shows a nearly fivefold increase in the storage capacity (4.0 wt% vs. <0.5 wt%) of the LiBH4
system by creating an alternate lower energy reaction pathway for the uptake/release of hydrogen (i.e. MgH2 first
decomposes into Mg and H2 wherein the Mg catalyzes the dehydrogenation of LiBH4)
 Graphite solid lubrication enhances ball milling efficiency by preventing cold welding and caking (i.e. graphite
particles encapsulate the metal hydride reactants during ball milling, effectively preventing intimate contact and
providing a buffer on the surface of the particle to prevent oxidation. Thus, cold welding and sintering do not occur
during ball milling and the result is a highly homogeneous product.)
 Hydrogenation and dehydrogenation rate limiting kinetics are shown to be diffusion-controlled for the overall H2
uptake and release processes in the 2LiBH4 + MgH2 mixtures.
 Mn and V addition demonstrate the need for proper choice in additive (i.e. Mn enhances only the hydrogenation
reaction of 2LiH + MgB2 mixtures via enhancement the diffusion coefficient of Mg in the (Mg1-xLi2x)B2 compound. As
the diffusion coefficient of the rate limiting species is increased, the overall kinetic rate is increased. V enhances
only the dehydrogenation reaction by improving the decomposition rate of MgH2, allowing free Mg to catalyze the
decomposition reaction of LiBH4, thus increasing dehydrogenation kinetics.)

30. Acknolwedgements/Thanks
 This work was supported under the U.S. Department of
Energy (DOE) Contract No. DE-FC36-05GO15008.
The vision and support of Dr. Ned T. Stetson, DOE
Technology Managers, are greatly appreciated.
 Thank you......
 Family and friends for supporting me throughout my
academic career
 UConn and IMS for offering the opportunity to pursue
higher education
 Dr Shaw for providing the project and funding opportunity
 Dr. Brody and Dr. Huey for sacrificing their time during
finals to serve on my panel

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36. LiBH4
LiBH4 crystal structure
•low temp (<110°C) = orthorhombic (top)
•high temp = hexagonal (bottom)
Grey = B
[BH4]-
Red = H
Blue = Li+
Interstitial sites
Octahedral – red
Tetrahedral - blue
Hartman, M., Rush, J., Udovic, T., Bowman, R.,
Hwang, S.J. “Sturcture and Vibrational Dynamics of
Isotropically Labeled Lithium Borohydride Using
Neutron Diffraction and Spectroscopy,” J. of Solid
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37. Storage Improvement Methods
 Structure directing agents
 Carbon aerogels
○ Confinement of particles restricts grain growth
during thermal cycling
 initial particle size retained throughout
hydro/dehydrogenation
 Surface activation treatment
 Ni catalyzes surface dissociation of H2
○ Increase kinetics of system
 High SSA materials
 Maxsorb carbon (3000 m2/g)

38. Point Defects
http://school.mech.uwa.edu.au/~liu/Lectures/ME203/Handouts/ME203-Crystal-4.pdf

39. No SEM/TEM
 Weak scattering by light elements (H, Li, B) restricts direct
observation
 High SSA, hydrophilic nanopowders are extremely reactive
in air
 Samples oxidize and “foam” up upon loading into
SEM/TEM
 Beam damage
 LiBH4 low melting temp, particles vaporize under beam

40. No SEM/TEM
80 kV
135 kx mag.
time

41. XRD Analysis
Sherrer Formula – crystallite size
Stokes-Wilson Formula – internal strain
Appearance of new peaks – new phase(s)
Peak shifting – solid solution formation
Orthorhombic
1/d2 = h2/a2 + k2/b2 + l2/c2
Hexagonal
1/d2 = 4/3(h2 + hk + k2/a2) + l2/c2

42. RGA Background
 Quadrupole gas analyzer
 Quadrupole analyzer uses four rods (two tandems) with
oscillating voltage
 RF voltage applied to one set of rods such that only ions
of a specific mass/charge (m/z) will reach the detector all
other ions will oscillate with unstable trajectories and
collide with the rod
 Voltage can be scanned continuously or set to detect a
single species

43. FTIR Background
Types of bond detection using FTIR
Measures absorbance or transmittance of IR wavelength – shows
molecular structure of the material

44. Raman
Types of energy shifts detected by Raman
Absorption
Rayleigh means equal before and after
Stokes means final state is more energetic than initial
Anit-Stokes means initial state is more energetic than final

45. BET
Gas adsorption in monolayers on the surface of a solid material based on
equilibrium and saturation pressures of the gas

46. Fuel Cell Classes
 MCFC (650°C, >1 MW)
 SOFC (1000°C, >200 kW)
 PEMFC (80°C, 250 kW) *
 PAFC (200°C, >50 kW)
 AFC (60-90°C, 20kW)
 DMFC (60-130°C, <10 kW) *
* Suitable for mobile applications

47. H2 Production
 Production
 Natural gas refining (48%)
○ Requires carbon sequestration
 Petroleum refining (30%)
○ Net usable is 0% : consumed internally in the
refinery
 Water electrolysis (4%)
 DOE target is $2.00-3.00/gge