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transcript
New Li-B-N-H Quaternary Hydrides
Frederick E. PinkertonMaterials and Processes Laboratory
General Motors R&D Center
International Symposium on Materials Issues in Hydrogen Production and Storage
Santa Barbara, CA, 21-25 August 2006
Acknowledgements
• Greg Meisner• Martin Meyer• Mike Balogh• Jan Herbst• Lou Hector• Charlene Hayden• Matt Kundrat• Matt Scullin• Aimee Bailey• Laura Confer• Richard Speer, Jr.
• Yaroslav Filinchuk• Klaus Yvon
• John Vajo• Sky Skeith
• Jason Graetz• Santanu Chaudhuri• Alex Ignatov
Outline
• Hydrogen storage requirements for solid hydrides
• Building high hydrogen capacity storage reactions
• New quaternary Li-B-N-H hydride– Synthesis from LiNH2 and LiBH4
– Hydrogen release properties– Crystal structure
• Metal additives to promote hydrogen release
• Concluding remarks
The hydrogen storage problem…
Dr Arnold Hydrogen Storage / TAA
Global Alternative Propulsion CenterWith thanks to Dr. Gert Arnold
Storage method
15 M
Pa gas
35 M
Pa gas
70 M
Pa gas
Liquid
H2
LaNi5H
6FeT
iH2
MgH2
Mg2NiH
4NaA
lH4
Li-N-H
2LiBH4+
MgH2
Li3BN2H
8Gas
oline
*
Vol
umet
ric d
ensi
ty (k
g H
2/lite
r)
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
Solid hydrides offer compact storage…
*energy equivalent
kg of hydrogen per liter of material
Storage method
15 M
Pa gas
35 M
Pa gas
70 M
Pa gas
Liquid
H2
LaNi5H
6FeT
iH2
MgH2
Mg2NiH
4NaA
lH4
Li-N-H
2LiBH4+
MgH2
Li3BN2H
8Gas
oline
*
Vol
umet
ric d
ensi
ty (k
g H
2/lite
r)
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
Solid hydrides offer compact storage…
system performance will be substantially reduced
*energy equivalent
Other aspects are more challenging
Equilibrium Temperature for PH2=1 atm (°C)0 100 200 300
Theo
retic
al h
ydro
gen
capa
city
(wei
ght %
)
0
2
4
6
8
10
12
Approximate ∆H (kJ/mol H2) [~T∆SH2]
30 40 50 60 70
MgH2
Mg2NiH4
LaNi5Hx
TiV1.6Ni0.4HxTiFeHx
NaAlH4 (stage 1)
Na3AlH6 (NaAlH4 stage 2)
Other aspects are more challenging
Equilibrium Temperature for PH2=1 atm (°C)0 100 200 300
Theo
retic
al h
ydro
gen
capa
city
(wei
ght %
)
0
2
4
6
8
10
12
Approximate ∆H (kJ/mol H2) [~T∆SH2]
30 40 50 60 70
MgH2
Mg2NiH4
LaNi5Hx
TiV1.6Ni0.4HxTiFeHx
NaAlH4 (stage 1)
Na3AlH6 (NaAlH4 stage 2)
LiNH2+LiH (Chen et al.)Mg(NH2)2+2LiH
(Luo)
LiBH4+½MgH2+TiCl3(hydrogenation)
(Vajo et al.)
Li3BN2H8+0.2NiCl2(dehydrogenation only)
New materials research• Capacity: High specific mass• Thermodynamics: Moderate ∆H (~35 kJ/mol H2)
– Hydrogen release temperature 20-80 C in 2-5 bar H2– Thermal management: insertion and extraction of ∆H
• Fast kinetics– Complex hydrides tend to be kinetically limited, requiring
high temperature even if the thermodynamics are good
GM “Sequel”Hydrogen Fuel Cell prototype
Li-B-N-H: Building high-capacity reactions
NaAlH4 1/3 Na3AlH6 + 2/3 Al + H2 3.7 wt%NaH + Al + 3/2 H2 5.6 wt% (7.5 wt%)
LiNH2 + LiH Li2NH + H2 6.5 wt% (9.8 wt%)Mg(NH2)2 + 2 LiH Li2Mg(NH)2 + 2 H2 5.6 wt% (8.4 wt%)LiBH4 LiH + B + 3/2 H2 13.9 wt% (18.5 wt%)LiBH4 + ½ MgH2 LiH + ½ MgB2 + 2 H2 11.5 wt% (14.4 wt%)
Not all of the hydrogen is released
Strategy: Identify HYDROGEN-FREE compounds involving light elements that could be the DECOMPOSITION PRODUCTS of
reactions between hydrogen-containing materials corresponding to COMPLETE HYDROGEN RELEASE
Hypothetical reaction
• Lithium Boronitride: Li3BN2– Several known polymorphs
• Tetragonal P42212 low temperature phase (<860°C)– a = 4.6435 Å c = 5.2592 Å
• Monoclinic P21/c high temperature phase– a = 5.1502 Å b = 7.0824 Å c = 6.7908 Å β = 112.96º
• High pressure phase (DeVries and Fleischer)
• Hypothetical reaction:2 LiNH2 + LiBH4 → Li3BN2 + 4 H2 11.9 wt% H
• Success! > 11 wt% H2 release– But here’s the twist:
We formed a new quaternary Li-B-N-H phase
Synthesis of 2 LiNH2 + LiBH4: Ball milling
2 LiNH2 + LiBH4
ball milled powders
2θ (degrees)
10 15 20 25 30 35 40 45 50 55
Inte
nsity
(arb
irary
uni
ts)
LiBH4
LiNH2
Li2O
α phase
0
10
2040
960
160
Millingtime(min)
300
Pinkerton et al., J. Phys. Chem. B 109, 6 (2005). Published on line: 17 Dec 2004
α phase
Premill LiNH2 and LiBH4separately for 10 min, then mix and heat
The in situ XRD data at 75ºC is identical to that at room temperature (RT) when the experiment started.
After mixing and storing for 12 days at RT, the mixture spontaneously formed a substantial quantity of the α phase!
Heating above ~95ºC completes the conversion to the α phase.
XRD Results: Mix & Heat
LiBH4 + 2 LiNH2 conversion to α Li-B-N-H by heating
2θ (degrees)
15 20 25 30 35 40 45 50 55
Inte
nsity
(arb
itrar
y un
its)
LiBH4
LiNH2
α phase
75°C
109°C
Pinkerton et al., J. Phys. Chem. B 109, 6 (2005).
In situ XRD: Evolution of α Li-B-N-H at 73 °C
100
25
500
200
50
0
Time(min)
2θ (degrees)LiBH4 LiNH2
αααα α
α
α
αααα
2 LiNH2 + LiBH4mixed powders
Time (min)
0 20 40 60 80
Tem
pera
ture
(°C
)
0
50
100
150
200
250
300
350
400
Wei
ght (
%)
86
88
90
92
94
96
98
100
102
Residual gas analysis
Time (min)
0 20 40 60 80
Par
tial p
ress
ure
(Tor
r)
10-11
10-10
10-9
10-8
10-7
Mass 2 - H2
Mass 17 - NH3
Mass 16 - NH2 radical, CH4
RGA mass spectrometry
13.1 wt%
~2 mole% NH3
11.5 wt% H2, 1.6 wt% NH3
Hydrogen desorption
(TGA)2 LiNH2 + LiBH4mixed powders(“mix and heat”)
13.1 wt% lossexceeds theoretical H2 content (11.9%)
Pinkerton et al., J. Phys. Chem. B 109, 6 (2005).
In situ XRD – ball milled 2LiNH2 + LiBH4
α-phase
Liquid
Li3BN2
Melts~190°C
Dehydrogenation> 250°C
Temperature(°C)
Reaction path
2 LiNH2 + LiBH4 → α Li-B-N-H (solid)
→ α Li-B-N-H (liquid) ~195ºC
→ Li3BN2 (solid) + 4 H2 >250ºC
“Destabilized LiBH4” ?
New compound, less stable than LiBH4
α Li-B-N-H: a new quaternary hydride
2θ (degrees)
5 10 15 20 25 30 35 40 45 50 55 60
Inte
nsity
(cou
nts)
0
2000
4000
6000
8000
10000
2 LiNH2 + LiBH4 ball-milled 5 hrs:α Li-B-N-H
Li2O
Plastic film
bcc crystal structurea = 10.78 Å
“Li3BN2H8” α phase in Li-B-N-H
2
α-phase crystal structure
• Single crystals formed by recrystallizing from the melt
• Body-centered cubic space group:
I213 (#199)a = 10.676 Å
• NH2− and nearly
tetrahedral BH4− units
persist in the structure• Equilibrium composition:
Li4BN3H10 !(= 3 LiNH2 + LiBH4)
Filinchuk et al., Inorg. Chem. 45, 1433 (2006).
Li
B
N
H
Lattice shift of ball milled material
2 LiNH2 + LiBH4 ball milled 16 hrs
2θ (degrees)
25 30 35 40 45 50
Inte
nsity
(cou
nts)
0
2000
4000
6000
8000
10000
Experimental patterna = 10.78 ACalculated Li4BN3H10
a = 10.68 A
0
10
20
30
40
50
10 20 30 40 50 60 70Angle (2θ)
Diff
ract
ion
Inte
nsity
(cou
nts/
sec)
x = 1
x = 0.75
x = 0.667
x = 0.655
x = 0.636
x = 0.6
x = 0.556
x = 0.5
x = 0.333
x = 0
LiNH2
α + δ
α
γ +α
β + γ + α
β + γ + α
β + γ
β
LiBH4 + β
LiBH4
X-Ray Diffraction Data for Ball Milled
(LiNH2)x(LiBH4)1-x
*
Meisner et al., J. Phys. Chem. B 110, 4186 (2006).
Li2O
3:1 α + δ2:1 α
1:1 β
} α+β+γ
What about 3 LiNH2 + LiBH4?
If the α phase is Li4BN3H10, then what is the dehydrogenation behavior of samples made
at the 3 LiNH2 + LiBH4 composition?
RGA mass spectrometry
Hydrogen desorption
(TGA)3 LiNH2 + LiBH4Ball milled 5 hrs
18 wt% loss(theoretical content
11.1 wt%)
3 LiNH2 + LiBH4ball milled 5 hrs
Time (min)
0 20 40 60 80 100 120
Tem
pera
ture
(°C
)
0
100
200
300
400
500
Wei
ght (
%)
80
85
90
95
100
Residual gas analysis
Time (min)
0 20 40 60 80 100 120
Parti
al p
ress
ure
(Tor
r)
10-10
10-9
10-8
10-7
Mass 2 - H2
Mass 17 - NH3
Mass 16 (x 1/2) - NH2 radical
18 wt%
~9 mole% NH3
9.6 wt% H2, 8.3 wt% NH3
0
2
4
6
8
10
12
14
16
18
20
22
0.3 0.4 0.5 0.6 0.7 0.8Composition (x)
Des
orpt
ion
(wt%
)
Total hydrogen contentHydrogen desorbed as HAmmonia desorbedTotal hydrogen desorbedTotal desorption
H2 and NH3 release in (LiNH2)x(LiBH4)1-x
Meisner et al., J. Phys. Chem. B 110, 4186 (2006).
2:1
3:1
Li3BN2
LiBH4 LiNH2
What’s so special about 2:1?
• Dehydrogenation from the liquid is not controlled by the starting α-phase, but rather by the product Li3BN2 phase
• For 2 LiNH2 + LiBH4:Li3BN2H8 (liquid) Li3BN2 + 4H2
• For 3 LiNH2 + LiBH4:Li4BN3H10 (liquid) Li3BN2 + ½ Li2NH + 4H2 + ½ NH3
Li3BN2 !
Dehydrogenated material: New Li3BN2 polymorph
Li3BN2 - I41/amd
2θ
10 20 30 40 50 60 70
Inte
nsity
0
1000
2000
3000
4000
5000
6000
DataFitDifferenceLi2O
101
112200
103
202
121004
301
204
105224
215
400233
305 107422
404051,341 244
Body-centered tetragonalcrystal structureI41/amd (#141)a = 6.60 Å, c= 10.35 Å
Pinkerton and Herbst, J. Appl. Phys. 99, 113523 (2006).
Li
B
N
Promoting H2 release with metal additives
• Composition: 2 LiNH2 + LiBH4 + additive
• All samples ball milled for 5 hrs– Fully converted to α phase
• Metals or metal compounds added prior to ball milling– Metal powder– Metal dichlorides– “Pt/Vulcan carbon”: 2 nm diameter Pt nanoparticles
supported on a Vulcan carbon substrate
TiCl3 additive
• 2 mole% TiCl3additive has been shown to be very effective in some hydrogen storage systems– NaAlH4
(Bogdanović et al.)– LiBH4 + ½ MgH2
(Vajo et al.)
• TiCl3 does not significantly improve dehydrogenation of Li-B-N-H
LiB0.33N0.67H2.67 ball-milled 5 hrs
Temperature (°C)150 200 250 300 350 400
Wei
ght (
%)
84
86
88
90
92
94
96
98
100
102
Without additive5 wt% TiCl3
Pinkerton et al., J. Phys. Chem. B 110, 7967 (2006).
Pt/Vulcan carbon additions
Temperature (°C)150 200 250 300 350 400
Wei
ght (
%)
84
86
88
90
92
94
96
98
100
102
Without additive5 wt% Pt powder6.8 wt% PtCl21 wt% Pt/Vulcan carbon 2 wt% Pt/Vulcan carbon3 wt% Pt/Vulcan carbon5 wt% Pt/Vulcan carbon10 wt% Pt/Vulcan carbon2.4 wt% Vulcan carbon
LiB0.33N0.67H2.67 with Pt
∆T = -90°C
Pinkerton et al., J. Phys. Chem. B 110, 7967 (2006).
In situ XRD – Pt/Vulcan carbon added
Temperature(°C)
α-phase
Li3BN2 + Li2Pt3BIntermediate solids
In situ XRD - 5 wt% Pt/Vulcan carbon
Quaternary α-phase
Intermediate 1
Li3BN2 + Li2Pt3B
Intermediate 2
Pinkerton et al., J. Phys. Chem. B 110, 7967 (2006).
20 40 60 80 100 120 140 160 180 200
Intensity(counts)
Accelerated isothermal H2 release
Li3BN2H8
Time (min)0 200 400 600 800
Wei
ght (
%)
86
88
90
92
94
96
98
100
102
Uncatalyzed (210°C)
5 wt% Pt/Vulcan carbon(200°C)
NiCl2 additions
Temperature (°C)150 200 250 300 350 400
Wei
ght (
%)
84
86
88
90
92
94
96
98
100
102
Without additiveNi powder (< 53 µm)Ni flake (< 44 x 0.37 µm thick)Raney Ni 2800Nanosized Ni (<40 nm)NiCl211 wt% NiCl2
LiB0.33N0.67H2.67 with Ni additives(5 wt% unless noted otherwise)
10 wt% Pt/Vulcan carbon
∆T = -112°C
Pinkerton et al., JALCOM, available online.
TEM: LiB0.33N0.67H2.67 + 5 wt% NiCl2
Nanocrystalline Ni3B (≤ 8 nm)
Mass spectrometry gas analysis
• Additive-free Li-B-N-H: – H2 and NH3 release occur
together above 250°C– Evolved gas ~2 mole% NH3
• NiCl2-added:– onset of H2 release is 120°C– Total NH3 release reduced
by an order of magnitude
LiB0.33N0.67H2.67
0 20 40 60 80
Wei
ght (
%)
86
88
90
92
94
96
98
100
102
Tem
pera
ture
(°C
)
0
100
200
300
400
0 20 40 60 80
Parti
al P
ress
ure
(Tor
r)
10-11
10-10
10-9
10-8
10-7
Time (min)0 20 40 60 80
Parti
al P
ress
ure
(Tor
r)
10-10
10-9
10-8
10-7
10-6
LiB0.33N0.67H2.67 + 5 wt% NiCl2
Mass 2 - H2~11.0 wt%
Mass 18 - H2O
Corrected NH3 ~0.2 wt%
Mass 17 - NH3, OH −
Mass 2 - H2~11.5 wt%
Corrected NH3 ~1.6 wt%Mass 17 - NH3, OH −
Mass 18 - H2O
(b) LiB0.33N0.67H2.67
(a)
(c) LiB0.33N0.67H2.67 + 5 wt% NiCl2
Pinkerton et al., JALCOM, available online.
5 wt% NiCl2 addition
Quaternary α-phase
Intermediate
Li3BN2
Distinct from both intermediates in Pt/Vulcan carbon!
Pinkerton et al., JALCOM, available online.
Comparison of intermediate phases
LiBH4 + 2 LiNH2 + 5 wt% Pt/Vulcan C226°C
Inte
nsity
(cou
nts)
020406080
100120140160
LiBH4 + 2 LiNH2 + 5 wt% Pt/Vulcan C261°C
Inte
nsity
(cou
nts)
0
20
40
60
80
100Li2Pt3B
LiBH4 + 2 LiNH2 + 11 wt% NiCl2
2θ (degrees)
5 10 15 20 25 30 35 40 45
Inte
nsity
(cou
nts)
0
20
40
60
80
100
120
Pt/Vulcan carbonIntermediate 1(226°C)
Pt/Vulcan carbonIntermediate 2(261°C)
NiCl2Intermediate(~210-~290°C)
What are the additives doing?
– Small quantities (~1 mole%) have a large effect
– ∆T½ scales with the specific surface area (m2/g) of the additive particles
– Effect appears to saturate at low addition levels (~2 mole% for NiCl2)
• Likely acting as a dehydrogenation catalyst
Ni additions
Specific surface area (m2/g)0.1 1 10 100 1000
| ∆T 1/
2 | (°
C)
0
20
40
60
80
100
120
Ni powder
Ni flake40 nm Ni nanoparticles
Raney Ni
NiCl2 (< 10 nm Ni3B)
(5 wt% Ni)
What about reversibility?
• Dehydrogenation appears to be exothermic
• Thermodynamically unstable
• => difficult to reverse (off-board regeneration)
• Caveat:It’s not a simple system: H2 release, NH3 release, and Li3BN2 solidification are happening simultaneously Pinkerton et al., J. Phys. Chem. B 110, 7967 (2006).
LiB0.33N0.67H2.67 ball milled 300 min
Temperature (°C)100 200 300 400
Hea
t flo
w (W
/g);
endo
ther
mic
up
-12
-10
-8
-6
-4
-2
0
2
4
No additive5 wt% Pt/Vulcan carbon
α-phasemelting
Desorptiononset
Desorptiononset
β-phasemelting
DSC
Exothermic
DFT estimates of reaction enthalpy
• 2 LiNH2 + LiBH4 Li3BN2 + 4 H2– ∆H ~ 23 kJ/mol H2 - Aoki et al., Appl. Phys. A 80, 1409 (2005)– ∆H = 18-24 kJ/mol H2 - Alapati et al., JPC B 110, 8769 (2006)– Caveats: zero T calculations excluding zero point energy– Both suggest reversibility of Li3BN2 to the two-phase mixture
• Li4BN3H10 Li3BN2 + ½ Li2NH + ½ NH3 + 4H2– ∆H = 24 kJ/mol H2 – Herbst & Hector, APL 88, 231904 (2006)– Includes zero point energies and phonons: 298 K values– Endothermic hydrogen release suggests reversibility– Caveat: does not include α-phase melting or Li3BN2 solidification
• May be too unstable: – 1 bar H2 equilibrium temperature is ~130-240 K
Aside:
• Reaction enthalpy for 3 LiNH2 + LiBH4 Li4BN3H10
– ∆H = -6 kJ/mol – Herbst & Hector, APL 88, 231904 (2006)
• Formation of Li4BN2H10 is slightly exothermic• Consistent with observed conversion
2 LiNH2 + LiBH4 α Li-B-N-H
Effect of H2 pressure
LiB0.33N0.67H2.67 + 5 wt% Pt/Vulcan carbon
Temperature (°C)150 200 250 300 350 400
Wei
ght (
%)
86
88
90
92
94
96
98
100
102
100 kPa Ar130 kPa H2
4200 kPa H2
Pinkerton et al., J. Phys. Chem. B 110, 7967 (2006).
Attempt to rehydride LiB0.33N0.67H2.67 + 5 wt% Pt/Vulcan carbon
LiB0.33N0.67H2.67 + 5 wt% Pt/Vulcan carbon
Time (min)0 2000 4000 6000
Pre
ssur
e (M
Pa)
0
2
4
6
8
Tem
pera
ture
(°C
)
0
20
40
60
80
100
120
140
160
180
Wei
ght (
%)
90
92
94
96
98
100
102
Switch to H2
8.4 MPaH2
150°C0.13 MPa He150°C
1.3 wt%
Pinkerton et al., J. Phys. Chem. B 110, 7967 (2006).
Challenges for quaternary Li-B-N-H
• Thermodynamics– Understand reaction enthalpies for dehydrogenation of
α Li-B-N-H at different compositions• Kinetics
– High temperatures required to overcome slow diffusion and strong hydrogen binding and in complex hydrides
• Catalysis– Why does Ni or Ni3B work so well?– Why doesn’t TiCl3 work?
• What if we could reduce the Li-B-N-H hydrogen release temperature below the α phase melting temperature (similar to what was done for NaAlH4)?– Reversibility?– Suppress NH3 release?– More practical? (Or at least, less impractical?)
On-board hydrogen storage materials-
• Compressed gas• Liquid H2• Physisorption at cryogenic temperatures
– Activated carbon, nanotubes, MOFs
• Hydrolysis hydrides– NaBH4 + H2O NaBO3 +
• Organic ring compounds• Solid hydrides
– Metal hydrides (LaNi5, Mg, Mg2Ni, AB, AB2 compounds– Complex hydrides (NaAlH4, LiBH4, LiAlH4, …)
H2
Quaternary hydrides are fertile hunting ground
in the search for new hydrogen storage materials
Summary
• Strategy of looking for hydrogen-free products has been successful
• We have discovered a new quaternary hydride, α Li-B-N-H (Li4BN3H10), that releases all of its hydrogen above 250°C– H2 and NH3 release are strong functions of composition, with
optimum H2 release near (LiNH2)0.67(LiBH4)0.33 [2:1]
• Numerous other Li-B-N-H phases exist– 4 phases along the (LiNH2)x(LiBH4)1-x tie line (2 metastable)– 4 additional phases during Li-B-N-H decomposition with additives– 3 more phases have been found in the Li-B-N-H phase diagram
(Torgersen et al., MRS 2004 Fall Meeting)
• Metal nanoparticle additions reduce the dehydrogenation temperature by up to 112°C (NiCl2)
• Quaternary hydrides are fertile hunting ground in the search for new hydrogen storage materials