1

Solid State Chemical Hydrides at PNNL

2010 NHA Conference and Expo

Long Beach Ca. May 3-6, 2010

By

Jamie Holladay

Pacific Northwest National Laboratory

Outline

MotivationH2 storage for fuel cells

ApproachCombine theory, experimental and engineering

Mechanistic studies of H2 release (and uptake) from molecular complexes

ResultsMultiple chemistries for H2 storage were developed

• [NH4] + [BH4]¯ NH3BH3 + H2

• NH3BH3 NH2BH2 + H2

• [Li]+ [NH2BH3]¯ LiNHBH2 + H2

2

0

4

8

12

16

-200 -100 0 100 200 300 400

Temperature for observed H2 release (deg C)

Ob

serv

ed

H2 w

eig

ht

fra

cti

on

(%

)

LiBH4/CA

Ca(BH4)2

Mg(BH4)2

LiNH2/MgH2

MgH2

LiMn(BH4)3

NaAlH4

Li3AlH6/LiNH2

solid AB

AB/LiNH2

AlH3

liq. AB/cat.

1,6 naphthyridine

AB ionic liq.IRMOF-177

PANI

metal-doped CA

C aerogel

bridged cat./AX21

bridged cat./IRMOF-8

DOE system targets metal hydrides

adsorbents

chemical hydrides

carbide-derived C

M-B-N-H

AB/AT/PS

PANI

H2 Sorption Temperature (deg C)

0-100-200

Mg(BH4)2(NH3)2

Mg(BH4)2(AlH4)

Mg(BH4)2(NH3)2

Li3AlH6/Mg(NH2)2

3 G. Thomas, et al.,

Motivation: Amine Boranes If we understand mechanism, can we decrease the temperature for hydrogen release?

LiNH2BH3

NH4BH4

Height of bar corresponds to mass of element

4

Courtesy P Edwards Oxford

Element choices to store H limitedLi, Be, B, C, N, O, Na, Mg, Al, Si, P, S

NH4BH4 (24 wt% H2)NH3BH3 (19 wt% H2)LiNH2BH3 (12 wt % H2)

Gravimetric density challenges

NHxBHx H-storage (multi-step pathways – lots of interesting chemistry

T (˚C)NH4BH4 NH3BH3 + H2 <20 NH3BH3 (NH2BH2) + H2 <100NH2BH2 (NHBH) + H2 >1002(NH2BH2)n (NH2BH—NHBH2) n H2 <1502(NHBH) (NHB—NBH) + H2 >150NHBH BN + H2 >500

5

Two plus sequential steps > 13 % mass hydrogen material

If we can understand the details of the chemistry we can optimize the performance of a hydrogen store

Important Science Questions

NH3BH3 (NH2BH2)n + H2 + ? <100 ˚C

6

Is the mechanism intra or intermolecular?What is the activation barrier?Can we control the decomposition pathways?

How is H2 formed from solid AB?How is H2 formed from solid AB?

Need approaches to study solid state kinetics

∂+ ∂-Molecular Electrostatic Potential

hydridic B-H and protonic N-H hydrogens impart unique ability to store and release hydrogen

ApproachesScanning calorimetry combined with mass detection and gravimetric analysis

Thermodynamics of hydrogen lossKinetics and insight into mechanism of H-release

NMR and Raman spectroscopy Variable temperature for in-situ kinetic investigations Solid state to study phase transitions and molecular dynamics

Neutron spectroscopy QENS (for dynamics of H motion)NPDF & INS (structural properties)

7

Combination of experiment & theory to gain understanding of chemical & physical properties of AB

0 500 1000 1500 2000 2500 3000

Rela

tive

Hea

t R

ele

as

ed

(a

. u

.)

Time (min)

85 °C

80 °C

75 °C70 °C

Neat AB

8

Kinetics: isothermal DSC solid AB

• Rates increase with temperature

• Activated process

• Sigmoidal kinetics

• Induction period

• Thermodynamics

• ΔHrxn = -21±3 kJ/mol

NH3BH3(s) (NH2BH2)(s) + H2

Kinetic model for hydrogen release

Nucleation:Physical or Chemical Change

9

Control chemistry if we know what is happening to ammonia borane during each phase of the reaction?

0.00

1.00

0 100 200 300 400

Sigmoidal kinetic behavior: Induction, Nucleation & Growth

Induction: How to decrease?

Growth: H2 formation

Ea ~ 150 kJ/mol

Ext

ent

of

reac

tio

n

Mechanism for Release from AB (induction, nucleation, growth)

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NH2

BH2

NH3

BH3

BH2

NH3

BH3

BH2

NH3

BH2

NH2

BH2NH3

NH2

BH4

BH4

NH3

NH3

H2

H

H di-H-bonddisruption

BH2

NH3H +

-DADB

D

DADB reacts with AB

NH3

BH2 BH4

NH3

+-

+ AB+-

+ AB

NH2

BH2

NH2

BH2

NH2

BH2

2 H2

CYCLICS

BH2

NH3

BH2

NH2

NH2

+-

BH2

NH3

BH

NH2

NH3

+-BH4

BH3BRANCHED

LINEAR

BH4

H2

H2

NH3

How can we ‘tweak’ or ‘meddle’ with the structure of AB, without sacrificing too much hydrogen, to improve the properties of AB for H2 storage?

Can we modify Ammonia Borane to:

• decrease exothermicity?

• increase the rate of hydrogen release?

• make it stable at 60°C?

• enhance the purity of H2 release?

• decrease the ‘foaming’ problem?

Tweaking Ammonia Borane: Additives on Release Kinetics

DADB – no induction period and a faster peak H2 release rate.

5% DADB & NH4Cl – similar kinetics, little induction period.

5% NaOH or NaBH4 – small effects.

Ammonia Borane at 80 ˚C

Diammoniate of Diborane

H2

Equ

ival

ents

Solid AB, 80 °C

Tweaking Ammonia Borane: Anti-Foaming AgentsSolid AB foamsExplored over 30 different additives

15wt% MC/AB

15wt% MC/AB heated to 180 oC

10wt% MC/AB heated to 180 oC

15wt% MC/AB (T2) heated to 180oC

Neat AB heated to 180oC

Best case:10-20 wt% of methyl cellulose (MC) prevents foaming with proper preparation. 100 mg AB >100 ml H2.

SEM images of MC/AB before

(above) and after (below) heating to

180 oC (loss of 2.5 eq of H2 (13 wt% H2)

13

0%

2%

4%

6%

8%

10%

12%

T=150°C T>150°C T > 150°C, AB:MCM

1:1

T > 150°C AB:BN 1:1

T>160°C, CoCl2

T> 160°C MAB

Wt.

% B

oraz

ine

Borazine Release at Atmospheric Pressure

Hydrogen Impurities

Solid ABAmmonia:100-250ppmBorazine: 0.8 wt% - 12 wt%

MABBorazine- 0 wt%Ammonia - 0.2 wt%

Remaining workHigh pressureNo sweepFilters

Catalysts, additives and temperature can control borazine.Ammonia is low

Medaling with ammonia borane

Medaling = Replacement of a hydrogen with a metal cation:

e.g., LiNH2BH3 (ca 12 wt% H2)

Can we modify thermodynamics (direct reversible?)

AB H2 loss is exothermic MH H2 loss is endothermic

Do we modify rate?break up di-hydrogen bonds

Do we maximize purity of H2

No NH3?No borazine?

MH-H2

Comparison H2 release AB vs LiAB

0 100 200 300 400 5000.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

gm

H2

/gm

of

ma

teri

al

Time (Sec)

LiAB

AB

LAB (at 130°C)

• 10 wt% H2

• no induction period• faster rate• more H2 (at 130°C)• no borazine• less exothermic

• 10X more NH3

Mechanism for H2 release from AB (induction, nucleation, growth)

Effect of other metals on MAB?What is the mechanism for H2 release from MAB?

0 3600 7200 10800 14400 18000 21600 252000

0.2

0.4

0.6

0.8

1

1.2

1.4

time (s)

eq

uiv

ale

nts

of

hyd

rog

en

What is effect of M (Li vs Na Vs K)?How do alkyl substituent's effect rates?

NaNH2BH

3 at 81 °C

KNH(Me)BH3 at 91 °C

LiNH2BH

3 at 81 °C

NaNH(Me)BH3 at 96 °C

KNH(tBu)BH3 at 131 °C

rate: Li < Na < K rate: tBu < Me < H

MAB release: metal mediated release of H2

i) bimolecular MH ‘elimination’ (formation of new B—N bond)

ii) 1,2 addition of [MH] with acidic NH (H2 release)

iii) unimolecular MH‘elimination’

iv) 1,4 addition of [MH] with acidic NH (H2 released)

Net Rxn 2 MNH2BH3 (M)NHBH(M)NHBH3 + 2 H2

HN

HH

M

NHBH BH3

NH2 NHBH

M

BH3

HH

M

BH2

NH2

H

NH

H

M

BH3

NH2 NHBH

BH3

BH2

NH2NHM

BH3

M

M

M

M

M

BH2

NH2

H

NH

H

M

BH3

M

BH2

NH2M

HBH3

NH2M4

5

6

7 HN

H3B

NHBHM

M+ H2

(1) (5t)

(5t)(6H2)

+ H2

(6H2) (7t)

(7t) (8)

Ammonia Borane

16 H2 wt% (material) usable gravimetric capacity (system target= 9 wt%)

120 gH2/L (material) usable volumetric capacity (system target= 80 gH2/L)

1.3 gH2/sec/kg AB release rate (system target = 0.022 gH2/sec/kg)Stability

50°C for over 90 days with no loss observedStable in air and water

Exothermic release 5 kcal/mol H2 (first equivalent)Release temperature – stepwise 90 – 160°CAdditives- improve performance

CoCl2 (IPHE collaboration)<1 wt% borazine60°C for release on-set – accelerated release

Anti-foaming additives demonstratedRegeneration

Off-board demonstrated

Metal Amidoborane Summary

Metal mediated releaseLi < Na < KtBu < Me < H

LiAB – 10 wt% H2

AdvantagesLower release temperature

Increased H2 purityLower exothermicity

Endothermic release demonstrated on low H2 capacity material

Is it possible to regenerate with H2 or an amine?Disadvantages

Lower H2 content Regeneration needs to be examined

Approach to Chemical Hydrogen Storage

DOE EERE Chemical Hydrogen Center of Excellence• Controlling release of hydrogen from AB

– Regeneration of AB off-board– Engineering, experiment and theory– Materials Discovery

DOE BES Hydrogen Fuel Initiative • Structure and dynamics (Neutron and NMR)

– Experimental and computational studies of di-hydrogen bonding interactions (H-/H+)

• Catalysis (XAFS and NMR)– In-situ spectroscopy and mechanistic investigations

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(amine boranes; T = 5 – 500K)

Abhi Karkamkar, Avery Luedtke, John Linehan, Wendy Shaw, Richard Zheng, Greg Schenter, Nancy Hess, Herman Cho, Tricia Smurthwaite, David Heldebrant, Shawn Kathmann, Don Camaioni, Michael Mock, Robert Potter, Dan Dubois, Jerry Birnbaum, Ashley Stowe, Doinita Neiner, Scott Smith, Bruce Kay, Mark Bowden, Roger Rousseau,

Jamie Holladay, Ewa Ronnebro, Yong Joon Choi

Summary Table H2 Release

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Summary of rates, enthalpies and purity of hydrogen. theoretical density (measured density). Bz = borazine. ? = not yet measured, will be determined in future work. All compositions tested are not shown. C= Continue, D = Discontinue for on or off

board transportation systems, still may be applicable for stationary or portable applications

compound gravimetric volumetric additive enthalpy peak rate temperature NH3 Bz notes

g H2/kg g H2/l kJ/mol g/s/kg C ppm wt%

NH3BH3 194 (160) 146 (120) none -23 1.3 160 100-250 4-12 foams

NH3BH3 " " none -23 0.93 145 100-250 2-4 foams

NH3BH3 " " none -23 0.43 130 100-250 2-4 foams

NH3BH3 + AF 155 (136) 117 (102) anti foaming -23 0.43 130 100-250 2-4 no foam

NH3BH3 155 117 CoCl2 ? ? 60 ? 0.8 no foam

AB:MCM " " scaffold (1:1) -1 (-22) 2.8 130 100-250 <1 no foam

AB:MCM " " scaffold (2:1) -10 ? 130 100-250 <1 no foam

AB:MCM " " scaffold (3:1) -12 1.9 130 100-250 <1 no foam

DADB 194 (160) ?? none -16 1.8 145 ? ? little foam

DADB " none -16 0.48 130 ? ? little foam

DADB " none -16 0.2 100 ? ? little foam

NH4BH4 240 130 none -63 ? 40 ? ? little foam

LiNH2BH3 109 52 none ? 1.76 130 200 0 no foam

LiNH2BH3 " " None ? 0.44 100 2000 0 no foam

LiNH2BH3 " " None -2 0.08 90 2000 0 no foam

LiNH2BH3 " " None 0.01 80 2000 0 no foam

NaNH2BH3 76 43 none ? 0.044 80 ? 0 no foam

NaMeNHBH3 30 ?? none ? 0.043 100 ? 0 no foam

KNH(Me)BH3 20 ? none ? ? 85 ? 0 no foam

KNH(tBu)BH3 15 ? none ? ? 130 ? 0 no foam

Backup

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Recent results

• Roger Rousseau, Greg K. Schenter, John F. Fulton, John C. Linehan, Tom Autrey. Operando XAFS and AI MD to characterize Rhodium Clusters in the Catalytic Dehydrogenation of Aminoboranes. J. Am. Chem. Soc. 2009 ASAP.

• Annalisa Paolone, Oriele Palumbo, Pasquale Rispoli, Rosario Cantelli, Tom Autrey, Abhi Karkamkar. Absence of the structural phase transition in ammonia borane dispersed in mesoporous silica: evidence of novel thermodynamic properties. J. Phys Chem.C 2009, 113, 10319.

• Nancy J. Hess, Gregory K. Schenter, Michael R. Hartman, Luc L. Daemen, Thomas Proffen, Shawn M. Kathmann, Christopher J. Mundy, David J. Heldebrant, Ashley C. Stowe and Tom Autrey. Neutron Powder Diffraction and Molecular Simulation Study of the Structural Evolution of Ammonia Borane from 15 to 340 K. J. Phys Chem. A. 2009 DOI: 10.1021/jp900839c.

• Annalisa Paolone, Oriele Palumbo, Pasquale Rispoli, Rosario Cantelli, Tom Autrey. Hydrogen dynamics and characterization of the tetragonal-to-orthorhombic phase transformation in ammonia borane. J. Phys Chem. C. 2009, 113, 5872.

• Li-Qiong Wang, Abhi Karkamkar, Tom Autrey, Gregory J. Exarhos. Hyperpolarized 129Xe NMR Investigation of Ammonia Borane in Mesoporous Silica. J. Phys. Chem. C 2009, 113, 6485.

• Shawn M. Kathmann, Vencislav Parvanov, Gregory K. Schenter, Ashley C. Stowe, Luc L. Daemen, Monika Hartl, John Linehan, Nancy J. Hess, Abhi Karkamkar and Tom Autrey. Experimental and Computational Studies on Collective Hydrogen Dynamics in Ammonia Borane: Incoherent Inelastic Neutron Scattering. J. Chem Phys, 2009, 130 024507.

• Doinita Neiner, Abhijeet Karkamkar, John C. Linehan, Bruce Arey Tom Autrey and Susan M. Kauzlarich. Promotion of Hydrogen Release from Ammonia Borane with Mechanically Activated Hexagonal Boron Nitride. J. Phys Chem C. 2009, 113, 1098.

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Comparison of Energy Storage Approaches

Alternative Power H2FC high energy density compare to Li battery 10X

• remote power• telecommunications

• emergency power• first responders

• transportation power• vehicles

Tweaking Ammonia Borane- Impurity Measurement and Mitigation

Our approachAnalysis tools: NMR, FTIR, Mass spec etc. Develop Borazine formation mechanismTheory to understand barriers

Experimental set upTrap impurities

THF/GlymeNMR

FTIRTG-Mass spec/ RGA

Ammonia borane (NH3BH3)

Structure dominated by di-hydrogen bonding interactionsNH --- BH

Very dynamic (NH3 & BH3) rapidly rotating in place

Alkali Metal Amidoboranes (LiNH2BH3)

Structure dominated by interactions between N Li --- HB

Very little dynamical motion

Synthesis of Alkali Metal Amidoboranes

I) NH3BH

3 + Li*NH2 *NH3 + LiNH2BH

3

THF

M = Li; R = HM = Na; R = H, Me

M = K; R = MeM = Li; R = MeM = K; R = tBu

Synthesis adapted from that reported for Ca(NH2BH3)2 Burrell, A. K. et al. Angew. Chem. Int. Ed. 2007, 46, 8995.

II) NH2(R)BH

3 + MH H2 + MNH(R)BH

3

THF

Thermolysis of Solid LiNH2BH

3

No. Release of 1st equivalent of H2 is faster than release of 2nd equavalent of H2.

3070(30) s820(12) s

138(6) s

0 3600 7200 10800 14400 180000

0.2

0.4

0.6

0.8

1

1.2

1.4

81 °C86 °C91 °C

time (s)

equiv

ale

nts

of

hyd

rogen