Materials for Hydrogen Storage:Materials for Hydrogen Storage:From Nanostructures to Complex From Nanostructures to Complex

HydridesHydrides

Virginia Commonwealth University, Richmond, VA.Virginia Commonwealth University, Richmond, VA.

International Symposium on Materials Issues in Hydrogen productiInternational Symposium on Materials Issues in Hydrogen production on and Storage and Storage –– Santa Barbara August 20Santa Barbara August 20--25, 200625, 2006

Puru Jena

Outline

Materials Requirement for Hydrogen Storage

Nanostructured materials:

Boron Nitride Nano Cage

Metal Coated Carbon Fullerenes

Organo-Metallic Frameworks

Complex light metal hydrides - Sodium Alanates

Acknowledgement

Carbon and Boron Nitride Nano Structures:

Q. Sun, Q. Wang, VCU

Organo-metallic frameworks

K. Boggavarapu, A. Kandalam

Sodium Alanates:

Sa Li, VCU,

C. M. Araujo, and R. Ahuja, Univ. of Uppsala Work Supported by the Department of Energy

Hydrogen Storage RequirementsHydrogen Storage Requirements

High gravimetric (9 wt %) and volumetric density High gravimetric (9 wt %) and volumetric density (70 g/L)(70 g/L)Fast kineticsFast kineticsFavorable thermodynamicsFavorable thermodynamicsEffective heat transferEffective heat transferLong cycle lifetime for hydrogen Long cycle lifetime for hydrogen absorption/desorptionabsorption/desorptionSafety, durability, and cost effectivenessSafety, durability, and cost effectiveness

75% of U.S. oil consumption is used to meet 75% of U.S. oil consumption is used to meet transportation energy needstransportation energy needs

Transportation ApplicationsTransportation Applications

Hydrogen Storage MediaHydrogen Storage Media

Gaseous storage Gaseous storage –– High PressureHigh PressureEnergy content = 4.4 MJ/L (at 10,000 Energy content = 4.4 MJ/L (at 10,000 psipsi))compared to that of 31.6 MJ/L for fossil fuel. compared to that of 31.6 MJ/L for fossil fuel. Costs associated with compression, leakage and safety Costs associated with compression, leakage and safety

are issues of concern. are issues of concern.

Liquid Storage Liquid Storage -- Cryogenic TemperaturesCryogenic TemperaturesDensity of liquid of HDensity of liquid of H22 at 20 K= 70 g/Lat 20 K= 70 g/LEnergy content = 8.4 MJ/L Energy content = 8.4 MJ/L

Solid State StorageSolid State Storage

Materials RequirementsMaterials Requirements

For high gravimetric density (9 wt %) host For high gravimetric density (9 wt %) host materials must consist of light elements: Li, Be, materials must consist of light elements: Li, Be, B, C, N, Na, Mg, AlB, C, N, Na, Mg, AlDifficulties: Bonding of hydrogen is strong Difficulties: Bonding of hydrogen is strong (covalent or ionic) and thermodynamics and (covalent or ionic) and thermodynamics and kinetics are not idealkinetics are not idealIdeal Bonding: not too weak or not too strongIdeal Bonding: not too weak or not too strongWays of altering the chemistry of hydrogen Ways of altering the chemistry of hydrogen bonding: bonding: nanostructuringnanostructuring or catalysisor catalysis

Atomic and Electronic StructureAtomic and Electronic Structure

Linear combination of atomic orbitalsLinear combination of atomic orbitalsGradient Corrected Density Functional TheoryGradient Corrected Density Functional TheoryGaussian Basis sets, and Gaussian 98 codeGaussian Basis sets, and Gaussian 98 codeGeometries optimized without symmetry constraintGeometries optimized without symmetry constraint

CrystalsCrystals

SupercellSupercell Band Structure Methods within Gradient Corrected Band Structure Methods within Gradient Corrected Density Functional TheoryDensity Functional Theory

Atomic Clusters

Boron Nitride Cage

Q. Sun, Q. Wang, and P. Jena, “Storage of molecular hydrogen in B-N cage: Energeticsand thermal stability”, Nano Letts. 5, 1273 (2005)

Passage of H2 into the B36N36 cage

square hexagon

BNH

How many H2 can be inserted inside the cage ?

36H2 24H2 18H220H2

0 2 4 6 8 10 12 14 16 18 20

3.6

3.8

4.0

4.2

4.4

4.6

4.8

5.0

5.2

5.4

∆ = -0.017n3+0.162n2-0.463n+5.332

calculation fitting

HO

MO

-LU

MO

gap

∆ (e

V)

n (number of H2)

0 2 4 6 8 10 12 14 16 18 20

0

5

10

15

20

25

30

35

40

ε = 0.1133n2-0.0684n-0.0247

calculation fitting

Form

atio

n en

ergy

ε (e

V)

n (number of H2)

Energy and gap

0 2 4 6 8 10 12 14 16 18 200.735

0.740

0.745

0.750

R2 = 0.736 + 0.0156exp(-0.157n)

calculation fitting

H-H

bon

d le

ngth

R2

n (number of H2)0 2 4 6 8 10 12 14 16 18 20

1.46

1.47

1.48

1.49

1.50

1.51

R1 = 1.4576 + 0.0067exp(0.1079n)

calculation fitting

B-N

bond

leng

th R

1

n (number of H2)

Changes in bond length

SummarySummary

Boron Nitride Cage can store hydrogen in Boron Nitride Cage can store hydrogen in molecular form, but the energy costs are high molecular form, but the energy costs are high and thermodynamically unstableand thermodynamically unstable

Boron Nitride Cages are not suitable for Boron Nitride Cages are not suitable for hydrogen storagehydrogen storage

Nature of Hydrogen BondNature of Hydrogen Bond

0.76 Å

> 3.0 Å

Nature of Hydrogen BondNature of Hydrogen Bond

Nature of Hydrogen BondNature of Hydrogen Bond

~0.90 Å

~2.5 Å~2.5 Å

Lessons from early studies on Lessons from early studies on clustersclusters

J. J. NiuNiu, B. K. Rao, and P. Jena, , B. K. Rao, and P. Jena, ““Binding of Binding of hydrogen molecules by a transitionhydrogen molecules by a transition--metal ionmetal ion””, , Phys. Rev. Letters Phys. Rev. Letters 6868, 2277 (1992), 2277 (1992)B. K. Rao and P. Jena, B. K. Rao and P. Jena, ““Hydrogen uptake by an Hydrogen uptake by an alkali metal ionalkali metal ion””, , EurophysEurophys. Lett. . Lett. 2020, 307 (1992), 307 (1992)J. J. NiuNiu, B. K. Rao, P. Jena, and M. Manninen, , B. K. Rao, P. Jena, and M. Manninen, ““Interaction of HInteraction of H22 and He with metal atoms, and He with metal atoms, clusters, and ionsclusters, and ions””, Phys. Rev. B , Phys. Rev. B 5151, 4475 (1995), 4475 (1995)G.J. G.J. KubasKubas, Acc. Chem. , Acc. Chem. ResRes, 21, 120(1988), 21, 120(1988)

Ti2: r =1.90 (exp. 1.91) EB = 3.68eV moment =2.0

H2: r =0.749 (exp. 0.741) EB= 4.536 eV (exp. 4.533)

2.992

1.751

117.4

EB = -1.115eV

TiH2

EB = -1.073eV

Ti+H2

0.774

2.01

+

TiH2 and Ti+H2 cluster

Ti coated C60

Q. Sun, Q. Wang, P. Jena, and Y. Kawazoe, J. Am. Chem. Soc. (Communication) 127, 14582 (2005).

E_ab = 0.55eV/H2

R(Ti-H) = 2.0

R(H-H) = 0.81

Moment = 2.0

1.902eV/Ti M=6.0 2.384eV/Ti M=4.0

2.915eV/Ti M=1.90 2.958eV/Ti M=2.0 3.03eV/Ti M=1.80

2.162

2.24

1

1.960.811

EB = 0.55 eV /H2

Moment = 4.0

1.9781.936

1.985

2.31

32.278

0.8050.827

EB = 0.378 eV / H2

Moment = 2.24

(0.0)(+ 0.924eV )

5 H2 molecules on each TiH2 seen to desorb

4 H2 molecules on each Ti atom

E = 0.40 eV / H2

R(Ti-Ti) = 2.855

R(Ti-C) =2.333—2.347

R(Ti-H2) =1.94

NM

E=0.0eV

M=0.0

C1

FM

E=+24.8eV

M=36.0

Ih

Ferri

E=+24.52eV

M=12.0

C2v

SummaryHexagonal site is the most stable site for Ti atom.

Ti atoms tend to form clusters on C60 surface.

For isolated Ti atom on hexagonal site, hydrogen is absorbed in molecular form.

Clustering of Ti atoms make some hydrogen molecules dissociate, resulting in hydrogen bonded to Ti in atomic form more strongly. This would affect the hydrogen release and storage efficiency.

Li Coated CLi Coated C6060 FullereneFullerene

Q. Sun, P. Jena, Q. Wang, and M. Marquez, Q. Sun, P. Jena, Q. Wang, and M. Marquez, ““First Principles Study of Hydrogen Storage of First Principles Study of Hydrogen Storage of LiLi1212CC6060,,”” J. Am. Chem. Soc, 128, 9741J. Am. Chem. Soc, 128, 9741--9745, 9745, (2006)(2006)

E=0.0eV E= + 2.20eV

0.755

0.755

2.072.07

2.236

C60-Li-H2

Li+-H2

C60-Li

2.04

0.75

2.04

2.229

1.461 1.461

C60

1.457

E=0.18 eV E=0.25 eV

H H

Li

C60

Interaction energy: 4.50eV

Weight percent: 13%

Interaction between Li12C60 clusters-I

E=0.4 eV

Interaction between Li12C60 clusters-II

E=1.18 eV

Interaction of H2 with Li12C60 dimer

EH2= 0.18 eV

E= 0.18 eV/H2

Interaction of H2 with Li12C60 dimer

SummarySummary

Li atoms do not cluster on CLi atoms do not cluster on C6060 fullerene surfacefullerene surfaceLi atoms bind strongly to the fullereneLi atoms bind strongly to the fullereneHydrogen atoms bind molecularlyHydrogen atoms bind molecularlyBinding energy of HBinding energy of H22 is small, but significantis small, but significantHigh gravimetric and volumetric densityHigh gravimetric and volumetric densityLiLi1212CC6060 has already been synthesized in the lab.has already been synthesized in the lab.Interaction between LiInteraction between Li1212CC6060 dimersdimers do not do not destroy the cluster geometrydestroy the cluster geometry

Interaction of HInteraction of H22 with Ti supported with Ti supported on organic moleculeson organic molecules

CC55HH55

CC44HH44

CC88HH88

1.75Å

2.40Å1.76Å1.76Å

0.832Å

1.91Å

0.82Å

1.75Å

1.76Å

1.96Å

1.98Å

0.80Å

0.80Å

1.95Å1.75Å

1.95Å 1.76Å

0.83Å

0.80Å

1.91Å

1.93Å

2.00Å 1.90Å

1.90Å

1.90Å

0.84Å

0.84Å

0.84Å

0.84Å

(b)(a) (b′)

(c) (c′) (d)

1.75Å

2.40Å

1.75Å

2.40Å1.76Å1.76Å

0.832Å

1.91Å

1.76Å1.76Å

0.832Å

1.91Å

0.82Å

1.75Å

1.76Å

1.96Å

1.98Å

0.82Å

1.75Å

1.76Å

1.96Å

1.98Å

0.80Å

0.80Å

1.95Å1.75Å

1.95Å

0.80Å

0.80Å

1.95Å1.75Å

1.95Å 1.76Å

0.83Å

0.80Å

1.91Å

1.93Å

2.00Å1.76Å

0.83Å

0.80Å

1.91Å

1.93Å

2.00Å 1.90Å

1.90Å

1.90Å

0.84Å

0.84Å

0.84Å

0.84Å1.90Å

1.90Å

1.90Å

0.84Å

0.84Å

0.84Å

0.84Å

(b)(a) (b′)

(c) (c′) (d)

Optimized geometries of Ti C5H5 (H2)n, (n=1-4) along with important bond lengths (Å). The energy difference (∆E) between (b) and (b′) is 0.12 eV; (c) and (c′) is 0.02 eV

with (b) and (c) being lower in energy than (b′) and (c′), respectively.

Hydrogen Storage and the 18 Hydrogen Storage and the 18 electron ruleelectron rule

Ti 3dTi 3d22 4s4s2 2 Total number of electrons = 4Total number of electrons = 4CC55HH55 Total number of electrons = 5Total number of electrons = 5TiCTiC55HH55(H(H22))4 4 Total number of electrons = 17Total number of electrons = 17TiCTiC55HH5 5 cannot accommodate more than 4 Hcannot accommodate more than 4 H22molecules molecules TiCTiC44HH44 can accommodate 5 Hcan accommodate 5 H22 moleculesmoleculesTiCTiC88HH88 can accommodate 3 Hcan accommodate 3 H22 moleculesmolecules

1.73Å

2.20Å

1.75Å0.82Å

2.22Å

1.89Å0.83Å

0.83Å

0.88Å

1.93Å

1.83Å1.90Å

2.20Å

0.84Å0.84Å

0.84Å0.84Å

1.90Å

2.20Å 0.83Å

0.83Å 0.84Å

0.84Å

0.77Å

2.17Å

1.89Å1. 90Å

2.23Å

0.81Å0.81Å

1.79Å

1.72Å

1.93Å

1.96Å

2.31Å

(b′)

(c′) (d)

(d′) (e) (f)

2.06Å

(a′)

2.20Å 2.04Å

1.72Å

(b)

(c)

2.04Å 0.92Å

0.92Å

1.82Å1.81Å

(a)

1.73Å

2.20Å

1.73Å

2.20Å

1.75Å0.82Å

2.22Å

1.89Å 1.75Å0.82Å

2.22Å

1.89Å0.83Å

0.83Å

0.88Å

1.93Å

1.83Å1.90Å

2.20Å

0.83Å

0.83Å

0.88Å

1.93Å

1.83Å1.90Å

2.20Å

0.84Å0.84Å

0.84Å0.84Å

1.90Å

2.20Å

0.84Å0.84Å

0.84Å0.84Å

1.90Å

2.20Å 0.83Å

0.83Å 0.84Å

0.84Å

0.77Å

2.17Å

1.89Å1. 90Å

2.23Å0.83Å

0.83Å 0.84Å

0.84Å

0.77Å

2.17Å

1.89Å1. 90Å

2.23Å

0.81Å0.81Å

1.79Å

1.72Å

1.93Å

1.96Å

2.31Å

0.81Å0.81Å

1.79Å

1.72Å

1.93Å

1.96Å

2.31Å

(b′)

(c′) (d)

(d′) (e) (f)

2.06Å2.06Å

(a′)

2.20Å

(a′)

2.20Å 2.04Å

1.72Å

2.04Å

1.72Å

(b)

(c)

2.04Å 0.92Å

0.92Å

1.82Å1.81Å

(c)

2.04Å 0.92Å

0.92Å

1.82Å1.81Å

(a)

Optimized geometries of Ti C4H4 (H2)n (n=1-5) along with important bond lengths (Å). The energy difference (∆E) between (a) and (a′) is 0.35 eV, (b) and (b′) is 0.29 eV,

(c) and (c′) is 0.07 eV, and (d) and (d′) is 0.05 eV with (a), (b), (c), and (d) being lower in energy than (a′), (b′), (c′), and (d′), respectively.

0.83Å0.83Å

1.96Å1.96Å

1.90Å 0.83Å

1.90Å

1.70Å

2.30Å

0.86Å0.86Å

1.90Å

1.85Å

0.81Å1.71Å

1.70Å 1.97Å

1.93Å

(a) (b)

(b′) (c)

0.83Å0.83Å

1.96Å1.96Å

1.90Å 0.83Å

1.90Å

0.83Å0.83Å

1.96Å1.96Å

1.90Å 0.83Å

1.90Å

1.70Å

2.30Å

1.70Å

2.30Å

0.86Å0.86Å

1.90Å

1.85Å 0.86Å0.86Å

1.90Å

1.85Å

0.81Å1.71Å

1.70Å 1.97Å

1.93Å 0.81Å1.71Å

1.70Å 1.97Å

1.93Å

(a) (b)

(b′) (c)

Optimized geometries of Ti C8H8 (H2)n (n=1-3) along with important bond lengths (Å). The energy difference (∆E) between (b) and (b′) is 0.02 eV with (b) being lower in

energy than (b′).

Table I. Energy gain ∆En (in eV) due to the successive addition of H2 molecules to

Ti(CmHm) complexes

System n ∆En (eV) DMola Gaussianb

TiC5H5(H2)n 1 1.36 1.26 2 0.51 0.47 3 0.45 0.54 4 0.56 0.56

TiC4H4(H2)n 1 1.03 1.10 2 0.26 0.43 3 0.47 0.30 4 0.75 0.77 5 0.22 0.35

TiC8H8(H2)n 1 1.07 1.12 2 0.28 0.30 3 0.36 0.20

a: PW91/DNP b: PW91PW91/(SDD: Ti; 6-31G**: C, H)

Hydrogen Storage in multiHydrogen Storage in multi--deckerdeckercomplexescomplexes

(C(C55HH55Ti)Ti)nn, (C, (C55HH55))n+1n+1TiTinn

(C(C66HH66Ti)Ti)nn, (C, (C66HH66))n+1n+1TiTinn

Choosing substrates to prevent clusteringChoosing substrates to prevent clustering

[(C[(C55HH55Ti)Ti)22] (H] (H22))88 [(C[(C55HH55Ti)Ti)22] (H] (H22))99

BE/HBE/H22 = 0.35 eV= 0.35 eV BE/HBE/H22 = 0.30 eV= 0.30 eV

(C(C55HH55Ti)Ti)22

(C(C55HH55Ti)Ti)22

∆∆E = 0.00 eVE = 0.00 eV ∆∆E = 0.50 eVE = 0.50 eV ∆∆E = 1.02 eVE = 1.02 eV

(C(C55HH55))33TiTi22

?? ??

Complex Light Metal Hydrides Complex Light Metal Hydrides

and and

Role of catalystsRole of catalysts

C.M. Araujo, R. Ahuja, J.M.O. Guillen, and P. Jena, Appl. Phys. Letts. 86, 251913 (2005); C. M. Araujo, S. Li, R. Ahuja, and P. Jena, Phys. Rev. B (in press)

Sodium Alanates

For more information, see website http://www.sc.doe.gov/bes/hydrogen.pdf

Structure of Alanates

Sodium Sodium AlanateAlanate –– NaAlHNaAlH44

4 3 6 2

3 6 2

1 23 3

3 32

NaAlH Na AlH Al H

Na AlH NaH Al H

↔ + +

↔ + +

Discovered: (Finholt & Schlesinger 1955)Direct Synthesis: THF, 140ºC, 150 bar H2 (Ashby 1958, Clasen 1961)Principal Use: Chemical Reducing AgentSensitive to air and water exposure reacting strongly with O2 and OH

NaAlH4 melts at 182ºCPCT Desorption Measurements2-step Decomposition

Dymova, T. N., Eliseeva, N. G., Bakum, S. I.,And Dergachev, Y. M., Doklady Akademii

Nauk. SSSR, 215 (6) (1974) 1369

4 3 6 2

3 6 2

1 23 3

3 32

NaAlH Na AlH Al H

Na AlH NaH Al H

↔ + +

↔ + +

Fundamental Questions

What is the nature of hydrogen bonding and how is it altered by the presence of TiCl3?

What happens to TiCl3?

Where does Ti go? (surface, substitutional, interstitial)

What does it do and how does it do it?

Hypotheses

TiCl3 + 3Na 3NaCl + Ti

Ti can occupy the Na or Al site on the surface, interstitial, or bulk site.

Ti can combine with Al to form TiAlx.

Vacancies can be created at the Na and/or Al site.

NaAlHNaAlH44 super cellsuper cell

2x2x1

96 atom

Total electron density of states of NaAlH4 crystal

Formation EnergyFormation Energy

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

(a) Intrinsic

(e) Alvac

(d) Navac

(c) Ti→Al

(b) Ti→Na

Form

atio

n en

ergy

(eV

)

Ti SubstitutionTi Substitution

Intrinsic Ti→Na

Na vacancyNa vacancy(AlH4)- perfect

Na vacancy –local minimum

Na vacancy –global minimum

Al vacancyAl vacancyAl vacancy –

global minimumAl vacancy –

local minimum(AlH4)- perfect

Hydrogen desorption energyHydrogen desorption energy

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

(b) Ti→Na

(d) Navac (e) Alvac

(a) Intrinsic

(c) Ti→Al

H2 d

esor

ptio

n en

ergy

(eV

)

ConclusionsConclusions

Boron nitride and carbon nanoBoron nitride and carbon nano--cages are not suitablecages are not suitable

Coating these cages with metal atoms may increase the Coating these cages with metal atoms may increase the hydrogen uptakehydrogen uptake

The presence of Na and Al vacancies are more important The presence of Na and Al vacancies are more important than Ti substitution at metal sites: Hydrogen desorption is than Ti substitution at metal sites: Hydrogen desorption is molecular and exothermicmolecular and exothermic

The dominant role of Ti in reducing hydrogen desorption The dominant role of Ti in reducing hydrogen desorption temperature may be an indirect one temperature may be an indirect one -- it leads to vacancy it leads to vacancy formation which in turn reduces hydrogen desorption formation which in turn reduces hydrogen desorption energy. energy.

November 12 - 15, 2007Richmond, Virginia

International Symposium on Scientific and Technological Issues in a Hydrogen

Economy

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