Energy Storage with Complex Hydrides

1
Energy Storage with Complex Hydrides
Nikolai Zarkevich

• Materials Science Engineering Department
• University of Illinois at Urbana-Champaign

Acknowledgement partial support by U.S.
Department of Energy Sandia Metal-Hydride Center
of Excellence (DE-FC36-05GO15064) National
Science Foundation computational grant at NCSA.
Collaborators Sudhakar Alapati (Carnegie
Mellon U.) Roland Stumpf (Sandia National
Lab) Dennis Graham, Ian M. Robertson, D.D.
Johnson (UIUC).
2
Importance Ecology Life on Earth

• Fossil Fuels are exhausting
• Non-renewable fuels oil, coal, natural gas.
• CO2 concentration is increasing
• in the atmosphere ? greenhouse effect
• ? global warming ? raising of the ocean.
• Global climate change can cause
• phase transition from life to no life.
• Pollution ? destruction of environment,
• can be avoided by using alternative fuels.
• Hydrogen (H2) is an ecologically clean fuel
• No pollution, no greenhouse effect.
• Non-exhaustible reversible fuel
• Produces water, obtained from water
• Can be used for energy storage.

Exponential increase C C0 C1exp(T/T1)
C0 280?5 before 1850
3
Alternative sources of Energy

• Hydroelectric limited natural resources.
• Solar, Wind, Geo-thermal broadly available, but
  expensive.
• Nuclear major source of electricity in Japan,
  France, Ukraine.
• Nuclear pollution (example Chernobyl in Ukraine,
  1986).
• Thermonuclear (expected in the future)
• ITER reactor in France - based on TOKAMAK
  invented in USSR.
• 3He isotope delivery from the Moon (planned by
  NPO Energia)
• None of the above is suitable for modern
  vehicles.
• Need high-capacity energy storage for
  transportation.

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Complex Hydrides for Hydrogen Storage

• Hydrogen is an alternative for exhausting fossil
  fuels.
• Today industry can produce enough hydrogen to
  meet the demands.
• Fuel for transportation can power rockets and
  automobiles.
• Hydrogen storage problem
• Low density of H2 gas.
• H2 mixture with air can explode ?? ? .
• Reversible Hydrogen Storage Materials
• Can hold more Hydrogen per volume than liquid H2
• Release enough fuel with moderate heating.
• Complex Hydrides for high-density storage
• Theoretical Computational methods
  Experiment.
• First-principles calculations of P-T plot and
• latent heat of reactions with high accuracy.

Energia (USSR, 1986)
5
Fueled by Liquid Hydrogen
???? - ????????, CCCP, 1986 ?.
??????? space rocket lifts ????? into space
(USSR, 1986).
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Hydrogen

• Fueled by hydrogen

H2 is a nearly ideal diatomic gasin a wide
temperature range 85K ltlt T ltlt 6000K.
Zero-point vibrational energy hv/2 272.84
meV (harmonic approximation is valid at Tltlt52000K)
??????? - ecologically clean space rocket fueled
by liquid hydrogen - can bring up to 100,000 kg
on the Earth orbit (USSR, 1986).
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Enthalpy and Entropy of H2 ideal diatomic gas at
85K ltlt T ltlt 6000K

• H2 enthalpy and entropy are well-described by
  ideal diatomic gas equations.

8
Hydrogen storage goals
Gravimetric, volumetric high density
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Complex Hydrides are molecular solids

• LiBH4 is a molecular solid consisting of Li and
  BH4- ions
• High-temperature phase above Tc 381K has
  unverified
• hexagonal P63mc structure

Low-T phase below 381K orthorhombic structure.
BH4 can rotate

• Non-zero phonon density at zero frequency
  imaginary phonon modes.

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LiBH4 high-T hexagonal structure
Low rotational barriers

• hex P63mc structure

Significant rotational free energy
BH4 can rotate
Imaginary phonon modes ? Harmonic approximation
fails!
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Hydrogen storage with destabilized LiBH4

• LiBH4 MgH2 ? LiH MgB2 H2?
• Reversible destabilization reaction up to 11.4
  wt. H2.
• Vajo, Skeith, and Mertens, J. of Phys. Chem. B
  109, p.3719 (2005).

• Enthalpy is reduced by destabilization,
• resulting in lower operating temperature.

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Calculated Electronic Energy difference

• 2 LiBH4 MgH2 ? 2 LiH MgB2 4 H2?
• ??e 552 meV/H2 53.26 kJ/mol-H2 at T gt 381K,
• 667 meV/H2 (relative to
  ground state) at T lt 381K.

• Calculated using Vienna Ab initio Simulation
  Package (VASP-PAW)
• G. Kresse, J. Furthmuller, Phys. Rev. B 54,
  11169 (1996).
• G. Kresse, D. Joubert, Phys. Rev. B 59, 1758
  (1999).

• Other contributions
• Atomic Vibrations,
• Molecular Translations
• Rotations
• Nuclear spins (entropy)

Important!

• Important to consider relevant phase of each
  material.

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Convergence of Electronic Energies

• Calculated in VASP-PAW
• G. Kresse, J. Furthmuller, Phys. Rev. B 54,
  11169 (1996).
• G. Kresse, D. Joubert, Phys. Rev. B 59, 1758
  (1999).

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Vibrational Energies and Free Energies of
Materials
Energy, meV/H2
Free energy

• Vibrations are important!

• Reversible Reaction
• 2LiBH4 MgH2 ? 2LiH MgB2 4H2?
• Vajo, Skeith, and Mertens, J. Phys. Chem. B 109,
  3719 (2005).

• Sudhakar Alapati provided vibrational data for
  component materials.

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Vibrational Energy and Free Energy difference

• 2LiBH4 MgH2 ? 2LiH MgB2 4H2?

E? F TS

• Vibrational Energy and Entropy are significant

• Sudhakar Alapati provided vibrational data for
  component materials.

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Vant Hoff plot Theory and Experiment
Reversible Reaction 2LiBH4 MgH2 ? 2LiH MgB2
4H2?
Vajo, Skeith, and Mertens, J. Phys. Chem. B 109,
3719 (2005).

Solving Gibbs G E PV ? TS ?G ?Gelecvibr
Hgas? TSgas 0
solution
Vant Hoff plot ln(P) vs. 1/T Experimentally,
?H is extracted via linear fit to low-T data.
Latent heat is the slope
17
Latent Heat DH from Theory and Experiment

• Excellent agreement with experiment

Vajo, Skeith, and Mertens, J. Phys. Chem. B 109,
3719 (2005).
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Conclusions

• Hydrogen can be used as a clean fuel for
  transportation
• was successfully used in USSR.
• Complex hydrides promising materials for
  H-storage.
• By taking into account all important effects
• (translational, rotational, vibrational,
  electronic)
• we calculated the latent heat (enthalpy) and
• Gibbs free energy and constructed the P-T plot
  for the
• reversible hydrogen-storage reaction
• 2LiBH4 MgH2 ? 2LiH MgB2 4H2?
• with high accuracy beyond harmonic
  approximation.
• Agreement with Experiment.
• Successful collaboration

Difference is size and capacity of the fuel tanks
The Past
The Future
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Fueled by Hydrogen
??????? space rocket with ????? space shuttle
(USSR, 1987).
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How far can vehicles travel on hydrogen fuel?

• Buran space shuttle lands after a space trip
  (USSR, 1987).

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Conclusions

• Hydrogen can be used as a clean fuel for
  transportation
• was successfully used in USSR.
• Complex hydrides promising materials for
  H-storage.
• By taking into account all important effects
• (translational, rotational, vibrational,
  electronic)
• we calculated the latent heat (enthalpy) and
• Gibbs free energy and constructed the P-T plot
  for the
• reversible hydrogen-storage reaction
• 2LiBH4 MgH2 ? 2LiH MgB2 4H2?
• with high accuracy beyond harmonic
  approximation.
• Agreement with Experiment.
• Successful collaboration

Difference is size and capacity of the fuel tanks
The Past
The Future