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11
NanoEngineering GroupNanoEngineering Group
Hydrogen StorageHydrogen Storage
Gang ChenGang ChenMassachusetts Institute of TechnologyMassachusetts Institute of Technology
Cambridge, MACambridge, MA
Collaborators:
Mildred S. Dresselhaus, MIT
Vincent Berube, MITGregg Radtke, MIT
Costas Grigoropoulos, UCB
Samuel Mao, UC Berkeley
Xiao Dong Xiang, Intematix
Taofang Zeng, NCSU
Sources:Thomas Audrey, PNNLJames Wang, SNL
Andreas Zuttel, IfRES
Department of Energy
ENIC Tutorial
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22
NanoEngineering GroupNanoEngineering Group
OutlineOutline
Why hydrogen economy?Why hydrogen economy?Hydrogen storage requirements/challengesHydrogen storage requirements/challenges
Ways to store hydrogenWays to store hydrogen
NanoscaleNanoscale effects on hydrogen storageeffects on hydrogen storage
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33
NanoEngineering GroupNanoEngineering Group
Energy Challenges: Climate ChangeEnergy Challenges: Climate Change
300
400
500
600
700
800
- 8
- 4
0
+ 4
400 300 200 100Thousands of years beforepresent (Ky before present)
0
∆ ∆∆ ∆ T
r e l a t i v e t o
p r e s e n t ( ° C )
CH4(ppmv)
-------- CO2
-------- CH4
-------- ∆∆∆∆T
325
300
275
250
225
200
175
CO2(ppmv)
12001000 1400 1600 1800 2000
240
260
280
300
320
340
360
380
Year AD
A t m o s p h
e r i c C O 2
( p p m v )
T e m p e r a t u r e
( ° C )
- 1.5
- 1.0
- 0.5
0
0.5
1.0
1.5
-------- CO2
-------- Global Mean Temp
Relaxation times
50% of CO 2 pulse to disappear:
50 - 200 years transport of CO 2 or heat to
deep ocean: 100 - 200 years
Intergovernmental Panel on Climate Change, 2001 http://www.ipcc.ch
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44NanoEngineering GroupNanoEngineering GroupFrom Patrovic & Milliken (2003) and James Wang Sandia National Laboratories
StorageProduction Use
.
DistributedGeneration
Transportation
ZERO/NEAR ZEROEMISSIONS
Biomass
HydroWindSolar
Coal
Nuclear
NaturalGas
Oil
W i t h C a r b o n S e q
u e s t r a t i o n
Storage is
Bottleneck
HIGH EFFICIENCY& RELIABILITY
.
DistributedGeneration
Transportation
ZERO/NEAR ZEROEMISSIONS
Biomass
HydroWindSolar
Coal
Nuclear
NaturalGas
Oil
W i t h C a r b o n S e q
u e s t r a t i o n
Biomass
HydroWindSolar
Coal
Nuclear
NaturalGas
Oil
W i t h C a r b o n S e q
u e s t r a t i o n
Storage is
Bottleneck
HIGH EFFICIENCY& RELIABILITY
Hydrogen EconomyHydrogen Economy
Nuclear
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55NanoEngineering GroupNanoEngineering Group
“Tonight I'm proposing $1.2 billion in research funding so
that America can lead the world in developing clean,
hydrogen-powered automobiles… With a new national
commitment, our scientists and engineers will overcomeobstacles to taking these cars from laboratory to
showroom, so that the first car driven by a child born
today could be powered by hydrogen, and pollution-free.”
President Bush, State-of the-Union Address,
January 28, 2003"America is addicted to oil, which is often imported from
unstable parts of the world,“
“The best way to break this addiction is through
technology..”
“..better batteries for hybrid and electric cars, and in
pollution-free cars that run on hydrogen’
President Bush, State-of the-Union Address,
January 31, 2006
Hydrogen: A National InitiativeHydrogen: A National Initiative
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66NanoEngineering GroupNanoEngineering Group
Ways to Store HydrogenWays to Store Hydrogen
Compressed gasCompressed gas
Liquid hydrogenLiquid hydrogenCondensed stateCondensed state
Volumetric densityVolumetric densityGravimetric densityGravimetric density
KineticsKinetics
Heat transferHeat transferEfficiencyEfficiency
ReversibilityReversibility
Operation temperatureOperation temperature
Key Issues
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77NanoEngineering GroupNanoEngineering Group
How large of a gas tank doHow large of a gas tank do youyou want?want?
Schlapbach & Züttel, Nature, 15 Nov. 2001
Volume Comparisons for 4 kg Vehicular H2 Storage
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88NanoEngineering GroupNanoEngineering Group
DOE TargetsDOE Targets
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99NanoEngineering GroupNanoEngineering Group
• Type IV all-composite tanks are available at 5000 psi (350 bar)
• 10,000 psi tanks being developed
Compressed Hydrogen GasCompressed Hydrogen Gas
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1010NanoEngineering GroupNanoEngineering Group
Liquid Hydrogen StorageLiquid Hydrogen Storage
From Patrovic & Milliken (2003)
dormancy
Linde Tank, GM
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1111NanoEngineering GroupNanoEngineering Group
Hydrogen Storage in Condensed StatesHydrogen Storage in Condensed States
PhysisorptionAdsorption on Surface ChemisorptionAbsorption into Matter
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1212NanoEngineering GroupNanoEngineering Group
Potential ElementsPotential Elements
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1313NanoEngineering GroupNanoEngineering Group
Hydrogen Density of MaterialsHydrogen Density of Materials
T. Audrey
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1414NanoEngineering GroupNanoEngineering Group
J. E.Lennard-Jones, Trans. FaradaySoc. 28 (1932),pp. 333.
Potential energy formolecular and
atomic hydrogenabsorption
Desired binding energy range
5000
AlH3 MgH2 TiH2 LiH H-I H-SH H-CH3 H-OH
C ar b on
ph y s or p t i on
Desirable rangeof binding energies:
10-60 kJ/mol(0.1 - 0.6 eV)
2H
Physisorption
Low temperatureMolecular H2
Bond strength [kJ/mol]
Chemisorption
High temperatureAtomic H
400300200100
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1515NanoEngineering GroupNanoEngineering Group
PhysisorptionPhysisorption
• Langmuir Isotherm
1Kp
Kpθ =
+
Molecules Adsorbed
Number of Adsorption Site
θ =
1/ 2exp
B
K T k T
ε −
∝ Assumption: Monolayer coverage
0
0.2
0.4
0.6
0.8
1
0 2 104
4 104
6 104
8 104
1 105
θ
PRESSURE
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1616NanoEngineering GroupNanoEngineering Group
PhysisorptionPhysisorption
S. Brunauer, P. H. Emmett and E. Teller,J. Am. Chem. Soc., 1938, 60, 309
Multilayer coverage
BET Area
22,414
m Asp
V N A
σ =
Vm cm3 /g at STP
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1717NanoEngineering GroupNanoEngineering Group
Research DirectionsResearch Directions
Increasing surface areaIncreasing surface area
Increasing binding energyIncreasing binding energy
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1818NanoEngineering GroupNanoEngineering Group
Increasing Surface AreaIncreasing Surface Area
Johnson, Chem. & Eng. News, 2002
MOF: Rosi et al., Science, 2003Roswell et al., JACS, 2004
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1919NanoEngineering GroupNanoEngineering Group
Increasing Binding EnergyIncreasing Binding Energy
http://www.wag.caltech.edu/f
uelcells/index.html
Boron Doping of CNT,Z. Zhou et al., Carbon, 44, 939, 2006
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2020NanoEngineering GroupNanoEngineering Group
ChemisorptionChemisorption
A. Zuttel
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2121NanoEngineering GroupNanoEngineering Group
ClassificationClassification
Metal hydrides: MgHMetal hydrides: MgH22
Complex hydrides: NaAlHComplex hydrides: NaAlH44
Chemical hydrides: LiBH4, NHChemical hydrides: LiBH4, NH33BHBH33
MgH2 NaAlH4NH3BH3
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2222NanoEngineering GroupNanoEngineering Group
The Hydrogen BottleneckThe Hydrogen Bottleneck
From JoAnn Milliken (2002)
<100<100 atmatm..OperatingOperating
pressurepressure
(too high)(too high)
--4040 -- 6060 °°°°°°°°CCOperatingOperating
temperaturetemperature
(too slow)(too slow)
30 s/kg30 s/kg--HH22Fueling timeFueling time
(reaction kinetics)(reaction kinetics)
$18/kWh$18/kWh$50/kWh$50/kWh$2/kWh$2/kWhSystem storageSystem storage
costcost
LimitedLimited1500 cycles1500 cyclesReversibilityReversibility
(cycle)(cycle)
81 kg/m81 kg/m33Storage vol. %Storage vol. %
9%9%Storage wt. %Storage wt. %
ChemicalChemical
hydridehydrideMetalMetal
hydridehydrideDOE goalDOE goal
(2015)(2015)
JoAnn Milliken (2002)
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2323NanoEngineering GroupNanoEngineering Group
PcTPcT RelationRelation
From A. Zuttel
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2424NanoEngineering GroupNanoEngineering Group
ThermodynamicsThermodynamics
A. Zuttel
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2525NanoEngineering GroupNanoEngineering Group
Stability of HydridesStability of Hydrides
A. ZuttelThermodynamic Equilibrium
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2626NanoEngineering GroupNanoEngineering Group
Energy BarrierEnergy Barrier
MHx
M+H2 /2∆E
Energy
Barrier
Energy
Separation
Thermodynamically Favorable Does Not Mean Kinetically Favorable
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2727NanoEngineering GroupNanoEngineering Group
Reversible Metal Hydride System Reversible Metal Hydride System
Sodium alanate doped with Ti is a reversible material hydrogen storage approach.
Low hydrogen capacity and slow kinetics are issues
NaAlH4
3NaAlH 4
Na 3 AlH
6 + 2Al + 3H
2 3NaH + Al + 3/2H
2
3.7 wt% 1.8 wt%
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2828NanoEngineering GroupNanoEngineering Group
System destabilizationSystem destabilization
•Reduce energy (temperature) needed to liberateH2 by forming dehydrogenated alloy•System cycles between the hydrogen-containing
state and the metal alloy instead of the pure metal
•Reduced energy demand means lowertemperature for hydrogen release.
Doping with a catalyst
•Reduces the activation energy.
•Allows both exothermic andendothermic reactions to happen atlower temperature.
Forming new alloys
R.A. Zidan et al, J. Alloys and Compounds 285 (1999), pp. 119.
Mechanically Doped NaAlH4
Gregory L. Olson DOE 2005 Hydrogen Program Annual Review
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2929NanoEngineering GroupNanoEngineering Group
A. Zuttel
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3030NanoEngineering GroupNanoEngineering Group
ImideImide (NH) and Amide (NH(NH) and Amide (NH22))
First step: LiNHFirst step: LiNH22 ++ LiHLiH LiLi22NH + HNH + H22 (6.55% @ 300C,1atm.)(6.55% @ 300C,1atm.)
Li H LiN
H
H
Li
N H
Li
Li
N
Li
Li
HH
HH
Second: LiSecond: Li22NH +NH + LiHLiH LiLi33N + HN + H22 (5% @ 300c 0.05atm)(5% @ 300c 0.05atm)
Release temperature too high and low release pressure.Release temperature too high and low release pressure.
Li
N H
Li
Li H
Partial Mg substitution reduces releasetemperature
Li1-xMgxNH2
S. Orimo et al., Appl. Phys. A:Materials Science & Processing, Vol 79, No 7, p. 1765 - 1767.
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3131NanoEngineering GroupNanoEngineering Group
Chemical HydridesChemical Hydrides
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3232NanoEngineering GroupNanoEngineering Group
Irreversible Chemical Hydrides Irreversible Chemical Hydrides
20 - 35% sol.Stabilized with
1-3% NaOH
Borax in NaOHCatalyst
NaBH4 + 2H2O →→→→ NaBO2 + 4H2
2LiH + 2H2O →→→→ 2LiOH + 2H2
Light mineral oil slurry,proprietary stabilizers
Pastebyproduct
2Na + 2H2O →→→→ 2NaOH + H2
Polyethylene-coated pellets,mechanically cut to expose Na
• Hydrogen capacity is high at around 10 wt% hydrogen.• Dehydrogenation kinetics are fast.• Reactions are irreversible on-board vehicle.
Regeneration costs area major issue
From Patrovic & Milliken (2003)
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3333NanoEngineering GroupNanoEngineering Group
Fueling CycleFueling Cycle
From DOE BES Hydrogen Report
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3434NanoEngineering GroupNanoEngineering Group
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3535NanoEngineering GroupNanoEngineering Group
NN--EthylcarbazoleEthylcarbazole (Air Products, Inc.)(Air Products, Inc.)
T. Audrey
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3636NanoEngineering GroupNanoEngineering Group
(kg m-3)
110120
Metal ammine complexesMetal ammine complexes
Mg(NHMg(NH33))66ClCl22 = MgCl= MgCl22 + 6NH+ 6NH33 (9.1%) @ T <620K(9.1%) @ T <620K
Ammonia is toxicAmmonia is toxic
Can be used in high T solid oxide fuel cells.Can be used in high T solid oxide fuel cells.
High temperature of hydrogen releaseHigh temperature of hydrogen release
2NH2NH33 3H3H22+ N+ N22 @ ~600K@ ~600K
Christensen et al., J. Mater. Chem., 2005, 15, 4106–4108
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3737NanoEngineering GroupNanoEngineering Group
••HyridingHyriding reaction:reaction:
~1 MW for 5 min.~1 MW for 5 min.
••NanostructuredNanostructured
materials impair heatmaterials impair heat
transfertransfer
••Temperature riseTemperature rise
suppressessuppresses hydridinghydriding
reactionreaction
••Typical hydrideTypical hydride
conductivity: k~0.1conductivity: k~0.1
W/mW/m--KKConductive foams,
fins and meshes
Expanded Graphite
Compacts
Klein et. al., Int. J. HydrogenEnergy 29 (2003) 1503-1511
See: Zhang et. al., J. Heat Transfer, 127 (2005) 1391-1399
Foams: Al, C, etc.Foams: Al, C, etc.
Wire meshWire mesh
SOLUTIONS
Thermal ManagementThermal Management
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3838NanoEngineering GroupNanoEngineering Group
Benefits of NanostructuresBenefits of Nanostructures
Increase kinetics: diffusion time ~ radius square/diffusivityIncrease kinetics: diffusion time ~ radius square/diffusivity
Possibility of coPossibility of co--existence ofexistence of chemichemi-- andand physiphysi--sorptionsorption
Possibility of changing thermodynamic propertiesPossibility of changing thermodynamic properties
• Yang’s Equation:
MHxMHx
2i o
p p
r
σ − =
Surface Tension
Radius
pi
po
• Kelvin Theory:
For multiphase system, transitiontemperature, equilibrium pressure
and enthalpy of reaction changewith radius.
For hydride, we can expect similar
dependence in release temperature,equilibrium pressure and enthalpy of
formation.
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3939NanoEngineering GroupNanoEngineering Group
SimultaneousSimultaneous PhysisorptionPhysisorption andand ChemisorptionChemisorption
0 5 10 15 20
0.0
0.5
1.0
1.5
2.0
2.5
3.0
h y d r o g e n
u p t a k e ( w t . % )
pressure (bar)
MgNi:SiO2 sorption
MgNi:SiO2 desorptionMgNi:SiO
2 sorption (7 days)
MgNi:SiO2 desorption (7 days)
SiO2 sorption
SiO2 desorption
target material
laser
pulse expanding
metal vapor
nanoporous sample
S.Mao, LBNL
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4040NanoEngineering GroupNanoEngineering Group
Size Effects on Thermodynamic PropertiesSize Effects on Thermodynamic Properties
Assuming the following reactionAssuming the following reaction
M + HM + H22 MHMH22 2
ln( ) MH o
M H
aG G RT
a P∆ = ∆ +
2ln eq o o
H
H S P
RT R
∆ ∆= −
2
( ) ( ) ln( )
3 ( , )
MH o
M H
M M MH
aG r G r RT
a P
V r
r
γ →
∆ = ∆ +
∆+
2/3
( , ) ( ( ) ( )) MH M MH MH M adsoption
M
V r r r E
V γ γ γ
→
∆ = − +
Bulk molar free energy of formation
Nanoparticle molar free energy of
formation
AtAt nanoscalenanoscale, surface and size, surface and sizeaffect reaction enthalpy.affect reaction enthalpy.
Increase the surface toIncrease the surface tovolume ratio.volume ratio.
Increase adsorption sites dueIncrease adsorption sites dueto low coordination surfaceto low coordination surfaceatoms.atoms.
Lower binding energy inLower binding energy insmall metallic clusters.small metallic clusters.
Van’t Hoff relation
M d li DFT R lM d li DFT R lt
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4141NanoEngineering GroupNanoEngineering Group
Modeling DFT ResultsModeling DFT Results
If internal energy dependence onIf internal energy dependence onradius is all contained in theradius is all contained in the
surface energy termsurface energy term3 ( , )
( ) M M MH Bulk
V r E r E
r
γ →
∆∆ ≈ ∆ +
FollowingFollowing Tolman’sTolman’s work, surfacework, surfacetension is allowed to vary withtension is allowed to vary with
radiusradius
1
o
ar
∆∆ =
+DFT values of internal energyDFT values of internal energycalculated bycalculated by WagemansWagemans et al.et al.J.AmJ.Am. Chem. Soc. 2005, 127. Chem. Soc. 2005, 127
E th l f R tiE th l f R ti
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4242NanoEngineering GroupNanoEngineering Group
• Nanoparticles with positive ∆∆∆∆ will have
Enthalpy of ReactionEnthalpy of Reaction
2
3ln eq o M M MH o
H
H V S P
RT rRT R
→∆ ∆ ∆
= + −
3 M M MH
eff o
V
H H r
→∆
∆ = ∆ +
Lower equilibrium temperatureLess heat release during hydrogenation
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4343NanoEngineering GroupNanoEngineering Group
ImprovingImproving sorptionssorptions properties with nanotechnologyproperties with nanotechnology
The bulk hydride sorption rate is prohibitively small and releasThe bulk hydride sorption rate is prohibitively small and release temperature ise temperature istoo high.too high.Reducing grain and particle size increases kinetics and uptake.Reducing grain and particle size increases kinetics and uptake.Surface energies and material properties at nanoscale offer ways to tune theenergetics of absorption and desorption.
NanoscafoldingNanoscafolding to improve kinetics and changeto improve kinetics and change
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4444NanoEngineering GroupNanoEngineering Group
NanoscafoldingNanoscafolding to improve kinetics and changeto improve kinetics and change
thermodynamics:thermodynamics: BorazaneBorazane (NH(NH33BHBH33))
Scaffolding decreases H wtScaffolding decreases H wt--%%
by half.by half.
Reversibility is still an issueReversibility is still an issue
T.T. AutreyAutrey et al.,et al., AngewAngew. Chem. Int. Ed. 2005, 44, 3578. Chem. Int. Ed. 2005, 44, 3578 – – 3582.3582.
NanoscaffoldingNanoscaffolding improvesimproveskinetics and reduces enthalpykinetics and reduces enthalpy
of formation (catalytic effect)of formation (catalytic effect)
ReducesReduces emmissionsemmissions ofof
unwanted chemicalsunwanted chemicals
Mass and Heat TransferMass and Heat Transfer
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4545NanoEngineering GroupNanoEngineering Group
Mass and Heat TransferMass and Heat Transfer
α αα α β ββ β
Hydriding/dehydridingReaction
H2 massdiffusion
Nanoscale
heat transfer
Nanostructured
material
• The strongly exothermic hydriding
reaction increases the sample’stemperature which reduces the reaction
rate or even stops the reaction altogether.
• Rapid hydriding reaction thus requireseffective heat removal solution.
• Nanostructures usually have poor heat
transfer characteristics. Therefore, weneed to balance mass diffusion kineticswith heat transfer.
• Diffusion limited hydridereaction.
• Optimal pore and particle
sizes: balance pore diffusionand diffusion in the solidparticle to control kinetics.
100
101
102
103
80 120 160 200 240 280
KX,BULK (FOURIER LAW)
KZ,BULK
(FOURIER LAW)
KZ,FILM
, EXPERIMENTAL
KX,FILM
, EXPERIMENTAL
T H E R M A L C O N
D U C T I V I T Y ( W / m K )
TEMPERATURE (K)
Si0.5
Ge0.5
BULK ALLOY (300K)
Lines--Fitting with Chen’s Model
P=0.6
P=0.5
P=0.6
Cross-Plane
In-Plane
100
101
102
103
80 120 160 200 240 280
KX,BULK (FOURIER LAW)
KZ,BULK
(FOURIER LAW)
KZ,FILM
, EXPERIMENTAL
KX,FILM
, EXPERIMENTAL
100
101
102
103
80 120 160 200 240 280
KX,BULK (FOURIER LAW)
KZ,BULK
(FOURIER LAW)
KZ,FILM
, EXPERIMENTAL
KX,FILM
, EXPERIMENTAL
T H E R M A L C O N
D U C T I V I T Y ( W / m K )
T H E R M A L C O N
D U C T I V I T Y ( W / m K )
TEMPERATURE (K)
Si0.5
Ge0.5
BULK ALLOY (300K)
Lines--Fitting with Chen’s Model
P=0.6
P=0.5
P=0.6
Cross-Plane
In-Plane
100
101
102
103
80 120 160 200 240 280
KX,BULK (FOURIER LAW)
KZ,BULK
(FOURIER LAW)
KZ,FILM
, EXPERIMENTAL
KX,FILM
, EXPERIMENTAL
SS mmar
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4646NanoEngineering GroupNanoEngineering Group
SummarySummary
Key issues:Key issues: volumetric and gravimetric density.volumetric and gravimetric density.
Thermodynamics:Thermodynamics: sorption/ sorption/ desorptiondesorption temperature.temperature.
Kinetics, mass and heat transfer:Kinetics, mass and heat transfer: pumping timepumping time
Reversibility:Reversibility: cycling timecycling time
NanoscaleNanoscale effects on storage density,effects on storage density,thermodynamics, kinetics, and heat transferthermodynamics, kinetics, and heat transfer