ENIC Tutorial
HydrogenHydrogen StorageStorage
Gang Chen Massachusetts Institute of Technology Cambridge, MA
Collaborators : Sources : Thomas Audrey, PNNL James Wang, SNL Mildred S. Dresselhaus, MIT Andreas Zuttel, IfRES Vincent Berube, MIT Gregg Radtke, MIT Costas Grigoropoulos, UCB Samuel Mao, UC Berkeley Department of Energy Xiao Dong Xiang, Intematix Taofang Zeng, NCSU
NanoEngineering Group 1 OutlineOutline
WhyWhy hydrogenhydrogen economy?economy? HydrogenHydrogen storagestorage requirements/challengesrequirements/challenges WaysWays toto storestore hydrogenhydrogen NanoscaleNanoscale effectseffects onon hydrogenhydrogen storagestorage
NanoEngineering Group 2 EnergyEnergy Challenges:Challenges: ClimateClimate ChangeChange
CO 2 CH 4 (ppmv) (ppmv) 800 Relaxation times 325 ------CO 2 + 4 50% of CO2 pulse to disappear: ------CH 4 300 700 ------∆∆∆T 50 - 200 years C)
0 ° 275 600 transport of CO2 or heat to 250 deep ocean: 100 - 200 years 500 - 4 T relative relative to T present ( ∆ ∆ 225 ∆ ∆
200 400 - 8 380 1.5
175 300 ------CO (°C) Temperature 360 2 1.0 400 300 200 100 0 ------Global Mean Temp (ppmv) 340
Thousands of years before 2 0.5 present (Ky before present) 320 0 300
280 - 0.5
260 - 1.0
Atmospheric CO 240 Intergovernmental Panel on Climate Change, 2001 - 1.5 http://www.ipcc.ch 1000 1200 1400 1600 1800 2000 Year AD
NanoEngineering Group 3 HydrogenHydrogen EconomyEconomy
Production Storage Use
Biomass Transportation Storage is Hydro Bottleneck Wind . Solar
Nuclear
Oil Distributed Generation Coal HIGH EFFICIENCY & RELIABILITY Natural ZERO/NEAR ZERO Gas EMISSIONS With Carbon Sequestration Sequestration Sequestration Carbon Carbon Carbon With With With From Patrovic & Milliken (2003) and James Wang Sandia National Laboratories NanoEngineering Group 4 Hydrogen:Hydrogen: AA NationalNational InitiativeInitiative
“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 overcome obstacles 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
NanoEngineering Group 5 WaysWays toto StoreStore HydrogenHydrogen CompressedCompressed gasgas LiquidLiquid hydrogenhydrogen CondensedCondensed statestate Volumetric density Gravimetric density Key Issues Kinetics Heat transfer Efficiency Reversibility
NanoEngineering Group Operation6 temperature How large of a gas tank do you want?
Volume Comparisons for 4 kg Vehicular H 2 Storage
Schlapbach & Züttel, Nature, 15 Nov. 2001
NanoEngineering Group 7 DOEDOE TargetsTargets
NanoEngineering Group 8 CompressedCompressed HydrogenHydrogen GasGas
• Type IV all-composite tanks are available at 5000 psi (350 bar) • 10,000 psi tanks being developed
NanoEngineering Group 9 LiquidLiquid HydrogenHydrogen StorageStorage
Linde Tank, GM From Patrovic & Milliken (2003)
dormancy
NanoEngineering Group 10 HydrogenHydrogen StorageStorage inin CondensedCondensed StatesStates
Physisorption Chemisorption Adsorption on Surface Absorption into Matter
NanoEngineering Group 11 PotentialPotential ElementsElements
NanoEngineering Group 12 HydrogenHydrogen DensityDensity ofof MaterialsMaterials
NanoEngineering Group 13 T. Audrey Desired binding energy range
Potential energy for molecular and atomic hydrogen absorption
Desirable range of binding energies: physorption Carbon 10-60 kJ/mol (0.1 - 0.6 eV) J. E.Lennard-Jones, Trans. FaradaySoc. 28 (1932),pp. 333. 2H
AlH 3 MgH 2 TiH 2 LiH H-I H-SH H-CH 3 H-OH
0 100 200 300 400 500 Physisorption Chemisorption Low temperature Bond strength [kJ/mol] High temperature NanoEngineeringMolecular Group H2 14 Atomic H PhysisorptionPhysisorption
1
0.8
• Langmuir Isotherm 0.6 θ Kp θ = 0.4 1+ Kp
0.2 θ = Molecules Adsorbed Number of Adsorption Site
0 ε 0 2 10 4 4 10 4 6 10 4 8 10 4 1 10 5 −1/ 2 K∝ T exp PRESSURE kB T Assumption: Monolayer coverage
NanoEngineering Group 15 PhysisorptionPhysisorption
S. Brunauer, P. H. Emmett and E. Teller, J. Am. Chem. Soc. , 1938, 60 , 309 Multilayer coverage
BET Area
V N σ A = m A sp 22,414
3 Vm cm /g at STP
NanoEngineering Group 16 ResearchResearch DirectionsDirections
IncreasingIncreasing surfacesurface areaarea IncreasingIncreasing bindingbinding energyenergy
NanoEngineering Group 17 IncreasingIncreasing SurfaceSurface AreaArea
Johnson, Chem. & Eng. News, 2002
MOF: Rosi et al., Science, 2003 Roswell et al., JACS, 2004
NanoEngineering Group 18 IncreasingIncreasing BindingBinding EnergyEnergy
http://www.wag.caltech.edu/f uelcells/index.html
Boron Doping of CNT, Z. Zhou et al., Carbon, 44, 939, 2006
NanoEngineering Group 19 ChemisorptionChemisorption
NanoEngineeringA. Zuttel Group 20 ClassificationClassification
MetalMetal hydrides:hydrides: MgHMgH 2
ComplexComplex hydrides:hydrides: NaAlHNaAlH 4
ChemicalChemical hydrides:hydrides: LiBH4,LiBH4, NHNH 3BHBH 3
MgH NH BH 2 NaAlH 4 3 3
NanoEngineering Group 21 TheThe HydrogenHydrogen BottleneckBottleneck
DOE goal Metal Chemical (2015) hydride hydride Storage wt. % 9% 3 Storage vol. % 81 kg/m Reversibility 1500 cycles Limited (cycle) System storage $2/kWh $50/kWh $18/kWh cost
Fueling time 30 s/kg -H2 (reaction kinetics) (too slow) Operating -40 - 60 °°°C temperature (too high) Operating <100 atm . pressure pressure From JoAnn Milliken (2002)
JoAnn Milliken (2002) NanoEngineering Group 22 PcTPcT RelationRelation
From A. Zuttel NanoEngineering Group 23 ThermodynamicsThermodynamics
NanoEngineering Group 24 A. Zuttel StabilityStability ofof HydridesHydrides
Thermodynamic Equilibrium NanoEngineering Group 25 A. Zuttel EnergyEnergy BarrierBarrier
Energy
Energy Barrier
M+H 2/2 ∆E MH x Separation
Thermodynamically Favorable Does Not Mean Kinetically Favorable
NanoEngineering Group 26 ReversibleReversible MetalMetal HydrideHydride SystemSystem
NaAlH 4
Sodium alanate doped with Ti is a reversible material hydrogen storage approach.
3NaAlH 4 Na 3AlH 6 + 2Al + 3H 2 3NaH + Al + 3/2H 2 3.7 wt% 1.8 wt% Low hydrogen capacity and slow kinetics are issues
NanoEngineering Group 27 SystemSystem destabilizationdestabilization
Forming new alloys •Reduce energy (temperature) needed to liberate
H2 by forming dehydrogenated alloy •System cycles between the hydrogen-containing state and the metal alloy instead of the pure metal •Reduced energy demand means lower temperature for hydrogen release.
Mechanically Doped NaAlH 4
Gregory L. Olson DOE 2005 Hydrogen Program Annual Review
Doping with a catalyst
•Reduces the activation energy. •Allows both exothermic and endothermic reactions to happen at lower temperature.
28 NanoEngineering Group R.A. Zidan et al, J. Alloys and Compounds28 285 (1999), pp. 119. A. Zuttel
NanoEngineering Group 29 ImideImide (NH)(NH) andand AmideAmide (NH(NH 2))
First step: LiNH 2 + LiH Li 2NH + H 2 (6.55% @ 300C,1atm.) H Li Li H N Li N H H H H Li
Second: Li 2NH + LiH Li 3N + H 2 (5% @ 300c 0.05atm) Release temperature too high and low release pressure.
Li Li Li H N H N Li H H Li Li
Partial Mg substitution reduces release temperature
Li 1-xMg xNH 2
NanoEngineering Group 30 S. Orimo et al., Appl. Phys. A:Materials Science & Processing, Vol 79, No 7, p. 1765 - 1767. ChemicalChemical HydridesHydrides
NanoEngineering Group 31 IrreversibleIrreversible ChemicalChemical HydridesHydrides
→→→ NaBH 4 + 2H 2O NaBO 2 + 4H 2
20 - 35% sol. Stabilized with Catalyst Borax in NaOH 1-3% NaOH
→→→ 2LiH + 2H 2O 2LiOH + 2H 2
Light mineral oil slurry, Paste proprietary stabilizers byproduct
• Hydrogen capacity is high at around 10 wt% hydrogen. • Dehydrogenation kinetics are fast. • Reactions are irreversible on-board vehicle. →→→ 2Na + 2H 2O 2NaOH + H 2
Polyethylene-coated pellets, Regeneration costs are mechanically cut to expose Na a major issue
32 NanoEngineering Group 32 From Patrovic & Milliken (2003) FuelingFueling CycleCycle
From DOE BES Hydrogen Report
NanoEngineering Group 33 NanoEngineering Group 34 NN--EthylcarbazoleEthylcarbazole (Air(Air Products,Products, Inc.)Inc.)
NanoEngineering Group 35 T. Audrey MetalMetal ammineammine complexescomplexes
(kg m -3)
110 120
Mg(NH 3)6Cl 2 = MgCl 2 + 6NH 3 (9.1%) @ T <620K Ammonia is toxic Can be used in high T solid oxide fuel cells. High temperature of hydrogen release
2NH 3 3H 2+ N 2 @ ~600K
Christensen et al., J. Mater. Chem., 2005, 15, 4106–4108 NanoEngineering Group 36 ThermalThermal ManagementManagement
•Hyriding reaction: Foams: Al, C, etcetc.. ~1 MW for 5 min. •Nanostructured materials impair heat Wire mesh transfer •Temperature rise suppresses hydriding reaction •Typical hydride Klein et. al., Int. J. Hydrogen Energy 29 (2003) 1503-1511 conductivity: k~0.1 W/m -K Conductive foams, Expanded Graphite fins and meshes Compacts SOLUTIONS
See: Zhang et. al., J. Heat Transfer, 127 (2005) 1391-1399
NanoEngineering Group 37 Benefits of Nanostructures
Increase kinetics: diffusion time ~ radius square/diffusivity Possibility of co -existence of chemi - and physi -sorption Possibility of changing thermodynamic properties • Yang’s Equation: po σ − = 2 Surface Tension pi p o r Radius • Kelvin Theory: MH MH x For multiphase system, transition p i temperature, equilibrium pressure and enthalpy of reaction change with radius. For hydride, we can expect similar dependence in release temperature, equilibrium pressure and enthalpy of formation. NanoEngineering Group 38 Simultaneous Physisorption and Chemisorption
target material laser MgNi:SiO sorption 3.0 2 MgNi:SiO desorption pulse 2 expanding MgNi:SiO sorption (7 days) 2.5 2 metal vapor MgNi:SiO desorption (7 days) 2 SiO sorption 2.0 2 SiO desorption 2
1.5 nanoporous sample 1.0
hydrogen uptake (wt.%) uptake hydrogen 0.5
0.0 0 5 10 15 20 pressure (bar)
S.Mao, LBNL
NanoEngineering Group 39 Size Effects on Thermodynamic Properties
Assuming the following reaction Bulk molar free energy of formation a ∆G =∆ G + RT ln(MH ) o a P M + H 2 MH 2 M H 2 Van’t Hoff relation At nanoscale , surface and size ∆H ∆ S ln Peq =o − o affect reaction enthalpy. H2 RT R Increase the surface to volume ratio. Nanoparticle molar free energy of formation Increase adsorption sites due to low coordination surface a ∆G( r ) =∆ G ( r ) + RT ln(MH ) atoms. o a P M H 2 Lower binding energy in small metallic clusters. ∆ γ + 3VM M→ MH (,) r r
2/3 V ∆ γ γ γ =MH −+ M→ MH(,)(r MH () r M ()) rE adsoption VM
NanoEngineering Group 40 ModelingModeling DFTDFT ResultsResults
If internal energy dependence on radius is all contained in the surface energy term 3V∆ (,)γ r ∆E( r ) ≈∆ E + M M→ MH Bulk r
Following Tolman’s work, surface tension is allowed to vary with radius radius ∆ ∆ = o a DFT values of internal energy 1 + calculated by Wagemans et al. r J.Am . Chem. Soc. 2005, 127
NanoEngineering Group 41 EnthalpyEnthalpy ofof ReactionReaction
∆H3 V ∆ ∆ S ln Peq =o + M M→ MH − o H2 RT rRT R
3V ∆ ∆H =∆ H + M M→ MH eff o r
• Nanoparticles with positive ∆∆∆ will have Lower equilibrium temperature Less heat release during hydrogenation
NanoEngineering Group 42 Improving sorptions properties with nanotechnology
The bulk hydride sorption rate is prohibitively small and releas e temperature is too high. Reducing grain and particle size increases kinetics and uptake. Surface energies and material properties at nanoscale offer ways to tune the energetics of absorption and desorption. NanoEngineering Group 43 Nanoscafolding to improve kinetics and change thermodynamics: Borazane (NH 3BH 3) Nanoscaffolding improves kinetics and reduces enthalpy of formation (catalytic effect) Reduces emmissions of unwanted chemicals
Scaffolding decreases H wt -% by half. Reversibility is still an issue
NanoEngineering Group T. Autrey et al., Angew . Chem. Int.44 Ed. 2005, 44, 3578 –3582. MassMass andand HeatHeat TransferTransfer
Hydriding/dehydriding Reaction • Diffusion limited hydride Nanoscale reaction. heat transfer
H2 mass • Optimal pore and particle diffusion
sizes: balance pore diffusion ααα βββ and diffusion in the solid Nanostructured particle to control kinetics. material • The strongly exothermic hydriding reaction increases the sample’s 10 3 KX,BULK (FOURIER LAW)
temperature which reduces the reaction KZ,BULK (FOURIER LAW) rate or even stops the reaction altogether. mK) mK) mK)
2 • Rapid hydriding reaction thus requires 10
KZ,FILM , EXPERIMENTAL effective heat removal solution. Si Ge K , EXPERIMENTAL 0.5 0.5 X,FILM BULK ALLOY (300K) • Nanostructures usually have poor heat 10 1 In-Plane transfer characteristics. Therefore, we P=0.6 need to balance mass diffusion kinetics P=0.5 with heat transfer. CONDUCTIVITYCONDUCTIVITYCONDUCTIVITYTHERMALTHERMALTHERMAL (W/ (W/ (W/ Cross-Plane Lines--Fitting with Chen’s Model P=0.6 10 0 80 120 160 200 240 280 NanoEngineering Group 45 TEMPERATURE (K) SummarySummary
KeyKey issues:issues: volumetric and gravimetric density. Thermodynamics:Thermodynamics: sorption/ desorption temperature. Kinetics,Kinetics, massmass andand heatheat transfer:transfer: pumping time Reversibility:Reversibility: cycling time NanoscaleNanoscale effectseffects onon storagestorage density,density, thermodynamics,thermodynamics, kinetics,kinetics, andand heatheat transfertransfer
NanoEngineering Group 46