Materials for the Hydrogen Economy (2009) Part 8 ppt

AlFe phase diagram showing intermetallic phases, such as FeAl3, Fe 2 Al 5 , FeAl 2 , and FeAl, which can form as separate layers in aluminized steel... Any of the methods mentioned in t

capability.of.producing.smooth.and.uniform.coatings.on.the.inner.surface.of.small-diameter, high aspect ratio cylindrical components or other confined geometries

Atomic Percent Aluminum

1600 1538°C

1400 1394°C

1200

1000 912°C

800 770°C 600

1232

1169°C ~1160°C 1102°C

fIgure .   AlFe phase diagram showing intermetallic phases, such as FeAl3, Fe 2 Al 5 ,

FeAl 2 , and FeAl, which can form as separate layers in aluminized steel.

The advantages of aluminizing steels go beyond hydrogen barrier formation,.

however, as such surface treatments also provide additional corrosion protection

The.fusion.materials.community.continues.to.study.these.processing.methods.and

may.continue.to.be.the.main.driving.force.for.research.in.this.area.until.hydrogen

infrastructure.issues.become.more.important.27

fIgure .   FeAl coating on the inner diameter of a 316SS tube that was deposited using

the EVE technique.

area.of.hydrogen.permeation.barriers,.particularly.in.the.development.of.new.meth-ods that can provide barriers over large areas for anticipated hydrogen economy.

infrastructure needs Low-cost methods and better reproducibility are required

Hydrogen.remains.an.elusive.species.in.this.regard,.and.a.perfect.solution.is.appar-ently.very.challenging

referenCes

1 Forcey, K.S et al., Hydrogen transport and solubility in 316L and 1.4914 steels for.

fusion.reactor.applications,.Journal of Nuclear Materials,.160,.117–124.(1988).

2 Gibala,.R and.R.F Hehemann,.Eds.,.Hydrogen Embrittlement and Stress Corrosion

Cracking,.ASM,.Metals.Park,.OH,.1984,.p 324.

3 Honeycombe,.R.W.K.,.Steels:.microstructure.and.properties,.in.Metallurgy and

Materi-als Science,.R.W.K Honeycombe.and.P Hancock,.Eds.,.London:.Edward.Arnold,.1981.

fIgure .   A typical aluminized steel surface following the polymer slurry method at

800˚C in air Any of the methods mentioned in this section about aluminized films will

pro-duce similar reaction layers Ease of processing and cost may dictate which method is

pre-ferred for a given application.

4 Hollenberg, G.W et al., Tritium/hydrogen barrier development, Fusion Engineering

and Design,.28,.190–208.(1995).

5 Roberts,.R.M et.al.,.Hydrogen.permeability.of.sintered.aluminum.oxide,.Journal of the

American Ceramic Society,.62,.495.(1979).

6 Yu, G.T and S.K Yen, Determination of the diffusion coefficient of proton in CVD.

gamma.aluminum.oxide.thin.films,.Surface and Coatings Technology,.166,.195.(2003).

7 Serra,.E et.al.,.Hydrogen.permeation.measurements.on.alumina,.Journal of the

Ameri-can Ceramic Society,.88,.15.(2005).

8 Brimhall,.J.L.,.E.P Simonen,.and.R.H Jones,.Data Base on Permeation, Diffusion,

and Concentration of Hydrogen Isotopes in Fusion Reactor Materials,.Fusion.Reactor.

Materials.Semiannual.Progress.Report,.DOE/ER-0313/16,.1994.

9 Forcey, K.S et al., Hydrogen transport and solubility in 316L and 1.4914 steels for.

fusion.reactor.applications,.Journal of Nuclear Materials,.160,.117.(1988).

10 Hollenberg, G.W et al., Tritium/hydrogen barrier development, Fusion Engineering

oxide,.Surface and Coatings Technology,.153,.114.(2002).

14 Song, R.G., Hydrogen permeation resistance of plasma-sprayed Al2O3 and Al2O3

-13wt%.TiO2.ceramic.coatings.on.austenitic.stainless.steel,.Surface and Coatings

Tech-nology,.168,.191.(2003).

15 Tazhibaeva,.I.L et.al.,.Hydrogen.permeation.through.steels.and.alloys.with.different.

protective.coatings,.Fusion.Engineering and Design,.51/52,.199.(2000).

16 Forcey, K.S et al., Formation of tritium permeation barriers by CVD, Journal of

Forcey,.K.S.,.D.K Ross,.and.L.G Earwalker,.Investigation.of.the.effectiveness.of.oxi-dised.Fecralloy.as.a.containment.for.tritium.in.fusion.reactors,.Zeitschrift fur

Physika-lische Chemie Neue Folge,.143,.213.(1985).

22 Shen,.J.-N et.al.,.Effect.of.alumina.film.prepared.by.pack.cementation.aluminizing.

and.thermal.oxidation.treatment.of.stainless.steel.on.hydrogen.permeation,.Yuanzineng

Kexue Jishu/Atomic Energy Science and Technology,.39,.73.(2005).

23 Aiello,.A et.al.,.Hydrogen.permeation.through.tritium.permeation.barrier.in.Pb-17Li,.

Fusion Engineering and Design,.58/59,.737.(2001).

24 Glasbrenner, H., A Perujo, and E Serra, Hydrogen permeation behavior of hot-dip.

aluminized.MANET.steel,.Fusion.Technology,.28,.1159.(1995).

25 Forcey,.K.S.,.D.K Ross,.and.C.H Wu,.Formation.of.hydrogen.permeation.barriers.on.

steels.by.aluminising,.Journal of Nuclear Materials,.182,.36.(1991).

30 Glasbrenner, H et al., The Formation of Aluminide Coatings on MANET Stainless

Steel as Tritium Permeation Barrier by Using a New Test Facility,.Vol 2,.Elsevier,.

Iordanova,.I.,.K.S Forcey,.and.M Surtchev,.X-ray.and.ion.beam.investigation.of.alu-mina.coatings.applied.on.DIN1.4914.martensitic.steel,.Nuclear Instruments and

Meth-ods in Physics Research, Section B: Beam Interactions with Materials and Atoms,.173,.

for On-Board Hydrogen Storage

G J Thomas

ConTenTs

9.1 Introduction 191

9.2 Hydride.Properties.and.Hydrogen.Capacity 192

9.3 Alanates 197

9.4 Borohydrides 200

9.5 Destabilized.Borohydrides 201

9.6 Nitrogen.Systems 202

9.7 Other.Materials 204

9.8 Summary 205

References 205

In.concept,.reversible.hydrides.offer.a.direct.means.of.storing.hydrogen.on-board

fuel.cell.vehicles.and.would.be.compatible.with.a.hydrogen-based.transportation.fuel

infrastructure A.tank,.or.perhaps.more.accurately.a.storage.system,.containing.an

appropriate.hydride.material.would.remain.fixed.on.a.vehicle.and.could.be.refueled

simply.by.applying.an.overpressure.of.hydrogen.gas Once.filled,.the.hydrogen.gas

would.remain.at.the.equilibrium.pressure.for.the.particular.hydride.material,.chang-ing.only.with.temperature.changes.induced.in.the.storage.tank When.hydrogen.was

needed,.it.would.be.released.endothermically,.using.the.waste.heat.from.the.fuel.cell

(or.internal.combustion.engine.[ICE]).to.supply.the.required.energy This.approach

offers.certain.advantages.over.high-pressure.compressed.gas.tanks.and.cryogenic

liquid hydrogen systems—it is inherently stable with regard to hydrogen release,

it can operate at a low or moderate gas pressure, and it could eliminate some of

the.energy.costs.of.compression.or.liquefaction It.also.has.the.potential.to.achieve

volumetric.hydrogen.densities.much.higher.than.those.of.compressed.gas.and.even

liquid.hydrogen

In.practice,.however,.the.use.of.hydrides.for.on-board.hydrogen.storage.is.much

more.complicated.than.is.described.above,.and.a.number.of.issues.arise.when.one

attempts.to.choose.a.material.and.design.a.storage.system These.issues.arise.because

(1).many.hydride.materials.do.not.meet.minimal.on-board.storage.requirements.for

The development of storage materials with properties that can encompass all.

of the required performance attributes for on-board hydrogen storage will be an

In 2001, Schlapbach and Zuttel published a paper on hydrogen storage4 and

included a plot of volumetric and gravimetric hydrogen densities in a variety of

be released by thermolysis, but must be regenerated through a chemical process

This means that the spent fuel must be removed and processed externally These

MgH 2

KBH 4 NaAlH 4

NaBH 4 LiAlH 4

LiBH 4

AlH 3 TiH 2

CaH 2 NaH

LiNH 2 (1)

fIgure .   Plot of hydrogen weight fraction and hydrogen volume density for some

rep-resentative hydrogen storage materials For comparison, the current 2010 and 2015 DOE/

FreedomCAR and Fuel Partnership targets for system weight and system volume densities are

indicated by the dashed lines The densities of compressed hydrogen at ambient temperature

and liquid hydrogen at 20K are also shown.

fuel.tank.is.nearly.empty)

Hydrogen transport in the high-capacity hydrides appears to be through the

movement.of.heavy.atoms,.complexes,.or.lattice.defects.rather.than.hydrogen.atoms,

with correspondingly higher activation energies for diffusion than for interstitial

hydrides In.Ti-.and.Zr-doped.NaAlH4.and.Na3AlH6,.for.example,.Sandrock.et.al.,13

Luo.and.Gross,14.and.Kiyobayashi.et.al.15

In the following sections, specific materials will be discussed in more detail,.

Cu

Ag Cs

Be

Mg Ca Mn Fe

Ti Ga

In Ce

Ti

Zr Sn

M(Al H 4 )

M(Al H4)2

M(Al H4)3M(Al H 4 ) 4

fIgure .   Trend of hydrogen weight fraction for various alanate compounds and cations

as a function of the molecular weight of the compound The trend is also representative of

other complex hydrides, such as borohydrides.

available This.can.be.seen.in.more.detail.using.a.description.of.the.Na–Al–H.sys-tem.as.an.example

NaAlH4.decomposes.to.Na.and.Al,.releasing.its.hydrogen.through.the.following

reaction.chain:

NaAlH4.(+.Ti).≡.1/3.Na3AlH6.+.2/3.Al.+.H2 ∆H.=.37.kJ/mol.H2

1/3.Na3AlH6.(+.Ti).≡.NaH.+.Al.+.½.H2. ∆H.=.47.kJ/mol.H2

of Na alanate Others extended this approach of using co-dopants to consider

Ti, Zr, Fe combinations,32 adding graphite33 and other catalytic complexes.34,35

Although.some.improvements.have.been.reported.with.these.alternative.additives

or.catalysts,.the.overall.performance.of.the.sodium.alanate.materials.has.not.been

significantly improved over the original Ti dopant initially reported by

Bogda-novic.and.Schwickardi.16

Considerable work has been directed toward other alanate compounds in an

effort to find materials with improved reversible properties (capacity, enthalpy,

Sachtler et al.47 studied the material phase space of Na-Li-Mg/AlH4 using an

8-reactor system to measure the reversible hydrogen content in NaAlH4, LiAlH4,

approach Theoretical estimates of material stability, if accurate, can be of great

value to experimental efforts by eliminating unstable candidates and identifying

.was.also.included.in.the.mixtures They.found.that.the.effec-tive enthalpy was reduced significantly, from ~69 kJ/mol H2 for the borohydride.

decomposition.alone.(to.LiH.and.H2).down.to.~45.kJ/mol.H2.when.the.borohydride

reacted.with.MgH2.to.form.MgB2.and.LiH The.lower.enthalpy.value.results.in.an

equilibrium.hydrogen.overpressure.of.1.bar.at.~200°C,.as.compared.to.~400°C.for

the.borohydride

The reaction yielded a reversible hydrogen capacity of 6.5 wt% If the imide.

al.80–83.and.others84,85.have.looked.at.mixtures.of.Li.amide.with.Li.alanate.and.with

Li borohydride DFT calculations86,87 suggest that these systems will behave in a

Another experimental study on the same material system was performed by.

the.increased.level.of.government.funding.in.the.U.S.,.Europe,.and.Asia.for.hydro-gen storage materials Industrial R&D has significantly increased as well

Corre-spondingly, much progress has been achieved, particularly toward understanding

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