hydrogen storage in light complex hydrideshj/h-school08/lecturenotes/sartori.pdf · sartori...

Sartori Sabrina, Summer School on Materials for the Hydrogen Society, Reykjavik, June 19-23, 2008

Sabrina SartoriPhysics Department, Institute for Energy Technology,

Kjeller, Norway

[email protected]

Hydrogen storage in light

complex hydrides


Solid material for hydrogen storage

Source: DoE 2007*

• Metal and complex hydrides

• Chemical hydrides

• Nanoporousstructures

*The goals are changing and also the achievements in high-temp PEM etc (meaning higher temperatures for H-desorption will be acceptable).


M(s) + x/2 H2 MHx(s) + energy

Storage as hydrides

Interstitial metal hydride Complex hydride

AlH4-

Li


• Alanates (Al): NaAlH4, LiAlH4, KAlH4,

Mg(AlH4)2, mixed alanates (Na2LiAlH6, K2LiAlH6) ;- Structures;- Undoped alanates;- Effect of additives;- Dehydrogenation/rehydrogenation

• Amides/imides (N)- Structures;- Dehydrogenation/rehydrogenation

• Borohydrides (B)- Structures;- Dehydrogenation/rehydrogenation- mixed systems

Content


� 2010: ≥≥≥≥ 6 wt%� 2015: ≥≥≥≥ 9 wt%

The Challenge: Goals for hydrogen storage


Status of hydrogen storage systems


Complex hydrides promising candidates

� > 5 wt% hydrogen:� LiAlH4: 10.6 wt%� NaAlH4: 7.5 wt%� Mg(AlH4)2: 9.3 wt%� LiNH2/Li2NH reactions (11.5 wt%)� LiBH4 (18.5 wt%), NaBH4 (10.7 wt%)� Ammonia-Borane systems: e.g. H3NBH3 (19.6 wt%)

� Why not used: problems of thermodynamic and kinetics. Not reversible at moderate conditions. Complicated desorption of H2

� Additives (Bogdanović et al., 1997):

� Reversible (NaAlH4 with Ti-additives). � Reduced desorption temperature.


High-energy ball-milling…

…brings about a broad variety of defects


Al

NaD

Using neutrons to ”see” hydrogen

In contrast to X-ray, neutrons are scattered by the nuclei of the atoms. X-ray data tends to give erroneously short metal-hydrogen distances and incertainties in determination of hydrogen coordinates

JEEP-II

Powder neutron diffraction (PND)


Synchrotron powder X-ray diffraction

Swiss-Norwegian Beamline (BM01)

Dehydrogenation reaction studied by in situ SR-XRD

Sample(capillary)

Heater

Evacuation

Heating under evacuation1˚C/min.

Diffraction data collectedevery 2min


Structural characteristics

AlH4-

Li

Mn+(AlH4)-n

• Anions: AlH4-, AlH6

3-, BH4-,

MgH3- etc. Covalent bonded.

• Metal ions: Alkaline, alkaline earth or 3d elements. Ionic bonded.


NaAlD4

Hauback, Brinks, Jensen, Murphy, Maeland (2003)

� AlD4– tetrahedra

� Al-D: 1.626 Å (at 295 K).� Na+: surrounded by 8 D atoms

from 8 different AlD4– :

� Na-D: 2.439, 2.431 Å.

AlD4

Na

LiAlD4

Combined neutron and X-ray diffraction

• AlD4 – tetrahedra connected

via Li.• Li+ : surrounded by a trigonal

bipyramid of 5 D from 5 different AlD4

– :• Li-D: 1.831 – 1.978 Å.• Al-D: 1.604 – 1.637 Å

Hauback, Brinks, Fjellvåg (2002)

AlD4

Li

KAlD4

� AlD4– isolated tetrahedra

� Al-D: 1.618 Å (at 295 K).� K+: surrounded by ten D

atoms:� K-D: 2.596 Å (at 295 K).

Hauback, Brinks, et al. (2005)


Li3AlD6

Brinks, Hauback (2003)

Li

AlD63-

• Isolated octahedra AlD63–:

• Al-D: 1.754 and 1.734 Å. • Li: 6-coordinated:

• Li-D: 1.892-2.120 Å.

AlD63-

Li

The structure can be described as a distorted bcc structure of AlD6

3–

units with all tetrahedral sites filled with Li

Each Li atom is connected to two corners and two edges of AlD6

3–

octahedra with in total six D atoms in the coordination sphere


Mg(AlH4)2• Isolated AlH4

- tetrahedra.• Mg surrounded by 6 H.• MgH6 octahedra share one

corner with each of six AlH4

- tetrahedra.• Sheet like structure along

c-axis.• Al – H: 1.561, 1.671 Å.

Fichtner et al. (2003)Fossdal, Brinks, Fichtner, Hauback (2005)

Sheets interconnected by van der Waals forces

• Mg(AlH4)2: Solvent-free and fast synthesis

• Details of thermal and isothermal decomposition of Mg(AlH4 )2

• Scale-up strategies promising, but reversibility not sufficient


Mixed alanates Na2LiAlD6 and K2NaAlH6

• Synthesized from NaAlD4+ LiAlD4

• Synthesized by ball milling KH+NaAlH4.

• SR-PXD + PND• Both Fm-3m.• Different size of

octahedron AlD6- and

LiD6-

• fcc geometry of AlD6

• K in tetrahedral sites• Na in octahedral sites

Brinks, Hauback, Jensen, Zidan (2005)Sørby, Brinks, Fossdal, Thorshaug, Hauback (2006)

AlD6

LiD6

Na

Na2LiAlD6 K2NaAlH6

a = 8.118(1) Åa = 7.3848(1) Å

Isostructural to Na2LiAlD6


Dehydrogenation and

rehydrogenation- Undoped alanates

Desorption ALANATES, e.g. NaAlH4 ( 7.5 wt%):3 NaAlH4 →→→→ Na3 AlH6 + 2 Al + 3 H2 3.7w% 180-230°°°°C

Na3 AlH6 →→→→ 3 NaH + Al + 3/2 H2 1.9wt% 230-250°°°°C

NaH →→→→ Na + ½H2 1.9wt% 425°°°°C

The reaction temperatures depend strongly on the heating rate


Study of dehydrogenation LiAlD4 - In-situ PXD

Brinks, Hauback, Fjellvåg, Norby (2003)

2θ

220°C

160°C

130°C

LiAlD4

Li3AlD6+Al

LiD +Al

0.5 °C/min.. T

•3LiAlH4 = Li3AlH6 + 2Al + 3H2 150ºC (R1) 5.3 wt%

•Li3AlH6 = 3LiH + Al + 3/2H2 210ºC (R2) 2.6 wt%

•3LiH +3Al= 3LiAl + 3/2H2 350ºC (R3) 2.6 wt%


Thermolysis of KAlH4 releases hydrogen and it consist on three steps of dehydrogenation,

3KAlH4 →→→→ K3AlH6 + 2Al + 3H2 (2.9 wt.%) at 300 ºC (1)K3AlH6 →→→→ 3KH + Al + 3/2H2 (1.4 wt.%) (2)3KH →→→→ 3K + 3/2H2 (1.4 wt.%) (3)

In step 1, KAlH4 decomposes to K3AlH6, followed by decomposition to KH in step 2. KAlH4 was found to be reversible without a catalyst. In situ diffraction investigations of KAlH4 powders published by Mamathaet al. J. Alloys Comp. (2006) revealed the appearance of unidentified phases during decomposition.

KAlH4


Mg(AlH4)2 – In situ PXD

MgH2

MgH2NaCl

AlMg(AlH4)2

Fossdal, Brinks, Fichtner, Hauback (2005)

Mg(AlH4)2 → MgH2 + 2Al + 3H2 135-163 ºC (R1) 7.0 wt%

(without the involvement of AlH63-, as an intermediate phase)

MgH2 + 2Al → AlxMgy + AlaMgb + H2 270-310 ºC (R2) 2.3 wt%


Additives in alanates

ball milling apparatus


Effect of additives – NaAlH4 +Ti-compounds

Bogdanovic et al. (1997)

undoped

The undoped NaAlH4 sample at 160 °C delivers H2 at an almost negligible rate and, even at 200 °C, the H2 evolution takes 22-24 h until completion. In contrast samples doped with Ti(OBu)4 is completed at 160 °C within 6-8 h and at 180 and 200 °C within 2-3 and 1 h respectively


Effect of TiCl3 in NaAlH4 (ball milled)

H2 desorptionT=125°°°°C

Bogdanovic et al. (1997); Sandrock et al. (2002); Srinivasan, Brinks, Hauback, Jensen (2004)

Multiple order-of-magnitude increases in kinetics. Decrease desorption temperatures

H2 absorptionT=125°°°°C, P=8 MPa


Doped NaAlH4


PCT at 160 ºC for 6 different mol% doping level of Ti

Bogdanovic et al., (2007)


Van’t Hoff plot


0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 20 40 60 80 100

Cycle number

Rel

ease

d h

yd

rog

en, w

t.%

100 cycles

Improve significantly reversibility (NaAlH4). Up to 4.5 wt% cyclic H-capacity

Effect of TiCl3 in NaAlH4 (ball milled)


NaAlH4 + TiCl3

Solid solution

Na1-3xTixAlH4

NaAl1-xTixAlH4

Could improve kinetics in grains.

PXD: Changes in unit-cell dimension of NaAlH4

Heterogenous catalyst

Catalyzing hydrogen splitting/combination and/or diffusion of metal- containing species.

PXD: Detection of secondary Ti-containing phases.

� The effect of the additives NOT understood:� Dopant or catalyst?� Solid solution or secondary phase?


11.3113(3)5.0102(1)NaAlD4 + 6% TiCl4

11.3069(2)5.0090(1)NaAlD4

11.3498(2)5.0233(1)NaH+Al+2%Ti(OBu)4@ 7 cycles

11.3493(2)5.0234(1)+ 6% TiF3

11.3493(2)5.0234(1)+ 6% TiCl4

11.3481(2)5.0231(1)+ 6% TiCl3

11.3483(2)5.0232(1)NaAlH4

c (Å)a (Å)

� NaAlH4 + TiCl3/TiCl4/TiF3/Ti(OBu)4�No significant changes in unit-cell dimensions of NaAlH4

•No significant solid-solution of Ti into NaAlH4

Brinks, Jensen, Srinivasan, Hauback, Sun, Murphy (2004)

Nature of additives – NaAlH4 +Ti-compounds


Ti-doped

Sc-doped

In comparison toTiCl3-doped NaAlH4, ScCl3and CeCl3dopants reduce hydrogenation times by a factor of 2 at high pressure and by a factor of 10 at low pressure.

Others additives NaAlH4

As TiCl3 is the best Ti-precursor compound (together with Ti-nanoparticles), trichlorides of the first-row transition metals are investigated as alternative dopants. ScCl3 results highly efficient, both with respect to storage capacity and kinetics.

Bogdanovic at al. (2006)


Sodium Alanate

• Synthesis of NaAlD4 with improved kinetics and reversibility (4 wt% H2)

• Improved synthesis of catalyst: Ti13*6THF

• 2NaAlH4+LiH+2mol%TiF3 leads to the formation of reversible Na2LiAlH6 (2.8 wt%)

• Adjustment of the stability of complex hydrides by anion substitution (H/F). Na3AlH6-xFx less stable than Na3AlH6

Na2LiAlD6

LiD6

Na

AlD6


LiAlD4 with additives

� VCl3 reduces thedesorptiontemperature more efficiently

� 3TiCl3•AlCl3decomposes more LiAlD4 into Li3AlD6during ball-milling (from PXD data) 0 100 200 300 400 500

0

2

4 Milled LiAlD

4 (/10)

LiAlD4 w/ 2% VCl

3

LiAlD4 w/ 5% VCl

3

LiAlD4 w/ 2% 3TiCl

3·AlCl

3

LiAlD4 w/ 5% 3TiCl

3·AlCl

3

P/

10

-4 m

bar

T/ OC

Thermal desorption spectroscopy

Blanchard, Brinks, Hauback, Norby Mater. Sci. Eng. B (2004) 2°C/min

Three separate peaks of hydrogen desorption in agreement with the 3 decomposition steps


LiAlD4 with additives - In-situ SR PXD

Blanchard, Brinks, Hauback, Norby (2004)

• VCl3 and TiCl3·1/3AlCl3 reduce desorption temperature by 60 and 50 °C respectively .

• Amount and type of additive important for the decomposition.

2 % VCl3

Heating rate 1 °C/min


TiF3 in Na2LiAlH6: thermal data

• Na2LiAlH6: (Diss enthalpy) ∆H0 = 56.4 kJ/mol H2 (more stable) • Na3AlH6: ∆H0 = 47 kJ/mol H2 (Bogdanovic 2000)Reversible decomposition, sample rehydrogenated in 1-2 h at 200 °CNa2LiAlH6 = 2NaH + LiH + Al + 3/2H2

1.90 1.95 2.00 2.05 2.10 2.15 2.20 2.25 2.30

1.0

1.5

2.0

2.5

3.0

3.5

4.0

170oC

200oC

250oC

lnP

1000/T (K-1)

TiF3 catalyst

Fossdal, Brinks, Hauback (2005)

van’t Hoff plotPCT data


K2NaAlH6: Stability

• Reaction reversible

• Very stable• Fast desorption

kinetics (60 min at 325°C and 90 min at 280°C)

1.66 1.68 1.70 1.72 1.74 1.76 1.78 1.80 1.82

-3.4

-3.2

-3.0

-2.8

-2.6

-2.4

-2.2

-2.0

-1.8

-1.6325ºC (170 mbar)

280ºC

K2NaAlH

6

∆Hº = 98.2 kJ/mol-H2

∆Sº = 149.9 J/K mol-H2

ln p

1000/T (K-1)

2 3 4 5 6

0.1

1

10

p (

bar

)

H / FU

Sørby, Brinks, Hauback (2006)

+ 1mol% TiF3


Amides - Structures

LiNH2

Mg(NH2)2

Li4BN3H10

Mechanical milling of LiNH2 and LiBH4in varying combination ratio

LiND2, Mg(ND2)2 and Li2ND(H) can be described as (pseudo-)fcc packing of amide/imide anions with cations in tetrahedral sites. Pure, well-crystallineMgND is hard to obtain from decomposition of Mg(ND2)2.


200 °C (better with TiCl3 )

320 °C

But competitive reaction: Li-amide decomposes in 2LiNH2 Li2NH + NH3Ammonia depletes one of the reactants and diminishes the hydrogen absorption capacity

Li-amide/imide systems


The Li-amide/imide – systems:

- LiNH2 + LiH dehydrogenation begins at approx. 277 ˚C (10 ˚C/min under Ar);

- Increasing Mg concentration, the temp. is decreased to c.a. 100 ˚C ;

- Mg(NH2)2 + 4LiH n=4, the main weight loss below 230 ˚C.

New systems:

Partial Mg-substitution and Mg-amide/imides.

•Amides of alkali or alkali-earth metals, e.g. LiNH2, Mg(NH2)2, Ca(NH2)2, react with metal hydrides to release hydrogen. • Among several combinations, reactions of Mg(NH2)2 with LiH have an advantage of providing a high capacity in wt%. However, the reaction mechanism is still not clear.


3Mg(NH2)2 + 8LiH 4Li2NH + Mg3N2 + 8H2

Reaction between Mg(NH2)2 and LiH in

different ratios

(n=8/3; 6.9 wt% Tdes > 400 ˚̊̊̊C) [2]

Mg(NH2)2 + 2LiH Li2Mg(NH)2 + 2H2 (n=2; 5.6 wt%

Tdes > 200 ˚̊̊̊C) [1]

[1] Xiong et al., Adv. Mater., 16 (2004) 1522. [2] Leng et al., J. Phys Chem B, 108 (2004) 8763. [3] Y. Nakamori et al., J. Alloys Compd., 370 (2004) 271.

3Mg(NH2)2 + 12LiH 4LiN3 + Mg3N2 + 12H2 (n= 4; 9.1 wt%

Tdes > 500 ˚̊̊̊C) [3]-What is an intermediate phase for each?

-Depends on the [Mg]/[Li] ratio or not ?


Reports for the 1:2 (n=2) systemMg(NH2)2 + 2LiH �� Li2MgN2H3.2 + 1.4H2

Li2MgN2H3.2 �� Li2Mg(NH)2 + 0.6H2

Rijssenbeek et al (GE, USA)[5]

From P-C itotherm and XRD

Luo et al (Sandia NL, USA)[4]

[4] Luo et al, J. Alloys Compd., 407 (2006) 274.

[5] Rijssenbeek et al , MH2006


Sample preparation

3Mg +8LiNH2: ball-milled,

dehydrogenated at 250 ˚C in vac

and rehydrogenated at 200 ˚C, 10 MPa H2

[Sample I]

3Mg(NH2)2 + 8LiH: ball-milled in 1 MPaH2 for 2h

[Sample II]

Synthesized from 3Mg +8LiND2 in a similar process to Sample II

A Li-Mg-N-D phase prepared by dehydrogenated at 200˚C in vac for

8h

a mixture of Mg(NH2)2 and LiH (+ Li-Mg-N-H) [1]

[Sample III, Deuterated sample]

[1] Okamoto et al. J.Alloys Compd.

Fully hydrogenated

Partly dehydrogenated


In situ SR-PXD for Sample I (prepared by milling Mg(NH2)2 and LiH)

10 20 30 402θ / deg

0

5000

10000

15000

20000

25000

Inte

nsity

/ a.

u.

Amorphousphase

LiH

Li2O MgO

New phase

200˚̊̊̊C

240˚̊̊̊C

100˚̊̊̊C

140˚̊̊̊C

Li2O MgO

The patterns of the new phase from 180 ˚̊̊̊C to 240 ˚̊̊̊C


In situ SR-PXD for Sample II(prepared from Mg and LiNH2)

Li2O MgO

Mg(NH2)2

LiH

Li-Mg-N-H

110˚̊̊̊C

Inte

nsity

/ a.

u.

0

5000

10000

15000

20000

5 10 15 20 25 30

2 θ / deg

New phase

210˚̊̊̊C

290˚̊̊̊C

150˚̊̊̊C

250˚̊̊̊C


Mg(NH2)2 + 2LiH Li2Mg (NH)2 + 2H2

1 : 2 ratio

3 : 8 ratio

3Mg(NH2)2 + 8LiH 3Li(2+x)MgN2H(2-x) + (2-3x) LiH + 3(2+x)H2

X depends on the condition0 x 2/3< ~<

LiH rich

Investigate by Chen, Luo et al., Zhao et al.


SR-PXD

Structure of the new intermediate phaseRefinement combined PND and SR-PXD

x~0.6 forLi(2+x)MgN2D(2-x)

PND

Li rich and D poor imide

Primitive cubica = 5.0246(2) Å

Li2.6MgN2D1.4

Li

Li or Mg

N

Mg

D

Rwp = 7.29%

Rwp = 10.4%


PCI: Mg(NH2)2 + nLiH (n=2, 8/3, 4)


Schematic view of the

reaction process


2LiNH2 +MgH2

Thermodynamic characterization

Luo (2006)


Borohydrides


LiBH4

• LiBH4 = LiH + B + 3/2 H2 (13.9 wt%)• Peq = 1 bar @ 410°C• Slow kinetics < 600°C

• NaBH4 and KBH4 more stable (670/830°C)

• LiBH4 “destabilized” by stabilizing the products• LiBH4 + ½ Mg = LiH + ½ MgB2 + 3/2 H2

• LiBH4 + ½ MgH2 = LiH + ½ MgB2 + 5/2 H2

• Cycled at 330°C • TiCl3 used as catalyst

J.J. Vajo, S.L. Skeith J. Phys. Chem. B 2005


Low- and high-temperature

structures of LiBH4


Dehydrogenation reactions

M(BH4) MgH + B + 3/2H2

A(BH4) AB + 2H2

M(BH4)2 MH2 + 2B + 3H2

M(BH4)2 MB2 + 4H2

M(BH4)2 2/3MH2 + 1/3MB6 + 10/3H2

Alkali metal borohydrides:

Alkaline earth borohydrides:


Thermal desorption from LiBH4


Ca(BH4)2

Riktor (2007)


Mg(BH4)2


Mixed systems MgH2 - LiBH4 for

changing the stability

Bösenberg, Acta Materialia (2007)


Upscaling of Solid Storage Tank

8 kg alanate Pilot tank (currently manufactured)

Length: 129 cm, Diameter: 34 cm. Capacity: 0.4 kg H2

Design and development of operational prototype solid storage tanksLaboratory tank for 0.5 kg of alanate

Length: 40 cm / Diameter: 6 cm Capacity: 20 g H2

0 10 20 30 40 50 600

1

2

3

4

5

simple preparation from NaH/Alwith TiCl

4, 125°C

100 bar (STORHY)

preparation from NaAlH

4

with Ti-nanoclusters, 100°C, 100 bar(Fichtner et al.)

H2-c

once

ntra

tion

[wt.%

]

Time [min.]

preparation from NaAlH

4 with TiCl

3, 125°C, 79-88 bar

(Sandrock et al.)

2nd absorption

Evaluation of low cost (< 1 Euro/kg) production routes for complex hydrides using catalysed NaAlH4 as model material

Up-scaling to kg amounts demonstrated

Concept for upscaling of material production processes


Safety experiments

t=0 ms

t=30 ms

t=320 ms

Ti doped NaAlH4High speed images at different times are shown on the left, the corresponding infrared images are shown on the right.


Estimation for system capacities in different

hydrogen storage systemsSolid materials:• Good safety aspect;• High volumetric density;• Other projects such as

NessHy/NanoHy/FlyHy learned a lot from StorHy work and indicate possibilities in improvement also in gravimetric densities

•Porosity of the bed: 20 % (compressing the powder)•Maximum operating pressure: 50 bars•Maximum temperature : 215 °C •Capacities of 0.0356 kg/L

Improved tank ?

Actual• Gravimetric capacity of the material: 4 wt%• Material density: 1270 kg/m3.• Porosity of the bed: 53 %• Maximum temperature: 300 °C• Heat transfer coefficient: 0.55 W/mK • Operating pressure: 100 bar, design pressure 150 bar.• Capacities of 0.0214 kg/L

Vision


�At present, no solid storage material fulfils the major targets for automotive applications;

�Up to now, storage densities of ~2 wt.% are achievable on system level with complex hydrides on alanate basis (capacity of the material 4 wt%);

�Further research for novel storage materials with improved storage densities, kinetics and thermodynamic behaviour as well as for advanced system components, e.g. heat exchanger, is still required;

�For on-board storage in fuel -cell-driven vehicles, the hydrogen in thealanates needs to be reversibly charged and discharged, which is only possible for the pure system under extreme conditions. To make the material reversible under practical conditions, it has to be added with a catalyst. Still not understood the effect of additives;

�For technical applications is not acceptable that after low-pressurerehydrogenation, the system is not rehydrogenated as quickly as prior (system without cycle stability);

�High charging rates under low pressures are still a challenge on the way to a practicable solid-state hydrogen- storage material for fuel-cell-powered cars.

Conclusion

hydrogen storage in light complex hydrideshj/h-school08/lecturenotes/sartori.pdf · sartori...

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