Hydrogen Storage in Metal-N-H Complexes - APS … APS March Meeting-2005 Hydrogen Storage in Metal-N-H Complexes Ping CHEN, Zhitao XIONG, Guotao WU, Jianjiang HU Physics Department,

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APS March Meeting-2005

Hydrogen Storage in Metal-N-H Complexes

Ping CHEN, Zhitao XIONG, Guotao WU, Jianjiang HU

Physics Department, Science Faculty

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Contents

I. Binary Metal-N-H systems

II. Li-Ca-N-H system

III. Li-Mg-N-H system

IV. Other systems

V. Summary

VI. Challenges in the practical applications

VII. Perspectives

VIII. Acknowledgement

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Systems under Investigations

M─NH

H

Amide

LiNH2

(M)n─N─H

Imide

Li2NHLi2MgN2H2

(M)n─N

Nitride

Li3N, Mg3N2

LiMgN

(M)n─N─M─H

Nitride Hydride

Ca2NH

4


50 100 150 200 250 300 350 400 450

0

2

4

6

8

10

Desorption

Absorption

Wt %

H2

Temperature (oC)

-- Chen P, Xiong ZT, Tan KL et al, Nature 2002, 420, 302-304

TPR & TPD of Li3N sample

I. Binary Systems

Li3N + 2H2 ↔ Li2NH + LiH + H2 ↔ LiNH2 + 2LiH

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H / Li-N-H0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00.0

Pres

sure

(bar

)

1000.1

110

100

0.11

10

0.11

10100

c

b

a

Des.

Ab.

Des.

Des.

Ab.

Ab.

0.01

Li2NH at 533K

Reversible of Li3N at 533K

Li3N at 533K


P-C-T Curves of Li-N-H

I. Binary Systems

6


TPR & TPD of Ca2NH sample

Inte

nsity

(a.u

.)

200 300 400 500 600 700

TPR TPD

462527

Temperature ( ºC)

-- Xiong ZT, Chen P, Tan KL et al, J. Mater. Chem. 2003, 13, 1767

I. Binary Systems

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P-C-T curves of Ca2NH

H / Ca2NH

0.01

0.1

1

10

100

0.1

1

10

100

0 0.5 1.0 1.5 2.0

Pres

sure

(bar

)

500oC

550oC

Ab.Des.

Ab.

Des.


I. Binary Systems

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2.1wt%

7.0wt%

11.4wt%

Capacity

723-973KCa2NH + H2 – CaNH + CaH2Ca2NH

323-673KLi2NH + H2 – LiNH2 + LiHLi2NH

323-673KLi3N + 2H2 – LiNH2 + 2LiHLi3N

Temperature ReactionMaterial


Reactions

I. Binary Systems

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Thermodynamic parameters –van’t Hoff plot

1.2x10-3 1.6x10-3 2.0x10-3 2.4x10-3-2.0

-1.6

-1.2

-0.8

-0.4

0.0

0.4

Li2NHCa2NH

Ln(P

)

1/T (K-1)

∆H = -66.1 kJ/mol Li2NH

∆H = -88.7 kJ/mol Ca2NH

I. Binary Systems

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Tuning the Thermodynamic Parameters

M-N-Hn+2 ↔ M-N-Hn + H2

∆G0 = -RTlnKp = RTlnPH2

∆G0 = ∆H0 - T ∆S0

∆S ≅ SH2

At PH2 = 1.0 bar, ∆G0 =0, thus,T = ∆H0 / SH2

∆H – determine the reaction temperature

Reactants

Products

Intermediates

Ener

gy

∆H

Ea

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Mechanism – Interaction between amide & hydrides

H atoms attached to N normally possess positive charges, however, H in ionic hydrides have negative one. The strong chemical potential for the combination of H+ and H- is one of the important driving forces!

Ca─N─H + H─Ca─H

Li─NH

Hδ+

H─Liδ-

Li2NH + H2

Ca2NH + H2

By changing amide or hydride, new reactions and new materials may be discovered.

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Li-based ternary imide I – Li-Ca-N-H

2LiNH2 + CaH2 → Li2CaN2Hn + (6-n)/2 H2

0 100 200 300 400 500

Li2NHLi-Ca-N-H

Temperature (°C)

210 270

130H2

Sign

al

-- Xiong ZT, Wu GT, Hu JJ, Chen P, Adv Mater, 2004, 16, 1522-1525

II. Ternary Systems Li-Ca-N-H

Hydrogen desorption occurs at lower temperature for the ternary system.

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Li-Ca-N-H – P-C-T curve at 220ºC

0.0 0.5 1.0 1.5 2.00.01

0.1

1

10

Pre

ssur

e (b

ar)

H content

~10%

Less than 2 hydrogen atoms can be reversibly stored by one ternary complex of Li-Ca-N-H, which is ~ 2.0 wt% of the starting material.



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2800 3000 3200 3400

Dehydrogenation

Hydrogenation

Inte

nsity

(a. u

.)

Wave Number (cm-1)

Space Group No.: 164 Short Hermann-MauguinSymbol: P- 3 M 1 Schoenflies Symbol: D3d3

Anti-La2O3 Structure

a = 3.56000 Åb = 3.56000 Åc = 5.93560 Å

Li

Ca

N


hydrogenation

20 40 60 80

dehydrogenation

2 theta

Inte

nsity

(a. u

.)

CaNH -like

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Li-based ternary imides II – Li-Mg-N-H

Mg(NH2)2 + 2LiH → Li2MgN2H2 + 2H2 5.55wt%

0 100 200 300 400 500

Li2NHLi-Mg-N-H

Temperature (°C)

174 270

H2

sign

al

Hydrogen desorption profiles of Li-Mg-N-H and Li2NH. Drastic temperature decrease in hydrogen desorption was achieved in ternary systems.


III. Ternary Systems Li-Mg-N-H

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Volumetric Release & Soak

0 50 100 150 200 250 300

0

1

2

3

4

5

6

Temperature (Degree C)

Desorption Absorption

H

con

tent

(wt%

)


-- Xiong ZT, Hu JJ, Wu GT, Chen P, Luo W, Gross K, Wang J, J Alloy Comp, in press

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Li-Mg-N-H – P-C-T at 180ºC

P-C-T measurement shows ~ 5.5wt% of storage achieved at temperature around 180ºC or below. The desorption pressure is pretty high, i. e., at 180ºC, the plateau pressure is above 20 bars.

Certain hysteresis exists.


0.1

1

10

100

1000

10000

0 1 2 3 4 5 6

Wt%

Pres

sure

(Psi

)

Desorption

Absorption


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Li-Mg-N-H - Thermodynamic Analysis

0.0020 0.0022 0.0024 0.0026 0.0028 0.00301

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Log(P) = -4683.65/RT +13.47

Pres

sure

(bar

)

1/T (K-1)

∆Hdes = 38.9 kJ/mol-H2

Theoretically, hydrogen desorption equilibrium pressure at 90ºC is 1.0 bar, close to the PEM fuel Cell operation temperature.

Van’t Hoff plot



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Kissinger’s plot d[Ln(β/Tm

2)]/d(1/Tm) = - Ea/R

Activation energy for hydrogen release form Mg(NH2)2+2LiH is: Ea =102kJ/mol-H2.

For the decomposition of Mg(NH2)2, it is ~ 130 kJ/mol

Mg(NH2)2

Mg(NH2)2+2LiH

100 200 300 400 500 6000

1K/min1.5K/min2K/min2.5K/min3K/min3.5K/min4K/min

Temperature (ºC)

Inte

nsity

(a. u

.)

Li-Mg-N-H - Kinetic Analysis



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Compositional Changes


0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0

M g /L i = 1 /3

M g /L i = 1 /2

M g /L i = 1 /1

Temperature (oC)

NH3

H2

Decrease in LiH content will lead to the release of ammonia at temperature around 200ºC.

Increase Li content further stabilizes N content in the complex and may also leads to the increase in total amount of H2 desorbed. However, part of the hydrogen could be only released at higher temperatures.

Mg(NH2)2 + n LiH → Li-Mg-N-H + H2 n =1, 2, 3

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P-C-T Measurements – 220 ºC


Hydrogen content (wt%)0 1 2 3 4 5 6

0.01

0.1

1

10

1000.1

1

10

100

Li/Mg = 2/1

Li/Mg=3/1

Pres

sure

(bar

)

Clearly, Li-Mg-N-H with Li/Mg=2/1 gives more usable hydrogen at lower temperature than that of Li/Mg=3/1, wherein part of the hydrogen retains in the complex until higher temperatures.

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Ammonia Control

• There are competing processes involved, i.e., Desorption of H2 and direct decomposition of NH containing compounds to NH3.

• Generally, desorption of H2 is favored at lower temperatures.

• To avoid ammonia, we can either lower down the operation temperature or increase hydride content in the reactant.


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IV. Other Systems Mg-Na-N-H

0 20 40 60 80 100 120 140 160 180 200

0

20000

40000

60000

80000

100000

H2

Sig

nal

Temperature (Degree C)

TPA65ºC

TPD

165ºCFast kinetics

Mg(NH2)2 + 2NaH ↔ Na2MgN2Hn + (6-n)/2H2

-- Xiong ZT, Hu JJ, Wu GT, Chen P,, J Alloy Comp, published on line

Desorption in the temperature range of 80 - 200ºC.

Absorption: Ambient temperature or above.

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IV. Other Systems Mg-Na-N-H

0.0 0.5 1.0 1.5 2.0 2.5 3.00.1

0.1

1

10

100

0.1

1

10

100

1

10

100

c

a

b

2.1 2.15 2.2 2.25 2.3 2.35

-0.5

0.0

0.5

1.0

1.5

2.0

P-C-T and van’t Hoff plot

Mg/Na =1/1

1/1.5

1/2

∆H = 19 kCal/mol-H2

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0 100 200 300 400 500 600

Starting materials

Hyd

roge

n Si

gnal

Temperature (ºC)

Synthesized sample

More than 2.0 wt % of hydrogen was released at room temperature or below. Hard to recharge.

Mg(NH2)2 + MgH2 ↔ MgNH (?) + H2

IV. Other Systems Mg-N-H

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In summary, reversible hydrogen storage has been confirmed in the following systems –

A. Li3NB. Li2NHC. Ca3N2

D. Ca2NHE. Li-Mg-N-H with different molar ratio of Li/Mg/NF. Li-Ca-N-H with different molar ratio of Li/Ca/NG. Li-Al-N-H with molar ratio of Li/Al = 3/1H. Mg-Na-N-H with different molar ratio of Mg/Na/NI. Mg-Ca-N-H etc..

V. Review

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VI. Challenges in the Practical Applications

• Chemical Instability – Competing chemical routes exist, exp. direct decomposition of reactants. Sensitive to moisture, CO2, O2 etc.

• Operation Temperature.

• Lifetime – sample segregation, which induces the slow kinetics.

• Material Synthesis and storage.

• Thermodynamic data.

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VII. Perspectives

• Plenty systems for exploration : Nitride, Imide, Nitride hydrides etc., binary, ternary or Multinary.

• Huge room for optimization: Catalyst, Additive, Crystal dimension, Morphology etc..

• New Chemistry – New chemicals, New reactions.

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Acknowledgements

Financial Support

Agency of Science, Technology and Research (A*STAR), Singapore.

The New Energy and Industrial Technology Development Organization (NEDO, Japan)

Collaboration

Institute of Applied Energy (Japan)

Collaborators

Dr. Weifang Luo, Dr. Karl Gross, Dr. James Wang (SNL)

Professor Gert Wolf (TU Bergakademie Freiberg)

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References

1. P. Chen, Z. Xiong, et.al. Nature 420 (2002) 302 2. T. Ichikawa, S. Isobe, N. Hanada, H. Fujii, J Alloy Compd., 365 (2004) 2713. Y. Hu, E. Ruckenstein, Ind Eng Chem Res 42 (2003) 51354. Z. Xiong, J. Hu, G. Wu, P. Chen Adv. Mater. 16 (2004) 1522.5. W. Luo, J. Alloy. Compd. 381 (2004) 284.6. H. Y. Leng, T. Ichikawa, S. Hino, N. Hanada, S. Isobe and H. Fujii, J. Phys.

Chem. B 108 (2004) 8763.7. Y. Nakamori and S. Orimo, J. Alloy. Compd. 370 (2004) 271-275.8. Z. Xiong, J. Hu, G. Wu, P. Chen, J. Alloy. Compd, published on line.9. Y. Nakamori, G. Kitahara, S. Orimo J. Power Source 138 (2004) 309.10. P. Chen, J. Z. Luo, Z. T. Xiong, J. Y. Lin and K. L. Tan, J. Phys. Chem. 107

(2003) 10967.11. T. Ichikawa, N. Hanada, S. Isobe, H. Leng, H. Fujii, J. Phys Chem. B 108

(2004) 7887.12. F. Pinkerton, G. Meisner, M. Meyer, M. Balogh and M. Kundrat, J. Phys

Chem B 109 (2005) 6.

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Hydrogen Storage in Metal-N-H Complexes - APS … APS March Meeting-2005 Hydrogen Storage in Metal-N-H Complexes Ping CHEN, Zhitao XIONG, Guotao WU, Jianjiang HU Physics Department,