Review …...Metal hydrides have higher hydrogen-storage density (6.5Hatoms/cm3 for MgH 2) than...

International Journal of Hydrogen Energy 32 (2007) 1121–1140www.elsevier.com/locate/ijhydene

Review

Metal hydride materials for solid hydrogen storage: A review�

Billur Sakintunaa,∗, Farida Lamari-Darkrimb, Michael Hirscherc

aGKSS Research Centre, Institute for Materials Research, Max-Planck-Str. 1, Geesthacht D-21502, GermanybLIMHP-CNRS (UPR 1311), Université Paris 13, Avenue J. B. Clément, 93430 Villetaneuse, France

cMax-Planck-Institut für Metallforschung, Heisenbergstr. 3, D-70569 Stuttgart, Germany

Received 31 July 2006; received in revised form 21 November 2006; accepted 21 November 2006Available online 16 January 2007

Abstract

Hydrogen is an ideal energy carrier which is considered for future transport, such as automotive applications. In this context storage ofhydrogen is one of the key challenges in developing hydrogen economy. The relatively advanced storage methods such as high-pressure gasor liquid cannot fulfill future storage goals. Chemical or physically combined storage of hydrogen in other materials has potential advantagesover other storage methods. Intensive research has been done on metal hydrides recently for improvement of hydrogenation properties. Thepresent review reports recent developments of metal hydrides on properties including hydrogen-storage capacity, kinetics, cyclic behavior,toxicity, pressure and thermal response. A group of Mg-based hydrides stand as promising candidate for competitive hydrogen storage withreversible hydrogen capacity up to 7.6 wt% for on-board applications. Efforts have been devoted to these materials to decrease their desorptiontemperature, enhance the kinetics and cycle life. The kinetics has been improved by adding an appropriate catalyst into the system and as wellas by ball-milling that introduces defects with improved surface properties. The studies reported promising results, such as improved kineticsand lower decomposition temperatures, however, the state-of-the-art materials are still far from meeting the aimed target for their transportapplications. Therefore, further research work is needed to achieve the goal by improving development on hydrogenation, thermal and cyclicbehavior of metal hydrides.� 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Keywords: Hydrogen storage; Review; Mg-based hydrides; Complex hydrides; Intermetallic compounds; Ball-milling; Kinetics; Storage capacity; Operatingtemperature and pressure

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11222. Mg-based metal hydrides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1123

2.1. Improvement on surface properties and mechanical ball-milling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11232.2. Cyclic stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11272.3. Catalyst effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11282.4. Chemical composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1129

3. Complex hydrides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11293.1. Sodium alanates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11303.2. Lithium and potassium alanates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11313.3. Lithium nitrides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11313.4. Lithium boro- and beryllium hydrides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1132

4. Intermetallic compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11335. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1135Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1136References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1136

� The work was carried out in LIMHP-CNRS.∗ Corresponding author. Tel.: +49 (0) 4152 872673; fax: +49 (0) 4152 872670.

E-mail address: [email protected] (B. Sakintuna).

0360-3199/$ - see front matter � 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.doi:10.1016/j.ijhydene.2006.11.022

http://www.elsevier.com/locate/ijhydene

mailto:[email protected]

1122 B. Sakintuna et al. / International Journal of Hydrogen Energy 32 (2007) 1121–1140

Nomenclature

BCC body centered cubicBM ball-millingCyc. cycleDOE US Department of EnergyH/M hydrogen atoms per metal atomMm misch metals

P–C pressure-compositionPabs hydrogen absorption pressurePdes hydrogen desorption pressureTabs hydrogen absorption temperatureTdes hydrogen desorption temperaturetabs hydrogen absorption timetdes hydrogen desorption timeXRD X-ray diffraction

1. Introduction

Hydrogen is the ideal candidate as an energy carrier for bothmobile and stationary applications while averting adverse ef-fects on the environment, and reducing dependence on importedoil for countries without natural resources.

Hydrogen storage is clearly one of the key challenges indeveloping hydrogen economy. Hydrogen can be stored as (i)pressurized gas, (ii) cryogenic liquid, (iii) solid fuel as chemicalor physical combination with materials, such as metal hydrides,complex hydrides and carbon materials, or produced on-boardthe vehicle by reforming methanol [1]. Each of these optionspossesses attractive attributes for hydrogen storage [2].

Available technologies permit directly to store hydrogenby modifying its physical state in gaseous or liquid form inpressurized or in cryogenic tanks. The traditional hydrogen-storage facilities are complicated because of its low boilingpoint (−252.87 ◦C) and low density in the gaseous state(0.08988 g/L) at 1 atm. Liquid hydrogen requires the additionof a refrigeration unit to maintain a cryogenic state [3] thusadding weight and energy costs, and a resultant 40% loss inenergy content [4]. High-pressure storage of hydrogen gas islimited by the weight of the storage canisters and the potentialfor developing leaks. Moreover, storage of hydrogen in liquidor gaseous form poses important safety problems for on-boardtransport applications. Designs involving the use of methaneas a hydrogen source require the addition of a steam reformerto extract the hydrogen from the carbon which adds weight,additional space requirements, and the need for a device tosequester CO2 [1].

The US Department of Energy (DOE) [5] published a long-term vision for hydrogen-storage applications considering eco-nomic and environmental parameters. The predicted minimumhydrogen-storage capacity should be 6.5 wt% and 65 g/L hy-drogen available, at the decomposition temperature between 60and 120 ◦C for commercial viability. It was also predicted lowtemperature of hydrogen desorption and low pressure of hydro-gen absorption (a plateau pressure of the order of a few barsat room temperature) and nonthermal transformation betweensubstrates and products of decomposition as reported by Schulz[6]. Furthermore, the cost of a storage medium and its toxicityproperties need to be carefully considered for the realization ofthe set goals.

Storage by absorption as chemical compounds or by ad-sorption on carbon materials have definite advantages from the

safety perspective such that some form of conversion or energyinput is required to release the hydrogen for use. A great dealof effort has been made on new hydrogen-storage systems, in-cluding metal, chemical or complex hydrides and carbon nanos-tructures.

Carbon materials such as activated carbons, carbon nan-otubes, and carbon nanofibers have been the subject of intensiveresearch. The research on hydrogen storage in carbon materialswas dominated by announcements of high storage capacitiesin carbon nanostructures. However, the experimental results onhydrogen storage in carbon nanomaterials scatter over severalorders of magnitude. The hydrogen-storage capacity for car-bon materials is reported between 0.2 and 10 wt% [7,8]. Theexperiments to date claiming very high values could not inde-pendently be reproduced in different laboratories. In view oftoday’s knowledge although they have good reversibility prop-erties, carbon nanostructures cannot store the amount of hydro-gen required for automotive applications [9].

Hydrogen forms metal hydrides with some metals and alloysleading to solid-state storage under moderate temperatureand pressure that gives them the important safety advantageover the gas and liquid storage methods. Metal hydrides havehigher hydrogen-storage density (6.5 H atoms/cm3 for MgH2)than hydrogen gas (0.99 H atoms/cm3) or liquid hydrogen(4.2 H atoms/cm3) [3]. Hence, metal hydride storage is asafe, volume-efficient storage method for on-board vehicleapplications.

There are two possible ways of hydriding a metal, direct dis-sociative chemisorption and electrochemical splitting of water.These reactions are:

M + x

2H2 ↔ MHx , (1)

M + x

2H2O + x

2e− ↔ MHx + x

2OH−, (2)

where M represents the metal.Metal hydrides compose of metal atoms that constitute a host

lattice and hydrogen atoms. Metal and hydrogen usually formtwo different kinds of hydrides, �-phase at which only somehydrogen is absorbed and �-phase at which hydride is fullyformed. Hydrogen storage in metal hydrides depends on differ-ent parameters and consists of several mechanistic steps. Met-als differ in the ability to dissociate hydrogen, this ability beingdependent on surface structure, morphology and purity [10].An optimum hydrogen-storage material is required to have the

B. Sakintuna et al. / International Journal of Hydrogen Energy 32 (2007) 1121–1140 1123

following properties; high hydrogen capacity per unit mass andunit volume which determines the amount of available energy,low dissociation temperature, moderate dissociation pressure,low heat of formation in order to minimize the energy necessaryfor hydrogen release, low heat dissipation during the exother-mic hydride formation, reversibility, limited energy loss duringcharge and discharge of hydrogen, fast kinetics, high stabilityagainst O2 and moisture for long cycle life, cyclibility, low costof recycling and charging infrastructures and high safety.

Hydrogen-storage as metal hydride has been the focus of in-tensive research. The hydrogen-storage systems have been re-ported in numerous studies [11–17]. The light metals such as Li,Be, Na, Mg, B and Al, form a large variety of metal–hydrogencompounds. They are especially interesting due to their lightweight and the number of hydrogen atoms per metal atom,which is in many cases at the order of H/M = 2. Heavierones may enter the multiple component system only as a low-abundant additive, most likely for alteration of properties or asa catalyst. There is enduring research both on modifying andoptimizing the known hydrogen-storage materials, and new re-sources. The studies are conducted on finding optimum solidhydrogen-storage system [18]. In this review, we briefly men-tion about hydrogenation properties, advantages and disadvan-tages of different metal-hydride systems such as Mg-basedmetal hydrides, complex hydrides, alanates and intermetalliccompounds. A brief review of state-of-the art is reported onmetal hydrides. This work will serve to evaluate solid fuelhydrogen store for industrial on-board hydrogen storage tankdesign.

2. Mg-based metal hydrides

There is considerable research on magnesium and its alloysfor on-board hydrogen storage due to their high hydrogen-storage capacity by weight and low cost [15]. Besides, the Mg-based hydrides possess good-quality functional properties, suchas heat-resistance, vibration absorbing, reversibility and recy-clability. In recent years, therefore, much attention has beenpaid to investigations on specific material properties of Mg al-loys for the development of new functional materials.

Magnesium hydride, MgH2, has the highest energy density(9 MJ/kg Mg) of all reversible hydrides applicable for hydrogenstorage. MgH2 combines a high H2 capacity of 7.7 wt% with thebenefit of the low cost of the abundantly available magnesium[19–22] with good reversibility [23,24].

The main disadvantages of MgH2 as a hydrogen store is thehigh temperature of hydrogen discharge, slow desorption kinet-ics and a high reactivity toward air and oxygen [25,26]. Ther-modynamic properties of the magnesium hydride system havebeen investigated. The results showed high operating tempera-ture which is too high for practical on-board applications [27].High thermodynamic stability of MgH2 results in a relativelyhigh desorption enthalpy, which corresponds to an unfavorabledesorption temperature of 300 ◦C at 1 bar H2 [15,20].

Hydrogen absorption/desorption properties of recently stud-ied Mg-based hydrides are summarized in Table 1. Many effortshas focused on Mg-based hydrides in recent years to reduce the

desorption temperature and to fasten the re/dehydrogenationreactions. These can be accomplished to some extent by chang-ing the microstructure of the hydride by ball-milling (mechan-ical alloying) with elements which reduce the stability of thehydrides and also by using proper catalysts to improve theabsorption/desorption kinetics [61].

2.1. Improvement on surface properties and mechanicalball-milling

A critical factor for hydrogen absorption by metals isthe metal surface, which activates dissociation of hydrogenmolecules and allows easy diffusion of hydrogen into the bulk.Diffusion is not the limiting step initially because no materialhas been reacted and there are sufficient active sites available[62], but chemisorption is the slowest step for pure Mg at thispoint [63]. As the reaction progresses, hydrogen diffusion takesplace and the hydride layer grows, producing a nearly imper-meable layer. Diffusion through this hydride layer becomesthe rate-limiting step in the hydride formation process [63].

In addition to formation of a compact hydride layer, exposureto oxygen also lowers absorption rates due to the formationof a highly stable oxide layer [25]. Andreasen et al. [64] havereviewed the kinetics in terms of apparent activation energiesand apparent prefactors of Mg-based hydrides. It was suggestedthat variations in apparent activation energies correlate with thepresence of MgO surface layer inhibiting diffusion of hydrogen.Thus, oxidized samples show large apparent activation energiesand well activated samples show smaller activation energies.

The ball-milling creating fresh surfaces during processing isan economic process that is widely applied to metal hydridesto achieve good surface properties [15]. The main effectsof ball-milling are increased surface area, formation of mi-cro/nanostructures and creation of defects on the surface andin the interior of the material. The induced lattice defects mayaid the diffusion of hydrogen in materials by providing manysites with low activation energy of diffusion. The inducedmicrostrain assists diffusion by reducing the hysteresis of hy-drogen absorption and desorption [30]. The increased surfacecontact with catalyst during ball-milling leads to fast kineticsof hydrogen transformations. It is possible to control proper-ties of the store material, according to specific applications.These include changing the alloy composition, surface prop-erties, microstructures and grain size by ball-milling withoutthe additional cost of catalyst and with minimal loss of stor-age capacity [58]. It is used for production of nanocrystallinemagnesium with superior powder morphology that gives re-markable improvement of kinetics and surface activity forhydrogenation [21,25]. The crystalline Mg2Ni alloy obtainedby ball-milling has excellent surface properties compared withthose prepared by a conventional metallurgical method [65].

Huot et al. [58] investigated the structural difference betweenmilled and unmilled MgH2. The specific surface area is de-creased by milling 10-fold. Faster hydrogen desorption kinetics,reduction in activation energy and enhanced kinetics observedfor the milled MgH2 compared to the unmilled one are seen inFig. 1. The activation energies for desorption were measured

1124 B. Sakintuna et al. / International Journal of Hydrogen Energy 32 (2007) 1121–1140Ta

ble

1H

ydro

gen

abso

rptio

n/de

sorp

tion

prop

ertie

sof

Mg-

base

dhy

drid

es

Mat

eria

lM

etho

dTe

mpe

ratu

re(◦

C)

Pres

sure

(bar

)K

inet

ics

(min

)C

yclin

gst

abili

tyM

axw

t%of

H2

Ref

.

MgH

2–5

mol

%Fe

2O

3B

MT

abs:

300

Pab

s:2–

15t a

bs:2

0N

oda

ta1.

37[2

8]30

wt%

Mg–

Mm

Ni 5

−x(C

oAlM

n)x

BM

Tab

s:15

Pab

s:6

t abs

:83

No

data

2.30

[22,

29]

Mg–

5w

t%Fe

Ti 1

.2B

MT

abs

and

Tde

s:40

0P

abs:

30N

oda

ta9

cyc.

:st

able

afte

rfo

urth

cycl

e2.

70[3

0]P

des:

1M

gH2–5

mol

%V

2O

5B

MT

abs:

250

Pab

s:15

t abs

:1.

6N

oda

ta3.

20[2

8]90

Mg–

10A

lB

MT

abs

and

Tde

s:40

0P

abs:

15t a

bs:

2.7–

19N

oda

ta3.

30[3

1,32

]P

des:

12t d

es:

0.5–

5.8

Mg–

50w

t%Z

rFe 1

.4C

r 0.6

BM

Tab

s:25

0–35

0P

abs:

20t a

bs:

12

cyc.

:st

able

3.40

[33]

Tde

s:30

0–35

0P

des:

1t d

es:

5M

g–10

wt%

CeO

2B

MT

abs

and

Tde

s:30

0P

abs:

11t a

bs:

605

cyc.

:no

tst

able

3.43

[34]

Pde

s:0.

5t d

es:

60M

g–20

wt%

Mm

(La,

Nd,

Ce)

BM

(pel

let

form

)T

abs:

300

Pab

s:10

t abs

:10

No

data

3.50

[35]

Tde

s:48

0P

des:

1t d

es:

5M

g–40

wt%

ZrF

e 1.4

Cr 0

.6B

MT

des:

270–

280

Pde

s:1

t des

:15

2cy

c.:

stab

le3.

60[3

6]L

a 2M

g 17–4

0w

t%L

aNi 5

BM

Tab

san

dT

des:

250–

303

Pab

san

dP

des:

4–7

t abs

:0.

4520

cyc.

:no

tst

able

3.70

[37,

38]

t des

:4

La 0

.5N

i 1.5

Mg 1

7H

ydri

ding

com

bust

ion

Tab

san

dT

des:

280–

400

Pab

s:2.

21–1

1.34

t abs

:15

Not

stab

le4.

03[3

9]sy

nthe

sis

Pde

s:1.

62–1

5.48

t des

:5

Mg–

50w

t%L

aNi 5

BM

Tde

s:25

0–30

0P

abs

and

Pde

s:10

–15

t abs

:3.

33N

otst

able

4.10

[40]

MgH

2–2

LiN

H2

BM

Tab

san

dT

des:

200

Pab

s:50

t des

:60

4cy

c.:

stab

leaf

ter

2nd

cycl

e4.

30[4

1,42

]P

des:

10M

g 2C

oH5

Mix

ing

Tab

s:45

0–55

0P

abs:

17–2

5N

oda

ta10

00cy

c.:

stab

le4.

48[4

3]M

gH2–5

mol

%A

l 2O

3B

MT

abs:

300

Pab

s:15

t abs

:67

No

data

4.49

[28]

1.1M

gH2–2

LiN

H2

BM

Tab

s:20

0P

abs:

30T

abs:

309

cyc.

:st

able

4.50

[44,

45]

Mg–

20w

t%T

iO2

BM

Tab

s:35

0P

abs:

20ba

rt a

bs:

2N

oda

ta4.

70[4

6]T

des:

330–

350

Pde

s:1

t des

:10

Mg–

30w

t%B

M(h

exan

em

ediu

m)

Tde

s:30

0–55

0P

des:

2t d

es:

30N

oda

ta5.

00[4

7]M

mN

i 4.6

Fe0.

4

MgH

2–5

wt%

VB

MT

abs

and

Tde

s:30

0P

abs

and

Pde

s:1–

3t a

bs:

220

00cy

c.:

stab

le5.

00[4

8]t d

es:

10M

g–Fe

–Mg 2

FeH

6M

ixin

gT

abs:

473–

552

Pab

s:77

–85

t abs

:90

600

cyc.

:st

able

5.00

[43]

MgH

2–M

g 2Fe

H6

Mix

ing

Tab

san

dT

des:

350–

525

Pab

san

dP

des:

3.6–

93.7

t abs

:90

–144

060

0cy

c.:

stab

le5.

00[4

9]M

gH2–5

at%

Ti

BM

Tab

s:20

0P

abs:

10t d

es:3

.33

No

data

5.00

[50]

Tde

s:30

0P

des:

0.15

t abs

:0.

83M

gH2–5

at%

Ni

BM

Tab

s:20

0P

abs:

10t d

es:

5N

oda

ta5.

00[5

0]T

des:

300

Pde

s:0.

15t a

bs:

16.7

Mg–

30w

t%L

aNi 2

.28

BM

Tab

s:28

0P

abs:

30t a

bs:

1.6

3cy

c.:

stab

le5.

40[5

1]M

gH2–5

at%

VB

MT

abs:

200

Pde

s:0.

15t d

es:

3.33

No

data

5.50

[50]

Tde

s:30

0P

abs:

10t a

bs:1

.66

Mg–

10w

t%Fe

2O

3B

MT

abs:

320

Pab

s:12

t abs

:60

3cy

c.:

stab

le5.

56[5

2]t a

bs:

10M

g–30

wt%

CFM

mN

i 5M

ixin

gan

dT

abs

and

Tde

s:50

0P

abs

and

Pde

s:3–

10t d

es:4

0N

oda

ta5.

60[5

3]en

caps

ulat

ion

Mg–

10w

t%A

l 2O

3B

MT

abs

and

Tde

s:30

0P

abs:

11t a

bs:

605

cyc.

:no

tst

able

5.66

[34]

Pde

s:0.

5t d

es:

60

B. Sakintuna et al. / International Journal of Hydrogen Energy 32 (2007) 1121–1140 1125M

gH2–5

wt%

VB

MT

abs:

200

Pab

s:10

t abs

:4.2

No

data

5.80

[54]

Tde

s:30

0P

des:

0.15

t des

:33

Mg–

10w

t%C

r 2O

3B

MT

abs

and

Tde

s:30

0P

abs:

11t a

bs:

605

cyc.

:no

tst

able

5.87

[34]

Pde

s:0.

5t d

es:

60M

g/M

gH2–5

wt%

Ni

Wet

-che

mic

alm

etho

dT

abs:

230–

370

Pab

san

dP

des:

4.0–

1.4

t abs

:90

800

cyc.

:st

able

6.00

[43]

MgH

2–5

at%

Mn

BM

Tab

s:20

0P

abs:

10t d

es:

8.33

No

data

6.00

[50]

Tde

s:30

0P

des:

0.15

t abs

:13

.33

MgH

2–0

.2m

ol%

Cr 2

O3

BM

Tab

san

dT

des:

300

Pab

san

dP

des:

1–2

t abs

:6

1000

cyc.

:st

able

6.40

[55]

t des

:10

–35

MgH

2–2

mol

%N

iB

MT

des:

150–

250

Pde

s:1

t des

:15

02

cyc.

:no

tst

able

6.50

[56]

MgH

2–1

mol

%C

r 2O

3B

MT

abs

and

Tde

s:30

0P

abs:

8.4

t abs

:2

No

data

6.70

[57]

Pde

s:va

cuum

t des

:6M

gH2

BM

Tab

s:30

0(m

illed

)P

abs:

3–10

t des

:12

.5(m

illed

)N

oda

ta7.

00[5

8]T

des:

350

(mill

ed)

Pde

s:0.

15t d

es:

50(u

nmill

ed)

3Mg(

NH

2) 2

–8L

iHB

MT

des:

140–

190

Pde

s:1

No

data

No

data

7.00

[59]

Mg–

0.5

wt%

Nb 2

O5

Mix

ing

Tab

san

dTde

s:30

0P

abs:

8.4

t abs

:1

No

data

7.00

[26]

Pde

s:va

cuum

t des

:1.5

MgH

2–1

at%

Al

BM

(ben

zene

and

Tab

s:18

0P

abs:

0.6

t abs

:42

0N

oda

ta7.

30[2

0]cy

cloh

exan

em

ediu

m)

Tde

s:33

5–34

7M

gH2–5

at%

Ge

BM

Tde

s:50

–150

No

data

No

data

No

data

�7.

60[6

0]

Fig. 1. Hydrogen desorption curves of unmilled MgH2 (solid symbols) andball-milled (hollow symbols) MgH2 under a hydrogen pressure of 0.15 bar[58].

as 120 and 156 kJ/mol for the milled and unmilled powders,respectively. It has been found that ball-milling of Mg2NiH4substantially decreases the desorption temperature. Dependingon the ball-milling conditions, the shift of the onset of desorp-tion temperature can be as large as 100 ◦C for MgH2 and 40 ◦Cfor Mg2NiH4 [66].

Hydrogenation properties are very sensitive to these surfacemodifications. The ball-milled powders do not require activa-tion compared to the conventional methods. For all nanocrys-talline hydrides investigated, the grain boundary does notdramatically affect the pressure–composition (P–C) isotherms.This describes the thermodynamic aspects of hydride forma-tion which is more visible in the Van’t Hoff plots that illustratethe relationship between equilibrium pressure and changes inenthalpy and entropy. The pressure for hydrogen desorptionof the unmilled MgH2 is lower than that of the milled one, asseen in Fig. 2.

Aoyagi et al. [67] proposed that ball-milling of the alloysunder inert environment leads to reduction in powder size andcreation of new surfaces, which are effective for the improve-ment of the hydrogen absorption rate. Hydrogen absorptionrate of Mg-based alloys also increases with the milling time.Liang et al. [30] proposed that ball-milling of Mg–5 wt%FeTi1.2 produces fine powder with nanometer-sized grains andlarge microstrain, which results in an increase in the hydrid-ing and dehydriding rates. The high absorption rate is due tothe large quantity of phase boundaries and the porous surfacestructure [40]. Nanocrystalline hydrides enhanced the hydro-genation kinetics, even at relatively low temperatures. These


Fig. 2. Pressure–concentration–temperature curves of the unmilled andball-milled MgH2 at 623 K [58].

structures can be obtained by means of local change in thestable atomic positions into the metastable configuration.Ball-milling of LiNH2/MgH2 results in low dehydrogenationtemperature (200 ◦C) but with markedly slow kinetics andlowered hydrogen uptake capacity [41]. Wagemans et al. [68]investigated the quantum chemical perspective of MgH2. SmallMgH2 clusters have much lower desorption energy than bulkMgH2, hence enabling hydrogen desorption at lower tempera-tures. The hydrogen desorption energy decreases significantlywhen the crystal grain size becomes smaller than 1.3 nm. AMgH2 crystallite size of 0.9 nm corresponds to a desorptiontemperature of only 200 ◦C [68]. Particles with nanocrystallinestructure with grain size of 10 nm or less, increase the densityof grain boundaries, resulting in easier activation [69].

In another approach, a hydrogen-absorbing material can behydrogenated during ball-milling [70]. It was shown that ball-milling under hydrogen atmosphere is a convenient method forthe formation of metal hydrides which causes simultaneous hy-drogen uptake and mechanical deformation resulting from ball-milling. Huot et al. [71] produced MgH2 under H2 atmosphereby ball-milling. This method improved the hydride formationkinetics. Chen et al. [72] studied also the formation of metalhydrides under H2 atmosphere. The results indicated that pul-verization and deformation processes occurring during high-energy ball-milling play a major role in the hydriding reaction.It is concluded that ball-milling is a simple and inexpensivemethod of producing high hydrogen content metal hydrides.

Mg–10 wt% Fe2O3 is synthesized by mechanical grindingunder H2 atmosphere [52]. It increases the H2-sorption rates

Fig. 3. Desorption curves of magnesium catalyzed with 0.1 mol% Nb2O5 andmilled for 2, 5, 10, 20, 50 and 100 h, at 573 K and vacuum [75].

with 5.56 wt% H2 absorption, by facilitating nucleation by cre-ating defects on the surface of Mg particles and reducing theparticle size of Mg and thus by shortening the diffusion dis-tances of hydrogen atoms. By using the same method, it wasproposed recently that the presence of nickel lowered the onsettemperature of MgH2 desorption to 225 ◦C by ball-milling un-der hydrogen atmosphere [71]. Tessier et al. [70] synthesizedMg2Ni with the same method. Furthermore, Orimo et al. [73]found that ball-milling of Mg2Ni under hydrogen resulted ina significant facilitation of hydrogen desorption. Alloying timehas a significant effect on hydride properties of Mg2Ni. Ab-dellaoui et al. [74] proposed that absorption capacity changeswith alloying duration. Barkhordarian et al. [75] investigatedthe effect of milling time on the magnesium hydrogen sorp-tion reaction. Reaction kinetics is enhanced by increasing themilling time, as shown in Fig. 3. Ball-milling is generally usedto produce powders in the range of 60.100 �m [25,76] to cre-ate more active sights for hydrogen penetration. Smaller parti-cle sizes also eliminate the formation of hydride layers greaterthan 50 �m [25].

Although extensive work has been done on hydrogen storagein bulk materials as thin film hydride is an emerging field ofresearch. Research performed on thin films of pure magnesiumconcluded that the thinner the magnesium sheet, the faster itachieved complete formation of MgH2. It was found that hy-drogen penetrated to an average depth of 30 �m and stopped[77]. Mg portions of the film have converted totally into MgH2at temperatures not higher than 200 ◦C [78]. Hydrogen-storageproperties of nanocomposite three-layered Pd/Mg/Pd filmshave been previously investigated. After hydrogenation undera hydrogen gas pressure of 1 bar at 100 ◦C, Pd layers containonly 0.15–0.30 wt% H2, whereas the Mg film contains 5.0 wt%hydrogen [79]. Pd/Mg films with different degree of crystal-lization in the Mg layer are prepared in different sputteringconditions [77]. The dehydriding temperature decreases withdecreasing the degree of crystallization in the Mg layer in


Table 2Hydrogen absorption/desorption properties of Mg–Ni-based hydrides

Material Method Temperature (◦C) Pressure (bar) Kinetics (min) Cycling stability Max wt% of H2 Ref.

Mg2Ni–1 wt% Pd BM Tabs : 200 Pabs : 15 tabs : 27 4 cyc.: stable 2.50 [86]

Mg2Ni BM Tabs: 300 Pabs: 29 5 cyc.: not stable 3.20 [87]

Mg2Ni BM Tabs: 300 Pabs: 11.6 tabs: 10 4 cyc.: stable 3.50 [86]

Mg2Ni BM Tabs and Tdes: 280 Pdes: 1–2 No data No data 3.53 [74,88]

Mg–Mg2Ni BM Tabs: 300 Pabs: 12 tabs: 83 2 cyc.: not stable 3.60 [89]

Mg2Ni BM Tabs and Tdes: 280–330 Pabs: 1–15 tabs: 1 No data 4.10 [82]

Pdes: 1–2 tdes: 170 wt% Mg–30 wt% LaNi5 BM Tabs and Tdes: 350 Pabs: 10 tabs: 30 10 cyc.: stable 4.66 [90]

Pdes: 1.5 tdes: 10 [91]65 wt% MgH2–35 wt% Mg2NiH4 BM Tdes: 220–240 Pdes: 0.5 tabs: 10 20 cyc.: stable 5.00 [66]

Pd/Mg films. The lowest crystallization of films absorb 5.6 wt%of hydrogen and all hydrogen desorbed at a temperature lowerthan 190 ◦C in a vacuum [77].

Mechanical alloying can be preformed in the presence of or-ganic solvents such as benzene, cyclohexane or carbon materi-als [80,81]. Nanosized MgH2 ball-milled with benzene showedreversible hydriding/dehydriding with high capacity under 1 barhydrogen pressure. It was proposed that the organic additivesof benzene or cyclohexane are essential for decisive character-istics of the resulting magnesium to sustain nanosized magne-sium with high-degree of dispersion [20]. Wet milling in thepresence of toluene leads to hydrogen and carbon pick up in thepowder, and also require much longer milling times [82]. Hy-driding properties of Mg-based composites which are preparedby mechanical milling of magnesium powder and graphite orgraphite supporting 5 wt% Pd in the presence of various ad-ditives (tetrahydrofuran, benzene or cyclohexane) have beenstudied [80]. In particular, the presence of tetrahydrofuran inthe milling process strongly affected the hydriding and dehy-driding kinetics of the resulting composites [80]. There is asynergetic interaction between Mg and aromatic carbon atomsof graphite containing charge transfer to some extent.

It has been found that the hydrogenation properties of Mg,such as hydrogenation/dehydrogenation temperature and hy-drogenation rate, can be more or less improved by formingcomposite structures. Zhu et al. [22,29] reported that the hy-drogen sorption properties of Mg and Mg–Ni-based alloys cansignificantly be improved by forming composites having propermicrostructural feature.

Mg2NiH4 attracts wide interest for being a promising hydro-gen store material due to its relatively high capacity, low cost,light weight and low-toxicity [83] and for its unusual struc-tural and bonding properties [84,85]. The hydrogen absorptionand desorption properties of Mg–Ni-based alloys are listed inTable 2. Mg2NiH4 forms eagerly by hydrogenating the alloyMg2Ni [92]:

Mg2Ni + 2H2 → Mg2NiH4. (3)

Upon hydrogenation, Mg2Ni reacts with 3.6 wt% of hydro-gen and transforms into the hydride phase, Mg2NiH4, and the

dehydriding temperature is 250.300 ◦C at desorption pressureof 2.1–3.0 bar [22,66,74,84,88]. High hydrogen capacity of fourhydrogen atoms per Mg2Ni, combined with the small specificweight of the alloy is the most important advantage of Mg2Niover other magnesium hydrides [93].

There are numerous publications regarding the upgrade ofhydrogenation properties of Mg2NiH4. Their hydriding prop-erties are thought to be strongly affected by their nanometer-scale structures by means of thermodynamic and kineticaspects. MgNi2 prepared by ball-milling is found to react withhydrogen even at room temperature, whereas polycrystallinematerial needs hydrogenation temperature of 250.350 ◦C andpressure of 15–50 bar [84]. Haussermann et al. [92] inves-tigated the structural stability and bonding properties of theMg2NiH4 using ab initio density functional calculations. Par-ticular changes of the hydriding properties of the nanostruc-tured Mg2NiH4 have been also reported [19,22,25,73,94].

The nanocrystalline Mg2Ni intermetallic compound formedby mechanical alloying of Mg and Mg2Ni can absorb hydro-gen rapidly without activation. The Mg + Mg2Ni compositesneed activation, but once activated, they absorb hydrogen morerapidly than Mg2Ni at low temperature of 150 ◦C under 12 barwith high capacity of 4.2 wt% [89]. Nanoparticles of Mg2Nileads to superior hydrogenation behavior including easy acti-vation and hydrogen uptake in the first cycle itself compared tothe conventional crystal phase [86,87]. Nanocrystalline Mg2Niwith Pd exhibits much faster absorption kinetics at 200 ◦C thanthe as-ball-milled samples (reaction halftime of 2 and 33 min,respectively) [86].

2.2. Cyclic stability

Cyclic stability is one of the major criteria for applicabilityof metal/metal hydride systems for reversible hydrogen storage.Depending on the nature of the additives, cycling temperaturesand starting microstructures, various structures and intermedi-ate phases can be obtained. Song et al. [34] synthesized magne-sium hydrides with additives of Cr2O3, Al2O3 and CeO2. Allthe samples absorb and desorb less hydrogen at the fifth cyclethan at the first cycle due to the agglomeration of the particles


Fig. 4. Cyclic stability of chemical Ni-doped Mg at 503–643 K and 4.0 bar,time for one full cycle 3 h [43].

during hydrogenation/dehydrogenation cycling. Misch metals(Mm) such as Ce, La, Nd and Pr, are used to increase the cyclicstability [95,35]. However, the increased concentration of Mmin the samples has an adverse effect on hydrogen-storage ca-pacity and their reaction rate [35]. Gross et al. [37] have re-ported formation phase changes, segregation and disintegrationof La2Mg17 + 40 wt% LaNi5 during cycling at temperaturesup to 350 ◦C. It was also reported that hydrogen capacity ofLa0.5Ni1.5Mg17 decreases with cycling [39].

There are few publications regarding high number of cyclictests. Reiser et al. [43] investigated the behavior of Ni-dopedMg and Mg2CoH5. They indicated that they are almost stableeven after 800 cycles with small fluctuations in the hydrogen ca-pacity, as shown in Fig. 4. The cyclic stability of MgH2–5 wt%V is studied by Dehouche et al. [48] up to 2000 cycles. Theyconcluded that there is no change in isotherms and no disinte-gration of the materials even when hydrogen content reached5 wt%. Also the cyclic stability of MgH2 + 0.2 mol% Cr2O3 ispreviously examined at 1000 cycles. Although desorption timeis increased, an increase of H2 storage capacity is reported byabout 8% between the first and the 500 or 1000 cycle due tostructural relaxations and crystallite growth [55]. Friedlmeieret al. [96] observed a decrease in the kinetics of hydrogen ab-sorption after 4300 cycles, but no loss in the hydrogen capacityof Mg–2 at% Ni alloy. However, to achieve the same storagecapacity, the system temperature had to be increased. Neverthe-less, Dehouche et al. [97] showed 15% decrease in hydrogencapacity after 2100 cycles with a starting material of nanocrys-talline Mg2Ni. This was attributed to the formation of the non-hydride forming MgNi2 phase, during the cycling process.

The resistance of metal hydrides to impurities is one of thecritical issues for on-board applications in order to maintainperformance over the lifetime of the material. The effects ofN2, O2, CO2 and CO on a pure magnesium powder have beenstudied [98]. Both O2 and N2 slowed the rate of hydrogen ab-sorption, while CO and CO2 entirely prevented the uptake ofhydrogen [98,99]. The performance of MgH2.V.Ti was eval-uated after 1000 cycles under a H2 atmosphere containing101 ppm moisture. Hydrogen-storage capacity increased 5% butdesorption properties deteriorated due to surface modificationof the particles [100].

2.3. Catalyst effect

Catalysis is one of the critical factors in the improvementof hydrogen sorption kinetics in metal hydride systems thatenables fast and effective dissociation of hydrogen molecules[21]. Effective catalysts, even added in small amounts enhancethe formation of a hydride in reasonable extent. There is in-tensive research about finding a proper catalyst to enhance thehydriding properties. It was reported that the rate of absorptionis controlled by the following factors: the rate of hydrogen dis-sociation at the surface, the capability of hydrogen to penetratefrom the surface which is typically covered by an oxide layerinto metal, the rate of hydrogen diffusion into the bulk metaland through the hydride already formed.

Palladium is a good catalyst for hydrogen dissociation re-action. The hydriding properties are enhanced by catalysisthrough nanoparticles of Pd located on magnesium surface[25]. The reactivity of palladium after exposure to oxygen isrecovered during exposure to hydrogen because of the easydecomposition of palladium oxide [93]. However, high costof palladium is the main disadvantage for the industrial ap-plications [15]. Zaluski et al. [86] have also reported on thepresence of Pd as a catalyst in nanocrystalline Mg2Ni, LaNi5and FeTi systems, enhance the absorption rates even at lowertemperatures and maintain less sensitivity to air exposures.

Hydrogen molecules have a strong affinity for nickel andreadily dissociate and adsorb onto surface-layer nickel clusters[101,102]. Through the addition of 1 at% of nickel to magne-sium, Holtz and Imam [76] achieved a 50% increase in hy-drogen capacity, a decrease in the temperature for the onset ofhydrogenation from 275 to 175 ◦C, and a lowering of the de-hydrogenation onset temperature from 350 to 275 ◦C.

In addition to Pd and Ni, Ge can be used for the catalysisof hydrogenation kinetics [60]. The presence of Ge decreasesthe hydride decomposition temperature in a range from 50 to150 ◦C, depending on the catalyst amount. But the catalytic ef-fect of Ge disappears after few hydrogen absorption/desorptioncycles [60]. Vanadium also acts as a catalyst for the dissoci-ation of hydrogen molecules. It was also reported using V asa catalyst, hydrogen capacity can be increased up to 5.8 wt%while the thermodynamic parameters of MgH2 were not altered[54], as shown in Fig. 5.

Titanium and vanadium block the oxidation of the alloy sur-face, and therefore, increase the discharge capacity over mul-tiple cycles [103]. A nanocrystalline Mg1.9Ti0.1Ni alloy showsgood absorption kinetics at room temperature [104]. The Ti de-creases the kinetic barriers of absorption while the Ni protectsthe alloy from deactivation due to oxide layer formation.

The poor kinetics of MgH2 are greatly improved by additionof different oxide catalysts that enhance hydriding propertiesat relatively low temperature, such as V2O5 [28] and Cr2O3[34,55]. The oxide particles may operate as a milling ball dur-ing high-energy ball-milling that creates many defects in theMg powder. Defects provide hydrogen an easy path to Mg [28].It was also proposed that Cr2O3 yields fast hydrogen absorp-tion, whereas V2O5 and Fe3O4 cause the most rapid desorp-tion of hydrogen [57]. The addition of TiO2 also resulted in


Fig. 5. Hydrogen desorption curves of mechanically milled MgH2–5 at% Vcomposite (hollow symbols) and MgH2 (solid symbols) under 0.15 bar [54].

a markedly improved hydrogenation performance of Mg, rapidkinetics, low working temperature and excellent oxidation re-sistance [46]. Liang et al. [40] suggested that La showed a cat-alytic effect on Mg–50 wt% LaNi5 nanocomposite.

In addition to catalyst type, the amount of catalysts usedhas a significant effect on hydrogen absorption behavior.Oelerich et al. [57] investigated different amounts of oxidesfor catalysis but it is shown that only 0.2 mol% of the cata-lyst is sufficient to provide fast sorption kinetics. The effectof Nb2O5 concentration on the kinetics of magnesium hydro-gen sorption reaction at 300 ◦C is studied. Fastest kinetics areobtained using 0.5 mol% Nb2O5 with a 7.0 wt% of hydrogencapacity [26].

In the search for efficient and inexpensive catalysts for hy-drogen sorption reactions, a new type of catalytic compoundsis developed [105]. These catalytic complexes demonstrated re-markable enhancement in sodium alanates and magnesium, aswell as in hydrogen generation through hydrolysis [105].

2.4. Chemical composition

The type and the chemical composition of the metal alloyis one of the most important factors in the metal–hydrogensystem [21]. Bouaricha et al. [31] prepared Mg/Al alloys byhigh-energy ball-milling. The measured hydrogen capacity ofthe material decreases with Al content, from H/M = 1.74 forpure unmilled Mg, to 1.38 for Mg:Al (90:10), and then to 1.05for Mg:Al (75:25). But it improves the kinetics. Ball-milling hasa possibility to combine two or more phases having differenthydrogenation characteristics [21].

Wang et al. [33,36] combined both the catalytic and millingeffect in a system of fine ZrFe1.4Cr0.6 particles coveringMg particles that resulted in an enhancement in absorp-tion/desorption rates. ZrFe1.4Cr0.6 dispersing homogeneouslyon the particle surfaces and in the interior of the material playedan important role in promoting the decomposition of MgH2.That probably could account for the decrease in activation en-ergy. In another study [51], mechanically alloyed Mg–30 wt%LaNi2.28 reported to have good hydriding properties with5.40 wt% hydrogen storage under 30 bar hydrogen pressure.

With energetic ball-milling, the solubility limit of magne-sium in lithium slightly increased [106]. Luo [44] developedLiNH2/MgH2 system by partial substitution of Li by Mg whichhas a storage capacity of 4.5 wt% at 200 ◦C and 30 bar. Me-chanical alloying of Mg with some elements such as Zn, Al,Ag, Ga, In or Cd resulted in reducing the stability of magne-sium hydride. Indium and cadmium gave the best results [107].

Bogdanovic et al. [49] and Reiser et al. [43] considered theMg2FeH6–MgH2 systems. The maximum amount of stored hy-drogen is 5.0 wt% which is one third less than magnesium dihy-dride with 7.7 wt%, but the Mg2FeH6.MgH2 system possessesnumerous advantages including the low price of starting mate-rials, the free choice and constancy of the heat delivery temper-ature by controlling the applied hydrogen pressure and absenceof heat losses with time. The intermetallic hydride Mg2FeH6shows the high volumetric hydrogen density of 150 kgH2/m3,which is more than double of liquid hydrogen [108].

Nanocomposites of MgH2 and 3d transition metals, Ti, V,Mn, Fe and Ni, have been investigated intensively [48,50,109].The composites containing Mg–Ti and Mg–V exhibited therapid absorption kinetics such as absorption time of 2–5 min.Formation enthalpy and entropy of magnesium hydride is dis-torted by milling with transition metals. Furthermore, the acti-vation energy of desorption for magnesium hydride is reducedat 200 ◦C.

3. Complex hydrides

Another class of light-weight storage materials is com-plex hydrides. Complex hydrides are known as “one-pass”hydrogen-storage systems which mean that H2 evolves uponcontact with water. Sodium, lithium and beryllium are the onlyelements lighter than magnesium that can also form solid-statecompounds with hydrogen. The hydrogen content reaches thevalue of 18 wt% for LiBH4. Use of complex hydrides forhydrogen storage is challenging because of both kinetic andthermodynamic limitations.

Intense interest has developed in low weight complex hy-drides such as alanates [AlH4]−, amides [NH2]−, imides andborohydrides [BH4]−. In such systems, the hydrogen is oftenlocated at the corners of a tetrahedron. The alanates and boratesare especially interesting because of their light weight and thecapacity for large number of hydrogen atoms per metal atom.Borates are known to be stable and decompose only at ele-vated temperatures. Alanates are remarkable due to their highstorage capacities; however, they decompose in two steps upondehydriding.


3.1. Sodium alanates

Sodium alanates are complex hydrides of aluminum andsodium. Sodium tetrahydroaluminate–NaAlH4 and trisodiumhexahydroaluminate–Na3AlH6 have been known for decades.Sodium aluminum hydride, NaAlH4, would seem to be apossible candidate for application as a practical on-boardhydrogen-storage material due to the theoretically reversiblehydrogen-storage capacity of 5.6 wt%, low cost and its avail-ability in bulk.

Although they have good hydrogen-storage capacity, com-plex aluminum hydrides are not considered as rechargeablehydrogen carriers due to irreversibility and poor kinetics.However, by using appropriate transition or rare-earth metalsas catalysts, the complex hydrides can be made reversible.Bogdanovic and Schwickardi [110,111] demonstrated upondoping with proper titanium compounds, the dehydriding ofaluminum hydrides could be kinetically enhanced and main-tain reversibility under moderate conditions in the solid state.Unlike intermetallic hydrides, these complex-based hydridesrelease hydrogen through a series of decomposition reactionsas described in two equations below, for the dehydrogenationreactions of NaAlH4:

NaAlH4 ↔ 13 Na3AlH6 + 2

3 Al + H2, (4a)

Na3AlH6 ↔ 3NaH + Al + 32 H2. (4b)

Theoretically, NaAlH4 and Na3AlH6 contain large amountsof hydrogen, 7.4 and 5.9 wt%, respectively. However, the re-lease of hydrogen does not occur in a single-step reaction.NaAlH4 first decomposes evolving molecular hydrogen andform an intermediate compound, Na3AlH6 and metallic Al.This intermediate phase then decomposes to NaH with ad-ditional metallic Al formation and hydrogen evolution. Thereversibility of these two reactions is a critical factor for thepractical applications.

Stoichiometrically, the first step consists of 3.7 wt% H2 re-lease and the second step 1.9 wt%, for a theoretical net reactionof 5.6 wt% reversible gravimetric hydrogen storage [111,112].The process is characterized by slow kinetics and reversibilityonly under severe conditions. The operating temperatures arebetween 185 and 230 ◦C, and 260 ◦C for the first and the sec-ond reaction, respectively. Finally, the decomposition of NaHoccurs at a much higher temperature, with the total hydrogenrelease of 7.40 wt%. For hydrogen storage, only the first tworeactions need to be considered, because the decomposition ofNaH occurs at too high temperature of 425 ◦C for practicalstorage systems.

Previously Jensen et al. [113] reviewed the catalytically en-hanced sodium aluminum hydrides. Recently, numerous stud-ies are being carried out to enhance the hydriding properties ofNaAlH4 as listed in Table 3.

The effects of liquid alkoxides Ti(Obun)4 + Zr(OPri )4 onhydriding properties of sodium alanates were investigatedby Sandrock et al. [116]. The liquid alkoxides contributeto hydrocarbon contamination of the released hydrogen.

Moreover the surface of sodium alanate is damaged by thecatalyst which causes decreasing the cyclic capacity.

The dry-doping TiCl3 catalyst is investigated by the samegroup [123]. It largely eliminates the high catalyst weight,low capacity and contamination problems noted above for thealkoxide catalysts [116]. Both the hydriding and dehydridingrates increases by doping [123]. Under the same rehydrogena-tion conditions, the amount of evolved hydrogen from theTi-doped NaAlH4 is about 50 times as much as that of theundoped NaAlH4. This clearly indicates that the addition of ti-tanium species enhances kinetically not only the dehydrogena-tion, but also the rehydrogenation reaction of NaAlH4 [118].With 2 mol% TiN as a doping agent, cyclic storage capacityof 5 wt% H2 is achieved after 17 cycles. However, decrease inhydrogenation rate with number of cycles is observed [122].Zirconium doping is also used for the same purpose. The dehy-driding kinetics of NaAlH4 is significantly improved. Althougheffects of zirconium are poorer than titanium as a catalyst forthe dehydriding of NaAlH4 to Na3AlH6 and Al, it is a superiorcatalyst for the dehydriding of Na3AlH6 to NaH and Al [119].

Sun et al. [124] examined the details of the doping roleof titanium and zirconium on NaAlH4 with XRD. Significantchanges occur in the lattice parameters of sodium alanates upondoping. Hence the enhancement of dehydriding kinetics is as-sociated with dopant induced lattice distortions rather than thecatalytic effect [124]. Phase transitions and crystal structuremodifications of doped-NaAlH4 were also observed by Grosset al. [125]. Contrary to Sun et al. [124], they proposed the cat-alytic effects of doping materials in the enhancement of kinet-ics of NaAlH4. It was earlier reported that the presence of Ti isnot enough rather a particular local arrangement is required forthe dehydrogenation reaction [126]. Ti-cluster-doped NaAlH4is investigated [122,127]. The hydrogenation and dehydrogena-tion measurements indicate that the state of the precursor is ofeven greater importance than the simple amount of Ti in thematerial. The small size of the Ti clusters seem to be responsi-ble for the increase of the reaction rate [127].

Although titanium has positive effects as a catalyst, kinet-ics is not fully enhanced. The hydrogen desorption can lastup to 4200 min in some cases [123]. To improve the kinet-ics Thomas et al. [128] investigated the effects of mechanicalball-milling on the microstructural character of NaAlH4 in thepresence of catalyst. Fracture and fragmentation of particlesare observed in particle morphology. The direct synthesis ofNa3AlH6 and Na2LiAlH6 by energetic mechanical alloying wasalso investigated earlier [129]. The milled NaAlH4 or Na3AlH6exhibited great improvement of the kinetics of absorption anddesorption. The addition of carbon in the milling process im-proved their performance as well [120]. Mechanically alloyedNa3AlH6 exhibits faster kinetics than Na3AlH6 obtained fromthe decomposition of NaAlH4 [130]. Moreover, the hydrogen-storage performance of NaAlH4 was found to be highly de-pendent on the milling time which increases with time [117].Consequently mechano-chemical synthesis method which in-volves simply ball-milling of the appropriate reagents at highenergy, is applied to prepare Na3AlH6 [114]. It can desorb thesame amount of hydrogen at 200 ◦C within only 150 min and


Table 3Hydrogen absorption/desorption properties of sodium alanates

Material Method Temperature (C◦) Pressure (bar) Kinetics (min) Cycling stability Maxwt%of H2

Ref.

Na3AlH6 Mechano-chemicalsynthesis

Tdes: 200 Pdes: 1 tdes: 150 No data 2.50 [114]

Na2LiAlH6 BM Tabs: 211 Pabs: 45 tabs: 100 No data 2.50 [115]NaAlH4–2 mol% BM Tabs and Tdes: 125–165 Pabs and Pdes: 101–202 tabs: 60 5 cyc.: not 3.00 [116]Ti(Obun)4–2 mol% tdes: 180 stableZr(OPri )4

NaAlH4–4 mol% Ti BM Tabs: 120 Pabs: 120 tabs: 60 8 cyc.: not 3.30 [117]Tdes: 150 Pdes: 1 tdes: 600 stable

NaAlH4–2 mol% Ti BM Tdes: 25–160 Pabs: 20–120 tabs: 300–720 No data 3.80 [118]Tabs: 25–193 Pdes: 1 tdes: 40

NaAlH4–2 mol% Mixing Tabs: 120 Pabs and Pdes: 60–150 tabs: 1020 25 cyc.: not 4.00 [111](Ti(Obun)4 Tdes: 180–260 tdes: 120–300 stable [112]NaAlH4–2 mol% Mixing Tabs: 135–120 Pabs and Pdes: 150–130 tabs: 330 33 cyc.: not 4.00 [110]Ti(Obun)4 Tdes: 180–160 tdes: 90 stableNaAlH4–2 mol% TiCl3 BM Tdes: 125–100 Pdes: 83–91 tdes: 20 5 cyc.: not stable 4.00 [116]NaAlH4–2 mol% Mixing Tdes: 200 Pdes: 1 No data 3 cyc.: stable 4.00 [119]Zr(OPr)4 3 after second cyc.NaAlH4–2 mol% Mixing Tabs: 104 Pabs: 88 tabs: 1020 3 cyc.: stable 4.00 [113](Ti(Obun)4) after second cyc.NaAlH4 Mechano-chemical Tabs and Tdes: 80–180 Pabs and Pdes: 76–91 tabs: 120–300 2 cyc.: not 5.00 [120]

synthesis tdes: 300 stableNaAlH4–2 mol% Mixing Tdes: 200 Pdes: 1 No data not stable 5.00 [121]Ti(Obun)4-CNaAlH4–2 mol% TiN BM Tabs: 104–170 Pabs: 115–140 tdes: 30–1200 25 cyc.: stable 5.00 [122]

after 17th cycle

without a catalyst, giving reaction rate about 10 times fasterthan conventionally produced, non-catalyzed hydrides [114].

3.2. Lithium and potassium alanates

A survey of important studies on lithium-based hydrogen-storage compounds are summarized in Table 4. It shows clearlyhigh capacities of stored hydrogen as weight percent material.

In theory, lithium alanates are very attractive for hydro-gen storage, because of their high hydrogen content. The to-tal hydrogen content is 10.5 and 11.2 wt% for LiAlH4 andLi3AlH6, respectively. Unfortunately, LiAlH4 has an extremelyhigh equilibrium pressure of hydrogen, even at room temper-ature. LiAlH4 is in fact an example of an unstable hydride,which decomposes easily, but which cannot be re-hydrogenated[114]. The desorption of LiAlH4 occurs in two steps:

3LiAlH4 → Li3AlH6 + 2Al + 3H2, (5a)

Li3AlH6 → 3LiH + Al + 32 H2. (5b)

The hydrogen released in the two reactions shown, corre-sponds to 5.3 wt% from the decomposition of LiAlH4 and2.65 wt% from the decomposition of Li3AlH6 at temperaturesbetween 160 and 200 ◦C. After completion of the reactions,2.65 wt% of the total hydrogen content in LiAlH4 remainsunreleased in form of LiH which can be desorbed only at

very high temperatures of above 680 ◦C [114]. Therefore, thecommercialization of lithium-based compounds is hinderedby their slow kinetics and high temperature absorption anddesorption.

The reversible hydrogen decomposition of KAlH4 has beenstudied previously [138]. The hydrogen capacity was above3.5 wt% under 10 bar of hydrogen in a temperature range of250–330 ◦C, the reversible reaction smoothly proceeds withoutany catalyst, which is different from the reactions of NaAlH4and LiAlH4 [138].

3.3. Lithium nitrides

Lithium nitride is usually employed as an electrode, or as astarting material for the synthesis of binary or ternary nitrides.Although the temperature required to release the hydrogenat usable pressures is too high for hydrogen-storage appli-cations it was suggested that the metal–N–H system couldprove to be a promising route for reversible solid hydrogenstorage [45].

The idea of hydrogen storage in lithium compounds goesback to 1910, when Dafert and Miklauz [139] reported thereaction between Li3N and H2 to Li3NH4. In fact Li3NH4 hasbeen proved to be the product of the following reaction, whichwas proposed by Ruff and Georges [140]:

Li3N + 2H2 → LiNH2 + 2LiH. (6)


Table 4Hydrogen absorption/desorption properties of Li-based hydrides

Material Method Temperature (◦C) Pressure (bar) Kinetics (min) Cycling stability Max wt%of H2

Ref.

LaNi3BH3 Arc melting Tabs: 25 Pabs: 4 tabs: 30 2 cyc.: not stable 0.84 [131]Li2NH Mixing Tabs and Tdes: 230–200 Pabs: 7 tabs: 10 15 cyc.: not 3.10 [132]

Pdes: 1 tdes: 300 stableLiNH2–LiH–1 mol% BM Tdes: 150–250 Pabs: 30 tabs: 30 3 cyc.: stable 5.00 [133]TiCl3 Tabs: 180Li2O–Li3N Partial oxidation Tabs: 180 Pabs: 7 tabs: 3 6 cyc.: stable 5.20 [134]Li2MgN2H2 Mixing Tabs and Tdes: 180 Pabs: 90 tabs: 60 No data 5.50 [42]

Pdes: 1 tdes: 60Li3N Mixing Tabs: 50 Pabs: 0.5 tabs: 20 No data 6.00 [135]

Tdes: 240–270 Pdes: 1Li2NH Mixing Tabs and Tdes: 255–285 Pabs: 10 No data No data 6.50 [45]

Pdes: 1.5Li3BN2H8 BM Tdes: 250–364 Pdes: 1 tdes: 228 No data 10.00 [136]LiBH4- 1

2 MgH2–2 mol% BM Tabs and Tdes: 315–450 Pabs: 4.5–19 tabs: 240 3 cyc.: not 10.00 [137]TiCl3 Pdes: 2–3 tabs: 240 stable

Consequently, Li3N can theoretically store 10.4 wt% hydro-gen. Li3N has two plateaus in the P–C isotherm. Desorptionisotherms cannot return to the origin. Under P–C isotherm con-ditions, about 55% of hydrogen can be desorbed at tempera-tures above 230 ◦C. More important for hydrogen storage, isthat this mixture could decompose to release hydrogen gas uponheating, according to the following reaction:

LiNH2 + 2LiH → Li2NH + LiH + H2. (7)

Hydrogen storage leads to the formation of LiNH2 and LiH.Theoretically 7 wt% of hydrogen can be reversibly stored inLi2NH [45].

A critical potential issue regarding this N-based storage ma-terial is the generation of NH3, which consumes some H2 andalso poisons the downstream processes. Hu et al. [141] demon-strated that NH3 produced via the decomposition of LiNH2 iscompletely captured by LiH. This ultrafast reaction betweenNH3 and LiH inhibits NH3 formation during the hydrogenationof Li3N [141].

Hu et al. [135] studied the temperature-programmed hydro-genation and dehydrogenation of Li3N and reported a reversiblehydrogen capacity of 6 wt%, within 240–270 ◦C temperaturerange. Another study of the same group was to investigate thefast kinetics of LiO2/Li3N mixture for hydrogen storage [134].They improved the activation characteristics of Li3N with thehydrogenation–dehydrogenation pretreatment, partially oxidiz-ing the surface layer. They reported a maximum of 5.20 wt%hydrogen capacity with very fast kinetics such as 3 min fordesorption.

A catalytic study of Ichikawa et al. [133] reported a 5.50 wt%storage with high reaction rate after three cycles, with the uti-lization of TiCl3 catalyst during ball-milling of the LiNH2 andLiH mixture. Recently Hu et al. [132] reported a reversible hy-drogen capacity of 3.10 wt%, that increases with the numberof cycles, due to improved porous structure of the material.Another study on a different class of solid hydride has beendone by Pinkerton et al. [136], reporting an extraordinarily high

storage capacity of above 10 wt%, however, reversibility is lack-ing. Although desorption conditions seem to be advantageous,irreversibility stands as an important problem for use of thesematerials to be utilized as storage medium. Authors reportedtheir attempts to rehydride the decomposition product by heat-ing at 8 MPa but without success.

A proposed way for lowering the hydrogen desorptiontemperatures of Li-based complex hydrides is partial cationsubstitutions using different valence cations with larger elec-tronegativities. It was predicted that the dehydriding reactionsof LiNH2 with partial Mg substitutions are useful as hydrogen-storage materials for fuel–cell applications [142]. The startingand ending temperatures for the hydrogen desorption reac-tion from LiNH2 are lowered about 50 K by the partial cationsubstitution of Li by Mg [143,144].

3.4. Lithium boro- and beryllium hydrides

The importance of boron for hydrogen-storage technologieshave been reported [145]. LiBH4 has a gravimetric hydrogendensity of 18 wt%. The compound was first synthesized bySchlesinger and Brown [146] in an organic solvent. Accord-ing to the work of Stasinevich and Egorenko [147] hydrogendesorbs from LiBH4 at temperatures greater than 470 ◦C.

Despite its great storage capacity, all attempts to synthesizeLiBH4 from the elements at elevated temperatures up to 650 ◦Cand pressure of 150 bar H2 failed to date [108,148]. Moreover,LiBH4 is an expensive compound [15].

It was found that the compound releases hydrogen indifferent reaction steps and temperature regimes. The lowtemperature desorption releases only a small amount (0.3 wt%)of hydrogen. The high temperature phase releases up to13.5 wt% of hydrogen. A total of 4.5 wt% of the hydrogenremains as LiH in the decomposition product.

Vajo et al. [137] show that LiBH4 can be reversibly store8–10 wt% hydrogen at temperatures of 315–400 ◦C by addi-tion of MgH2 including 2–3 mol% TiCl3. Formation of MgB2


stabilizes the dehydrogenated state and destabilizes the LiBH4[137]. However, the kinetics is too slow with the absorptiontime up to 6000 min hinder practical applications.

Besides alanates, nitrides and borohydrides, lithium–berylliumhydrides are a new group of metal hydrides for hydrogen stor-age. They show high reversible hydrogen capacity with morethan 8 wt% at 150 ◦C. The reaction of hydride formation isfully reversible. Since lithium and beryllium are the lightesthydride-forming metals, reversible hydrogen capacity in thesecomplex compounds is higher than in any other known hy-drides [149]. On the other hand, the Li3Be2H7 is a highly toxicmaterial [15].

4. Intermetallic compounds

Research on intermetallic compounds for hydrogen storagewas already attempted more than 20 years ago. The discoveryof hydrogen absorption by LaNi5 [150] and FeTi [151], openednew possibilities for industrial developments. However, for on-board storage, they remained at the stage of prototypes duetheir weight penalty and low hydrogen-storage capacity [152].

The different families of intermetallic compounds classifiedon the basis of their crystal structures, such as AB2 type (Lavesphase), AB5 type phases and Ti-based body centered cubic,BCC, alloys are well known as hydrogen-storage materials.Intermetallic compounds are often obtained by combining anelement forming a stable hydride with an element forming anonstable hydride. As for the metallic hydrides, the dissociativechemisorption of hydrogen is followed by hydrogen diffusioninto the interstitial sites.

The hydriding properties of these compounds are summa-rized in Tables 5 and 6. For practical applications at ambienttemperature and pressure, their low energy density per unitweight is an important critical disadvantage. For instance,the hydrogen capacity of the most popular LaNi5-based al-loys operating at moderate temperature does not exceed1.4 wt%.

Among the AB5 type alloys, due to their low working tem-perature and pressure, metal alloys containing high amounts ofLaNi5 have been studied as hydrogen-storage materials by var-ious research groups around the world [176–180]. Some of thestudies were carried with pure compounds, while others stud-ied blending of the material with various metals through melt-ing or mechanical alloying techniques. Important results fromthese studies are represented below.

The parent compound LaNi5 absorbs about 1.0 H/LaNi5(1.5 wt%), however, its cost is relatively high and the plateaupressure is low. The P–C diagram shows a flat plateau, lowhysteresis, but unfortunately the hydrogen capacity is de-graded after a few cycles. Therefore, these materials are stillfar from meeting the US DOE goal of 6.5 wt% reversiblehydrogen capacity. Due to their potential for commercial appli-cations, researchers have been studying the effects of milling,mechanical alloying or melting with other metals and surfacetreatment techniques such as carbon monoxide treatment.Table 6 presents the major outputs from a number of studieson AB5 type compounds for hydrogen storage.

The early studies on LaNi5 as hydrogen-storage material hasbeen reported by Aoyagi et al. [67]. The effect of ball-millingon hydrogen absorption properties has been investigated, andmaximum hydrogen content has been reported as 0.25 wt%. Itis concluded that activation treatment is necessary for LaNi5to be useful for hydrogen-storage applications. Kaplan et al.[181] have investigated the hydrogen absorption in pure LaNi5both theoretically and experimentally. The group reported thatLaNi5 has 1.28 wt% hydrogen-storage capacity for 8.3 min hy-driding process. They characterized the hydriding process byexothermic reaction between LaNi5 and H2 that leads to rapidtemperature increase. These supported the results from theoret-ical calculations.

With different stoichiometric addition of other metals, LaNi5compounds were shown to be enhanced for hydrogen-storageby the works of Chen et al. [182], Corre et al. [175], and Lu et al.[174]. They achieved hydrogen-storage capacities with differ-ent stoichiometric LaNi5 samples such as 1, 1.44 and 1.32 wt%,respectively. Chen et al. [182] applied chemical coating by cop-per and achieved kinetics and cycling behavior during hydro-genation /dehydrogenation process. By CO surface treatment,1.44 wt% hydrogen capacity is achieved in LaNi5. Lu et al.[174] processed the LaNi5 using a twin roll process in order toachieve uniform nanocrystalline structure with 1.32 wt% stor-age capacity.

Apart from the above reported works, a few important stud-ies in the literature are worth mentioning. Liu et al. [183], Wanget al. [184], and Suda et al. [185] reported on the fluorination ofhydriding alloys and its effects on properties. The aim of theseexperiments was to form a Ni-rich layer in order to improvethe initial activation and impurity tolerance. There are alsotheoretical studies found in the literature, on LaNi5 utilizationfor hydrogen storage, tank design and optimization. Kikkinideset al. [186] showed the direct relation between hydrogen-storage performance and optimization in LaNi5 systems.Storage time could be improved by 60% through optimization.

The mechanism of hydrogen diffusion in LaNi3BHx is inves-tigated. The results suggested that hydrogen occupies sites co-ordinated by lanthanum and nickel only, while the basal La–Bplanes act as barriers to hydrogen diffusion along the hexag-onal axis. Boron has an adverse effect on the hydrogen sorp-tion properties of intermetallic compounds because it acts asa barrier for hydrogen diffusion and favors localization of thehydrogen atoms in the metal matrix away from the boron atomsites [131].

The AB2 type compounds are derived from the Laves phasescrystal structures. The potential AB2 types are obtained withTi and Zr on the A site. The B elements are represented mainlyby different combinations of 3d atoms, V, Cr, Mn and Fe. Thehydrogen-storage capacity can reach up to 2 wt% in Laves phaseV–7.4%Zr–7.4%Ti–7.4%Ni [166]. The Laves phase series ofcompounds has attracted large attention in the last decade dueto their good hydrogen-storage capacity. Most of Laves phasesshow relatively high capacities faster kinetics, longer life and arelatively low cost in comparison to the LaNi5-related systems[155]. However, their hydrides are too stable at room temper-ature [187]. In general the AB2 type compounds seem to be


Tabl

e5

Hyd

roge

nab

sorp

tion/

deso

rptio

npr

oper

ties

ofin

term

etal

licco

mpo

unds

Mat

eria

lM

etho

dTe

mpe

ratu

re(◦

C)

Pres

sure

(bar

)K

inet

ics

(min

)C

yclin

gst

abili

tyM

axw

t%of

H2

Ref

.

MgS

BM

Tab

s:−1

96P

abs:

50N

oda

taN

oda

ta0.

50[1

53]

La 0

.90C

e 0.0

5N

d 0.0

4Pr

0.01

Ni 4

.63Sn

0.32

Mel

ting

Tab

san

dT

des:

100,

25P

abs:

5–10

t abs

and

t des

:6.

6N

oda

ta0.

95[1

54]

Pde

s:0.

24Z

r(C

r 0.8

Mo 0

.2) 2

Indu

ctio

nm

eltin

gT

abs:

120

Pab

s:30

No

data

No

data

0.99

[155

]M

l 0:8

5C

a 0:1

5N

i 5R

Fm

eltin

gT

des:

25P

des:

10t d

es:

6010

0cy

c.:

stab

le1.

10[1

56]

LaN

i 4.8

Sn0.

2A

rcm

eltin

gT

des

and

Tab

s:80

Pde

s:3–

4N

oda

ta10

00cy

c.:

stab

le1.

16[1

57]

La 0

.55Y

0.45

Ni 5

Indu

ctio

nm

eltin

gT

des:

−20

Pde

s:3.

5N

oda

ta5

cyc.

:st

able

1.30

[158

]T

i 0.9

Zr 0

.15M

n 1.6

Cr 0

.2V

0.2

RF

mel

ting

Tde

s:25

Pde

s:10

t des

:60

100

cyc.

:st

able

1.30

[156

]M

mN

i 4.6

Al 0

.4M

eltin

gT

abs

and

Tde

s:25

Pde

s:25

t des

:5

11cy

c.:

stab

leaf

ter

nint

hcy

cle

1.30

[159

]M

mN

i 4.6

Fe0.

4M

eltin

gT

abs

and

Tde

s:25

Pab

s:35

t abs

:15

11cy

c.:

stab

leaf

ter

nint

hcy

cle

1.44

[159

]M

l 0.7

5C

a 0.2

5N

i 5R

Fle

vita

tion

mel

ting

Tab

s:20

Pab

s:10

0N

oda

taN

oda

ta1.

45[1

60]

Pde

s:6.

880

wt%

TiC

r 1.1

V0.

9–2

0w

t%M

eltin

g+

BM

Tab

san

dT

des:

30P

abs:

17N

oda

taN

oda

ta1.

50[1

61]

LaN

i 5P

des:

0.5

Ti 0

.97Z

r 0.0

3C

r 1.6

Mn 0

.4R

Fle

vita

tion

mel

ting

Tab

s:20

Pab

s:10

0N

oda

taN

oda

ta1.

55[1

60]

Pde

s:81

La 0

.7M

g 0.3

Ni 2

.65M

n 0.1

Co 0

.90

Mel

ting

Tab

san

dT

des:

30P

abs:

5N

oda

taN

oda

ta1.

56[1

62]

Pde

s:0.

33Z

r 0.7

5T

i 0.2

5C

r 1.5

Ni 0

.5A

rcm

eltin

gT

abs:

40P

abs:

47N

oda

taN

oda

ta1.

75[1

63]

Ti 1

.1C

rMn

Arc

mel

ting

Tab

san

dT

des:

23P

abs:

33t a

bs:

110

00cy

c.:

stab

le1.

80[1

64]

Pde

s:1

t des

:5

FeT

iB

MT

abs:

25P

abs:

100

No

data

No

data

1.92

[165

]V

–7.4

%Z

r–7.

4%T

i–7.

4%N

iA

rcm

eltin

gT

abs:

40P

abs:

10N

oda

ta10

cyc.

:no

tst

able

2.00

[166

]P

des:

1V

0.37

5T

i 0.2

5C

r 0.3

0M

n 0.0

75A

rcm

eltin

gT

abs

and

Tde

s:30

Pab

s:50

No

data

No

data

2.20

[167

]P

des:

0.2

Ti 4

5Z

r 38N

i 17

BM

Tab

s:30

0P

abs:

80t a

bs:

1200

No

data

2.23

[168

]Q

uasi

crys

tal

pow

ders

Tde

s:42

7T

i–V

–Cr

Arc

mel

ting

Tab

san

dT

des:

40P

abs:

100

No

data

No

data

2.80

[169

]T

i–10

Cr–

18M

n–27

V–5

FeM

agne

ticle

vita

tion

mel

ting

Tab

s:60

Pab

s:30

t abs

:8.

3N

oda

ta3.

01[1

70]

Pde

s:1

Ti–

10C

r–18

Mn–

32V

Mag

netic

levi

tatio

nm

eltin

gT

abs:

60P

abs:

30t a

bs:

8.3

No

data

3.36

[170

]P

des:

1T

iCr 1

.1V

0.9

Mel

ting

+B

MT

abs

and

Tde

s:30

Pab

s:17

No

data

No

data

3.50

[161

]P

des:

0.5

Ti 4

3.5V

49Fe

7.5

Arc

mel

ting

Tab

s:−2

0P

abs:

100

t abs

:20

50cy

c.:s

tabl

e3.

90[1

71]

Tde

s:30

0P

des:

10T

i–V

–Cr–

Mn

Mag

netic

levi

tatio

nm

eltin

gT

des:

247–

472

Pab

s:30

No

data

No

data

3.98

[172

]P

des:

0.03

La 1

.8C

a 0.2

Mg 1

4N

13B

MT

abs

and

Tde

s:27

–327

Pab

s:40

t abs

:15

6cy

c.:

not

stab

le5.

00[1

73]

Pde

s:1

t des

:10


Table 6Hydrogen absorption/desorption properties of LaNi5 compounds

Material Method Temperature (◦C) Pressure (bar) Kinetics (min) Cycling stability Max wt%of H2

Ref.

LaNi5 BM Tabs: 20 Pabs : 20 tabs: 1.6 8 cyc.: not stable 0.25 [67]La0.59Ce0.29Pr0.03Ni4Co0.45Mn0.45Al0.3 Twin-rolling Tabs: 60 Pabs: 10 No data No data 1.27 [174]

Pdes: 0.6La0.9Ce0.1Ni5 CO surface

treatmentTabs: 0–100 Pabs: 50 tdes: 1.8 20 cyc.: stable

after fifth cycle1.40 [175]

Tdes: 25LaNi5 CO surface

treatmentTabs: 0–100 Pabs: 50 tdes: 13.6 20 cyc.: stable

after fifth cycle1.44 [175]

Tdes: 25

more sensitive to gaseous impurities than the AB5 type com-pounds. Thus, a small amount of oxygen can be a poison forthe AB2s, while, for the AB5s, it acts as a reactant, reducing thestorage capacity slightly. CO is a poison for both types of com-pounds, although capacity recovery is possible by recycling inpure hydrogen [188].

Hydrogen absorption of FeTi powders has previously beenextensively studied. FeTi is a well-known hydrogen-storagecompound with a total hydrogen capacity of around 1.90 wt%with inexpensive elements. Hydrogen capacity of FeTi can beaccomplished to 1.90 wt% by the catalytic effect of 1 wt% Pdaddition [165]. However, the activation process of FeTi is trou-blesome due to the formation of titanium oxide layer. Bothhigh-pressure and high temperature are required to achieve areproducible absorption/desorption of the maximum amount ofhydrogen in the compound [151,187].

New BCC solid solution alloys have been reported to ab-sorb more hydrogen than the conventional intermetallic com-pounds. In recent years, study of Ti-based BCC phase alloyshas been studied in several laboratories because of their remark-able hydrogen capacities. However, the high cost is one of thecritical drawbacks limiting their successful practical applica-tions. Ti–10Cr–18Mn–27V–5Fe and Ti–10Cr–18Mn–32V hashydrogen-storage capacities of 3.01 and 3.36 wt%, respectively[170]. Increasing the V content is effective in accelerating hy-drogen absorption, enhancing the hydrogen absorption capacityand flattening the hydrogen desorption plateau, while decreas-ing hydrogen desorption plateau pressure. The maximum andeffective hydrogen-storage capacities of Ti–V–Cr–Mn alloysare 3.98 and 2.51 wt%, respectively [172].

It is well known that vanadium is expensive; therefore, de-creasing of the vanadium content is another goal of the investi-gations. In Ti–V–Cr–Mn compounds, increasing the Cr contentand the addition of Mn is necessary to increase the effective hy-drogen capacity by increasing the plateau pressure, but also todecrease costs by decreasing the vanadium content. The BCCphase solid solution of V0.375Ti0.25Cr0.30Mn0.075 exhibited aneffective hydrogen capacity of 2.20 wt% [167].

In order to improve the hydrogen-storage properties and re-duce the cost of Ti–V-based BCC alloys, the effect of Fe substi-tution in Ti–10Cr–18Mn–32V alloy is also investigated [170].It was reported that Fe addition increases the activation perfor-

mance, hydrogen absorption–desorption plateau pressure, hy-drogen desorption capacity and reduce the hysteresis of hydro-gen absorption–desorption plateau, and the cost of alloy [170].

The quasicrystals have a new type of translational long-rangeorder, display non-crystallographic rotational symmetry. Theycontain high amounts of interstitial sites. The quasicrystallineTi45Zr38Ni17 has 2.23 wt% storage capacity [168]. The sorp-tion of hydrogen between the layers of the multilayered wallof nanotubular TiO2 was studied in the temperature range of195–200 ◦C and at pressures of up to 6 bars. Hydrogen can in-tercalate between layers in the walls of TiO2 nanotube [189].

5. Conclusion

Hydrogen storage is a key issue in the success and realiza-tion of hydrogen technology and economy. According to USDOE, the hydrogen-storage capacity target for commercializa-tion is 6.5 wt% at the decomposition temperature between 60and 120 ◦C with high cycle life. Although pure water contains11.1 wt% of hydrogen, its decomposition requires much ther-mal, electric, or chemical energy [15].

Since the conventional hydrogen fuel storage methods ofpressurized H2 gas and cryogenic liquid H2 pose safety and per-meation problems along with high cost, they do not meet futureon-board applications goals set for hydrogen economy. Solidstate hydrogen fuel storage either absorption in the intersticesof metals and metallic alloys or adsorption on high surface areamaterials such as activated carbons gain the attention for pos-sible future hydrogen applications. The present article reviewsthe hydrogen-storage materials for transport applications whichrequire research into further aspects of tank technology, heatmanagement and solid fuel recycling. The work is carried outin an attempt to facilitate prospectus material choice for furthertank design aiming at on-board vehicle applications.

Hydrogen can be stored in metal hydrides under moderatetemperature and pressure. Metal hydrides are the promisingcandidates due to their safety advantage with high volume-efficient storage capacity for on-board applications. Intensiveresearch has been recently conducted on the metal hydrides forimproving adsorption/desorption properties based on hydrogen-storage capacity, kinetics, thermal properties, toxicity, cyclingbehavior and cost.


Group of Mg-based hydrides is a promising candidate forcompetitive mobile hydride storage with the reversible hydro-gen capacity of up to 7.6 wt%. However, slow kinetics and highhydrogen desorption temperatures up to about 300 ◦C reducethe efficiency and applicability in vehicles. Although much ef-fort has been devoted to those materials in order to decreasetheir decomposition temperature, enhance the kinetics and cy-cle life by using appropriate catalysts and production methodof ball-milling, further research is needed.

The complex hydrides released hydrogen by the step reac-tions unlike the metallic hydrides. Although the storage ca-pacities of complex hydrides are theoretically high, there is abig difference between the theoretical and the presently practi-cal attainable hydrogen capacities. Repeated hydrogenation cy-cles need to be applied for the potential applications to ensurethe reversibility of these materials. Moreover, the slow kineticsproblem is a significant obstacle for practical on-board applica-tions. The intermetallic compounds do not satisfy the require-ments for mobile storage for the reason that their low storagecapacities up to 2 wt% for available use and along with highcosts. An alternative application may be seen in effective useas thermodynamic devices [188].

There is no perfect choice of hydrogen store material tomeet the set US DOE goals for transport applications. Althoughsome results are encouraging, such as improved kinetics andlower decomposition temperatures for metal hydrides, furtherresearch is needed to develop materials satisfying the needs fortechnical applications. In the light of the achievements, there ishigh potential in developing better hydride materials with highreversible hydrogen capacity at ambient temperatures. In ad-dition, technological improvements in vehicle design and sys-tem integration along with cost efficiency will determine theon-board applicability of the selected material [2]. The successand realization of hydrogen economy using hydrogen storedsolid fuel technology will be dependent on the meeting ofabove goals.

Acknowledgments

Support for this work was provided by the EU FP6 RTNProject HyTRAIN; Hydrogen Storage Research Training Net-work. Figs. 1–5 reprinted from indicated references with kindpermission of the Elsevier and International Journal of Hydro-gen Energy are acknowledged.

References

[1] Ogden JM. Developing an infrastructure for hydrogen vehicles: aSouthern California case study. Int J Hydrogen Energy 1999;24(8):709–30.

[2] Dogan B. Hydrogen storage tank systems and materials selectionfor transport applications. ASME Conference PVP2006- ICPVT-11,Vancouver, Canada, July 23–27, 2006, Conference Proceedings CD,Track: Materials and Fabrication, Session: Materials for HydrogenService, Paper No. 93868, pp. 1–8.

[3] Weast RC, Astle MJ, Beyer WH. CRC handbook of chemistry andphysics. 64th ed., Boca Raton, FL: CRC Press; 1983.

[4] Trudeau ML. Advanced materials for energy storage. MRS Bull1999;24:23–6.

[5] DOE: US Department of Energy. Website: 〈http://www.doe.gov〉.[6] Schulz R, Huot J, Liang G, Boily S, Lalande G, Denis MC. et al.

Recent development in the applications of nanocrystalline materials tohydrogen technologies. Mater Sci Eng A 1999;267:240.

[7] Darkrim FL, Malbrunot P, Tartaglia GP. Review of hydrogen storageby adsorption in carbon nanotubes. Int J Hydrogen Energy 2002;27:193–202.

[8] Hirscher M, Becher M, Haluska M, Zeppelin F, Chen X, Dettlaff-Weglikowska U. et al. Are carbon nanostructures an efficient hydrogenstorage medium?. J Alloys Compds 2003;356–357:433–7.

[9] Hirscher M, Becher M. Hydrogen storage in carbon nanotubes.J Nanosci Nanotech 2003;3(1–2):3–17.

[10] David E. An overview of advanced materials for hydrogen storage.J Mater Process Technol 2005;162–163:169–77.

[11] Zhou L. Progress and problems in hydrogen storage methods. RenewSustain Energy Rev 2005;9:395–408.

[12] Schlapbach L, Züttel A. Hydrogen-storage materials for mobileapplications. Nature 2001;414:353–8.

[13] Zuttel A. Materials for hydrogen storage. Mater Today 2003; 24–33.[14] Zhou L, Zhou Y, Sun Y. Studies on the mechanism and capacity

of hydrogen uptake by physisorption-based materials. Int J HydrogenEnergy 2006;31(2):259–64.

[15] Grochala W, Edwards PP. Thermal decomposition of the non-interstitialhydrides for the storage and production of hydrogen. Chem Rev2004;104:1283–315.

[16] Eberle U, Arnold G, Helmholt RV. Hydrogen storage inmetal—hydrogen systems and their derivatives. J Power Sour2006;154(2):456–60.

[17] Latroche M. Structural and thermodynamic properties of metallichydrides used for energy storage. J Phys Chem Solids 2004;65:517–22.

[18] HyTRAIN: Hydrogen Storage Research Training Network, EC-MRTN-CT-2004-512443. Website: 〈http://www.imr.salford.ac.uk〉.

[19] Zaluska A, Zaluski L, Ström-Olsen JO. Structure, catalysis and atomicreactions on the nano-scale: a systematic approach to metal hydridesfor hydrogen storage. Appl Phys A 2001;72:157–65.

[20] Imamura H, Masanari K, Kusuhara M, Katsumoto H, Sumi T, Sakata Y.High hydrogen storage capacity of nanosized magnesium synthesizedby high energy ball-milling. J Alloys Compds 2005;386:211–6.

[21] Zaluski L, Zaluska A, Ström-Olsen JO. Nanocrystalline metal hydrides.J Alloys Compds 1997;253–254:70–9.

[22] Zhu M, Wang H, Ouyang LZ, Zeng MQ. Composite structure andhydrogen storage properties in Mg-based alloys. Int J Hydrogen Energy2006;31(2):251–57.

[23] Wiswall R. Topics in applied physics. Hydrogen Met II 1978;29:209.[24] Fukai Y. The metal–hydrogen system, basic bulk properties. Springer

series in materials science, 1993.[25] Zaluska A, Zaluski L, Ström-Olsen JO. Nanocrystalline magnesium for

hydrogen storage. J Alloys Compds 1999;288:217–25.[26] Barkhordarian G, Klassen T, Bormann R. Effect of Nb2O5 content on

hydrogen reaction kinetics of Mg. J Alloys Compds 2004;364:242–6.[27] Bogdanovic B, Bohmhamme K, Christ B, Reiser A, Schlichte K, Vehlen

R. et al. Thermodynamic investigation of the magnesium–hydrogensystem. J Alloys Compds 1999;282:84–92.

[28] Jung KS, Lee EY, Lee KS. Catalytic effects of metal oxide onhydrogen absorption of magnesium metal hydride. J Alloys Compds2005;421(1–2):179–84.

[29] Zhu M, Zhu WH, Chung CY, Chea ZX, Lia ZX. Microstructure andhydrogen absorption properties of nano-phase composite prepared bymechanical alloying of MmNi (CoAlMn) and Mg. J Alloys Compds1999;293–295:531–5.

[30] Guoxian L, Erde W, Shoushi F. Hydrogen absorption and desorptioncharacteristics of mechanically milled Mg–35 wt% FeTi1.2 powders.J Alloys Compds 1995;223:111–4.

[31] Bouaricha S, Dodelet JP, Guay D, Huot J, Boily S, Schulz R. Hydridingbehavior of Mg–Al and leached Mg–Al compounds prepared by high-energy ball-milling. J Alloys Compds 2000;297:282–93.

[32] Bououdina M, Guo ZX. Comparative study of mechanical alloyingof (Mg:Al) and (Mg:Al:Ni) mixtures for hydrogen storage. J AlloysCompds 2002;336:222–31.

http://www.doe.gov

http://www.imr.salford.ac.uk


[33] Wang P, Wang A, Zhang H, Ding B, Hu Z. Hydriding properties ofa mechanically milled Mg–50 wt% ZrFe1.4Cr0.6 composite. J AlloysCompds 2000;297:240–5.

[34] Song MY, Bobet J-L, Darriet B. Improvement in hydrogen sorptionproperties of Mg by reactive mechanical grinding with Cr2O3, Al2O3and CeO2. J Alloys Compds 2002;340:256–62.

[35] Tran NE, Lambrakos SG, Imam MA. Analyses of hydrogen sorptionkinetics and thermodynamics of magnesium–misch metal alloys.J Alloys Compds 2006;407:240–8.

[36] Wang P, Zhang HF, Ding BZ, Hu ZQ. Direct hydrogenation of Mgand decomposition behavior of the hydride formed. J Alloys Compds2000;313:209–13.

[37] Gross KJ, Spatz P, Züttel A, Schlapbach L. Mechanically milledMg composites for hydrogen storage: the transition to a steady statecomposition. J Alloys Compds 1996;240:206–13.

[38] Gross KJ, Chartouni D, Leroy E, Züttel A, Schlapbach L. Mechanicallymilled Mg composites for hydrogen storage: the relationship betweenmorphology and kinetics. J Alloys Compds 1998;269:259–70.

[39] Li Q, Chou K-C, Xu K-D, Jiang L-J, Lin Q, Lin G-W, Lu X-G,Zhang J-Y. Hydrogen absorption and desorption characteristics in theLa0.5Ni1.5Mg17 prepared by hydriding combustion synthesis. Int JHydrogen Energy 2006;31(4):497–503.

[40] Liang G, Boily S, Huot J, Neste AV, Schulz R. Hydrogen absorptionproperties of a mechanically milled Mg–50 wt.% LaNi5 composite.J Alloys Compds 1998;268(1–2):302–7.

[41] Chen Y, Wu C-Z, Wang P, Cheng H-M. Structure and hydrogen storageproperty of ball-milled LiNH2/MgH2 mixture. Int J Hydrogen Energy2006, in press.

[42] Xiong Z, Wu G, Hu J, Chen P. Ternary imides for hydrogen storage.Adv Mater 2004;16(17):1522–5.

[43] Reiser A, Bogdanovic B, Schlichte K. The application of Mg-basedmetal-hydrides as heat energy storage systems. Int J Hydrogen Energy2000;25:425–30.

[44] Luo W. (LiNH2–MgH2): a viable hydrogen storage system. J AlloysCompds 2004;381:284–7.

[45] Chen P, Xiong Z, Luo J, Lin J, Tan KL. Interaction of hydrogen withmetal nitrides and imides. Nature 2002;420:302–4.

[46] Wang P, Wang AM, Zhang HF, Ding BZ, Hu ZQ. Hydrogenationcharacteristics of Mg–TiO (rutile) composite. J Alloys Compds2000;313:218–23.

[47] Davidson DJ, Raman SS Sai, Srivastava ON. Investigation on thesynthesis, characterization and hydrogenation behaviour of new Mg-based composite materials Mg–x wt% MmNiFe prepared throughmechanical alloying. J Alloys Compds 1999;292:194–201.

[48] Dehouche Z, Djaozandry R, Huot J, Boily S, Goyette J, BoseTK. et al. Influence of cycling on the thermodynamic and structureproperties of nanocrystalline magnesium based hydride. J AlloysCompds 2000;305:264–71.

[49] Bogdanovic B, Reiser A, Schlichte K, Spliethoff B, Tesche B.Thermodynamics and dynamics of the Mg–Fe–H system and itspotential for thermochemical thermal energy storage. J Alloys Compds2002;345:77–89.

[50] Liang G, Huot J, Boily S, Nestea AV, Schulz R. Catalytic effect oftransition metals on hydrogen sorption in nanocrystalline ball milledMgH2–Tm (Tm5Ti, V, Mn, Fe and Ni) systems. J Alloys Compds1999;292(1–2):247–52.

[51] Fabing L, Lijun J, Jun D, Shumao W, Xiaopeng L, Feng Z. Synthesisand hydrogenation properties of Mg–La–Ni–H system by reactivemechanical alloying. Int J Hydrogen Energy 2006, in press.

[52] Song MY, Kwon IH, Kwon SN, Park CG, Park HR, Bae J-S. Preparationof hydrogen-storage alloy Mg–10 wt% Fe2O3 under various millingconditions. Int J Hydrogen Energy 2006;31:43–7.

[53] Raman SS Sai, Srivastava ON. Hydrogenation behaviour of the newcomposite storage material Mg–x wt% CFMmNi5. J Alloys Compds1996;241:167–74.

[54] Liang G, Huot J, Boily S, Neste AV, Schulz R. Hydrogen storageproperties of the mechanically milled MgH2–V nanocomposite. J AlloysCompds 1999;291:295–9.

[55] Dehouche Z, Klassen T, Oelerich W, Goyette J, Bose TK, Schulz R.Cycling and thermal stability of nanostructured MgH2–Cr2O3composite for hydrogen storage. J Alloys Compds 2002;347:319–23.

[56] Hanada N, Ichikawa T, Fuji H. Catalytic effect of nanoparticle 3d-transition metals on hydrogen storage properties in magnesium hydrideMgH2 prepared by mechanical milling. J Phys Chem B 2005;109:7188–94.

[57] Oelerich W, Klassen T, Bormann T. Metal oxides as catalysts forimproved hydrogen sorption in nanocrystalline Mg-based materials.J Alloys Compds 2001;315:237–42.

[58] Huot J, Liang G, Boily S, Neste AV, Schulz R. Structural study andhydrogen sorption kinetics of ball-milled magnesium hydride. J AlloysCompds 1999;293–295:495–500.

[59] Leng HY, Ichikawa T, Isobe S, Hino S, Hanada N, Fujii H. Desorptionbehaviours from metal–N–H systems synthesized by ball milling.J Alloys Compds 2005;404–406:443–7.

[60] Gennari FC, Castra FJ, Urretavizcaya G, Meyer G. Catalytic effect ofGe on hydrogen desorption from MgH2. J Alloys Compds 2002;334:277–84.

[61] Reule H, Hirscher M, Weißhardt A, Krönmuller H. Hydrogen desorptionproperties of mechanically alloyed MgH2 composite materials. J AlloysCompds 2000;305:246–52.

[62] Holtz RL. Basic user’s guide for NRL 6323 hydrogen storage system,1996.

[63] Friedlmeier G, Groll M. Experimental analysis and modeling ofthe hydriding kinetics of Ni-doped and pure Mg. J Alloys Compds1997;253–254:550–5.

[64] Andreasen A, Vegge T, Pedersen AS. Compensation effect in thehydrogenation/dehydrogenation kinetics of metal hydrides. J Phys ChemB 2005;109:3340–4.

[65] Chen J, Dou SX, Liu HK. Crystalline Mg2Ni obtained by mechanicalalloying. J Alloys Compds 1996;244:184–9.

[66] Zaluska A, Zaluski L, Strom-Olsen JO. Synergy of hydrogen sorptionin ball-milled hydrides of Mg and Mg2Ni. J Alloys Compds 1999;289:197–206.

[67] Aoyagi H, Aoki K, Masumoto T. Effect of ball milling on hydrogenabsorption properties of FeTi, Mg2Ni and LaNi5. J Alloys Compds1995;231:804–9.

[68] Wagemans RWP, Lenth JHV, Jongh PE de, Dillen AJV, Jong KP de.Hydrogen storage in magnesium clusters: quantum chemical study.J Am Chem Soc 2005;127:16675–80.

[69] Hong T-W. Dehydrogenation properties of nano-amorphous Mg2NiHx

by hydrogen induced mechanical alloying. J Alloys Compds2000;312:60–7.

[70] Tessier P, Enoki H, Bououdina M, Akiba E. Ball-milling of Mg2Niunder hydrogen. J Alloys Compds 1998;268:285–9.

[71] Huot J, Akiba E, Takada T. Mechanical alloying of Mg–Ni compoundsunder hydrogen and inert atmosphere. J Alloys Compds 1995;231:815–9.

[72] Chen Y, Williams JS. Formation of metal hydrides by mechanicalalloying. J Alloys Compds 1995;217:181–4.

[73] Orimo S-I, Fujii H. Effects of nanometer-scale structure on hydridingproperties of Mg–Ni alloys: a review. Intermetallics 1998;6:185–92.

[74] Abdellaoui M, Cracco D, Percheron-Guegan A. Structuralcharacterization and reversible hydrogen absorption properties ofMg2Ni rich nanocomposite materials synthesized by mechanicalalloying. J Alloys Compds 1998;268:233–40.

[75] Barkhordarian G, Klassen T, Bormann R. Kinetic investigation ofthe effect of milling time on the hydrogen sorption reaction ofmagnesium catalyzed with different Nb2O5 contents. J Alloys Compds2006;407:249–55.

[76] Holtz RL, Imam MA. Hydrogen storage characteristics of ball-milled magnesium–nickel and magnesium–iron alloys. J Mater Sci1999;34:2655–63.

[77] Higuchi K, Kajioka H, Toiyama K, Fujii H, Orimo S, Kikuchic Y.In situ study of hydriding–dehydriding properties in some Pd/Mg thinfilms with different degree of Mg crystallization. J Alloys Compds1999;293–295:484–9.


[78] Akyildiz H, Özenbas M, Öztürk T. Hydrogen absorption in magnesiumbased crystalline thin films. Int J Hydrogen Energy 2006;31(10):1379–83.

[79] Higuchi K, Yamamoto K, Kajioka H, Toiyama K, Honda M, Orimo S.et al. Remarkable hydrogen storage properties in three-layeredPd/Mg/Pd thin films. J Alloys Compds 2002;330–332:526–30.

[80] Imamura H, Sakasai N, Kajii Yi. Hydrogen absorption of Mg-based composites prepared by mechanical milling: factors affecting itscharacteristics. J Alloys Compds 1996;232:218–23.

[81] Shang CX, Guo ZX. Effect of carbon on hydrogen desorption andabsorption of mechanically milled MgH2. J Power Sources 2004;129:73–80.

[82] Vija R, Sundaresan R, Maiya MP, Murthy SS. Comparative evaluation ofMg–Ni hydrogen absorbing materials prepared by mechanical alloying.Int J Hydrogen Energy 2005;30:501–8.

[83] Han SS, Goo NH, Lee KS. Effects of sintering on composite metalhydride alloy of Mg2Ni and TiNi synthesized by mechanical alloying.J Alloys Compds 2003;360(1–2):243–9.

[84] Orimo S, Fujii H. Materials science of Mg–Ni-based new hydrides.Appl Phys A 2001;72:167–86.

[85] Sato T, Blomqvist H, Noreus D. Attempts to improve Mg2Ni hydrogenstorage by aluminium addition. J Alloys Compds 2003;356–357:494–6.

[86] Zaluski L, Zaluska A, Ström-Olsen JO. Hydrogen absorption innanocrystalline Mg2Ni formed by mechanical alloying. J AlloysCompds 1995;217:245–9.

[87] Singh AK, Singh AK, Srivastava ON. On the synthesis of the Mg2Nialloy by mechanical alloying. J Alloys Compds 1995;227:63–8.

[88] Abdellaoui M, Mokbli S, Cuevas F, Latroche M, Guegan A Percheron,Zarrouk H. Structural, solid–gas and electrochemical characterization ofMg2Ni-rich and MgxNi100−x amorphous-rich nanomaterials obtainedby mechanical alloying. Int J Hydrogen Energy 2006;31(2):247–50.

[89] Liang G, Boily S, Huot J, Neste AV, Schulz R. Mechanical alloyingand hydrogen absorption properties of the Mg–Ni system. J AlloysCompds 1998;267:302–6.

[90] Terzieva M, Khrussanova M, Peshev P, Radev D. Hydriding anddehydriding characteristics of mixtures with a high magnesium contentobtained by sintering and mechanical alloying. Int J Hydrogen Energy1995;20(1):53–8.

[91] Terzieva M, Khrussanova M, Peshev P. Hydriding and dehydridingcharacteristics of Mg–LaNi5 composite materials prepared bymechanical alloying. J Alloys Compds 1998;267:235–9.

[92] Haussermann U, Blomqvist H, Noreus D. Bonding and stability of thehydrogen storage material Mg2NiH4. Inorg Chem 2002;41:3684–92.

[93] Zaluski L, Zaluska A, Tessier P, Ström-Olsen JO, Schulz R. Catalyticeffect of Pd on hydrogen absorption in mechanically alloyed Mg2Ni,LaNi5 and FeTi. J Alloys Compds 1995;217:295–300.

[94] Aymard L, Ichitsubo M, Uchida K, Sekreta E, Ikazaki F. Preparationof Mg2Ni base alloy by the combination of mechanical alloying andheat treatment at low temperature. J Alloys Compds 1997;259:L5–8.

[95] Tran NE, Imam MA, Feng CR. Evaluation of hydrogen storagecharacteristics of magnesium–misch metal alloys. J Alloys Compds2003;359:225–9.

[96] Friedlmeier G, Manthey A, Wanner M, Grollm M. Cyclic stabilityof various application-relevant metal hydrides. J Alloys Compds1995;231(1–2):880–7.

[97] Dehouche Z, Djaozandry R, Goyette J, Bose TK. Thermal cyclic chargeand discharge stability of nanocrystalline Mg2Ni alloy. J Alloys Compds1999;288:312–8.

[98] Pedersen AS, Larsen B. The storage of industrially pure hydrogen inmagnesium. Int J Hydrogen Energy 1993;18:279–300.

[99] Bouaricha S, Huot J, Guay D, Schulz R. Reactivity during cycling ofnanocrystalline Mg-based hydrogen storage compounds. Int J HydrogenEnergy 2002;27(9):909–13.

[100] Dehouche Z, Goyette J, Bose TK, Schulz R. Moisture effect onhydrogen storage properties of nanostructured MgH2–V–Ti composite.Int J Hydrogen Energy 2003;28(9):983–8.

[101] Baer R, Zeiri Y, Kosloff R. Hydrogen transport in nickel (1 1 1). PhysRev B 1997;55(16):952–74.

[102] Bloch J, Mintz MH. Kinetics and mechanisms of metal hydrideformation—a review. J Alloys Compds 1997;253–254:529–41.

[103] Iwakura C, Nohara S, Zhang SG, Inoue H. Hydriding and dehydridingcharacteristics of an amorphous Mg2Ni–Ni composite. J Alloys Compds1999;285:246–9.

[104] Liang G, Huot J, Boily S, Neste AV, Schulz R. Hydrogen storageproperties of nanocrystalline Mg1.9Ti0.1Ni made by mechanicalalloying. J Alloys Compds 1999;282:286–90.

[105] Zaluska A, Zaluski L. New catalytic complexes for metal hydridesystems. J Alloys Compds 2005;404–406:706–11.

[106] Huot J, Swainson IP, Shulz R. Neutron diffraction study of lixiviatednanocrystalline Mg–Li compound. J Alloys Compds 1999;292:292–5.

[107] Liang G. Synthesis and hydrogen storage properties of Mg-based alloys.J Alloys Compds 2004;370:123–8.

[108] Züttel A, Wenger P, Rentsch S, Sudan P, Mauron Ph, Emmenegger Ch.LiBH4 a new hydrogen storage material. J Power Sources 2003;118:1–7.

[109] Kyoi D, Sato T, Rönnebro E, Kitamura N, Ueda A, Ito M. et al.A new ternary magnesium–titanium hydride Mg7TiHx with hydrogendesorption properties better than both binary magnesium and titaniumhydrides. J Alloys Compds 2004;372:213–7.

[110] Bogdanovic B, Schwickardi M. Ti-doped NaAlH4 as a hydrogen-storage material—preparation by Ti-catalyzed hydrogenation ofaluminum powder in conjunction with sodium hydride. Appl Phys A2001;72:221–3.

[111] Bogdanovic B, Scwickardi M. Ti-doped alkali metal aluminiumhydrides as potential novel reversible hydrogen storage materials.J Alloys Compds 1997;253–254:1–9.

[112] Bogdanovic B, Brand RA, Marjanovic A, Schwickardi M, Tölle J.Metal-doped sodium aluminium hydrides as potential new hydrogenstorage materials. J Alloys Compds 2000;302:36–58.

[113] Jensen CM, Gross KJ. Development of catalytically enhanced sodiumaluminum hydride as a hydrogen-storage material. Appl Phys A2001;72:213–9.

[114] Zaluski L, Zaluska A, Ström-Olsen JO. Hydrogenation propertiesof complex alkali metal hydrides fabricated by mechano-chemicalsynthesis. J Alloys Compds 1999;290:71–8.

[115] Genma R, Okada N, Sobue T, Uchida H-H. Mechanically milledalanates as hydrogen storage materials. Int J Hydrogen Energy2006;31(2):309–11.

[116] Sandrock G, Gross KJ, Thomas G, Jensen C, Meeker D, Takara S.Engineering considerations in the use of catalyzed sodium alanates forhydrogen storage. J Alloys Compds 2002;330–332:696–701.

[117] Wang P, Jensen CM. Method for preparing Ti-doped NaAlH4 using Tipowder: observation of an unusual reversible dehydrogenation behavior.J Alloys Compds 2004;379:99–102.

[118] Sun D, Srinivasan SS, Kiyobayashi T, Kuriyama N, Jensen CM.Rehydrogenation of dehydrogenated NaAlH4 at low temperature andpressure. J Phys Chem B 2003;107:10176–9.

[119] Zidan RA, Takara S, Hee AG, Jensen CM. Hydrogen cycling behaviorof zirconium and titanium–zirconium-doped sodium aluminum hydride.J Alloys Compds 1999;285:119–22.

[120] Zaluska A, Zaluski L, Ström-Olsen JO. Sodium alanates for reversiblehydrogen storage. J Alloys Compds 2000;298:125–34.

[121] Jensen CM, Zidan R, Mariels N, Hee A, Hagena C. Advanced titaniumdoping of sodium aluminum hydride segue to a practical hydrogenstorage material. Int J Hydrogen Energy 1999;24:461–5.

[122] Bogdanovic B, Felderhoff M, Kaskel S, Pommerin A, Sclichte K,Schüth F. Improved hydrogen storage properties of Ti-doped sodiumalanate using titanium nanoparticles as doping agents. Adv Mater2003;15(12):1012–5.

[123] Sandrock G, Gross KJ, Thomas G. Effect of Ti-catalyst content on thereversible hydrogen storage properties of the sodium alanates. J AlloysCompd: s 2002;339:299–308.

[124] Sun D, Kiyobayashi T, Takeshita HT, Kuriyama N, Jensen CM. X-raydiffraction studies of titanium and zirconium doped NaAlH4 elucidationof doping induced structural changes and their relationship to enhancedhydrogen storage properties. J Alloys Compds 2002;337:L8–L11.


[125] Gross KJ, Guthrie S, Takara S, Thomas G. In situ X-ray diffractionstudy of the decomposition of NaAlH4. J Alloys Compds 2000;297:270–81.

[126] Chaudhuri S, Muckerman JT. First principles study of Ti-catalyzedhydrogen chemisorption on an Al surface: a critical first stepfor reversible hydrogen storage in NaAlH4. J Phys Chem B2005;109(15):6952–7.

[127] Fichtner M, Fuhr O, Kircher O, Rothe J. Small Ti clusters for catalysisof hydrogen exchange in NaAlH4. Nanotechnology 2003;14:778–85.

[128] Thomas GJ, Gross KJ, Yang NYC, Jensen C. Microstructural character-ization of catalyzed NaAlH4. J Alloys Compds 2002;330–332:702–7.

[129] Huot J, Boily S, Güther V, Schulz R. Synthesis of Na3AlH6 andNa2LiAlH6 by mechanical alloying. J Alloys Compds 1999;383:304–6.

[130] Kircher O, Fichtner M. Kinetic studies of the decomposition ofNaAlH4 doped with a Ti-based catalyst. J Alloys Compds 2005;404–406:339–42.

[131] Filinchuk YE, Yvon K. Boron-induced hydrogen localization in thenovel metal hydride LaNi3BHx (x = 2.5.3.0). Inorg Chem 2005;44:4398–406.

[132] Hu YH, Ruckenstein E. Hydrogen storage of Li2NH prepared byreacting Li with NH3. Ind Eng Chem Res 2006;45(1):182–6.

[133] Ichikawa T, Isobe S, Hanada N, Fujii H. Lithium nitride for reversiblehydrogen storage. J Alloys Compds 2004;365:271–6.

[134] Hu HH, Ruckenstein E. Highly effective Li2O/Li3N with ultrafastkinetics for H2 storage. Ind Eng Chem Res 2004;43:2464–7.

[135] Hu YH, Ruckenstein E. H2 storage in Li3N. Temperature programmedhydrogenation and dehydrogenation. Ind Eng Chem Res 2003;42:5135–9.

[136] Pinkerton FE, Meisner GP, Meyer MS, Balogh MP, Kundrat MD.Hydrogen desorption exceeding ten weight percent from the newquaternary hydride LiBN2H8. J Phys Chem B 2005;109:6–8.

[137] Vajo JJ, Skeith SL, Mertens F. Reversible storage of hydrogen indestabilized LiBH4. J Phys Chem B 2005;109(9):3719–22.

[138] Morioka H, Kakizaki K, Chung S-C, Yamada A. Reversible hydrogendecomposition of KAlH4. J Alloys Compds 2003;353:310–4.

[139] Dafert FW, Miklauz R. Uber einige neue Verbindungen von Stick-stoffand Wasserstoff mit Lithium. Diese Sitzungsberichte Bd. CXVIII, July1910. p. 981–96.

[140] Ruff O, Georges H. Uber das Lithium-imid und einige Bemerkungenzu der Arbeit von Dafert und Miklauz: Über einige neue Verbindungenvon Stickstoff und Wasserstoff mit Lithium. Anorganischen undelektrochemischen Laboratorium der Kgt. Techn. Hochschule Danzig,February 13, 1911. p. 502–6.

[141] Hu YH, Ruckenstein E. Ultrafast reaction between LiH and NH3 duringH2 storage in Li3N. J Phys Chem A 2003;107(46):9737–9.

[142] Orimo S, Nakamori Y, Kitahara G, Miwa K, Ohba N, Noritake T.et al. Destabilization and enhanced dehydriding reaction of LiNH2: anelectronic structure viewpoint. Appl Phys A 2004;79:1765–7.

[143] Nakamori Y, Orimo S-I. Destabilization of Li-based complex hydrides.J Alloys Compds 2004;370:271–5.

[144] Nakamori Y, Orimo S. Li–N based hydrogen storage materials. MaterSci Eng B 2004;108:48–50.

[145] Fakioglu E, Yürüm Y, Veziroglu TN. A review of hydrogen storagesystems based on boron and its compounds. Int J Hydrogen Energy2004;29:1371–6.

[146] Schlesinger HI, Brown HC. J Am Chem Soc 1940;62:3429.[147] Stasinevich DS, Egorenko GA. J Russ Inorg Chem 1968;13(3):341–3.[148] Züttel A, Rentsch S, Fischer P, Wenger P, Sudan P, Mauron PL.

et al. Hydrogen storage properties of LiBH4. J Alloys Compds2003;356–357:515–20.

[149] Zaluska A, Zaluski L, Ström-Olsen JO. Lithium–beryllium hydrides:the lightest reversible metal hydrides. J Alloys Compds 2000;307:157–66.

[150] Vucht JV, Kuijpers FA, Bruning H. Philips Res Rep 1970;25:133.[151] Reilly JJ, Wiswall RH. Formation and properties of iron titanium

hydride. Inorg Chem 1974;13(1):218–22.[152] Reilly JJ, Sandrock GD. Hydrogen storage in metal hydrides. Sci Am

1980;242(2):118–9.

[153] Goo NH, Hirscher M. Synthesis of the nanocrystalline MgS itsinteraction with hydrogen. J Alloys Compds 2005;404–406:503–6.

[154] Iosub V, Latroche M, Joubert J-M, Percheron-Guégan A. Optimisationof MmNi5−xSnx (Mm = La, Ce, Nd and Pr, 0.27 < x < 0.5)compositions as hydrogen storage materials. Int J Hydrogen Energy2006;31:101–8.

[155] Bououdina M, Soubeyroux JL, Rango P de, Fruchart D. Phasestability and neutron diffraction studies of the Laves phase compoundsZr(Cr1−xMox)2 with 0.0 < x < 0.5 and their hydrides. Int J HydrogenEnergy 2000;25:1059–68.

[156] Chen Y, Sequeira CAC, Chen C, Wang X, Wang Q. Metal hydride bedsand hydrogen supply tanks as minitype PEMFC hydrogen sources. IntJ Hydrogen Energy 2003;28:329–33.

[157] Dehouche Z, Grimard N, Laurencelle F, Goyette J, Bose TK. Hydridealloys properties investigations for hydrogen sorption compressor.J Alloys Compds 2005;399:224–36.

[158] Challet S, Latroche M, Percheron-Guegan A, Heurtaux F.Crystallographic and thermodynamic study of La0.55Y0.45Ni5.H2,a candidate system for hydrogen buffer tanks. J Alloys Compds2005;404–406:85–8.

[159] Muthukumar P, Maiya MP, Murthy SS. Experiments on a metalhydride-based hydrogen storage device. Int J Hydrogen Energy 2005;30:1569–81.

[160] Wang X, Chen R, Zhang Y, Chen C, Wang Q. Hydrogen storage alloysfor high-pressure suprapure hydrogen compressor. J Alloys Compds2006;420(1–2):322–5.

[161] Santos DS dos, Bououdina M, Fruchart D. Structural and hydrogenationproperties of an 80 wt% TiCr1.1V0.9–20 wt% LaNi5 composite material.Int J Hydrogen Energy 2003;28:1237–41.

[162] Liu Y, Pan H, Gao M, Li G, Sun X, Lei Y. Investigation on thecharacteristics of La0.7Mg0.3Ni2.65Mn0.1Co0.75+x (x = 0.00.0.85)metal hydride electrode alloys for Ni/MH batteries. Part I: phasestructures and hydrogen storage. J Alloys Compds 2005;387:147–53.

[163] Bououdina M, Enoki H, Akiba E. The investigation of theZr1−yTiy(Cr1−xNix)2–H2 system phase composition analysis andthermodynamic properties. J Alloys Compds 1998;281:290–300.

[164] Kojima Y, Kawai Y, Towata S-I, Matsunaga T, Shinozawa T, KimbaraM. Development of metal hydride with high dissociation pressure.J Alloys Compds 2005, in press.

[165] Zaluski L, Zaluska A, Tessier P, Strörn-Olsen JO, Schulz R. Effects ofrelaxation on hydrogen absorption in Fe–Ti produced by ball-milling.J Alloys Compds 1995;227:53–7.

[166] Kuriiwa T, Tamura T, Amemiya T, Fuda T, Kamegawa A, Takamura H.et al. New V-based alloys with high protium absorption and desorptioncapacity. J Alloys Compds 1999;293–295:433–6.

[167] Seo C-Y, Kim J-H, Lee PS, Lee J-Y. Hydrogen storage properties ofvanadium-based B.C.C. solid solution metal hydrides. J Alloys Compds2003;348:252–7.

[168] Takasaki A, Kelton KF. Hydrogen storage in Ti-based quasicrystalpowders produced by mechanical alloying. Int J Hydrogen Energy2006;31(2):183–90.

[169] Okada M, Kuriiwa T, Tamura T, Takamura H, Kamegawa A.Ti–V–Cr B.C.C. alloys with high protium content. J Alloys Compds2002;330–332:511–6.

[170] Yu XB, Yang ZX, Feng SL, Wu Z, Xu NX. Influence of Fe addition onhydrogen storage characteristics of Ti–V-based alloy. Int J HydrogenEnergy 2006;31(9):1176–81.

[171] Nomura K, Akiba E. H2 Absorbing–desorbing characterization of theTi–V–Fe alloy system. J Alloys Compds 1995;231:513–7.

[172] Yu XB, Wu Z, Xia BJ, Xu NX. Enhancement of hydrogen storagecapacity of Ti–V–Cr–Mn BCC phase alloys. J Alloys Compds2004;372:272–7.

[173] Gao L, Chen C, Chen L, Wang X, Zhang J. et al. Hydriding/dehydridingbehaviors of La1.8Ca0.2Mg14Ni3 alloy modified by mechanical ball-milling under argon. J Alloys Compds 2005;399:178–82.

[174] Lu D, Li W, Hu S, Xiao F, Tang R. Uniform nanocrystalline AB5-typehydrogen storage alloy: preparation and properties as negative materialsof Ni/MH battery. Int J Hydrogen Energy 2006;31(6):678–82.


[175] Corre S, Bououdina M, Fruchart D, Adachi G-Y. Stabilisation of highdissociation pressure hydrides of formula La1−xCexNi5 with carbonmonoxide. J Alloys Compds 1998;275(277):99–104.

[176] Broom DP, Kemali M, Ross DK. Magnetic properties of commercialmetal hydride battery materials. J Alloys Compds 1999;293–295:255–9.

[177] Joubert J-M, Cerny R, Latroche M, Percheron-Guegan A, SchmittB. Hydrogenation of LaNi5 studied by in situ synchrotron powderdiffraction. Acta Mater 2006;54:713–9.

[178] Joubert J-M, Latroche M, Cerny R, Percheron-Guegan A, Yvon K.Hydrogen cycling induced degradation in LaNi5-type materials. J AlloysCompds 2002;330–332:208–14.

[179] Joubert J-M, Cerny R, Latroche M, Leroy M, Guenee L, Percheron-Guegan A. et al. A structural study of the homogeneity domain ofLaNi5. J Solid State Chem 2002;166:1–6.

[180] Joubert J-M, Latroche M, Cerny R, Bowman RC, Percheron-GueganA, Yvon K. Crystallographic study of LaNi5−xSn2−x (0.2 < x < 0.5)

compounds and their hydrides. J Alloys Compds 1999;293–295:124–9.[181] Demircan A, Demiralp M, Kaplan Y, Mat MD, Veziroglu TN.

Experimental and theoretical analysis of hydrogen absorption inLaNi5–H2 reactors. Int J Hydrogen Energy 2005;30:1437–46.

[182] Chen Y, Sequeira CAC, Chen C, Wang X, Wang Q. Metal hydride bedsand hydrogen supply tanks as minitype PEMFC hydrogen sources. IntJ Hydrogen Energy 2003;28:329–33.

[183] Liu FJ, Suda S. Properties and characteristics of fluorinated hydridingalloys. J Alloys Compds 1995;231:742–50.

[184] Wang XL, Suda S. Surface characteristics of fluorinated hydridingalloys. J Alloys Compds 1995;231:380–6.

[185] Suda S, Sun Y-M, Liu B-H, Zhou Y, Morimitsu S, Arai K. et al.Catalytic generation of hydrogen by applying fluorinated-metal hydridesas catalysts. Appl Phys A 2001;72:209–12.

[186] Kikkinides ES, Georgiadis MC, Stubos AK. On the optimizationof hydrogen storage in metal hydride beds. Int J Hydrogen Energy2006;31(6):737–51.

[187] Bououdina M, Grant D, Walker G. Review on hydrogen absorbingmaterials—structure, microstructure and thermodynamic properties. IntJ Hydrogen Energy 2006;31(2):177–82.

[188] Dantzer P. Properties of intermetallic compounds suitable for hydrogenstorage applications. Mater Sci Eng A 2002;329–331:313–20.

[189] Bavykin DV, Lapkin AA, Plucinski PK, Friedrich JM, Walsh FC.Reversible storage of molecular hydrogen by sorption into multilayeredTiO2 nanotubes. J Phys Chem B 2005;109:19422–7.

Review …...Metal hydrides have higher hydrogen-storage density (6.5Hatoms/cm3 for MgH 2) than...

Documents

Transcript of Review …...Metal hydrides have higher hydrogen-storage density (6.5Hatoms/cm3 for MgH 2) than...