Alkalinebattery

5 ct / Wh

Li-SOCl2battery

60 ct / Wh

NaH(η = 0.45)16 ct / Wh

Diesel(η = 0.15)

0.1 ct / Wh

Methanol(η = 0.40)

0.05 ct / Wh

MgH2(η = 0.45)12 ct / Wh

LiH(η = 0.45)11 ct / Wh

Electric energy density

Wh / kg Wh / ℓ

0

1000

2000

3000

4000

191

760

1259

1890

2240 2295

3800

478

12201450

15721774

2607

2371

HYDROGEN GENERATION VIA HYDROLYSIS OF METAL HYDRIDES

1 Metal hydride powders and surface

activation through ball milling

2 Lab-scale testing of different catalysts

3 Electric energy densities and costs of

various storage materials

FraunhoferInstitutefor

ManufacturingTechnology

andAdvancedMaterialsIFAM

BranchLabDresden

Winterbergstrasse 28

01277 Dresden | Germany

Contact

Dr. rer. nat. Lars Röntzsch

Phone: +49 351 2537 411

E-mail: Lars.Roentzsch

@ifam-dd.fraunhofer.de

Dr. rer. nat. Marcus Tegel

Phone: +49 351 2537 413

E-mail: Marcus.Tegel

@ifam-dd.fraunhofer.de

Fax: +49 351 2537 399

www.h2materials.de

www.ifam-dd.fraunhofer.de

2 3

HydrolysisofMetal

Hydrides

Hydrogen is an environmentally friendly

energy carrier with a very high gravi-

metric energy density. Its chemical energy

can be readily converted to electrical

energy by means of fuel cells. However,

direct storage of pressurized H2 is difficult

as it involves expensive, heavy and bulky

tanks as well as safety fittings, which

goes far beyond the requirements for

many portable applications. In low power

applications especially, diffusion losses

limit the direct storage of hydrogen.

Metal hydrides as lightweight, compact,

non-volatile, safe and reasonably priced

compounds overcome these issues. In

combination with water they can thus

serve as energy sources similar to conven-

tional or special batteries (e.g. Li-SOCl2)

but with a gravimetric and volumetric

energy density at least one order of

magnitude higher.

Applications

• backup / emergency power supplies

• standalone radiocommunication

• beacons

• sensors

• probes

PropertiesofLightweight

MetalHydrides

• NaH

- gravimetric H2 density of 8.4 %*)

- electric energy density 1259 Wh/kg*)

- very fast hydrolysis kinetics

• MgH2 - gravimetric H2 density 15.3 %

*)

- electric energy density 2295 Wh/kg*)

- slow hydrolysis kinetics

• LiH

- gravimetric H2 density 25.4 %*)

- electric energy density 3800 Wh/kg*)

- fast hydrolysis kinetics

*) under the assumption that H2O is

recuperated / available in excess

21

F R AUNHO F E R I N S T I T U T E F O R MANU FA C T U R I N G T E C HNO LOGY

A ND A D VAN C E D MAT E R I A L S I FAM , B R AN CH L A B D R E S D E N

Fig. 1 Time-dependent hydrogen generation for mixtures of commercially available MgH2 and activated MgH2 with various solid catalysts

1

4 Crystal structures and

proportions of different

metal hydrides

5 Outline of a hydrolysis reactor

in combination with a fuel cell

HydrolysisReactions

MeH + H2O H2 + MeOH

In hydrolysis reactions both the total

amount of released hydrogen and the

reaction kinetics strongly depend on a

number of factors:

- type of hydride

- active surface area

- pH

- presence of buffers

- salinity of water

- water temperature

Beyond that the reaction is catalyzed by the

addition of certain Lewis acids. Therefore,

an optimization of hydrolysis reactions

is feasible for a wide range of different

applications.

FraunhoferR&DServices

• Development of storage materials with

regard to specific requirements, e.g.

- suitable kinetics

- high energy density

- environment-related aspects

• Development of materials processing

technologies

• Specialized water treatment (e.g.

for sea water applications)

• Construction, test and evaluation of

metal hydride cartridges suitable for

hydrolysis

• Safety and reliability tests

• System development and testing

• System integration with fuel cells

• Software development

Metal Hydride Pellets

Water

Hydrolysis Reactor

Recuperation of Water

Exhaust (H2O)

Air (O2)

e−

H+

H2

Fuel Cell4 5

0 15 30 45 60

Time (min)

Hyd

roge

n co

nver

sion

(%)

75 90 105

Hydride mixture

MgH2 + Lewis acid III

MgH2 + Lewis acid II

MgH2 + Lewis acid I

MgH2 + Brønsted acid

MgH2

120

0

20

40

60

80

100

All measurements were perfor-med with de-ionized water at pH[t0] = 4.5; T[t0] = 20 °Cand a weight ratio of 1:100.