Hydrogen as Energy Carrier
F. Schüth
MPI für Kohlenforschung, Mülheim
Why do we need a new energy
infrastructure?
Oil discoveries are decreasing
Reason for constant reserves/production is enhanced recovery
„Peak oil“ is not too far away, may have already been reached
Roles of hydrocarbons in our economy

Source of energy

Transport and storage of energy
(around 20 Mio. t of oil in strategic energy reserve)

Alternative storage
» Reservoirs (Pumpspeicherkraftwerke), but the total installed
capacity in germany only covers some minutes of the primary
energy demand
» Pressured gas storage, one system operating in Germany, but
storage capactiy limited as well
» Electrochemical: would need gigantic batteries
Hydrogen as future energy storage and
transportation form
Bild der Wissenschaft 2004






With renewable hydrogen clean electrical energy
In principle zero emission
High efficiency for energy conversion
But still to solve…
Reduce or replace platinum based catalyst
Better stability / higher temperature membranes
Why Hydrogen
Advantages



Very high mass based energy density (120 MJ/kg)
Combustion exclusively to water (with oxygen)
Easily generated by electrolysis or from biomass
Roh-H2
WasserBiomasse
dampf
Vergasung
Rein-H2
Eisenoxid
Eisen
Why Hydrogen
Advantages





Very high mass based energy density (120 MJ/kg)
Combustion exclusively to water (with oxygen)
Easily generated by electrolysis or from biomass
Efficient conversion to electricity in fuel cells
Non-toxic, odorless
Disadvantages



Explosive within wide limits
Electricity-to-hydrogen-to-electricity substantial
losses
Storage problem unsolved
Explosion danger
Why Hydrogen Storage for Mobile
Applications?




Fuel cell technology envisaged as future
replacement of internal combustion engine
Well-to-wheel studies indicate that hydrogen in
combination with fuel cells can reduce greenhouse
gas emissions substantially (close to zero for
renewable hydrogen)
System decision for hydrogen as energy carrier in
Germany has been taken
Available technologies for hydrogen storage not
fully satisfactory
Source: U. Eberle, GM FCA
„If you want to name a single obstacle for the introduction of
fuel cell technology in cars, it is the hydrogen storage“
The markets




50 Million cars/years worldwide
Costs for storage 500 €/car
Total market volume 25 Billion €/year
Also other markets, such as laptops, mobile
phones, houses
Available technology: Liquid storage
Characteristics of liquid storage

Liquid hydrogen in superinsulated containers at
-254 °C

Liquifaction/transport in principle managed
technology

Boil-Off problems

Liquifaction highly energy intensive

Volumetric storage density unsatisfactory
Source: U. Eberle, GM FCA
Available technology: High pressure
storage
Characteristics high pressure storage

Compression of hydrogen up to 700 bar

In principle managable technology

Tanks presently much too expensive

Compression very energy intensive

Volumetric storage density unsatisfactory

Cylinders cause packaging problems
Source: U. Eberle, GM FCA
Storage Capacity: Comparison for
400 km range
Source: U. Eberle, GM FCA
Main cost drivers
Chemical storage systems
Sorptive storage in high surface area
materials





Exceedingly high capacities reported for storage in
carbon nanotubes
Results could not be reproduced, reason clarified
All different high surface area materials fall on
common line capacity vs. surface area
MOFs reported to deviate from this line, but not
confirmed
Panella et al., Carbon 43, 2209 (2005)
If to be used, only
in combination with 77 K
cryosystems
Reforming of liquid fuels


Methanol or hydrocarbons have a high storage
capacity
Methanol reforming possible at 200-300°C
CH3OH + H2O  CO2 + 3 H2


Hydrocarbon reforming above 500°C
Partial oxidation more attractive
CH3OH + ½ O2  CO2 + 2 H2
The fuel processor system
Power
Water-Gas Shift
CO
Cleanup
Steam Reformer
Combustor
Fuel
Cell
Air
Recuperator
Fuel
Water
Vaporizer
Exhaust
Decrease CO-formation in reforming
metal-alkoxide
precursor solution
n-heptane + surfactant
Zr(OC4H9)4
Zr(OH)4
(+ n-butanol CuO/ZrO2
Cu(OH)2
(+ n-butanol
sol-gel synthesis in
reverse microemulsion
H2O
Cu(NO3)2
Cu/ZrO2
Cu(NO3)2 anionic aliphatic
in H2O surfactant solvent
conversion
MeOH steam reforming:
Same activity
Much less CO
0.59% CO
100
90
80
70
60
50
40
30
20
10
0
240
0. 12% CO
Commercial Cu/ZnO/Al2O3
Microemuslion
250 260
270
280
290 300
310
Temperature/°C
I. Ritzkopf et al., Appl.Catal.A-Gen. 2006
NH3 as storage material?

Production well established

Efficient with respect to energy consumption

Decomposition without trace to N2 and H2

Easy liquifaction

High hydrogen content
Unfavorable activity of commercial catalysts
Catalyst
Corporation
Loading(%)
T(oC)
SV(h-1)
XNH3
From
Ni-Pt/Al2O3
United Catalyst
5%Ni,1%Pt
600
5,000
78%
Appl.Catal.A 227(2002)231
Raney Ni
Grace Davison
93.8%
700
5,000
82%
Appl.Catal.A 227(2002)231
Ni/MgO
Tianjin Univ.
10%
650
800
98%
Acta Petrolei Sinica (2002) 8 43
Ni/MOx
Airox Nigen Equip.
—
800
2,000
90%
www.indiandata.com
Ni-Ru/Al2O3
Apollo Energy Sys.
—
700
1,000
97%
www.electricauto.com
Ru/Al2O3
Johnson Matt.
0.5%
700
5,000
84%
Appl.Catal.A 227(2002)231
Summary
1) Typical operation temperature is as high as 700oC
2) H2 productivity is low, NH3 space velocity is always < 5000 h-1
Bayer MWCNTs
(Co as the impurity)
Effect of Temperature
100%
100%
80%
80%
Conversion
NH3 Conversion
Effect of space velocity
60%
40%
60%
40%
20%
20%
0%
0
10,000
20,000
30,000
NH3 SV (ml g–1 h–1 )
Pure NH3, 700 oC, 100 mg
40,000
0%
500
550
600
o
Temperature ( C)
Pure NH3, SV= 5,000 cm3/gcat h, 100 mg
~100% conversion could be achieved at 700oC and 20000 h-1
650
Alternative: Metal hydrides
Volume of the tank for 4 kg H2
Schlapbach and Züttel, Nature 414, 353 (2001)
Two alternatives for hydrides

Hydrolytic processes

Reversible Hydrides
Hydrogen on demand™
NaBH4 + 2 H2O
4 H2 + NaBO2
H2
25wt.%
NaBH4
in H2O,
2 % NaOH
Advantages:
Kat.
NaBO2
in H2O
Liquid fuel as conventional
harmless without catalyst
10.8 %
Hydrogen on demand in practice
Problems with Hydrolytic Storage

Modules have to be exchanged (solid)

Quite difficult control problems (solid)

Not very energy efficient
» production of alkali metals
» or production of metal hydrides

Expensive, even if prices would drop

Probably applications only in high-end niches
Consequently:
Reversible Hydrides: Requirements
Property
Target
Gravimetric storage density
> 6.5 %
Volumetric storage density
> 6.5 %
De-/rehydrogenationrate
Rehydrogenations pressure
Dehydrogenation < 3 h
Rehydrogenation < 5 min
< 50 bar
Equilibrium pressure
Around 1 bar at room temperatrue
Heat effects
As low as possible (but related to
equilirium pressure)
Safety
Cycle stability
As high as possible, i.e. no ignition with
air or moisture
> 500
Memoryeffect
Ideally absent
Cost
As low as possible (ball park figure: 100
€/kg H2)
A reversible hydride in technical
applications
U 212 HDW
Volumetric storage density [kg H2 m-3 ]
The „materials landscape“
5 g cm-3 2 g cm-3
Mg2FeH6
160
BaReH6
120
MgH2
KBH4
C8
LiAlH4
80
NaAlH4
40
3 NaAlH4
Na3AlH6
0
5
0.7 g cm-3
LiBH4
NaBH4
LaNi5H6
FeTiH1.7
0
1 g cm-3
10
C1
C3
H2,l
H on C
Ti
Ti
15
Na3AlH6 + 2 Al + 3 H2
3 NaH + Al + 1.5 H2
20
25
Mass storage density [wt.%]
Adapted from Schlapach and Züttel, Nature 414, 353 (2001)
The alternative: reversible hydrides
Dissociation pressure [atm]
300
200
100
50
25
0
-20
100
10
1
HT
0.1
1.5
MT
2.0
LT
2.5
3.0
1/T [10-3 K-1]
3.5
4.0
B. Bogdanovic et al. J.Alloy Compd. 302, 36 (2000)
The doping procedure
Ti-compound

From solution
NaAlH4 in Toluene

By ball-milling
Most advanced system: ScCl3 in situ
doped
116
114
160
112
110
140
108
120
0
2
4
6
8
Time / min
System heated to 120°C, then pressurized. Capacity: 3.2 %
Temperature / °C
Pressure / bar
180
Other Alanates
Unsuitable thermodynamics
CaAlH5 possibly useful
A Nitride-based system: Li3N/LiNH2
Li3N + H2 
Li2NH + LiH
Li2NH + H2  LiNH2+ LiH
Problems:
5.4 wt.%
6.5 wt.% at 250°C
Ammonia release
Temperature too high
P. Chen et al., Nature 420, 302 (2004)
Summary and Outlook

Chemical storage systems promising
as long term solution

Methanol reforming largely developed,
but complex

NaAlH4 presently most advanced
system, but too low capacity

Innovation potential in improved
catalysts, hydrides with higher
storage capacity
! ! ?! ? ! !
? !! ?
Many problems solved with purpose-built
vehicles
But will we have a hydrogen-based
economy?




Probably strong tendency towards increased use
of electricity directly, with smart grid technology
providing some buffer
Materials based storage and transportation form of
energy probably needed nevertheless
Hydrogen has many advantages, at present
serious alternatives are methanol and synthetic
hydrocarbons
Develop all systems further, until final decision can
be made
M. Felderhoff, B. Bogdanovic
M. German
M. Härtel
T. Kratzke
M. Mamatha
R. Pawelke
A. Pommerin
K. Schlichte
W. Schmidt
M. Schwickardi
N. Spielkamp
B. Spliethoff
G. Streukens
A. Taguchi
J. von Colbe de Bellosta
C. Weidenthaler
B. Zibrowius
H. Bönnemann, Mülheim
S. Kaskel, Mülheim
W. Grünert, Bochum
K. Klementiev, Bochum
U. Eberle, Adam Opel AG
F. Mertens, Adam Opel AG
G. Arnold, Adam Opel AG
Further reading: F. Schüth et al., Chem.Commun. 2249 (2004)
Adam Opel AG
Powerfluid
FCI
DFG