hydrogen as energy carrier f. schüth mpi für kohlenforschung, mülheim
TRANSCRIPT
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
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
Bild der Wissenschaft 2004
Why Hydrogen
Very high mass based energy density (120 MJ/kg) Combustion exclusively to water (with oxygen) Easily generated by electrolysis or from biomass
Advantages
BiomasseVergasung
Roh-H2
EisenoxidEisen
Wasser-dampf
Rein-H2
Why Hydrogen
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
Explosive within wide limits Electricity-to-hydrogen-to-electricity substantial
losses Storage problem unsolved
Advantages
Disadvantages
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
„If you want to name a single obstacle for the introduction of fuel cell technology in cars, it is the hydrogen storage“
Source: U. Eberle, GM FCA
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
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
Characteristics of liquid storage
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
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
If to be used, only in combination with 77 K cryosystems
Sorptive storage in high surface area materials
Panella et al., Carbon 43, 2209 (2005)
Reforming of liquid fuels
Methanol or hydrocarbons have a high storage capacity
Methanol reforming possible at 200-300°C
Hydrocarbon reforming above 500°C Partial oxidation more attractive
CH3OH + H2O CO2 + 3 H2
CH3OH + ½ O2 CO2 + 2 H2
The fuel processor system
FuelFuel
Water-Gas ShiftWater-Gas ShiftWater-Gas ShiftWater-Gas Shift
Steam ReformerSteam Reformer
RecuperatorRecuperatorRecuperatorRecuperator
VaporizerVaporizerVaporizerVaporizer
COCOCleanupCleanup
COCOCleanupCleanup
CombustorCombustorCombustorCombustor
FuelFuelCellCell
FuelFuelCellCell
PowerPower
AirAir
ExhaustExhaust
WaterWater
Decrease CO-formation in reforming
H2O
n-heptane + surfactant
Zr(OC4H9)4
Cu(NO3)2
Zr(OH)4
(+ n-butanol
Cu(OH)2
(+ n-butanol
CuO/ZrO2
Cu(NO3)2
in H2O
Cu(NO3)2
in H2O
anionicsurfactant
anionicsurfactant
aliphaticsolvent
aliphaticsolvent
sol-gel synthesis inreverse microemulsion
metal-alkoxideprecursor solution
metal-alkoxideprecursor solution
I. Ritzkopf et al., Appl.Catal.A-Gen. 2006
Cu/ZrO2
0102030405060708090
100
240 250 260 270 280 290 300 310
co
nv
ers
ion
Temperature/°C
Commercial Cu/ZnO/Al2O3
Microemuslion
0.59% CO
0. 12% COMeOH steam reforming:Same activityMuch less CO
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
Catalyst Corporation Loading(%) T(oC) SV(h-1) XNH3From
Ni-Pt/Al2O3United 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/MOxAirox Nigen Equip. — 800 2,000 90% www.indiandata.com
Ni-Ru/Al2O3Apollo Energy Sys. — 700 1,000 97% www.electricauto.com
Ru/Al2O3Johnson Matt. 0.5% 700 5,000 84% Appl.Catal.A 227(2002)231
Unfavorable activity of commercial catalysts
Summary1) Typical operation temperature is as high as 700oC2) H2 productivity is low, NH3 space velocity is always < 5000 h-1
0%
20%
40%
60%
80%
100%
0 10,000 20,000 30,000 40,000
NH3 SV (ml g–1 h–1)
NH
3 C
on
vers
ion
Pure NH3, SV= 5,000 cm3/gcat h, 100 mgPure NH3, 700 oC, 100 mg
~100% conversion could be achieved at 700oC and 20000 h-1
Effect of space velocity Effect of Temperature
Bayer MWCNTs(Co as the impurity)
0%
20%
40%
60%
80%
100%
500 550 600 650
Temperature (oC)
Co
nve
rsio
n
Alternative: Metal hydrides
Volume of the tank for 4 kg H2Schlapbach and Züttel, Nature 414, 353 (2001)
Two alternatives for hydrides
Hydrolytic processes
Reversible Hydrides
Hydrogen on demand™
NaBH4 + 2 H2O 4 H2 + NaBO2 10.8 %
25wt.%NaBH4 in H2O,
2 % NaOH
Kat.
H2
NaBO2 in H2O
Advantages: Liquid fuel as conventionalharmless without catalyst
Finalche.rm
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
As low as possible (ball park figure: 100 €/kg H2)
Cost
Ideally absentMemoryeffect
> 500Cycle stability
As high as possible, i.e. no ignition with air or moisture
Safety
As low as possible (but related to equilirium pressure)
Heat effects
Around 1 bar at room temperatrueEquilibrium pressure
< 50 barRehydrogenations pressure
Dehydrogenation < 3 hRehydrogenation < 5 min
De-/rehydrogenationrate
> 6.5 % Volumetric storage density
> 6.5 % Gravimetric storage density
TargetProperty
A reversible hydride in technical applications
U 212 HDW
The „materials landscape“
0
160
80
120
40
0 5 10 15 20 25
Mg2FeH6
BaReH6
LaNi5H6
FeTiH1.7
MgH2
NaAlH4
KBH4
NaBH4
LiAlH4
LiBH4
C8
C3
C1
H2,lH on C
Mass storage density [wt.%]
Vo
lum
etri
c s
tora
ge
de
ns
ity
[k
g H
2 m
-3 ] 5 g cm-3 2 g cm-3 1 g cm-3 0.7 g cm-3
3 NaAlH4 Na3AlH6 + 2 Al + 3 H2
Ti
Na3AlH6 3 NaH + Al + 1.5 H2
Ti
Adapted from Schlapach and Züttel, Nature 414, 353 (2001)
The alternative: reversible hydrides
1.5 2.0 2.5 3.0 3.5 4.0
1/T [10-3 K-1]
300 200 100 50 25 0 -20 100
10
1
0.1Dis
soci
atio
n p
ress
ure
[at
m]
MgH
2M
g2 N
iH4
Na3 AlH
6
NaAlH4
HT MT LT
FeTiHLaNi5 H
6
CoNi5 H
4
MNi5 H
6
TiCr1.8 H
1.7
B. Bogdanovic et al. J.Alloy Compd. 302, 36 (2000)
The doping procedure
From solution
By ball-milling
NaAlH4 in Toluene
Ti-compound
Most advanced system: ScCl3 in situ doped
0 2 4 6 8
Time / min
108
116
114
112
110
120
160
180
140
Tem
peratu
re / °CP
ress
ure
/ b
ar
System heated to 120°C, then pressurized. Capacity: 3.2 %
Other Alanates
Unsuitable thermodynamics
CaAlH5 possibly useful
A Nitride-based system: Li3N/LiNH2
Li3N + H2 Li2NH + LiH 5.4 wt.%
Li2NH + H2 LiNH2+ LiH 6.5 wt.% at 250°C
P. Chen et al., Nature 420, 302 (2004)
Problems: Ammonia releaseTemperature too high
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
Adam Opel AGPowerfluidFCIDFG
H. Bönnemann, MülheimS. Kaskel, MülheimW. Grünert, BochumK. Klementiev, BochumU. Eberle, Adam Opel AGF. Mertens, Adam Opel AGG. Arnold, Adam Opel AG
M. German M. HärtelT. KratzkeM. MamathaR. PawelkeA. PommerinK. Schlichte W. SchmidtM. SchwickardiN. SpielkampB. SpliethoffG. StreukensA. Taguchi J. von Colbe de BellostaC. WeidenthalerB. Zibrowius
Further reading: F. Schüth et al., Chem.Commun. 2249 (2004)
M. Felderhoff, B. Bogdanovic