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