1

Hydrogen Storage Useful refs:See http://people.bath.ac.uk/cestjm/Shared/DTC/ch50182-Mays-Day2/

Energy White Paper

3

Why Hydrogen for Energy?2H2 + O2 = 2H2O + Energy

Three Major Attractions(1) Clean combustion of a non-toxic fuel

(2) Delivered energy / mass is very high

(energy gain / electron best of all the chemical elements)

(3) Offers greatest potential for “Sustainable Energy Future”

FUEL CONTENTS OF POLLUTING MATTER IN FUMES (Kg/Kg of fuel)

Formula

CO2

SO2

NOx

Dust and Unburned

Matter

H2O

Pb(C2H5)4

C 1.893 0.012 0.008 0.1 0.633 0 CH4 2.75 0.03 0.0075 0 2.154 0

C8H17 3.09 0.010 0.0115 0.85 1.254 0.001 H2 0 0 0.016 0 7 0

4

• Economic recyclable/rechargeable vessels

• Near ambient temperature pressure operation

• High hydrogen storage capacity/small volume

• Fast recharge and discharge kinetics

• Impact Safety

• Tolerant to trace poisoning

Hydrogen Storage Systems for Mobile Applications

• On a weight basis H2 has nearly three times the

energy content of gasoline. – 120 MJ/kg vs. 44 MJ/kg (LHV)

• On a volume basis the situation is reversed. – 3 MJ/L (5000 psi), 8 MJ/L (LH2) vs. 32 MJ/L

• Physical storage of hydrogen is bulky.• Capacity of reversible chemical storage at useful T, P is low.• Other challenging issues include energy efficiency, cost, and safety.

Storing enough hydrogen on vehicles to achieve greater than 300 miles driving range is difficult.

On-Board Hydrogen Storage Challenge

JoAnn Milliken, US DOE Status Report, 22 Oct 2002

6

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

20.4 K

87 kg m-3 [Silvera, Rev Mod Phys 52 (1980) 393]

critical point

solid

normal boiling point

real gasideal gas

real gas

de

nsi

ty / k

g m

-3

pressure / MPa

triple point

77 K

298 K

ideal gas

liqu

id d

ensi

ties

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

20.4 K

87 kg m-3 [Silvera, Rev Mod Phys 52 (1980) 393]

critical point

solid

normal boiling point

real gasideal gas

real gas

de

nsi

ty / k

g m

-3

pressure / MPa

triple point

77 K

298 K

ideal gas

liqu

id d

ensi

ties

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

20.4 K

87 kg m-3 [Silvera, Rev Mod Phys 52 (1980) 393]

critical point

solid

normal boiling point

real gasideal gas

real gas

de

nsi

ty / k

g m

-3

pressure / MPa

triple point

77 K

298 K

ideal gas

liqu

id d

ensi

ties

Leachman’s EOS for Normal HydrogenLeachman, et al. J Phys Chem Ref Data 38 (2009) 721

7

Cryogenic Storage of Hydrogen

Spherical designs best S/V

3% / day boil off (@ 20 K)

Insulation bulky

40% liquefaction penalty

High pressure options

Liq H2

Liq N2

Steel/Aluminium

Low emmittance multilayers

8

Compression Storage of Hydrogen

Composite H2 Cylinder – 12 wt%

Conformable geometricsHigher wt% via increased pressureHeating on filling

H2 : 350 bar

Glass/Carbon fibreAluminium/Thermoplastic

9

10

11

Advanced Materials for Hydrogen-Storage: 3 Strategic Challenges

I. Storage Capacity ≥ 6.5 wt%II. Reversibility of thermal absorption / desorption

cycles (at an accessible temperature)III. Low cost, low toxicity, low risk of explosion, etc.

(Source: www.doe.gov)

There is, as yet, no material known to meet simultaneously all of these requirements

12

Volume of 4 kg of hydrogen compacted in different ways, with size relative to the size of a car.

Mg2NiH4 LaNi5H6 H2 (liquid) H2 (200 bar)

Schlapbach and Züttel, Nature, 15 Nov 2001

13

Carbon

15Reversibly stored amount of hydrogen on various carbon materials versus the specific surface area of the samples.

Louis Schlapbach & Andreas Züttel, Nature 414, 15 Nov 2001

= nanotube samples (best-fit line indicated)

= other nanostructured carbon samples

16

Magnesium-based Storage Materials

Problems associated with magnesium:

• Stability of the MgH2.

• Surface oxidation of magnesium based powders.

• Slow diffusion of hydrogen through MgH2.

Possible Solutions:

• Milling to develop a nanocrystalline material.

• Introduction of catalysts to dissociate hydrogen by co-milling or by developing multilayers.

• Alloying with other metals such as Ni, Al etc….

17

Conclusions

Mobile

• Carbon Nanotubes - Less than 0.5 wt% uptake at RT. Adsorption related to surface area.- There may be a means of creating high hydrogen storage capacity CNT, but despite a large global effort, it remains elusive and lacking independent verification.

• Milled Magnesium + Alloys - Continuing to optimise milling conditions / PGM additions, in an effort to produce a practical on-board auto hydrogen store.- Operating Temperature still a problem

18

• Low-cost storage material

• Able to scale up storage solution to large-scale?

• Relatively high hydrogen storage capacity

• Reasonably fast recharge and discharge kinetics

• Tolerant to trace poisoning

• Long-term cycling

Hydrogen Storage Systems for Stationary Applications

19

zeolite A zeolites X and Y zeolite RHO.

The corners on each framework represent Si or Al and these are linked by oxygen bridges represented by the lines on the frameworks

Zeolite Framework Structures

20

Zeolite A – Si-Al network.

Zeolite Preparation

• Hydrothermal Procedure

• Ion exchange using metal nitrate

• Characterisation•XRD

•SEM with EDX

•BET surface area (N2 at 77K)

21

H2 uptake (wt.%)Material -196ºC RT 270ºCNaA 1.54 0.28 0.30CdA 1.14 0.25 0.30MgA 1.19 - -NaCsRHO 0.00 0.18 0.20CdRHO 0.08 0.19 0.25LiX 2.15 - -NaX 1.79 - 0.25CdX 1.42 - -MgX 1.61 - 0.28CuX - - 0.25NaY 1.81 - -CdY 1.47 - -MgY 1.74 - -

Hydrogen uptake in Zeolites

-196°C

-196°C

15bar H2

22

Wt% Hydrogen plotted against BET surface area for activated carbon and zeolites samples.

23

Conclusions

Stationary

Activated CarbonSignificant amounts of hydrogen can be stored reversibly (up to 4wt%) at 77 K and 15 bar.

Zeolites- Up to 2wt% at 77 K and 15 bar.- Hydrogen storage capacity of certain zeolites can be increased by manipulation of the zeolite exchangeable cations, e.g. Zeolite RHO

Unfortunately, at room temperature storage properties are below 1wt%, for both activated carbon and zeolites.

24

THE STORAGE OF HYDROGEN IN SOLIDS

• Carbon: A deeper understanding of the unique interaction between H2 (H) and carbon;

– nature of physi-, vs chemi-sorption, in nanostructured carbon– the role of dangling bonds.

• Light Hydrides: A deeper understanding of the thermodynamics and kinetics of decomposition / absorption reactions and (intermediate) processes;

– metallicity, chemical reactivity and electronic states,– innovation in the synthesis and stabilisation (handling) of hydrides.

• Nanostructured Porous Solids: The tailoring of pore geometry, and (interior) chemical reactivity for hydrogen activation, storage and release;

– the interaction between H2 (H) and porous solids.