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Metal organic frameworks for Hydrogen
Storage
Rajesh Tripathi
CHEM 710
University of Waterloo
November 20 , 2008
1 – Hydrogen tank
2 – Radiator
3 – Stack Module (Hydrogen Fuel Cell)
4 – System Module (Hydrogen Fuel Cell)
5 – Power Distribution Unit
6 – LiPoly Battery to start the fuel cell system
7 – Total Rescue System
Why store Hydrogen?
• We need Clean energy.
• Hydrogen if combined with Oxygen releases energy (an energy carrier).
• Water is the byproduct (Completely harmless, clean). This reaction can
replace another popular but polluting source of energy-gasoline.
• Hydrogen generated from diverse domestic resources can reduce demand
for oil by more than 11 million barrels per day by the year 2040.
• For this reaction we need a source of hydrogen. (Attaching a hydrogen tank
with the mobile vehicle.)
http://www.fuelcells.org/hydrogen/basics.html
How much Hydrogen?
DOE Targets (for 2010) : Future hydrogen cars should have :
Hydrogen storage tank carrying approximately 5 kg of H2 (a range of
300 miles (480 km)).
Maximum allowed pressure of 100 bar for a storage device.
Capacity targets for a fueling system (including the tank and it's
accessories) set at 6 wt% and 45g/l of unstable H2.
System should show not decay for 1000 consecutive fueling cycles and
should allow filling to full capacity in 3 minutes.
for 2015 - 9 wt%, 60g/l, 1500 cycles. and 2.5 min.
Storing Hydrogen (Conventional methods)
Compressed gas method requires huge amount of initial pressures and
safety issues arise.
Cryogenic storage requires large amount of energy input for initial
condensation of hydrogen.
In complex hydrides (eg. Mg2NiH4 ) desorption usually occurs at higher
temperatures than targeted conditions.
Other drawbacks are high cost, susceptibility to impurities and low
reversible gravimetric capacity.
One way to improve the kinetics of storage is to maintain the Molecular
identity of H2 during the process.
Physiosorbtion of molecular hydrogen in to highly porous materials.
Metal Organic Frameworks
Storing Hydrogen in MOFs
• MOFs have large apparent surface MOF-177 MIL-53
areas.
• The dinitrogen isotherm measured
for MOF-177 at 77 K exhibits the
highest uptake of N2 for any
material to date, and gives rise to IRMOF-8
a monolayer-equivalent surface Zn2-(bdc)2(dabco)
area of 4500 m2 /g.
• This framework has cavities in the
range of 11-12 A0.
(C: black, N : green,O : red,
Zn : blue polyhedra, M: green octahedra).
O. M. Yaghi and J. L. C. Rowsell, Angew. Chem. Int. Ed. 2005, 44, 4670 –4679
Storing Hydrogen in MOFs
Kinetic diameter of H2 molecule = 2.98 A0
• For an ideal adsorbate:
1. Pore size should be same as it’s
own diameter. C: black,
H : white,
O : red
2. Walls of the pore should be made Zn : blue
of light elements (should be as thin tetrahedra
as possible)
3. Walls should be highly segmented
(achieved in MOFs by reticular
synthesis).
MOF-5: Pore diameter 15.2 A0 (Yellow sphere)
4. Smaller pores in MOFs are needed An smaller pore analogue of MOF-5 can be
to surpass the storage density of stabilized by using a rigid linear dicarboxylate
liquid hydrogen.
A compromise between gravimetric and volumetric density of storage must be found out.
Storing Hydrogen in MOFs
To bind the hydrogen in a better
way, another adsorbate surface
can be inserted inside the pore
(approach is called impregnation)
These surfaces also reduce the
pore diameter.
In this case also a compromise
between gravimetric and
volumetric capacity is reached.
MOF-177 molecule with C60
molecule inside it’s pore.
O. M. Yaghi and J. L. C. Rowsell, Angew. Chem. Int. Ed. 2005, 44, 4670 –4679
Storing Hydrogen in MOFs
Storing hydrogen by framework catenation:
Repeat unit Interpenetration Interweaving Modified Interweaving
Catenation of two identical frameworks can be used to restrict the dimensions of
the pore considerably by interpenetration.
Though interpenetrated framework is more capacitive than interwoven but it has
comparatively less stability.
O. M. Yaghi and J. L. C. Rowsell, Angew. Chem. Int. Ed. 2005, 44, 4670 –4679
Storing Hydrogen in MOFs
Using coordinatively unsaturated
metal sites:
An unsaturated metal site can attach
to H2 directly (a substantial increase
in H2 binding affinity)
Some strategies for synthesizing such
materials are:
1. Metal building units with
coordinatevely unsaturated
centers through solvent removal.
2. Incorporating Coordinatively Unsaturated
Unsaturated Metal Centers within metal centre
the Organic Linkers
3. Impregnation of Metal-Organic
Frameworks with Metal Ions
J. R. Long and M. Dinca Angew. Chem. Int. Ed. 2008, 47, 6766 – 6779
O. M. Yaghi and J. L. C. Rowsell, Angew. Chem. Int. Ed. 2005, 44, 4670 –4679
Storing Hydrogen in MOFs
Other methods
Modifying organic linkers to
increase the H2 affinity
Introducing additional adsorptive
sites on the SBUs.
Using light metals to reduce the
framework density.
J. R. Long and M. Dinca Angew. Chem. Int. Ed. 2008, 47, 6766 – 6779
O. M. Yaghi and J. L. C. Rowsell, Angew. Chem. Int. Ed. 2005, 44, 4670 –4679
Conclusions
Metal Organic frameworks are new candidates for Hydrogen storage
These materials are extraordinarily micro porous and has the capacity to
store enough hydrogen meeting DOE requirements.
Various strategies have been developed to increase the H2 affinity inside
these pores so that molecular hydrogen can be adsorbed on these sites.
Field is under intense investigation and various strategies developed so far
will have to be realized through synthetic chemistry routes.
MOFs display very optimistic results for future hydrogen storage systems
still much is needed to be done before these materials can be put under
practical use.
Thank You
