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Metal organic frameworks for Hydrogen Storage

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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

				
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