Infrared Study of Molecular Hydrogen Adsorption in Metal-Organic Frameworks

Undergrad StudentsMichael FriedmanJesse HopkinsBrian BresslauerBen ThompsonJordan Gotdank

Phys. Rev. B. 81, 104305 (2010)

Motivation: Hydrogen Storage for Fuel Cells

High Pressure

350-700 bar

Liquid Hydrogen

Metal-Organic Frameworks

Binding Energy too Weak

van der Waals Interactions

5 -10 kJ/mol

30 - 40 kJ/mol is ideal value

Act like a 3-D “Tinker Toy”

Metal ions linked by organic chains

Vast number of possible structures

Voids of ~ 10 – 20 Å

Loading Isotherm at 77 K

MOF-74

Infrared Spectroscopy to Study Adsorbed H2???

• Problem: H2 not infrared active: no dipole moment

• Matrix - H2 interactions induce dipole moments

• Spectrum is very sensitive to the intermolecular potential

• Problem: spectra are very weak

Diffuse Reflectance Spectroscopy

• Light bounces around

within powder sample

• Very long path length

enhances absorption signal

• Problem: requires large

collecting optics

Diffuse Reflectance Spectroscopy: Cryostat Assembly

Rev. Sci. Instr. 77, 093110 (2006)

Infrared Selection Rules for Adsorbed H2 (cold)

• Pure Vibrational modes called Q transitions J = 0

• Rotational Sidebands called S Transitions J = 2

• Q(0) and Q(1) should be very close in energy ~ 6 cm-1 apart

Q(0)S(0)

J = 0

J = 2

J = 1

J = 1

Para H2 Ortho H2

J = 0

J = 3

Q(1)

S(1)

Typical Spectra for H2 in MOFs at 30 KA

bso

rban

ce

48004600440042004000Frequency (cm

-1)

Q(0) and Q(1) S(0) S(1)

MOF-5

MOF-74

ZIF-8

HKUST-1

MOF-74 (M2C8H2O6) where M can be Mn, Fe, Co, Ni, and Zn

~1 nm

Neutron Diffraction Shows H2 sites

Typical Spectra for H2 in MOFs at 30 KA

bso

rban

ce

48004600440042004000Frequency (cm

-1)

Q(0) and Q(1) S(0) S(1)

MOF-5

MOF-74

ZIF-8

HKUST-1

Typical Spectra for H2 in MOFs at 30 KA

bso

rban

ce

48004600440042004000Frequency (cm

-1)

Q(0) and Q(1) S(0) S(1)

MOF-5

MOF-74

ZIF-8

HKUST-1

Pure Vibrational Q-region of H2 : Zn_MOF-74 at 30 KA

bso

rban

ce (

a.u

.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

Pure Vibrational Q-region of H2 in MOF-74 at 30 KA

bso

rban

ce (

a.u

.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Pure Vibrational Q-region of H2 in MOF-74 at 30 KA

bso

rban

ce (

a.u

.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Pure Vibrational Q-region of H2 in MOF-74 at 30 KA

bso

rban

ce (

a.u

.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2Liu et al. Langmuir 24, 4772 (2008)

Pure Vibrational Q-region of H2 in MOF-74 at 30 KA

bso

rban

ce (

a.u

.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Pure Vibrational Q-region of H2 in MOF-74 at 30 KA

bso

rban

ce (

a.u

.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Pure Vibrational Q-region of H2 in MOF-74 at 30 KA

bso

rban

ce (

a.u

.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

1 Q(1) gas phase

Q(0) gas phase

2

T

Pure Vibrational Q-region of H2 in MOF-74 at 30 KA

bso

rban

ce (

a.u

.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

1 Q(1) gas phase

Q(0) gas phase

2

T

MOF-74 Hydrogen Sites (Neutron Diffraction)

Primary Sites Separated by ~ 5 Å

Primary Sites Separated by ~ 5 Å

Primary-Secondary Separation ~ 2.9 Å

MOF-74 Hydrogen Sites (Neutron Diffraction)

Pure Vibrational Q-region of H2 in MOF-74 at 30 KA

bso

rban

ce (

a.u

.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

1 Q(1) gas phase

Q(0) gas phase

2

T

Para Enhanced H2 (J =0) in MOF-74 at 30 KA

bso

rban

ce (

a.u

.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

1 Q(1) gas phase

Q(0) gas phase

2

T

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

1 Q(1) gas phase

Q(0) gas phase

2

T

Para Enhanced H2 (J =0) in MOF-74 at 30 KA

bso

rban

ce (

a.u

.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

Q(1) gas phase

Q(0) gas phase

2

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

1 Q(1) gas phase

Q(0) gas phase

2

T

Ab

sorb

ance

(a.

u.)

4200416041204080

Frequency (cm-1)

1 Q(1) gas phase

Q(0) gas phase

2

T

Ortho to Para Conversion with TimeA

bso

rban

ce (

a.u

.)

412041104100409040804070

Frequency (cm-1)

5 minutes 15 minutes 25 minutes 35 minutes 100 minutes

Q(1)

Q(0)

MOF-74 Metal Ion Comparison

Ab

sorb

ance

42004150410040504000Frequency (cm

-1)

Zn

Mn

Co

Ni

Sc Ti V Cr Mn Fe Co Ni Cu Zn

Primary Site - Metal Separated by 2.6 Å

Secondary Site – Metal Separated by 4.3 Å

MOF-74 Metal Hydrogen Distance

Ab

sorb

ance

42004150410040504000Frequency (cm

-1)

Zn

Mn

Co

Ni

Irving-Williams SeriesSc Ti V Cr Mn Fe Co Ni Cu Zn

Irving-Williams Ligand Stability Mn < Fe < Co < Ni > Zn

Vibrational Red-Shift vs Binding Energy

12

10

8

6

4

2

0

Bin

ding

Ene

rgy

(kJ/

mol

)

120100806040200

Redshift (cm-1)

Mn-MOF-74Co-MOF-74

Ni-MOF-74

Zn-MOF-74

HKUST-1

MOF-5

ZIF-8

3.2

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

416041404120410040804060404040204000

Frequency (cm-1

)

160K

3.2

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

416041404120410040804060404040204000

Frequency (cm-1

)

140K

160K

1

3.2

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

416041404120410040804060404040204000

Frequency (cm-1

)

120K

140K

160K

1

3.2

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

416041404120410040804060404040204000

Frequency (cm-1

)

100K

120K

140K

160K

1

3.2

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

416041404120410040804060404040204000

Frequency (cm-1

)

90K

100K

120K

140K

160K

1

3.2

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

416041404120410040804060404040204000

Frequency (cm-1

)

80K

90K

100K

120K

140K

160K

1

2

3.2

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

416041404120410040804060404040204000

Frequency (cm-1

)

70K

80K

90K

100K

120K

140K

160K

12

3.2

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

416041404120410040804060404040204000

Frequency (cm-1

)

60K

70K

80K

90K

100K

120K

140K

160K

12

3.2

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

416041404120410040804060404040204000

Frequency (cm-1

)

50K

60K

70K

80K

90K

100K

120K

140K

160K

12

3.2

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

416041404120410040804060404040204000

Frequency (cm-1

)

40K

50K

60K

70K

80K

90K

100K

120K

140K

160K

1 2

3

3.2

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

416041404120410040804060404040204000

Frequency (cm-1

)

30K

40K

50K

60K

70K

80K

90K

100K

120K

140K

160K

1 23

3.2

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

416041404120410040804060404040204000

Frequency (cm-1

)

30K

40K

50K

60K

70K

80K

90K

100K

120K

140K

160K

20K

1 2 3

3.2

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

416041404120410040804060404040204000

Frequency (cm-1

)

30K

40K

50K

60K

70K

80K

90K

100K

120K

140K

160K

20K

15K

1 2 3

Temperature Dependent Spectra Co-MOF-74

Overtones of H2 in MOF-74

0.6

0.4

0.2

0.0

Ab

sorb

ance

80007000600050004000Frequency (cm

-1)

Overtones of H2 in MOF-74

Ab

sorb

ance

-250 -200 -150 -100 -50 0Frequency (cm

-1)

Ab

sorb

ance

-120 -100 -80 -60 -40 -20 0Frequency (cm

-1)

Fundamental Red Shift Overtone Red Shift

Intense overtone peak only present for exposed metal site

Conclusion

• Diffuse Reflectance Infrared Spectroscopy ideal for probing adsorbed H2

• Concentration dependent spectra provide information about the nature of the binding site

• In MOF-74 vibrational red-shift follows Irving Williams sequence Zn < Mn < Co < Ni

• Intense overtone peak for H2 in exposed metal site

• Data analysis qualitatively ok. Need real modeling