Infrared Study of Molecular Hydrogen Adsorption in Metal- Organic Frameworks Undergrad Students Michael Friedman Jesse Hopkins Brian Bresslauer Ben Thompson Jordan Gotdank Phys. Rev. B. 81, 104305 (2010)
Jan 19, 2016
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