Hydrogen Adsorption and Storage on Porous Materials

K. M. Thomas.

School of Chemical Engineering and Advanced Materials

Newcastle University

United Kingdom

H2FC SUPERGEN Conference

Birmingham University,

16-18th December 2013

Structure of Presentation • Background on the Hydrogen Economy • H2 adsorption capacities for carbon,

polymer and metal organic framework porous materials

• Quantum kinetic molecular sieving of H2 and D2

• H2 surface interaction energy, adsorption enthalpies at zero surface coverage

• Hysteretic adsorption of H2 on porous metal organic frameworks

• Conclusions

Why are we considering the possibility of the hydrogen economy?

• We are close to, or at, peak oil production

• Future decline in petroleum reserves

will probably lead to high cost of petroleum

• Security of supply issues, environment

• Medium Term Replacement: Shale gas

• Longer term: Hydrogen

Current Hydrogen Use

• Hydrogen is widely used in industry where safety issues and use can be controlled. It is distributed in pipelines over a limited area to different chemical processes.

• The problems arise in the use of hydrogen for transport applications

• Storage of hydrogen with a 300 mile refuelling range is an unsolved problem. The problem is fitting the required volume of the fuel tank into a car

Hydrogen Storage

• Storage Amount for vehicles:

• 5 – 13 kg

Storage Methods:

• Compressed Gas (~ 700 bar)

• Liquid Hydrogen (20 K)

• Storage on Solid State Materials

• Other Factors; refuelling time, driving distance range, safety

Storage of Solid State Materials

• Metal Hydrides

• Porous Materials

a) carbons

b) zeolites

c) porous polymers

d) metal organic framework materials

Hiden Isochema IGA

Isotherm and Kinetic Studies

High Pressure Volumetric Instrument

The Variation of H2 Adsorption at Saturation

(wt%) and 77 K versus BET Surface Area

Updated version Dalton Trans 2009, 1487-1505

0 1000 2000 3000 4000 5000 6000

0

1

2

3

4

5

6

7

8

9H

2 A

dso

rb

ed

at

Hig

h P

ress

ure

an

d 7

7 K

/w

t%

BET N2Surface Area/ m

2 g

-1

MOFs

Carbons

Zeolites

Silicas(MCM-41)

Polymers/PAFs

B doped carbon

COFs

Variation of H2 Adsorption at Saturation and 77 K versus Total Pore Volume

0 1 2 3 40

2

4

6

8

H2 A

dso

rb

ed

at

Hig

h P

ress

ure

an

d 7

7 K

/w

t%

Total Pore Volume/ cm3

g-1

MOFs

Liquid H2

Carbons

Polymers/PAFs

Line for liquid H2

Updated version

Dalton Trans 2009.1487.

Acidic forms H4L1, H4L

2, and H4L3 (left) of the ligands viewed along

the c axes (middle) and along the a axes (right) of the structures Cu

blue, C grey, H white, O red. Angew. Chemie, Int. Ed. (2006), 45(44), 7358.

JACS 2009. 131.2159

Hydrogen Adsorption Capacities

• 7-12 wt% maximum surface excess hydrogen can be adsorbed at 77 K

• The highest values (MOF200, MOF210 and NU100) are achieved for very low density materials, which, as a consequence, have low volumetric capacities

The Variation of H2 Adsorption at Saturation (gL-1)and 77 K versus BET

Surface Area for MOFs

0 1000 2000 3000 4000 5000 60000

10

20

30

40

50

60

Volumetric

Volumetric 80 bar

H2 V

olu

metr

ic C

ap

city

g L

-1

BET Surface Area/ m2 g

-1

Comparison of Hydrogen isobars on Porous Metal Organic Framework and

Carbon Materials

-200 -180 -160 -140 -120 -100 -80

0

20

40

60

80

100

Am

ou

nt

Ad

sorb

ed/

%

T/o

C

E MOF

C

M MOF

AC

Zhao et al, Science 2004, 304, 1012

Hydrogen adsorption at ambient temperatures

• Usually very small amounts (< 1 wt%) of hydrogen are adsorbed at room temperature and up to 100 bar.

• Multivalent manganese hydrazide gels are reported 1.8 wt% at 85 bar 298 K and titanium hydrazide 2.63 wt% at 143 bar and 298 K

• Temperature dependence of adsorption is now the key issue

• H2–surface interactions need to be increased

Aspects of hydrogen adsorption

• Quantum effects for porous carbons and metal organic frameworks

• Enhanced surface interactions in metal organic frameworks

• Hysteretic hydrogen adsorption in metal organic framework materials

Schematic of Kinetic Measurement Technique

Pressure

Amount

Adsorbed

Kinetic

profiles Time

Quantum Effects in Adsorption • Kinetic Isotope Molecular Sieving • This occurs when the differences between the

adsorptive and the pore sizes are similar to the de Broglie wavelength.

• First experimental observation was for H2 and D2 adsorption on a carbon molecular sieve used for air separation and the corresponding activated carbon substrate.(J Phys Chem B 2006,110,9947)

• In the case of carbons the pores size is not known precisely but probe molecules show that molecular cross sections of 4.5 A are the upper limit (J Phys Chem B 2001,105, 10619)

• In contrast, the pore sizes in MOFs are known from crystallographic studies.

Stretched Exponential Model

)(1 kt

e

t eM

M

The SE model is described by the following equation:

where Mt is the uptake at time t, Me is the equilibrium

uptake, k is the rate constant and is the exponential

parameter of the adsorption process.

Comparison of H2 and D2 Adsorption and Desorption on CMS T3A at 77 K

0.0

0.2

0.4

0.6

0.8

1.0

0 2000 4000 6000 8000 10000 12000 14000

0.0

0.2

0.4

0.6

0.8

1.0 M

t/M

e

H2

SE model

D2

SE model

a)

Time / s

H2

SE model

D2

SE model

b)

Pressure Increment

1-2 kPa

Pressure decrement

2-1 kPa

Normalised

kinetic profiles

The variation of the ratio of the rate constants for H2 and D2 adsorption (kD2/kH2) with pressure

and surface coverage on CMS T3A at 77 K

0 20 40 60 80 100

1.0

1.2

1.4

1.6

1.8

2.0

2.2

kD

2/k

H2

Pressure / kPa

Adsorption

Desorption

0.0 0.2 0.4 0.6 0.8 1.01.0

1.2

1.4

1.6

1.8

2.0

2.2

kD

2/k

H2

H2 n/nm

Zhao, X.B; Villar-Rodil, S.; Fletcher, A. J.; Thomas, K. M.

J Phys. Chem.B (2006), 110(20), 9947-9955.

H2 and D2 Adsorption on Two Mixed Metal Organic Frameworks with

Formula Zn3(bdc)3[Cu(salen)]

• Interactions with open metal centres and

• Confinement in porosity <6Å.

• Quantum effects are observed when the difference between adsorptive (H2 and D2) and pores sizes are similar to the de Broglie wavelengths (1.76 and 2.49 A)

• Zn3(bdc)3[Cu(Pyen)] J Am. Chem. Soc. 2008, 130(20), 6411-6423.

©2007 by National Academy of Sciences

Kubas Coordination Kubas G. J. PNAS 2007;104:6901-6907

Pyen

d) Down c axis

e) Down b axis

b) and c) Zn3(bdc)3[Cu(salen)]

Chen et al JACS 2008. 130.6411

H2 and D2 Isotherms for Adsorption on Zn3(bdc)3[Cu(Pyen)] at 77.3 and 87.3 K

0 20 40 60 80 100

0

1

2

3

4

5

Am

ou

nt

Ad

sorb

ed/

mm

ol

g-1

Pressure/ kPa

D2 (77.3 K)

H2 (77.3 K)

D2 (87.3 K)

H2 (87.3 K)

Virial Equation

ln(n/p) =A0 + A1n + A2n2 -----

where n is the amount adsorbed at pressure p and the first virial coefficient A0 is related to the Henry’s law constant K0 by the equation K0 = exp(A0).

Zhao et al J Phys. Chem. B (2005), 109(18), 8880-8888

Virial Graphs for H2 and D2 Adsorption on Zn3(bdc)3[Cu(Pyen)]

0.000 0.001 0.002 0.003 0.004 0.005

-17

-16

-15

-14

-13

-12

ln(n

/p)

/ln

(mo

l g

-1 P

a-1)

n/ mol g-1

D2 (87.3 K)

H2 (87.3 K)

D2 (77.3 K)

H2 (77.3 K)

D2 (77.3 K) (HR)

H2 (77.3 K) (HR)

Comparison of H2 and D2 Adsorption Enthalpies as a function of amount adsorbed for Zn3(bdc)3[Cu(Pyen)]

0.000 0.001 0.002 0.003

9

10

11

12

QS

T/

kJ

mo

l-1

n/mol g-1

H2

D2

2 H2 or D2 molecules per

Cu in formula unit

Quantum Kinetic Effects for H2 and D2 Adsorption on

Zn3(bdc)3[Cu(Pyen)]

• 2-dimensional porous structure in the bc crystallographic plane

Double Exponential (DE) Kinetic Model for Two Types of Pores

tktk

e

t eAeAM

M21 111 11

Mt = mass uptake at time t

Me = mass uptake at equilibrium

A1 = fractional contribution of process 1

k1 = rate constant for process 1

k2 = rate constant for process 2

tk

e

t eM

M11

LDF and SE Models

)(1 kt

e

t eM

M

Comparison of H2 and D2 Normalised Kinetic Profiles for pressure increment 0.2-0.4 kPa for Zn3(bdc)3[Cu(Pyen)] at 77.3 K

0 500 1000 1500 2000 2500 3000 3500 4000

0.0

0.2

0.4

0.6

0.8

1.0

0 500 1000 1500 2000 2500 3000 3500 4000

-0.02

0.00

0.02

Re

sid

ua

lsM

t/Me

Time/ s

D2

DEmodel

H2

DEmodel

77.3 K

Pressure

0.2-0.4 kPa

D2

H2

Comparison of H2 and D2 Normalised Kinetic Profiles for pressure increment 0.2-0.5 kPa for Zn3(bdc)3[Cu(Pyen)] at 87.3 K

0 200 400 600 800 1000 1200 1400

0.0

0.2

0.4

0.6

0.8

1.0

0 200 400 600 800 1000 1200 1400

-0.02

0.00

0.02

Time/ s

Mt/M

e

D2

DEmodel

H2

DEmodel

87.3 K

Pressure

0.2 - 0.5 kPa

Re

sid

ua

ls

D2

H2

Variation of ln(k) for H2 and D2 Adsorption with Amount Adsorbed at 77.3 K

0.0 0.5 1.0 1.5 2.0 2.5 3.0

-8

-7

-6

-5

-4ln

(k)/

ln

(s-1)

Amount Adsorbed/ mmol g-1

k1 D

2 (77.3 K)

k2 D

2 (77.3 K)

k1 H

2 (77.3 K)

k2 H

2 (77.3 K)

Linear Regression k1 D

2

Linear Regression k2 D

2

Linear Regression k1 H

2

Linear Regression k2 H

2

Variation of ln(k) for H2 and D2 Adsorption with Amount Adsorbed at 87.3 K

0.0 0.5 1.0 1.5 2.0 2.5

-6

-5

-4

ln(k

)/ l

n(s

-1)

Amount Adsorbed / mmol g-1

k1 D

2 (87.3 K)

k2 D

2 (87.3 K)

k1 H

2 (87.3 K)

k2 H

2 (87.3 K )

Linear Regression k1 H

2

Linear Regression k2 H

2

Linear Regression k1 D

2

Linear Regression k2 D

2

Activation Energies for the Two Kinetic Components for Zn3(bdc)3[Cu(Pyen)]

Gas

Slow component, ln(k1, n=0)/ ln(s-1)

Ea/ kJ mol-1

77.3 K 87.3 K

H2 -8.475 ± 0.042 -6.111 ± 0.047 13.35 0.59

D2 -7.957 ± 0.015 -5.740 ± 0.023 12.52 0.47

Gas Fast component, ln(k2, n=0)/ln(s-1)

Ea/ kJ mol-1 77.3 K 87.3 K

H2 -6.320 ± 0.042 -4.805 ± 0.027 8.56 0.41

D2 -5.966 ± 0.017 -4.542 ± 0.031 8.04 0.35

c axis pores

b axis pores

The Variation of Activation Energy with Amount Adsorbed

0.0 0.5 1.0 1.5 2.0

6

8

10

12

Ea

/ k

J m

ol-1

Amount Adsorbed/ mmol g-1

EaH2k1

EaH2k2

EaD2k1

EaD2k2

Influence of Pore Size: H2 Adsorption Zn3(bdc)3[Cu(PyCy)]

N

N N

NO O

Cu

RR

A homochiral mixed metal organic framework with Enatioselective separation.

Adsorption on a Mixed Metal Organic Framework Zn3(bdc)3[Cu(PyCy)]

0 200 400 600 800 1000

0

1

2

3

4A

mount

Adso

rbed

/mm

ol

g-1

Pressure/mbar

n H2 77.3 K

n D2 77.3 K

n H2 87.3 K

n D2 87.3 K

Virial Graphs for H2 and D2 Adsorption on Zn3(bdc)3[Cu(PyCy)]

0.000 0.001 0.002 0.003 0.004

-18

-17

-16

-15

-14

-13

-12ln

(n/p

)/ln

(mol

g-1

Pa

-1)

n/mol g-1

H2Lnnp77K

D2lnp77K

H2lnnp87K

D2lnnp87K

2 molecules per Cu

Comparisons of enthalpies of adsorption (kJ mol-1) of H2 and D2 on Zn3(bdc)3[Cu(Pyen)] and Zn3(bdc)3[Cu(PyCy)] at zero surface coverage

Zn3(bdc)3[Cu(Pyen)]

H2 12.29

D2 12.44

Zn3(bdc)3[Cu(PyCy)]

H2 9.65

D2 9.76

The Qst at zero surface coverage, which is a measure

of the H2-surface interaction influenced by

a) the narrow porosity or

b) Surface chemistry?

Comparison of D2 Normalised Kinetic Profiles for pressure increment 0.2-0.5 kPa for

Zn3(bdc)3[Cu(Pyen)] Zn3(bdc)3[Cu(PyCy)] at 87.3 K

0 500 1000 1500 2000 2500

0.0

0.2

0.4

0.6

0.8

1.0

Mt/M

e

Time/ s

Zn(bdc)3(PyCy), D

2 at 2 - 5 mbar, 87.3 K

Zn(bdc)3(Pyen), D

2 at 2 - 5 mbar, 87.3 K

Comparison of D2 Normalised Kinetic Profiles for pressure increment 10-15 kPa for

Zn3(bdc)3[Cu(Pyen)] Zn3(bdc)3[Cu(PyCy)] at 77.3 K

0 200 400 600 800 1000 1200 1400 1600 1800

0.0

0.2

0.4

0.6

0.8

1.0M

t/Me

Time/ s

MtMePyen

MtMePycy

H2 kinetics at P 100 -- 150 mbar, 77 K

Comparisons of adsorption of H2 and D2 on Zn3(bdc)3[Cu(Pyen)] and Zn3(bdc)3[Cu(PyCy)]

• Crystallographic studies show smaller pore sizes and adsorption kinetics for Zn3(bdc)3[Cu(PyCy)] are slower than for Zn3(bdc)3[Cu(Pyen)] indicating narrower porosity.

• nD2/nH2 ratios do not vary greatly with surface coverage and are ~1.1 at 77 and 87 K

• Isosteric Enthalpies for adsorption at Zero Surface Coverage are higher for Zn3(bdc)3[Cu(Pyen)] than for Zn3(bdc)3[Cu(PyCy)]

• The Qst at zero surface coverage is very sensitive to the spatial and/or electronic environments around Cu2+ sites which influence interactions with hydrogen molecules. Smaller pores do not necessarily increase Qst

Hysteretic Adsorption

Hydrogen Adsorption on

Porous Materials Zhao et al, Science 2004,

304, 1012

0

2

4

6

8

10

0 200 400 600 800 1000

0

1

2

3

4

AC

AC

C

C

AA

mou

nt

Ad

sorb

ed

/ m

mol

g-1

Pressure/ mbar

M

M

E

E

B

Hydrogen Desorption

0 50 100 150 500 1000 1500 2000 2500 3000 3500 4000

80

84

88

92

96

100

40

50

60

70

80

90

100

Am

ou

nt

Ad

sorb

ed/

%

Time/s

H2 amount adsorbed

on E at 49 mbar

Pre

ssu

re/

mb

ar

P

Comparison of Hydrogen isobars on Porous Metal Organic Framework and

Carbon Materials

-200 -180 -160 -140 -120 -100 -80

0

20

40

60

80

100

Am

ou

nt

Ad

sorb

ed/

%

T/o

C

E MOF

C

M MOF

AC

Possible Mechanism

• Adsorption of hydrogen may result in stiffening of the metal organic framework. In this case the desorption should change with hydrogen loading

• Thermally activated structural change

How can we improve the adsorption capacity and temperature dependence?

• Larger pore volumes,

• Cage structures

• Narrow windows in the structure

• Surface chemistry: Unsaturated metal centres,

NPC-4 structure

Windows )

H2 adsorption at 77 K on NPC-4

0 5000 10000 15000 20000

0

1

2

3

4

5

H2 s

urf

ace e

xcess u

pta

ke (

wt

%)

Pressure (mbar)

Adsorption at 77K

Desorption at 77K

H2 adsorption on NPC-4 at 77 K

Absolute uptake =5.03 wt% at 20 bar

H2 density in pores = 0.0644 g cm

-3

H2 adsorption at 77 K on NPC-4

0 5000 10000 15000 20000

0

1

2

3

4

5

20 bar 2 nd

20 bar 1st

Su

rfa

ce

Ex

ce

ss

H2

Up

tak

e (

wt%

)

Pressure (mbar)

H2 adsorption at 195 K

0 5000 10000 15000 20000

0.0

0.5

1.0

1.5

2.0

H2 adsorption on NPC-4 at 195 K

Adsorption

Desorption

Su

rfa

ce

Ex

ce

ss

Up

tak

e a

t 1

95

K (

wt%

)

Pressure (mbar)

Absolute uptake = 1.86 wt% at 19 bar

Conclusions

• High pressure hydrogen capacity on a weight basis correlates with pore volume and surface area for all porous materials

• Hydrogen capacity on a volumetric basis has only limited correlation at surface areas up to 2000 m2 g-1

• Quantum kinetic molecular sieving effects are observed for H2 and D2 for all porous materials

Conclusions: Surface Interactions

• Mechanisms for improving temperature dependence of hydrogen adsorption on metal organic frameworks involve ; surface chemistry modification: for example, stronger adsorption on open or unsaturated metal centres is an example (Kubas type interactions).

• Adsorption on the metal centres shows the relationship between adsorption characteristics and stoichiometry of the H2-surface interaction consistent with adsorption on both sides of the CuO2N2 Salen pillars in Zn3(bdc)3[Cu(salen)]

• However, most interactions observed so far are not strong enough for true Kubas coordination

Conclusions

• Qst values are sensitive to the spatial and/or electronic environments around Cu2+ sites, which influence interactions with hydrogen molecules.

• Cage structures with narrow windows have some interesting temperature dependent characteristics, which are being investigated further

Acknowledgements • Adsorption Studies: X. B. Zhao, B. Xiao, A. Putkham,

J. Bell, R. Gill, A. J. Fletcher, M. Kennedy, J Armstrong and T Rexer.

• Synthesis and Structure Zn3(bdc)3[Cu(Pyen)], Zn3(bdc)3[Cu(PyCy)] B. Chen, K. Hong, E. B. Lobkovsky, E. J. Hurtado, S. Xiang, M-H Xie, C. D Wu,

• Synthesis and Structures of Ni2(bpy)3.(NO3)4 phases

D. Bradshaw, J. Barrio and M. J. Rosseinsky

• M. Schroder (Nottingham University, Angew. Chemie. 2006, 45, 7358; Chem. Comm. 2008,6108; JACS 2009,131,2159) and R. Morris (St Andrews University; JACS 2007, 129.1203 and Nature Chem 2009 and 2011)