Hydrogen Adsorption and Storage on Porous Materials K. M. Thomas. School of Chemical Engineering and Advanced Materials H2FC SUPERGEN Conference Birmingham University, 16-18 th December 2013 Newcastle University United Kingdom
Structure of Presentation Background on the Hydrogen Economy H 2 adsorption capacities for carbon, polymer and metal organic framework porous materials Quantum kinetic molecular sieving of H 2 and D 2 H 2 surface interaction energy, adsorption enthalpies at zero surface coverage Hysteretic adsorption of H 2 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
Isotherm and Kinetic Studies Hiden Isochema IGA
High Pressure Volumetric Instrument
The Variation of H 2 Adsorption at Saturation (wt%) and 77 K versus BET Surface Area H 2 Adsorbed at High Pressure and 77 K /wt% 9 8 7 6 5 4 3 2 1 0 0 1000 2000 3000 4000 5000 6000 BET N 2 Surface Area/ m 2 g -1 MOFs Carbons Zeolites Silicas(MCM-41) Polymers/PAFs B doped carbon COFs Updated version Dalton Trans 2009, 1487-1505
H 2 Adsorbed at High Pressure and 77 K /wt% Variation of H 2 Adsorption at Saturation and 77 K versus Total Pore Volume Line for liquid H 2 8 6 4 Updated version Dalton Trans 2009.1487. 2 0 0 1 2 3 4 Total Pore Volume/ cm 3 g -1 MOFs Liquid H 2 Carbons Polymers/PAFs
Acidic forms H 4 L 1, H 4 L 2, and H 4 L 3 (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 H 2 Adsorption at Saturation (gl -1 )and 77 K versus BET Surface Area for MOFs 60 H 2 Volumetric Capcity g L -1 50 40 30 20 10 0 Volumetric Volumetric 80 bar 0 1000 2000 3000 4000 5000 6000 BET Surface Area/ m 2 g -1
Amount Adsorbed/ % Comparison of Hydrogen isobars on Porous Metal Organic Framework and Carbon Materials 100 80 E MOF C M MOF AC 60 40 20 0-200 -180-160 -140-120 -100-80 Zhao et al, Science 2004, 304, 1012 T/ o C
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 H 2 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 Amount Adsorbed Pressure 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 H 2 and D 2 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 The SE model is described by the following equation: M M t e 1 e ( kt ) where M t is the uptake at time t, M e is the equilibrium uptake, k is the rate constant and is the exponential parameter of the adsorption process.
Comparison of H 2 and D 2 Adsorption and Desorption on CMS T3A at 77 K 1.0 0.8 0.6 0.4 0.2 a) H 2 SE model D 2 SE model Pressure Increment 1-2 kpa M t /M e 0.0 1.0 0.8 0.6 b) H 2 SE model D 2 SE model Pressure decrement 2-1 kpa 0.4 0.2 0.0 0 2000 4000 6000 8000 10000 12000 14000 Time / s Normalised kinetic profiles
The variation of the ratio of the rate constants for H 2 and D 2 adsorption (kd 2 /kh 2 ) with pressure and surface coverage on CMS T3A at 77 K 2.2 2.0 1.8 Adsorption Desorption 2.2 2.0 1.8 kd 2 /kh 2 1.6 1.4 kd 2 /kh 2 1.6 1.4 1.2 1.2 1.0 0 20 40 60 80 100 Pressure / kpa 1.0 0.0 0.2 0.4 0.6 0.8 1.0 H 2 n/n m Zhao, X.B; Villar-Rodil, S.; Fletcher, A. J.; Thomas, K. M. J Phys. Chem.B (2006), 110(20), 9947-9955.
H 2 and D 2 Adsorption on Two Mixed Metal Organic Frameworks with Formula Zn 3 (bdc) 3 [Cu(salen)] Interactions with open metal centres and Confinement in porosity <6Å. Quantum effects are observed when the difference between adsorptive (H 2 and D 2 ) and pores sizes are similar to the de Broglie wavelengths (1.76 and 2.49 A) Zn 3 (bdc) 3 [Cu(Pyen)] J Am. Chem. Soc. 2008, 130(20), 6411-6423.
Kubas Coordination Kubas G. J. PNAS 2007;104:6901-6907 2007 by National Academy of Sciences
Pyen b) and c) Zn 3 (bdc) 3 [Cu(salen)] d) Down c axis e) Down b axis Chen et al JACS 2008. 130.6411
H 2 and D 2 Isotherms for Adsorption on Zn 3 (bdc) 3 [Cu(Pyen)] at 77.3 and 87.3 K 5 Amount Adsorbed/ mmol g -1 4 3 2 1 D 2 (77.3 K) H 2 (77.3 K) D 2 (87.3 K) H 2 (87.3 K) 0 0 20 40 60 80 100 Pressure/ kpa
Virial Equation ln(n/p) =A 0 + A 1 n + A 2 n 2 ----- where n is the amount adsorbed at pressure p and the first virial coefficient A 0 is related to the Henry s law constant K 0 by the equation K 0 = exp(a 0 ). Zhao et al J Phys. Chem. B (2005), 109(18), 8880-8888
ln(n/p) /ln(mol g -1 Pa -1 ) Virial Graphs for H 2 and D 2 Adsorption on Zn 3 (bdc) 3 [Cu(Pyen)] -12-13 -14 D 2 (87.3 K) H 2 (87.3 K) D 2 (77.3 K) H 2 (77.3 K) D 2 (77.3 K) (HR) H 2 (77.3 K) (HR) -15-16 -17 0.000 0.001 0.002 0.003 0.004 0.005 n/ mol g -1
Q ST / kj mol -1 Comparison of H 2 and D 2 Adsorption Enthalpies as a function of amount adsorbed for Zn 3 (bdc) 3 [Cu(Pyen)] H 2 D 2 12 2 H 2 or D 2 molecules per Cu in formula unit 11 10 9 0.000 0.001 0.002 0.003 n/mol g -1
Quantum Kinetic Effects for H 2 and D 2 Adsorption on Zn 3 (bdc) 3 [Cu(Pyen)] 2-dimensional porous structure in the bc crystallographic plane
Double Exponential (DE) Kinetic Model for Two Types of Pores LDF and SE Models Mt A 1 2 1 1 M e k t k t e 1 1 A 1 e M t = mass uptake at time t M e = mass uptake at equilibrium A 1 = fractional contribution of process 1 k 1 = rate constant for process 1 k 2 = rate constant for process 2 M t 1 e k1t M e M M t e 1 e ( kt )
Comparison of H 2 and D 2 Normalised Kinetic Profiles for pressure increment 0.2-0.4 kpa for Zn 3 (bdc) 3 [Cu(Pyen)] at 77.3 K 1.0 0.8 Residuals M t /M e 0.6 0.4 0.2 0.0 0.02 0.00 77.3 K Pressure 0.2-0.4 kpa D 2 DEmodel H 2 DEmodel 0 500 1000 1500 2000 2500 3000 3500 4000 D 2 H 2-0.02 0 500 1000 1500 2000 2500 3000 3500 4000 Time/ s
Residuals Comparison of H 2 and D 2 Normalised Kinetic Profiles for pressure increment 0.2-0.5 kpa for Zn 3 (bdc) 3 [Cu(Pyen)] at 87.3 K 1.0 0.8 M t /M e 0.6 0.4 0.2 87.3 K Pressure 0.2-0.5 kpa D 2 DEmodel H 2 DEmodel 0.0 0.02 0.00-0.02 0 200 400 600 800 1000 1200 1400 D 2 H 2 0 200 400 600 800 1000 1200 1400 Time/ s
ln(k)/ ln(s -1 ) Variation of ln(k) for H 2 and D 2 Adsorption with Amount Adsorbed at 77.3 K -4-5 -6-7 -8 k 1 D 2 (77.3 K) k 2 D 2 (77.3 K) k 1 H 2 (77.3 K) k 2 H 2 (77.3 K) Linear Regression k 1 D 2 Linear Regression k 2 D 2 Linear Regression k 1 H 2 Linear Regression k 2 H 2 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Amount Adsorbed/ mmol g -1
ln(k)/ ln(s -1 ) Variation of ln(k) for H 2 and D 2 Adsorption with Amount Adsorbed at 87.3 K -4-5 -6 k 1 D 2 (87.3 K) k 2 D 2 (87.3 K) k 1 H 2 (87.3 K) k 2 H 2 (87.3 K ) Linear Regression k 1 H 2 Linear Regression k 2 H 2 Linear Regression k 1 D 2 Linear Regression k 2 D 2 0.0 0.5 1.0 1.5 2.0 2.5 Amount Adsorbed / mmol g -1
Activation Energies for the Two Kinetic Components for Zn 3 (bdc) 3 [Cu(Pyen)] b axis pores Gas Slow component, ln(k 1, n=0 )/ ln(s -1 ) 77.3 K 87.3 K Ea/ kj mol -1 H 2-8.475 ± 0.042-6.111 ± 0.047 13.35 0.59 D 2-7.957 ± 0.015-5.740 ± 0.023 12.52 0.47 c axis pores Gas Fast component, ln(k 2, n=0 )/ln(s -1 ) 77.3 K 87.3 K Ea/ kj mol -1 H 2-6.320 ± 0.042-4.805 ± 0.027 8.56 0.41 D 2-5.966 ± 0.017-4.542 ± 0.031 8.04 0.35
The Variation of Activation Energy with Amount Adsorbed 12 Ea/ kj mol -1 10 EaH2k1 EaH2k2 EaD2k1 EaD2k2 8 6 0.0 0.5 1.0 1.5 2.0 Amount Adsorbed/ mmol g -1
Influence of Pore Size: H 2 Adsorption Zn 3 (bdc) 3 [Cu(PyCy)] R R N Cu N N O O N A homochiral mixed metal organic framework with Enatioselective separation.
Adsorption on a Mixed Metal Organic Framework Zn 3 (bdc) 3 [Cu(PyCy)] 4 Amount Adsorbed/mmol g -1 3 2 1 0 n H 2 77.3 K n D 2 77.3 K n H 2 87.3 K n D 2 87.3 K 0 200 400 600 800 1000 Pressure/mbar
ln(n/p)/ln(mol g -1 Pa -1 ) Virial Graphs for H 2 and D 2 Adsorption on Zn 3 (bdc) 3 [Cu(PyCy)] -12 2 molecules per Cu -13-14 -15-16 -17 H2Lnnp77K D2lnp77K H2lnnp87K D2lnnp87K -18 0.000 0.001 0.002 0.003 0.004 n/mol g -1
Comparisons of enthalpies of adsorption (kj mol -1 ) of H 2 and D 2 on Zn 3 (bdc) 3 [Cu(Pyen)] and Zn 3 (bdc) 3 [Cu(PyCy)] at zero surface coverage Zn 3 (bdc) 3 [Cu(Pyen)] H 2 12.29 D 2 12.44 Zn 3 (bdc) 3 [Cu(PyCy)] H 2 9.65 D 2 9.76 The Q st at zero surface coverage, which is a measure of the H 2 -surface interaction influenced by a) the narrow porosity or b) Surface chemistry?
Comparison of D 2 Normalised Kinetic Profiles for pressure increment 0.2-0.5 kpa for Zn 3 (bdc) 3 [Cu(Pyen)] Zn 3 (bdc) 3 [Cu(PyCy)] at 87.3 K 1.0 0.8 0.6 M t /M e 0.4 0.2 0.0 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 0 500 1000 1500 2000 2500 Time/ s
Comparison of D 2 Normalised Kinetic Profiles for pressure increment 10-15 kpa for Zn 3 (bdc) 3 [Cu(Pyen)] Zn 3 (bdc) 3 [Cu(PyCy)] at 77.3 K 1.0 0.8 M t /M e 0.6 0.4 MtMePyen MtMePycy H2 kinetics at P 100 -- 150 mbar, 77 K 0.2 0.0 0 200 400 600 800 1000 1200 1400 1600 1800 Time/ s
Comparisons of adsorption of H 2 and D 2 on Zn 3 (bdc) 3 [Cu(Pyen)] and Zn 3 (bdc) 3 [Cu(PyCy)] Crystallographic studies show smaller pore sizes and adsorption kinetics for Zn 3 (bdc) 3 [Cu(PyCy)] are slower than for Zn 3 (bdc) 3 [Cu(Pyen)] indicating narrower porosity. nd 2 /nh 2 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 Zn 3 (bdc) 3 [Cu(Pyen)] than for Zn 3 (bdc) 3 [Cu(PyCy)] The Q st at zero surface coverage is very sensitive to the spatial and/or electronic environments around Cu 2+ sites which influence interactions with hydrogen molecules. Smaller pores do not necessarily increase Q st
Hysteretic Adsorption
Amount Adsorbed/ mmol g -1 10 8 6 4 2 0 4 3 2 1 A B AC AC C C M M E E Hydrogen Adsorption on Porous Materials Zhao et al, Science 2004, 304, 1012 0 0 200 400 600 800 1000 Pressure/ mbar
Amount Adsorbed/ % Pressure/ mbar Hydrogen Desorption 100 96 H 2 amount adsorbed on E at 49 mbar 100 90 92 80 70 88 84 P 60 50 80 40 0 50 100 150 500 1000 1500 2000 2500 3000 3500 4000 Time/s
Amount Adsorbed/ % Comparison of Hydrogen isobars on Porous Metal Organic Framework and Carbon Materials 100 80 E MOF C M MOF AC 60 40 20 0-200 -180-160 -140-120 -100-80 T/ o C
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
H 2 surface excess uptake (wt %) H 2 adsorption at 77 K on NPC-4 5 4 3 2 1 0 H 2 adsorption on NPC-4 at 77 K Absolute uptake =5.03 wt% at 20 bar H 2 density in pores = 0.0644 g cm -3 0 5000 10000 15000 20000 Pressure (mbar) Adsorption at 77K Desorption at 77K
Surface Excess H 2 Uptake (wt%) H 2 adsorption at 77 K on NPC-4 5 4 3 2 1 0 20 bar 2 nd 20 bar 1st 0 5000 10000 15000 20000 Pressure (mbar)
Surface Excess Uptake at 195 K (wt%) H 2 adsorption at 195 K 2.0 H 2 adsorption on NPC-4 at 195 K 1.5 1.0 0.5 0.0 Absolute uptake = 1.86 wt% at 19 bar Adsorption Desorption 0 5000 10000 15000 20000 Pressure (mbar)
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 m 2 g -1 Quantum kinetic molecular sieving effects are observed for H 2 and D 2 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 H 2 -surface interaction consistent with adsorption on both sides of the CuO 2 N 2 Salen pillars in Zn 3 (bdc) 3 [Cu(salen)] However, most interactions observed so far are not strong enough for true Kubas coordination
Conclusions Q st values are sensitive to the spatial and/or electronic environments around Cu 2+ 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 Zn 3 (bdc) 3 [Cu(Pyen)], Zn 3 (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 Ni 2 (bpy) 3.(NO 3 ) 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)