1. Physisorption of Hydrogen on B/C Materials Prepared by Organoborane Precursors
Youmi Jeong, T. C. Mike Chung
Pennsylvania State University
DOE Center of Excellence on Carbon-based Hydrogen Storage Materials

2. H2 Adsorption in C Materials
(At 77 K)
Ahn et al, Chem. Mat. 18, 6085, 2006
Light Weight and High Surface Area
H2 adsorption (> 5 wt%) at 77 K, with binding energy < 3 KJ/mol

3. Objective: Increasing Binding Energy in Hydrogen Physisorption
Ideal Material
H2 binding energy ~ KJ/mol
High Surface Area
RT reversible adsorption-desorption
Capacity > 6 wt%

4. Boron-Hydrogen Interaction
Empty p-orbital on B provides Complexization with H2

5. Boron Substituted C (B/C) Materials
B has similar atomic size with C.
B exhibits trivalent coordination.
B enhances thermodynamic stability of graphitic structure.
B/C could be prepared by pyrolysis with proper precursors.

6. Synthesis of B/C Materials by Using B-containing Precursors
Advantages
Simple process
Large scale production
Varying pyrolysis temp.
Control Crystal structure
Control B content (up to 10%)
Hu, R.; Chung, T. C. Carbon, 34, 1181, 1996;
34, 595, 1996; 35, 641, 1997; 35, 1101, 1997.

7. Synthesis C/B Material (I) by CBF Precursor
Liquid crystalline phase transformation
Substitutional B tranformed from precursor to B/C Material
Excellent precursor to form B/C material with 7-8 % B content.
Difficult in forming porous structure.

8. B/C materials (I) Carbonized at 600°C and 800°C
XRD
SEM
800 oC
600 oC
Evaluation of B/C Sample (800 oC )
B content is 8.25% (PGAA, NIST).
Surface area is 0.08 m2/g (BET by NREL).
No H2 uptake under 2 bar and at 77K (NREL)

9. C/B materials (I) Carbonized at Higher Temp.
l000°C
l500°C
l800°C
2100°C
2300°C
XRD Pattern
D-Spacing
(002) (A)
3.461
3.411
3.383
3.363
3.347
Boron
Content
7.65%
7.58%
(PGAA, NIST)
7.42%
6.96%
3.46%
* Crystallinity increases with temp. ** B in B/C is stable up to 2000 oC

10. Synthesis C/B Material (II) Using PBDE Precursor
Solid phase transformation
B content ~ 1.5 % (PGAA, NIST)
Surface area: 150 m2/g (BET)

11. H2 Uptake in B/C Materials (II)
vs. pressure vs. temperature
PDA sample
At RT
PDA
1300 psi
1100 psi PA
900 psi
PDA: 1.5 B%; SA: 150 m2/g
PA: 0.8 B%; SA: 180 m2/g

12. 1H NMR Measurement of H2 Gas in the presence of B/C Material (II)
NMR sample container H NMR Spectrum
Capillary RT 1 2 3 4
Yue Wu (UNC)

13. Molecular Dynamics
Peak 1 and peak 2&3 show T2 (spin-spin relaxation time) dependent linearly on pressure as expected for free H2 gas.
Peak 4 shows T2 almost independent on pressure, consistent with the adsorbed H2 in restricted regions. There, the rate of collisions between H2 molecules is less important for T2 than interactions with adsorption sites.
Using the Langmuir equation, an estimate of Eads =9.2 kJ/mol, but rather weak intensity (0.2 wt% at 100 atm).

14. Synthesis C/B Material (III) Using PBDA Precursor
Mp: 605°C,
Bp: 1300°C
B content: 5.66 % (PGAA by NIST)
Surface area: 528 m2/g (BET by NREL and PSU)

15. Pore Size Distribution in B/C Material (III)
(Surface area= 528 m2/g)

16. Hydrogen Uptake in B/C Material (III) (NREL)
Measurement
PBDA
(BC-600)
(BC-800)
(BC-1500)
N2 BET SSA, as received
800 m2/g
528 m2/g
33 m2/g
Sieverts RT H2 Uptake at ~2 bar, as received
0.02 wt%
0.004 wt%
Sieverts 77 K H2 Uptake at ~ 2 bar, as received
1.4 wt%
0.07 wt%
TPD from 77 K to 800ºC
Physisorption only
BET after 800ºC degas
619 m2/g
Sieverts 77 K H2 Uptake at ~ 2 bar, After 800ºC degas
1.6 wt%

17. Hydrogen Uptake in B/C Material (528 m2/g) in Low Pressure Range

18. Hydrogen Uptake in B/C Material (III) (800 m2/g) Under High Pressure
C Materials
(77 K, 30 bar)
Ahn et al, Chem. Mat.
18, 6085, 2006

19. Conclusion
New B/C Materials with substitutional B (up to 8%) have been prepared using the designed B-precursors and pyrolysis process.
CBF precursor (with liquid crystalline phase thermal transformation) produces only dense B/C material.
PCDA precursor (with solid phase thermal transformation) produces nano-porous B/C material with SA > 500 m2/g.
B in B/C increases H2 binding energy (~10 KJ/mol) and absorption capacity (estimated increase ~ 50%).

20. Acknowledgement Penn State U.: Youmi Jeong
NREL: Jeffrey Blackburn, Lin Simpson, Philip Parilla, Mike Heben
NIST: Yun Liu, Dan Neumann, Craig Brown
UNC: Yue Wu
DOE and DOE Center of Excellence on Carbon-based Hydrogen Storage Materials