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

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

Objective: Increasing Binding Energy in Hydrogen Physisorption Ideal Material H2 binding energy ~ 10-20 KJ/mol High Surface Area RT reversible adsorption-desorption Capacity > 6 wt%

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

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.

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.

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.

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)

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

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

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

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

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).

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)

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

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%

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

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

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%).

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