Hydrogen storage based on physisorption.
Physisorption of molecular hydrogen based on neutral and negatively charged aromatic molecular systems has been evaluated using ab initio calculations to estimate the binding energy, {Delta}H, and {Delta}G at 298 ({approx}77 bar) and 77 K (45 bar) in order to compare calculated results with experimental measurements of hydrogen adsorption. The molecular systems used in this study were corannulene (C{sub 20}H{sub 10}), dicyclopenta[def,jkl]triphenylene (C{sub 20}H{sub 10}), 5,8-dioxo-5,8-dihydroindeno[2,1-c]fluorene (C{sub 20}H{sub 10}O{sub 2}), 6-hexyl-5,8-dioxo-5,8-dihydroindeno[2,1-c]fluorene (C{sub 26}H{sub 22}O{sub 2}), coronene (C{sub 24}H{sub 12}), dilithium phthalocyanine (Li{sub 2}Pc, C{sub 32}H{sub 16}Li{sub 2}N{sub 8}), tetrabutylammonium lithium phthalocyanine (TBA-LiPc, C{sub 48}H{sub 52}LiN{sub 9}), and tetramethylammonium lithium phthalocyanine (TMA-LiPc, C{sub 36}H{sub 28}LiN{sub 9}). It was found (a) that the calculated term that corrects 0 K electronic energies to give Gibbs energies (thermal correction to Gibbs energy, TCGE) serves as a good approximation of the adsorbent binding energy required in order for a physisorption process to be thermodynamically allowed and (b) that the binding energy for neutral aromatic molecules varies as a function of curvature (e.g., corannulene versus coronene) or if electron-withdrawing or -donating groups are part of the adsorbent. A negatively charged aromatic ring, the lithium phthalocyanine complex anion, [LiPc]{sup -}, introduces charge-induced dipole interactions into the adsorption process, resulting in a doubling of the binding energy of Li{sub 2}Pc relative to corannulene. Experimental hydrogen adsorption results for Li{sub 2}Pc, which are consistent with MD simulation results using x-Li{sub 2}Pc to simulate the adsorbent, suggest that only one side of the phthalocyanine ring is used in the adsorption process. The introduction of a tetrabutylammonium cation as a replacement for one lithium ion in Li{sub 2}Pc has the effect of increasing the number of hydrogen molecules adsorbed from 10 (3.80 wt %) for Li{sub 2}Pc to 24 (5.93 wt %) at 77 K and 45 bar, suggesting that both sides of the phthalocyanine ring are available for hydrogen adsorption. MD simulations of layered tetramethylammonium lithium phthalocyanine molecular systems illustrate that doubling the wt % H{sub 2} adsorbed is possible via such a system. Ab initio calculations also suggest that layered or sandwich structures can result in significant reductions in the pressure required for hydrogen adsorption.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); SUF-USR
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 952923
- Report Number(s):
- ANL/CSE/JA-62767; JPCBFK; TRN: US200914%%154
- Journal Information:
- J. Phys. Chem. B, Vol. 113, Issue 14 ; Apr. 9, 2009; ISSN 1089-5647
- Country of Publication:
- United States
- Language:
- ENGLISH
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