Lamonte, Kevin Anthony (2008-05). Modeling H2 adsorption in carbon-based structures. Master's Thesis. Thesis uri icon

abstract

  • Hydrogen storage has been identified as a primary bottleneck in the large-scale implementation of a hydrogen-based economy. Many research efforts are underway to both improve the capacity of existing hydrogen storage systems and develop new systems. One promising area of research is hydrogen physi-sorbed into carbonbased structures such as nanotubes and graphene. Two novel systems consisting of a phthalocyanine salt with a large cation were studied. Ab initio, density functional theory, and molecular dynamics simulations of tetramethylammonium lithium phthalocyanine (TMA-LiPc) and trimethyl-(2-trimethylazaniumylethyl) azanium phthalocyanine (TMA2-Pc) were undertaken to estimate the H2 gas-solid adsorption uptake (wt/wt) as a function of pressure and temperature. For TMA-LiPc, the maximum H2 binding energy was approximately 0.9 kcal/mol for an isolated system and 1.2 kcal/mol for a crystal. H2 adsorption at the optimal inter-layer distance of 8.49 ? ranged from 2.1% to 6.0% (wt/wt) at 300 K, 2.5% to 6.5% at 273K, 3.3% to 7.2% at 236K, 5.2% to 8.6% at 177K, and 10.4% to 11.7% at 77K. At ILD 10 ? H2 adsorption was about 1.5% (wt/wt) higher at all points. For TMA2-Pc, the maximum H2 binding energy was approximately 1.3 kcal/mol for an isolated system and 1.2 kcal/mol for a crystal. H2 adsorption at the optimal inter-layer distance of 8.12 ? ranged from 0.5% to 2.6% (wt/wt) at 300 K, 0.6% to 2.8% at 273K, 0.8% to 3.2% at 236K, 1.4% to 3.9% at 177K, and 4.5% to 6.0% at 77K. At ILD 10 ? H2 adsorption ranged from about 0.1% (wt/wt) at 40 bar to 0.5% higher at 250 bar. The behavior of H2 adsorption for both TMA-LiPc and TMA2-Pc were compared. The adsorbed H2 probability density was compared to pair correlation function data and surfaces of constant binding energy. Regions of relatively high H2 density appear to correlate well with the binding energy, but the total adsorption does not, indicating that the adsorption is driven by factors other than binding energetics. Lithium ion transport in TMA2-Pc was also investigated for suitability as an electrolyte medium for use in lithium ion battery systems.
  • Hydrogen storage has been identified as a primary bottleneck in the large-scale implementation
    of a hydrogen-based economy. Many research efforts are underway
    to both improve the capacity of existing hydrogen storage systems and develop new
    systems. One promising area of research is hydrogen physi-sorbed into carbonbased
    structures such as nanotubes and graphene. Two novel systems consisting
    of a phthalocyanine salt with a large cation were studied.
    Ab initio, density functional theory, and molecular dynamics simulations of
    tetramethylammonium lithium phthalocyanine (TMA-LiPc) and trimethyl-(2-trimethylazaniumylethyl)
    azanium phthalocyanine (TMA2-Pc) were undertaken to
    estimate the H2 gas-solid adsorption uptake (wt/wt) as a function of pressure and
    temperature. For TMA-LiPc, the maximum H2 binding energy was approximately
    0.9 kcal/mol for an isolated system and 1.2 kcal/mol for a crystal. H2 adsorption
    at the optimal inter-layer distance of 8.49 ? ranged from 2.1% to 6.0% (wt/wt) at
    300 K, 2.5% to 6.5% at 273K, 3.3% to 7.2% at 236K, 5.2% to 8.6% at 177K, and 10.4%
    to 11.7% at 77K. At ILD 10 ? H2 adsorption was about 1.5% (wt/wt) higher at all
    points. For TMA2-Pc, the maximum H2 binding energy was approximately 1.3
    kcal/mol for an isolated system and 1.2 kcal/mol for a crystal. H2 adsorption at the
    optimal inter-layer distance of 8.12 ? ranged from 0.5% to 2.6% (wt/wt) at 300 K,
    0.6% to 2.8% at 273K, 0.8% to 3.2% at 236K, 1.4% to 3.9% at 177K, and 4.5% to 6.0%
    at 77K. At ILD 10 ? H2 adsorption ranged from about 0.1% (wt/wt) at 40 bar to
    0.5% higher at 250 bar. The behavior of H2 adsorption for both TMA-LiPc and TMA2-Pc were compared.
    The adsorbed H2 probability density was compared to pair correlation
    function data and surfaces of constant binding energy. Regions of relatively high
    H2 density appear to correlate well with the binding energy, but the total adsorption
    does not, indicating that the adsorption is driven by factors other than binding
    energetics.
    Lithium ion transport in TMA2-Pc was also investigated for suitability as an
    electrolyte medium for use in lithium ion battery systems.

publication date

  • May 2008