Hypothetical High-Surface-Area Carbons with Exceptional Hydrogen Storage Capacities: Open Carbon Frameworks

Abstract

A class of high-surface-area carbon hypothetical structures has been investigated that goes beyond the traditional model of parallel graphene sheets hosting layers of physisorbed hydrogen in slit-shaped pores of variable width. The investigation focuses on structures with locally planar units (unbounded or bounded fragments of graphene sheets), and variable ratios of in-plane to edge atoms. Adsorption of molecular hydrogen on these structures was studied by performing grand canonical Monte Carlo simulations with appropriately chosen adsorbent-adsorbate interaction potentials. The interaction models were tested by comparing simulated adsorption isotherms with experimental isotherms on a high-performance activated carbon with well-defined pore structure (approximately bimodal pore-size distribution), and remarkable agreement between computed and experimental isotherms was obtained, both for gravimetric excess adsorption and for gravimetric storage capacity. From this analysis and the simulations performed on the new structures, a rich spectrum of relationships between structural characteristics of carbons and ensuing hydrogen adsorption (structure-function relationships) emerges: (i) Storage capacities higher than in slit-shaped pores can be obtained by fragmentation/truncation of graphene sheets, which creates surface areas exceeding of 2600 m(2)/g, the maximum surface area for infinite graphene sheets, carried mainly by edge sites; we call the resulting structures open carbon frameworks (OCF). (ii) For OCFs with a ratio of in-plane to edge sites ≈1 and surface areas 3800-6500 m(2)/g, we found record maximum excess adsorption of 75-85 g of H(2)/kg of C at 77 K and record storage capacity of 100-260 g of H(2)/kg of C at 77 K and 100 bar. (iii) The adsorption in structures having large specific surface area built from small polycyclic aromatic hydrocarbons cannot be further increased because their energy of adsorption is low. (iv) Additional increase of hydrogen uptake could potentially be achieved by chemical substitution and/or intercalation of OCF structures, in order to increase the energy of adsorption. We conclude that OCF structures, if synthesized, will give hydrogen uptake at the level required for mobile applications. The conclusions define the physical limits of hydrogen adsorption in carbon-based porous structures.

Ultrafast sol–gel synthesis of graphene aerogel materials

“…Graphene, a two-dimensional (2D) structure of carbon atoms bonded in a hexagonal lattice, has attracted considerable attention within the scientific community for its outstanding properties, such as its electrical and thermal conductivity (1738 S m -1 and ~5·10 3 W m -1 K -1 respectively), [1][2][3][4] intrinsic carrier mobility (> 2·10 5 cm 2 V -1 s -1 ), [5,6] theoretical surface area (~2600 m 2 g -1 ), [7] mechanical strength (~118 GPa), and elastic modulus (~1 TPa). [8] The realization of a three-dimensional (3D) network of graphene sheets would significantly expand the usability of this remarkable material.…”

A Rationally Designed Nitrogen-Rich Metal-Organic Framework and Its Exceptionally High CO2 and H2 Uptake Capability

“…Typically, MOFs are built by the self-assembly of metal ions or clusters and polytopic bridging ligands under solvothermal conditions67. In contrast to inorganic porous materials such as zeolites or activated porous carbons, numerous choices of organic linkers together with many coordination geometries indicate that MOFs could be tailored by judicious combinations of the building blocks for specific applications6789. Theoretically, the incorporation of accessible nitrogen-donor groups, such as pyridine, imidazole, and tetrazole, into the pore walls of porous materials can dramatically affect the gas uptake capacity and selectivity of the materials, especially for CO 2 capture on account of the dipole-quadrupole interactions between the polarizable CO 2 molecule and the accessible nitrogen site10.…”

“…Literature reports also indicated that the incorporation of accessible nitrogen-donor groups into the porous materials could enhance the CO 2 uptake capacity and selectivity111213141516. Such approach is strategically important for developing a low-carbon future by increasing the capacity of selective CO 2 capture and by enhancing the storage capacity of clean energy source, such as H 2 191112131415161718. However, competitive coordination of these Lewis basic nitrogen sites with metal ions or clusters is a great challenge in direct synthesis of MOFs1920.…”

Low temperature mechanism of adsorption of methane: Comparison between homogenous and heterogeneous pores

“…The pore width has been defined as the distance between the centers of the carbon atoms in the graphene sheet. The CH 4 -graphene interaction has been described by the standard analytical Steele potential [15][16][17][18]. This potential assumes that a CH 4 molecule interacts with carbon atoms in the graphene sheet through the Lennard-Jones (6-12) potential and renders the energy of the adsorbed particle as an integral over the whole graphene sheet.…”

“…However, atomic corrugation of the graphitic wall is not explicitly treated in this paper as it represents a small fraction of the CH 4 -wall interaction energy. Its influence is negligible for the total storage capacity [15,18].…”