High-Surface-Area Biocarbons for Reversible on-Board Storage of Natural Gas and Hydrogen

Abstract

An overview is given of the development of advanced nanoporous carbons as storage materials for natural gas (methane) and molecular hydrogen in on-board fuel tanks for nextgeneration clean automobiles. The carbons are produced in a multi-step process from corncob, have surface areas of up to 3500 m 2 /g, porosities of up to 0.8, and reversibly store, by physisorption, record amounts of methane and hydrogen. Current best gravimetric and volumetric storage capacities are: 250 g CH 4 /kg carbon and 130 g CH 4 /liter carbon (199 V/V) at 35 bar and 293 K; and 80 g H 2 /kg carbon and 47 g H 2 /liter carbon at 47 bar and 77 K. This is the first time the DOE methane storage target of 180 V/V at 35 bar and ambient temperature has been reached and exceeded. The hydrogen values compare favorably with the 2010 DOE targets for hydrogen, excluding cryogenic components. A prototype adsorbed natural gas (ANG) tank, loaded with carbon monoliths produced accordingly and currently undergoing a road test in Kansas City, is described. A preliminary analysis of the surface and pore structure is given that may shed light on the mechanisms leading to the extraordinary storage capacities of these materials. The analysis includes pore-size distributions from nitrogen adsorption isotherms; spatial organization of pores across the entire solid from small-angle x-ray scattering (SAXS); pore entrances from scanning electron microscopy (SEM) and transmission electron microscopy (TEM); H 2 binding energies from temperature-programmed desorption (TPD); and analysis of surface defects from Raman spectra. For future materials, expected to have higher H 2 binding energies via appropriate surface functionalization, preliminary projections of H 2 storage capacities based on molecular dynamics simulations of adsorption of H 2 on graphite, are reported.

Boron substituted graphene: energy landscape for hydrogen adsorption

“…Early euphoric reports of over 60 wt% storage of hydrogen in carbon nanofibers at ambient temperatures and 112 bar pressure (Chambers et al 1998) and of up to 20 wt% in alkali-doped nanotubes at 1 bar pressure (Chen et al 1999) have been however scaled down by subsequent studies. Proven storage for carbon nanotubes remains at less than 8 wt% of hydrogen even at cryogenic conditions of 77 K, and a meager 1.5 wt% at ambient temperature (Schlapbach and Zuttel 2001;Pfeifer et al 2008;Poirier et al 2004). Similar conclusion comes out from numerical simulation (Wang and Johnson 1999;Bathia and Myers 2006;Gigras et al 2007).…”

Adsorption of Natural Gas Mixtures of Methane, Ethane, and Propane in Nanoporous Carbon: Fully Atomistic Numerical Studies

“…Periodic boundary conditions (PBCs) are used in all directions with a simulation box of size ( L x , L y , L z ) = (33 a , 120 Å, 3 H ). The simulation box containing the layered nanostructure was constructed to allow interpore diffusion into the graphene pores along the y direction. ,, Figure shows the simulation setup with a typical (equilibrated) configuration of methane and propane molecules adsorbed in the pores and in the gas phase. Molecules with centers of mass located between the graphene sheets are deemed adsorbed, and the region marked with yellow boxes was used to determine the density of the gas phase.…”

“…One promising technology in effective natural gas storage is physisorption in approximately nanometer-scale pores of activated carbon (AC). Carbon-based porous adsorbents are profuse and have both a high stability and low specific weight. , The van der Waals interactions within the nanometer-scale pores result in a high-density phase of NG resulting in volumetric and gravimetric storage capacities that at relatively low pressures ( P ≈ 35 bar) are comparable to those in compressed natural gas (CNG) tanks at significantly higher pressures ( P ≈ 200 bar). ,,− Additionally, AC adsorbents are inexpensive and their interaction with methane is optimal for room-temperature adsorption. ,,, The lower operational pressures allow simpler single-stage compressors and could permit the construction of tanks with thinner walls and/or shaping to conform to existing cavities in vehicles resulting in optimized space utilization. ,, …”

Substrate structure and dynamics effect on sorption properties : Theory and experiment||Substrate structure and dynamics effect on sorption properties : theory and experiment

“…Activated carbon is an inexpensive and lightweight adsorbent material which is being studied for the storage of hydrogen and natural gas [4][5][6][7][8][9][10][11]. Abundant resources such as corn cobs, wood, coal, and other carbonaceous materials are "activated" to create a highly porous solid, composed of flakes of graphene-like structures with a 2 large specific surface area.…”

“…Adsorbent materials such as activated carbon [6] and metal-organic frameworks (MOFs) [47] have received significant attention as potential low-pressure, high-capacity storage materials [1,10]. Hydrogen and natural gas (methane) are desirable for energy storage as they result in zero (for H 2 ) or reduced (for CH 4 ) CO 2 emissions per unit energy when compared to gasoline [48].…”