Enhanced Hydrogen Dipole Physisorption, Final Report

Abstract

literature 9 . The surface excess can be depicted schematically as shown in Figure 4. Near the adsorbent surface, in the region labeled "adsorbed layer", the local adsorptive density is considerably higher than in the bulk gas phase. It is assumed that at a suitably large distance from the adsorbent surface, the adsorptive density decays back to a constant bulk density (bulk). This region is labeled as the "bulk gas". Important quantities for the adsorption model are defined in Table 1.The standard practice is to express adsorption as a Gibbs surface excess quantity. This is the amount of adsorptive which is present in the adsorbed layer in excess of the bulk gas density, indicated in Figure 4 by the dark gray region. Conveniently, the surface excess amount is the quantity which is measured in a standard volumetric measurement. The expression for the Gibbs surface excess amount is therefore Equation 3The surface excess amount n_is an extensive quantity. Typically, however, data are presented as a specific surface excess amount Equation 4where ms is the sorbent mass. 9 S. Sircar, Gibbsian surface excess for gas adsorption-revisited, Ind Eng Chem Res 38 (10), 3670-3682 (1999).

Hydrogen Storage for Mobility: A Review

“…While the gravimetric hydrogen storage capacity is interesting, the storage temperature is extremely low. Similar results were obtained by other carbon structures such as a graphitic structure but also at extremely low temperatures [130,131]. The Chahine rule is a widely accepted concept which states that, in general, there is 1 wt % hydrogen adsorption for every 500 m 2 /g of surface area.…”

High-Pressure Hydrogen Adsorption on a Porous Electron-Rich Covalent Organonitridic Framework

“…35−37 Several candidate materials have been hypothesized to exceed Chahine’s rule by incorporating metal ions into a high surface area carbon or by other functionalization of the surface to alter hydrogen packing and densify the adsorbed phase, though most of these ideas are untested. 24−26…”

“…PECONF-4 has a high isosteric heat compared to other experimentally measured microporous carbons. 19,24,45,46 This result can in part be attributed to the small pore sizes of PECONF-4 (Supporting Information, Section 4), in which overlapping wall potentials increase the overall dispersion interactions. Schindler and LeVan have calculated that slit-pore carbons with 4–6 Å pores can have Henry’s law regime isosteric heats of 7–10 kJ mol –1 .…”

“…18−21 Notable exceptions are oxygen-rich microporous carbons developed by Blankenship et al 22 and the carbide derived carbons of Yushin et al 23 Alternative strategies to increase the isosteric heat of hydrogen adsorption have included implanting metal ions or nanoparticles and/or otherwise functionalizing the carbonaceous surface. 24−26…”

“…The capacity of an adsorbent is largely dependent on the porosity accessible to the gas (quantified by specific surface area or micropore volume) and the strength of the attractive physical interactions between the adsorbate and the adsorbent (quantified by the isosteric heat of adsorption). The optimal isosteric heat of adsorption to maximize hydrogen delivery (at standard operating conditions) is between 15 and 20 kJ mol –1 . , Carbonaceous adsorbents have high specific surface areas but isosteric heats generally less than 9 kJ mol –1 . − Notable exceptions are oxygen-rich microporous carbons developed by Blankenship et al and the carbide derived carbons of Yushin et al Alternative strategies to increase the isosteric heat of hydrogen adsorption have included implanting metal ions or nanoparticles and/or otherwise functionalizing the carbonaceous surface. − …”