Model for the hydrogen adsorption on carbon nanostructures

Abstract

The hydrogen sorption capacity of carbon nanostructures was for several years a very controversial subject. Theoretical models have been published demonstrating a great potential for a large hydrogen sorption capacity of carbon nanostructures. Here we present a simple empirical model where condensation of hydrogen as a monolayer at the surface of nanotubes as well as bulk condensation in the cavity of the tube is assumed. The maximum potential amount of hydrogen absorbed according to the model was calculated to be 2.28 × 10 −3 mass % S[m 2 g −1 ] = 3.0 mass % for the adsorption of a monolayer hydrogen at the surface. The condensation of hydrogen in the cavity of the tube leads to a potential absorption for single wall nanotubes starting at 1.5 mass % and increasing with the diameter of the tubes. The experimentally measured hydrogen capacity of the nanotube samples correlates with the B.E.T. specific surface area. The slope of the linear relationship is 1.5 × 10 −3 mass %/m 2 g −1 . Therefore, the extrapolated maximum discharge capacity of a carbon sample is 2 mass %. Furthermore, it can be concluded, that the hydrogen sorption mechanism is related to the surface of the sample, i.e. a surface adsorption process.

High capacity hydrogenstorage materials: attributes for automotive applications and techniques for materials discovery

“…84 The maximum expected excess capacity can be estimated by assuming that hydrogen adsorbs as a monolayer on the sorbent with a density equal to that of liquid hydrogen. 85 Thus, under this approximation, excess capacity is proportional to the sorbent surface area where the proportionality constant is: 2.28 Â 10 À3 wt% H 2 m À2 g (often referred to as the 'Chahine Rule'). 86 That is, a sorbent possessing a specific surface area of 500 m 2 /g should store up to approximately 1 wt% hydrogen.…”

Hydrogen Adsorption in Metal–Organic Frameworks: Cu‐MOFs and Zn‐MOFs Compared

“…[9][10][11][12] Figure 7 shows the maximum hydrogen uptake at 77 K versus the BET SSA for different crystalline microporous materials. The saturation values for MOFs of the present work and previous results [14] are compared to zeolites.…”

“…In fact, it has been previously demonstrated that for other microporous materials, such as carbon materials and zeolites, the maximum hydrogen uptake is correlated to the SSA of the adsorbent. [9][10][11][12] Compared with hydrogen storage in metal hydrides and complex hydrides, physical adsorption has the great advantage of being completely reversible and of exhibiting very fast kinetics. On the other hand, because of the low adsorption enthalpy involved in physisorption, high storage capacities are reached only at lower temperatures.…”

Investigation of Hydrogen Physisorption Active Sites on the Surface of Porous Carbonaceous Materials

“…[18] However, hydrogen condensation may only occur under cryogenic conditions. In addition to the uncertain capacity, H 2 adsorption and desorption kinetics may be a limiting factor as well, due to the H 2 diffusion rate inside the carbon nanotubes.…”