Adsorption mechanism of supercritical hydrogen in internal and interstitial nanospaces of single-wall carbon nanohorn assembly

The exact physical adsorption amounts of supercritical hydrogen on the single-wall carbon nanohorn (SWNH) assemblies were determined at 77, 196, and 303 K. There are two physical adsorption sites of interstitial and internal spaces on SWNH assemblies. The interaction potential depths of interstitial and internal spaces are -1000 and -600 K, respectively. However, both hydrogen densities in interstitial and internal spaces were about 70 g L-1 at 77 K at 5 MPa, though the hydrogen densities in interstitial and internal spaces were 15 and 10 g L-1 at 303 K and 6.5 MPa. The similar enhancement in the internal spaces was observed even at 196 K. The additional stabilization by the strong fluid-fluid interaction due to the cluster formation in the internal spaces. On the other hand, hydrogen molecules adsorbed in the interstitial spaces cannot form the stable cluster owing to the space limitation. The enthalpy of adsorption supports the presence of the stable cluster of hydrogen adsorbed in the internal spaces below 303 K.