Xuesheng Lu

Temperature-dependent state of hydrogen molecules within the nanopore of multi-walled carbon nanotubes

Abstract In observation of the state of hydrogen molecules within the carbon nanopore, the excess adsorption amounts of hydrogen on the multi-walled carbon nanotubes (MWCNTs) were measured at equilibrium pressure–temperatures from 0.1 to 12.3 MPa and 123 to 310 K . The principles of thermodynamic equilibrium and a higher order Virial adsorption coefficient were applied to determining the maximum surface coverage of hydrogen molecules on the adsorbent surface. The thermodynamic equilibrium-based adsorption model was linearized to estimate the interaction energy among the adsorbed hydrogen molecules at each adsorption equilibrium state. The results demonstrate that the interaction energies among adsorbed hydrogen molecules are positive in the lower temperature region ( K ) and reach the maximum value around a temperature from 160 to 180 K . However, it will gradually be negative when the temperature is approaching 230 K . In other words, the confined hydrogen molecules repulse each other in the low-temperature environment while they attract each other at the ambient temperature. It implies that the dissociativeness of hydrogen occurred in the experimental pressure–temperature range, and it is also suggested that the temperature between 160 and 180 K could be a preferable condition to make full use of physical and chemical adsorption of hydrogen molecules on the adsorbent.

A study of the optimum temperature for hydrogen storage on Carbon Nanostructures

Publisher Summary This chapter studies the temperature dependent state of hydrogen molecules on multi-walled carbon nanotubes (MWCNTs) at a temperature range from 123–310 K. The energy of intermolecular interaction is used to probe into the optimum temperature for hydrogen storage by adsorption on carbon nanostructures. Thermodynamic analysis is undertaken based on the lattice theory to the adsorption data of hydrogen on MWCNTs over a temperature range of 123–310 K and pressure up to 12.5 MPa. The isosteric heat of hydrogen adsorption in low limit of the surface concentration on the MWCNTs is smaller than that on the graphitized carbon black. The hydrogen–hydrogen interaction energy shows characteristics of physical adsorptions of supercritical gases, the optimum adsorption temperature has not been revealed by the determined results and should still be in researching. Results show that the hydrogen–hydrogen interaction energy captures characteristics of physical adsorptions of supercritical gases; almost linearly increases with increases of adsorption temperatures and surface loadings.

Chapter 207 – The characterization of carbon nanofibres based on N2 adsorption isotherms at 77K

Publisher Summary In this chapter the BJH method is applied to determine the pore size distribution of several carbon nanofibres based on N2 adsorption isotherms at 77K. Carbon nanofibres are porous adsorbents specially developed for hydrogen adsorption storage. The microstructure characterization of carbon nanofibres is critical for its application in hydrogen storage and understanding of supercritical hydrogen adsorption mechanism. The study results show that the carbon nanofibres used in the present study include abundant mespores of 20nm. The adsorption data between 0.01 and 0.99 of relative pressure show features of gas adsorption in mespores adsorbents, and only the mesopores size distribution could be determined with the BJH method. The adsorption data at lower relative pressure (<0.01) must be collected if the micropores size distribution is determined. To determine the micropore size distribution, the adsorption data at relative pressure less than 0.01 must be gotten. But it seems unnecessary to determine the micropores size distribution because of little micropores volume.