Hydrogen sorption hysteresis and superior storage capacity of silicon-carbide nanotubes over their carbon counterparts

Abstract

We report for the first time the results of an extensive experimental study of hydrogen sorption in silicon-carbide nanotubes (SiCNTs), which were synthesized using the reaction between SiO vapor and carbon nanotubes (CNTs) in an argon atmosphere in the temperature range 1200 o C-1500 o C. The as-synthesized SiCNTs were then purified using a sodium hydroxide solution in order to remove the side products of the synthesis reaction. The hydrogen sorption characteristics of the as-synthesized SiCNTs, as well as those of the purified SiCNTs were then measured at 25 o C and for pressures of up to 100 bars. The results reveal hysteresis between the adsorption and desorption isotherms, which we attribute to the presence of metal impurities and/or the multilayer structure of the nanotubes. The hydrogen storage capacity of the as-synthesized SiCNTs is similar to that of the CNTs, whereas for the purified SiCNTs it is 50% higher than that of the CNTs, in agreement with the results of molecular simulations reported previously. In addition, the hydrogen uptake rate in the SiCNTs is about five times faster than that in the CNTs and, in contrast with the CNTs, its desorption from SiCNTs is completely reversible under vacuum.

Synthesis of reduced graphene oxide wrapped-copper sulfide hollow spheres as electrode material for supercapacitor

“…According to the equation, the specific capacitance of CuS hollow spheres is calculated to be 917.6 F g À1 compared to 2317.8 F g À1 of CuS-rGO composite. This value of CuS-rGO composite is higher than that for flower-like CuS synthesized in glycerol (597 F g À1 ) and measured in aqueous 2 M KOH solution [41], CuS nanoplatelets fabricated by low temperature chemical bath deposition technique (72.85 F g À1 ) and measured in 1 M H 2 SO 4 aqueous electrolyte [42], CuS ultrafine nanoneedles supported on a carbon nanotube backbone fabricated by an efficient template-engaged chemical conversion route (114 F g À1 ) and measured in 2 M aqueous KOH solution [23], CuS microspheres with polypyrrole uniformly inserted into the sheet like subunit structure (427 F g À1 ) and measured in the electrolyte of 1 M KCl [24].…”

Solubility and diffusivity of H2 and CO2 in the ionic liquid [bmim][PF6]

“…After the degasing step was completed, the system's temperature was set to the value at which gas absorption was to be investigated, in this study in the range 25 Ce55 C. The system pressure was then increased stepwise by injecting the absorptive gas into the gravimetric vessel, and the sample's weight was recorded. More details about the experimental set-up used in this work and the operating procedures followed are given in our previous papers [28,29]. Fig.…”

“…In our previous studies of the adsorption of hydrogen in carbon and silicon-carbide nanotubes [28,29], we utilized a highly accurate gravimetric measurement technique involving the use of a magnetic suspension microbalance. A key goal of the present paper is to extend the applicability of this technique as a viable experimental tool to simultaneously measure the solubility and diffusivity of various gases in ionic liquids.…”

An Overview of the Recent Progress in Modifications of Carbon Nanotubes for Hydrogen Adsorption

“…The strongest proof of chemisorption in carbon nanotubes is the requirement of high temperature to completely remove hydrogen from hydrogenated CNTs [55]. Although it has been reported that the hysteresis phenomenon between the adsorption/desorption isotherms of CNTs can also suggest the chemisorption [12], Barghi et al [66] attributed hysteresis to the metal impurities formed during CNT synthesis and/or the multilayer structure of the CNTs.…”