Study of storage and adsorption/desorption characteristics of H-2 on MWCNTs modified by metal potassium

Abstract

Storage capacity of H-2 in a kind of potassium-modified multiwalled carbon nanotubes, K-0-MWCNTs, was measured by using high-pressure volumetric method combined with desorption water-displacement method. It was experimentally shown that appropriate incorporation of a certain amount of metallic potassium into the MWCNTs could significantly increase the storage capacity of hydrogen. Under conditions of 7.25 MPa and ambient temperature, H-2 uptake of 3.8 wt% could be achieved by the x%K-0-MWCNTs (x%=30%-35%, mass percentage), which was 2.5 times as high as that by the KO-free MWCNTs under the same conditions. It was also indicated that adsorption of 99% of the H2 was reversible, and that 88% of the stored hydrogen (equalling storage capacities of 3.36 wt%) could be desorbed while the pressure was relieved to atmospheric pressure and similar to 11% of the stored hydrogen (equalling storage capacities of 0.41 wt%) was desorbed in the following process of elevating temperature from room temperature to 673 K. The Raman-spectroscopic and TPD-MS/GC investigations of the H-2/K-0-MWCNTs adsorption systems showed that adsorption of H-2 on the MWCNTs could occur in associative and dissociative forms, with the observed v(s)(C-H) for CH2, v(C-H) for CH and v(H-H) for H-2 (a) at 2856, 3228 and 3946 cm(-1), respectively, and that H-2 Was the predominant products desorbed at temperatures lower than 723 K, whereas in addition to H-2, light hydrocarbons such as CH4, C2H4, C2H2, etc. were also involved in the products desorbed at temperatures higher than 723 K.