Sub-Nanometer Carbon Nanotube Arrays: A Pathway to High-Capacity and Reversible Hydrogen Storage

Abstract

The utilization of adsorbents composed of single-walled carbon nanotube (SWCNT) pores, characterized by mono-dispersed and molecular-scale diameters, is widely sought after due to their exceptional capacity for selective hydrogen storage at ambient conditons. Nonetheless, materials with accurate pore sizes and uniformity, as well as the examination of the mechanisms linked to adsorption present significant difficulties. In this study, aluminophosphate zeolites (specifically, FeAPO-5 with an AFI crystal structure) were cultivated. These zeolites possess 1-D, monodisperse parallel pores with an approximate diameter of 7 Å. These zeolites were employed as templates for the growth of single-walled carbon nanotubes (SWCNTs) within the aforementioned pores. Thereafter, these CNTs were removed from the pores of the AFI channels and analyzed for their potential applications as adsorbents for hydrogen storage. The SWCNTs growing in the Fe-richer, TPA occluded AFI host demonstrated a notable gravimetric hydrogen absorption of 1.8 wt% at 25 0C and 1 bar. Cyclic stability measurements were conducted on the SDA derived SWCNT adsorbents. Among them, the TPA occluded Fe-rich APO@SWCNT adsorbent demonstrated the highest gravimetric measurement, which remained consistent for 5 cycles. This can be attributed to the presence of larger and more densely packed AFI crystals, as well as a higher number of SWCNT-filled pores resulting in densely packed CNTs post etching. These characteristics are associated with the higher Fe catalyst content in the adsorbent coupled with the use of TPA as the SDA. Notably, the synthesized sub-nanometer uniform porous single-walled carbon nanotubes (SWCNTs) demonstrated a significant gas selectivity of 18.5, favoring hydrogen (H2) over carbon dioxide (CO2) at ambient conditons.

Date of Award	24 Dec 2023
Original language	American English
Supervisor	Khalid Al Ali (Supervisor)