Effects of different acid-treatment on the nanostructure and performance of carbon nanotubes in electrochemical hydrogen storage
Digest Journal of Nanomaterials and Biostructures
University of Limpopo, School of Physical and Mineral Sciences, Department of Chemistry, Private Bag X 1106, Sovenga, South Africa
The effects of various acids on the nanostructure and hydrogen storage performance of multi-walled carbon nanotubes (MWCNTs) were investigated. MWCNTs were sonicated in nitric acid (HNO3), hydrogen peroxide (H2O2), sulphuric acid (H2SO4) and their mixtures. FTIR revealed that the ratio of oxygen-containing groups on the surface of CNTs depends on the type of oxidiser. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Thermal gravimetric analysis (TGA) showed an intact and stable nanostructure of MWCNTs treated by H2O2+HNO3, with an improve functionality due to different kinds of pores. The Brunauer-Emmett-Teller (BET) surface area of MWCNTs treated by H2O2+HNO3increased to 343.1 m2/g, as compared to 251.5 and 223.7 m2/g of the raw and HNO3+H2SO4treated MWCNTs, respectively. The MWCNTs treated by a mixture of H2O2+HNO3gave the highest discharge capacity of 72.6 mAh/g (electrochemical hydrogen storage of 0.27 wt.%), as compared to a preferred mixture of HNO3+H2SO4, which gave a discharge capacity of 3.0 mAh/g; due to a structural damage of MWCNTs walls and low BET surface area. A H2O2+HNO3mixture promotes larger BET surface area and low reductive overpotential of hydrogen at the electrode. © 2014 Inst Materials Physics. All rights reserved.