Single Walled Carbon Nanotube-Metal Oxide Nanocomposites for Reversible and Reproducible Storage of Hydrogen D. Silambarasan, † V. J. Surya, ‡ V. Vasu,* ,† and K. Iyakutti § † School of Physics, Madurai Kamaraj University, Madurai 625021, Tamil Nadu, India ‡ New Industry Creation Hatchery Center, Tohoku University, Sendai 980-8579, Japan § Department of Physics & Nanotechnology, SRM University, Kattankulathur 603203, Tamil Nadu, India * S Supporting Information ABSTRACT: Composite material consisting of single walled carbon nanotubes (SWCNTs) and metal oxide nanoparticles has been prepared and their hydrogen storage performance is evaluated. Metal oxides such as tin oxide (SnO 2 ), tungsten trioxide (WO 3 ), and titanium dioxide (TiO 2 ) are chosen as the composite constituents. The composites have been prepared by means of ultrasonication. Then, the composite samples are deposited on alumina substrates and at 100 °C in a Sieverts-like hydrogenation setup. Characterization techniques such as transmission electron microscopy (TEM), Raman spectroscopy, scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, energy dispersive spectroscopy (EDS), CHN elemental analysis, and thermogravimetric (TG) measurements are used to analyze the samples at various stages of experiments. Hydrogen storage capacity of the composites namely, SWCNT-SnO 2 , SWCNT-WO 3 , and SWCNT-TiO 2 are found to be 1.1, 0.9, and 1.3 wt %, respectively. Hydrogenated composite samples are stable at room temperature and desorption of hydrogen is found to be 100% reversible. Desorption temperature ranges and binding energy ranges of hydrogen have been measured from the desorption studies. The hydrogenation, dehydrogenation temperature, and binding energy of hydrogen fall in the recommended range of a suitable hydrogen storage medium applicable for fuel cell applications. Reproducibility and deterioration level of the composite samples have also been examined. KEYWORDS: single walled carbon nanotube-metal oxide composite, hydrogen, storage capacity, desorption temperature, reproducibility, deterioration ■ INTRODUCTION Currently, hydrogen is emerging as a clean fuel for trans- portation applications. The main issues related to safety and leakage while its storage in the form of gas and liquid have led to the storage of hydrogen in its solid state form in materials particularly, nanomaterials. In the group of nanomaterials, carbon nanotubes (CNTs) are emerging as one of the possible hydrogen storage media. 1-4 Primary investigations of hydrogen storage on bare CNTs indicate that CNTs are not suitable material for hydrogen storage. 5-7 But, further investigations based on the modification of CNTs via functionalization and addition of metal ions/atoms show enhanced hydrogen storage performance over bare CNTs. 8-15 Recent reports show that the nanostructured composite materials comprising CNTs and metal oxides are efficient hydrogen storage materials. 16-19 The composite material made up of CNTs and metal oxides such as tin dioxide (SnO 2 ), tungsten trioxide (WO 3 ), and titanium dioxide (TiO 2 ) have been extensively investigated for gas sensor applications, 20-23 and interestingly, the interactions between hydrogen and these metal oxides have also been reported. 24-27 A single walled carbon nanotube (SWCNT) SnO 2 composite thin film prepared by electron beam evaporation technique show a storage capacity of 2.4 wt %, while SnO 2 alone shows a storage capacity of 0.6 wt %. The desorption temperature of hydrogen from the SWCNT-SnO 2 composite is found to be in the range of 200-350 °C. 16 A composite material containing SWCNTs and WO 3 prepared by an electron beam evaporation technique exhibits a hydrogen storage capacity of 2.7 wt %, in which WO 3 shows a storage capacity of 0.5 wt % single handedly, and desorption of hydrogen from the composite occurred in the temperature range of 175-305 °C. 17 Mishra et al. 18 examined the hydrogen storage capacity of CNT-TiO 2 nanotubular hybrid material at 77 and 298 K. The uptake of hydrogen at 77 and 298 K are found to be 2.5 wt % at 25 bar and 1.04 wt % at 22 bar, respectively. In this, TiO 2 nanotubes alone stored 2 wt % of hydrogen at 77 K and 0.9 wt % at 298 K and CNTs stored 0.4 wt % under identical conditions at 77 K. The CNTs impregnated with TiO 2 -nanorods and nanotubes show a hydrogen storage capacity of 0.35 and 0.4 wt %, respectively at 298 K and 18 atm, which is nearly five times higher uptake than pristine CNTs. 19 These reports exploring the synergistic Received: August 29, 2013 Accepted: October 11, 2013 Published: October 11, 2013 Research Article www.acsami.org © 2013 American Chemical Society 11419 dx.doi.org/10.1021/am403662t | ACS Appl. Mater. Interfaces 2013, 5, 11419-11426