IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 13, NO. 2, MARCH2014 261 Water Soluble Polymer-SWCNT-Based Composite for Hydrogen Storage D. Silambarasan, V. Vasu, and K. Iyakutti Abstract—In this study, water soluble polymers such as poly vinyl alcohol (PVA) and poly vinyl pyrrolidone (PVP) were chosen as the base material for hydrogen storage with the aim of produc- ing recyclable and water-soluble polymer-based hydrogen storage material. Initially, the polymers were acid treated using concen- trated hydrochloric acid (conc. HCl) to incorporate Cl ions into the polymeric matrices. Furthermore, single-walled carbon nan- otubes (SWCNTs) were added to those acid-treated polymers by means of ultrasonication in an aqueous medium as the compos- ite material to increase the hydrogen adsorption. The homogenous composite solution resulted from ultrasonication was then made in the form of film by using the general spin-coating technique. Then, the composite films were hydrogenated in Seiverts’ like hydrogena- tion setup. The preliminary results on hydrogen storage capability of the polymer-SWCNTs composite materials and desorption tem- perature range of hydrogen are reported. The prepared composite films exhibit good water-soluble properties and recyclability, i.e., they can be formed and dissolved in water. Hydrogen storage in these acid-treated polymer-SWCNTs composite is reported here for the first time. The presence of Cl ions and the adsorption sites offered by SWCNTs were responsible for hydrogen binding in the composite films. The nature of binding of hydrogen in the compos- ite films was found to be weak chemisorption. Index Terms—Carbon nanotubes, hydrogen storage, polymer films. I. INTRODUCTION B ECAUSE of the diminishing availability of the fossil fuel and increasing global warming, there is a compulsion to seek for an alternate green (revolutionary) fuel, which can re- place the traditional fossil fuel in near future. Hydrogen would be a worthy perfect candidate because of its abundance and pollutant-free advantages [1], [2]. Researchers are facing ob- stacles on its storage for onboard applications [3], [4]. Classi- cal methods of storage in the form of gas and liquid involve high unsafe pressure and large amount of energy. Storage of Manuscript received July 4, 2013; accepted January 6, 2014. Date of publi- cation January 9, 2014; date of current version March 6, 2014. This work was supported by Madurai Kamaraj University (MKU), University Grants Com- mission (UGC), Council of Scientific and Industrial Research (CSIR), and Sri Ramaswamy Memorial (SRM) University. The review of this paper was ar- ranged by Associate Editor G. Ramanath. D. Silambarasan and V. Vasu are with the School of Physics, Madurai Ka- maraj University, Madurai-625021, Tamil Nadu, India (e-mail: simbuphysics@ yahoo.com; vvasumku@gmail.com). K. Iyakutti is with the Department of Physics and Nanotechnol- ogy, SRM University, Kattankulathur-603203, Tamil Nadu, India (e-mail: iyakutti@yahoo.co.in). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TNANO.2014.2299287 hydrogen in its solid state form on nanostructure materials [5]–[7], zeolites [8] and metal organic frameworks [9] are being investigated extensively. The storage of hydrogen in these mate- rials comprises the processes namely physisorption that involves the weak interaction of hydrogen with the host in binding energy range of 0.01–0.1 eV and chemisorption that involves strong chemical bonding of hydrogen to the host material with the binding energy range of ∼2–3 eV. Generally, physisorption of hydrogen is stable at lower temperatures only and chemisorption of hydrogen requires higher temperature to release. Hence, the storage of hydrogen in the host material with the binding energy in between these two limits is necessary for onboard applica- tions. Hydrogen storage in polymers is emerging as a hot topic in recent years, because of being lightweight, porous nature, and possible large scale production technology [10]. In addition, generally polymer contains a high concentration of hydrogen covalently bound to the polymer structure; hence, it is conceiv- able that hydrogen could interact on a molecular level [11]. A triptycene-based polymer showed a reversible hydrogen storage capacity of 1.65 wt.% at 1 bar, 77 K and 2.71 wt.% at 10 bar, 77 K [12]. Lee et al. [13] showed that the hyper cross-linked polystyrene can reversibly adsorb upto 3.04 wt.% H 2 at 77 K and 15 bar. A hydrogen storage capacity of 7 wt.% was obtained at 77.3 K and 48 bar using a new kind of organic material based on the diamond like structure [14]. Budd et al. [15] reported that the polymer of intrinsic microscopy incorporated with trip- tycene subunit is taking up 2.7% H 2 by mass at 77 K and 10 bar. Doping of Li + ions to the conjugated micro-porous polymers leads to the highest storage capacity of 6.1 wt.% at 77.3 K and 1 bar [16]. A poly–ether–ether–ketone (PEEK) base polymeric matrix functionalized in situ by manganese oxide formation, exhibited 1.2 wt.% hydrogen adsorption capabilities at 77 K. Interestingly, at 60 bar this material showed a hydrogen sorp- tion capacity of 0.24 wt.% at just above room temperature, 50 ◦ C and 0.06 wt.% at around room temperature, 32 ◦ C [17]. First- principles electronic structure calculations for hydrogen binding to trans-polyacetylene decorated by Ti and Sc atoms exhibited the storage capacities of 12 and 14 wt.%, respectively [18]. Hydrogen storage in polyaniline (PANI)-based nanocomposites such as PANI-SnO 2 , PANI-MWCNTs, and PANI-Al were also investigated and found that the incorporation of CNTs into poly- mer can also improve the performance of hydrogen storage via offering more adsorption sites [19]. Cho et al. [20] proposed the concentrated (conc. ) HCl acid-treated PANI and polypir- role (Ppy) as hydrogen storage materials, and they measured the storage capacities of 6 and 8 wt.%, respectively, at 90 atm and 298 K. These reports reveal that the polymer-based mate- rial having the ability to store the hydrogen. On the other hand, 1536-125X © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information.