Hydrogen storage in TiO2 functionalized (10, 10) single walled carbon nanotube (SWCNT) – First principles study
Introduction
The energy needs of humanity in the form of fuel have led to search for suitable alternate energy and the consideration of hydrogen (H2) as one of the possible energy sources. Moreover, hydrogen is abundant in nature and it is light. The burning of this novel element in fuel cells results almost no pollution. Lot of initiatives are taken worldwide to build reliable and sustainable hydrogen storage systems that shape up hydrogen economy. The hydrogen economy depends mainly on five key aspects such as production, storage, transportation, conversion, and applications. Storage of hydrogen is a technologically challenging task. The problem is in the storage of this lightest element in higher density, by taking into account that the intermolecular forces are very weak. One of the easiest ways to think is to lock the gas in the form of liquid. However, at room temperature, pressure over 1000 bar will be needed to achieve such high densities in order to accomplish liquefaction [1]. Hence, solid state storage automatically comes into play. Nanomaterials play an important role in the area of hydrogen storage. Among the nanomaterials identified for hydrogen storage, carbon nanomaterials are the preferred ones. In particular, carbon nanotubes (CNTs) are one of the possible hydrogen storage media used for fuel cell applications.
Many studies support the importance of carbon nanotubes (CNTs) for storing hydrogen in a more convenient way [2], [3], [4], [6], [7], [8], [13], [14], [15], [16], [25], [28], [30]. The results proposed by Dillion et al. [2] on high hydrogen uptake in single walled carbon nanotubes (SWCNTs), are still remaining a landmark for the study of CNTs as a promising candidate for storing hydrogen. As it is known that pristine CNT has very poor hydrogen storage capacity [3], functionalization in a proper way is required to improve the H2 storage capacity. Earlier work [4], [5], [6] of our research group indicated that SWCNTs coated with hydrogen-rich metal hydride like AlH3 could enhance the hydrogen storage capacity; but the binding energy per H2 did not lie in the range recommended for ideal hydrogen storage medium, i.e. 0.2–0.4 eV [7]. It has been proven that heavy transition metal hydride like NiH2 is also not suitable to store/deliver hydrogen at ambient conditions [5], [6].
Indeed, light transition metal atoms may promote hydrogen binding [8]. Hence, a light transition metal atom (titanium) is chosen for functionalization in our work. Further, functionalization with metal atoms gives rise to formation of metal hydride which is not favorable for hydrogen desorption process [9], hence going for metal oxide (titanium oxide) is preferred. Iwaki [10] has reported the interaction of hydrogen with titanium dioxide in connection with the formation of surface hydroxyl groups. The oxygen vacancies (intrinsic defects) have been proposed to act as specific adsorption site for H2 [11], [12]. Recently, it is reported that nanostructured composites made up of carbon nanotubes and metal oxides are good hydrogen storage materials [13], [14], [15], [16]. There are experimental investigations available for the hydrogen storing properties of TiO2 doped CNT. Rather et al. [16] reported that CNT-TiO2 composites store up to 0.4 wt.% of hydrogen at 298 K and 18 atm which is nearly five times higher the hydrogen uptake of pristine CNTs. Through first principles study, Yildirim et al. [17] have shown that each Ti atom adsorbed on an SWCNT can bind up to four hydrogen molecules. Although metal oxides overcome the problem of metal hydride formation, heavy and/or unstable molecules are not suitable for this functionalization. So a light transition metal oxide, TiO2 is adopted for functionalization in order to make the binding energy per H2 molecules lie within the ideal range [7]. Above all, TiO2 itself can be used to store hydrogen [18], [19]. Also, recent work of our experimental group on hydrogen storage in SWCNTs/TiO2 composites is highlighted to support theoretical predictions [14], [15]. In this work, a linear TiO2 molecule is considered for functionalization that facilitates the SWCNT to have high H2 storage capacity with optimal binding energy per H2.
Section snippets
Method of calculation
The first principles calculations are done using density functional theory (DFT) as implemented in Vienna Ab-initio Simulation Package (VASP) [20], [21] code. The plane wave ultrasoft pseudopotentials are used with local density approximation (LDA) [22]. The 2s2 2p2 in carbon (C), 4s2 3d2 in titanium (Ti), 2s2 2p4 in oxygen (O) atoms are treated as the valence states. Two unit cells of (10, 10) armchair SWCNT with 80 carbon atoms is considered for the study. The super cell dimensions are taken
Results and discussion
Fig. 2(a) shows C10+TiO2 structure. In that structure, TiO2 molecule is attached at larger distance on top of the ‘C’ atom with Ti–O bond length as 1.95 Å, in order to allow it to occupy a preferred position on the SWCNT. After relaxation, TiO2 gets placed on the nearest neighbor ‘C’ atom, approximately at the center of unit cell height, with a decreased Ti–O bond length of about 1.7 Å. The distance profile of the initial and relaxed structures of TiO2 functionalized and H2 adsorbed systems are
Conclusions
The hydrogen storing properties of (10, 10) armchair SWCNT functionalized with transition metal oxide, TiO2 has been investigated theoretically by exploring the adsorption behavior of hydrogen molecules. The usable storage capacity of the system is about 5.7 wt.% and it is considered as optimal value as per US DOE target. The hydrogen adsorption is molecular except one or two and this lead to improve the storage capacity in terms of getting ideal binding energy range. The change in electronic
Acknowledgments
The author RL and VV thank Department of Science and Technology (DST-PURSE), University Grants Commission – Major Research Project (UGC-MRP). The author KI thanks Council of Scientific and Industrial Research (CSIR), India, for financial assistance under Emeritus Scientist Scheme. Authors VJS and YK are thankful to Japan Society for the Promotion of Science (Grant no. 23241027) for their financial support. The authors would like to express their sincere thanks to the crew of Centre for
References (33)
- et al.
Aluminum hydride coated single-walled carbon nanotube as a hydrogen storage medium
Int J Hydrogen Energy
(2009) - et al.
Reactivity of a reduced metal oxide surface: hydrogen, water and carbon monoxide adsorption on oxygen defective rutile TiO2(110)
Surf Sci
(2003) - et al.
One-step process of hydrogen storage in single walled carbon nanotubes-tin oxide nano composite
(2013) - et al.
Single step preparation and hydrogenation of single walled carbon nanotubes-titanium dioxide
Int J Hydrogen Energy
(2014) - et al.
Hydrogen storage of nanostructured TiO2 impregnated carbon nanotubes
Int J Hydrogen Energy
(2009) - et al.
Spillover of physisorbed hydrogen from sputter-deposited arrays of platinum nanoparticles to multi-walled carbon nanotubes
Chem Phys Lett
(2007) Hydrogen adsorption by alkali metal graphite intercalation compounds
(2010)- et al.
Storage of hydrogen in single-walled carbon nanotubes
Nature
(1997) - et al.
Carbon nanotubes applications: solar and fuel cells, hydrogen storage, lithium batteries, supercapacitors, nanocomposites, gas, pathogens, dyes, heavy metals and pesticides
- et al.
Clustering of functional molecules on a single-walled carbon-nanotube surface and its effect on hydrogen storage
Phys Status Solidi B
(2009)
Single walled carbon nanotubes functionalized with hydrides as potential hydrogen storage media: a survey of intermolecular interactions
Phys Stat Solidi B
Computational studies of molecular hydrogen binding affinities: the role of dispersion forces, electrostatics, and orbital interactions
Phys Chem Chem Phys
Adsorption and dissociation of hydrogen molecules on bare and functionalized carbon nanotubes
Phys Rev B
Predicting formation enthalpies of metal hydrides
Studies of the surface of titanium dioxide
J Chem Soc Faraday Trans I
Intrinsic defects of TiO2&(110): interaction with chemisorbed O2, H2, CO and CO2
Phys Rev B
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