Hydrogen Storage In Carbon Nanotubes Research Articles

A DFT investigation of Osmium decorated single walled carbon nanotubes for hydrogen storage

The investigation for hydrogen storage in armchair single walled carbon nanotubes (SWCNTs) with decoration of osmium atom on the surface of tube has been done using ab-initio method utilizing Density Functional Theory (DFT). In the present work, single/dual osmium atoms decoration on the surface of SWCNTs (5,5) has been investigated regarding the effects on structural, electronic and thermodynamic properties. Frontier molecular orbital (FMO) i.e. HOMO and LUMO structures and electrostatic potential surfaces (ESP) of all geometrically optimized and stable species are studied. Investigations regarding metal-metal clustering are carried out by calculating diffusion barrier energy for osmium atoms and atomistic molecular dynamic simulations performed at 300°K temperature for 1ps. It is found that osmium decoration on SWCNTs enhances the hydrogen storage capacity via spillover mechanism. It is observed that the adsorption energy per hydrogen molecule in case of Pristine SWCNT is -0.001eV, which is increased with decoration of osmium atoms and finally found to be -0.575eV/H2 in case of single osmium decorated SWCNT (Os-CNT) and -0.681eV/H2 due to double osmium decoration on SWCNT (2Os-CNT). This study reveals gravimetric hydrogen storage capacity of 1.32 wt% and 2.53 wt% for Os-CNT and 2Os-CNT respectively at 298.15 K temperature and 10 atm pressure. Average Van't Hoff desorption temperature for osmium decorated SWCNTs are also calculated.

Can endohedral transition metals enhance hydrogen storage in carbon nanotubes?

The safe and efficient use of hydrogen energy, which is in high demand worldwide today, requires efficient hydrogen storage. Despite significant advances in hydrogen storage using carbon-based nanomaterials, including carbon nanotubes (CNTs), efforts to substantially increase the storage capacity remain less effective. In this work, we demonstrate the effect of endohedral transition metal atoms on the hydrogen storage capacity of CNTs using reactive molecular dynamics simulations. We find that an increase in the volume fraction of endohedral nickel atoms leads to an increase in the concentration of physisorbed hydrogen molecules around single-walled CNTs (SWNTs) by approximately 1.6 times compared to pure SWNTs. The obtained results provide insight into the underlying mechanisms of how endohedral transition metal atoms enhance the hydrogen storage ability of SWNTs under nearly ambient conditions.

Nonlinear dynamic analysis and structural optimization design of Ni/Mg modified single wall carbon nanotube for hydrogen storage

The combustion calorific value of hydrogen is three times of gasoline and the burning product of hydrogen is water, which makes hydrogen the representative of clean energy. The hollow part of single-walled carbon nanotube (SWNT) is an excellent container space, which has great potential as hydrogen storage materials. This paper considers the micro-scale effect of SWNT based on Eringen's nonlocal elastic theory, and constructs a nanobeam model and analyzes the nonlinear dynamic characteristics. Based on these, the effects of different modification components on hydrogen storage properties of SWNT is discussed. The analysis exhibits that different modification positions also have a great influence on the hydrogen storage efficiency. The results of theoretical analysis and numerical simulation show that the modification components' optimization plays a certain role in improving the hydrogen storage efficiency of SWNT. The maximum increase hydrogen storage efficiency can be 12.7% by selecting appropriate decorative elements and appropriate positions.

Topological defects embedded large-sized single-walled carbon nanotubes for hydrogen storage: A molecular dynamics study

In this paper, we investigate the performance of large-sized single-walled carbon nanotubes (SWCNTs) incorporated with mono vacancy (MV), double vacancy (DV), and Stone-Wales (SW) topological defects as a medium for hydrogen adsorption using molecular dynamics (MD) simulations. A novel potential energy distribution (PED) method is employed with MD simulations to determine the adsorbed hydrogen molecules and associated binding energy. In addition, we extended our work to bundles of defected SWCNT (D-SWCNT) that provided the most prominent adsorption capacity subjected to temperature and pressure variations. In particular, four representative (8,8), (13,13), (19,19), and (33,0) SWCNTs are simulated under various thermodynamic conditions, and collected adsorption isotherms data reveals higher gravimetric density for large-sized SWCNT. At 77 K and 100 bar, the maximum hydrogen uptake in pristine SWCNTs is 6.88–7.73 wt%, depending on the size of the nanotubes. In contrast, the binding energy decreases as the nanotube size increases. At 77 K, (8,8) and (19,19) SWCNTs have average binding energies of 0.043 and 0.021 eV, respectively. Meanwhile, (19,19) SWCNT incorporated with 1% DV defects having 5–8 rings (DV1) and MV defects yields the maximum storage capacity of 9.07 wt% and 8.62 wt%, respectively, at 77 K. Furthermore, the increment of about 43.29% in wt.% is obtained for DV1 defected nanotube relative to pristine SWCNT at 300 K and 100 bar. Moreover, our results indicate the maximum hydrogen uptake of 8.65, 7.15, 2.57, and 1.33 wt% in the square array of DV1 defect embedded SWCNTs at 77, 100, 200, and 300 K, respectively, compared to 9.07, 6.65, 2.24, and 1.11 wt% in the isolated D-SWCNT at identical conditions. As a result, the D-SWCNT bundles are better suited for hydrogen storage at high temperatures than the isolated D-SWCNT. Our present study paves the way to progress toward the efficient usage of D-SWCNTs with few chemical alterations for scaled-up applications.

Modified carbon nanotubes for hydrogen storage at moderate pressure and room temperature

In this study, the cup stacked carbon nanotubes (CSCNTs) co-modified by KOH activation and Ni decoration are used for hydrogen storage at room temperature and 2 MPa for the first time. The TEM and N2 sorption analyses indicate that the micropore volume of CSCNTs can be improved over 12 times by KOH activation due to their unique graphene layer stacking structure, consequently, the hydrogen adsorption capacity of them increases nine times. Removing the amorphous carbon layers of CSCNTs by KOH etching is the precondition for successful Ni decoration. If the micropore volume of CSCNTs keeps unchanged, the hydrogen storage capacity of them can be further improved 85% by Ni decoration due to the spillover effect. However, during actual Ni decoration, the high micropore volume of CSCNTs obtained by KOH activation is reduced unavoidably because of the blocking effect of Ni nanoparticles, consequently, the resultant hydrogen adsorption capacity increases only 25%.

An Overview of the Recent Progress in Modifications of Carbon Nanotubes for Hydrogen Adsorption.

Many researchers have carried out experimental research and theoretical analysis on hydrogen storage in carbon nanotubes (CNTs), but the results are very inconsistent. The present paper reviewed recent progress in improving the hydrogen storage properties of CNTs by various modifications and analyzed the hydrogen storage mechanism of CNTs. It is certain that the hydrogen storage in CNTs is the result of the combined action of physisorption and chemisorption. However, H2 adsorption on metal-functionalized CNTs still lacks a consistent theory. In the future, the research of CNTs for hydrogen adsorption should be developed in the following three directions: (1) A detailed study of the optimum number of metal atoms without aggregation on CNT should be performed, at the same time suitable preparation methods for realizing controllable doping site and doped configurations should be devised; (2) The material synthesis, purification, and activation methods have to be optimized; (3) Active sites, molecular configurations, effectively accessible surface area, pore size, surface topology, chemical composition of the surface, applied pressure and temperature, defects and dopant, which are some of the important factors that strongly affect the hydrogen adsorption in CNTs, should be better understood.

The activation and hydrogen storage characteristics of the cup-stacked carbon nanotubes

In this study, the cup-stacked carbon nanotubes (CSCNTs) are chemically modified and used for the hydrogen storage for the first time. The SEM and TEM analyses indicate that because they are formed by the stacking of the truncated conical graphene layers the inner- and outer-edges of which are completely exposed, during KOH activation the catalyst particles at the tips of them can be removed completely. The graphene layers of them are exfoliated seriously to form plenty of microcavities. Moreover, many nanosized straight caves and through-holes are formed in the walls of them. As a result, the micropore volume of them increases twelve times and the maximum hydrogen adsorption capacity of them reaches over ten times that of the pristine CSCNTs. These increases exceed the reported data for the conventional coaxial CNTs activated by the same method. Our findings indicate that due to the special graphene layer stacking mode, the micropore structure of CSCNTs can be improved more significantly than the conventional CNTs during KOH activation. They may be a kind of promising carbon nanotube for hydrogen storage.

Ruthenium decorated boron-doped carbon nanotube for hydrogen storage: A first-principle study

In this paper, the adsorption of molecular hydrogen on Ruthenium (Ru) decorated boron-doped single-walled carbon nanotube (CNT) is theoretically studied, based on the density-functional theory (DFT). The projected density of states (PDOS) and charge density difference are computed, and Mulliken population analysis is conducted to investigate the molecular hydrogen adsorption ability of a boron-doped CNT (BCNT) system and a pure CNT system. As for the pure CNT system, a single Ru atom can absorb up to four H2 molecules with a binding energy of −1.057eV/H2; and for the boron-doped CNT system, the binding energy of H2 molecules increases to −1.151eV/H2 and it displays much higher binding energy of Ru with the increase of 21.19%. This implies that the BCNT system is more stable and has better ability to adsorb hydrogen molecules. The enhanced ability to adsorb H2 molecules implies that Ru decorated BCNT may be a useful and promising nanomaterial for hydrogen energy storage.

Li-Functionalized Carbon Nanotubes for Hydrogen Storage: Importance of Size Effects

We investigated Li-doped carbon nanotubes (CNTs) as a promising hydrogen storage media. In this computational model, we considered isolated lithium atom adsorbed on a CNT wall as an adsorption site for hydrogen. We focused on the influence of size effects on the structural and energetic characteristics of CNT(n,n)@Li+kH2 complexes where n = 5, 7, 9; k = 1, ..., 6; Nc = 4, 5, 6 (Nc is translation length of CNT, expressed in terms of a number of CNT unit cells). We proved that modeled CNT length substantially influences internal sorption of Li and hydrogen on the narrow tube (5,5), which subsequently alters the adsorption energies of H2 molecules and causes the deformation of the carbon framework. Moreover, the size effects are not pronounced in the case of external sorption for all considered CNT translation lengths and diameters. We have not observed any noticeable qualitative difference between internal and external hydrogen sorption in the nanotube wider than CNT(5,5). In the case of external adsorption on all considered nanotubes, doping with Li increases hydrogen adsorption energies of up to four H2 molecules by 100 meV in comparison with pure CNTs. And the local density approximation estimations (∼250 meV/H2) of adsorption energy on Li-decorated CNTs exceed the lowest requirement proposed by the U.S. Department of Energy (200 meV/H2). In the case of internal sorption on Li-functionalized tubes, the generalized gradient approximation also gives hydrogen adsorption energies in the desired range of 200–600 meV/H2. However, steric hindrances could prevent sufficient hydrogen uptakes (less than 2 wt % inside CNT(5,5)). We believe that our findings on the size effects are important for estimation of CNT’s hydrogen storage properties.

The synthesized nickel-doped multi-walled carbon nanotubes for hydrogen storage under moderate pressures

Hydrogen adsorption capacity of Multiwalled carbon nanotubes (MWCNTs) decorated with Nickel (Ni) nanoparticles has been presented at room temperature and under moderate pressures of 4–20 bar. The functionalization of carbon nanotubes was carried by H2SO4-HNO3 reducing agents and the Ni supported MWCNTs (Ni-MWCNTs) were prepared by wet chemical method. The structure and morphology characterization of samples were performed by XRD, TEM, EDX and SEM analyses. These nanotubes then subjected to hydrogenation step by using Sievert's-like apparatus. The hydrogenation of the Ni-MWCNTs was performed at 298 K and moderate hydrogen pressures of 4–20 bar. The obtained results show that there is a correlation between hydrogen storage capacity and hydrogen pressure that; as the pressure was increased, hydrogen uptake capacity enhanced due to physisorption. In addition, maximum hydrogen storage capacity of Ni-MWCNTs was found to be 0.298 wt % at room temperature and under pressure of 20 bar.

Scandium and Titanium Containing Single-Walled Carbon Nanotubes for Hydrogen Storage: a Thermodynamic and First Principle Calculation.

The generalized gradient approximation (GGA) to density functional theory (DFT) calculations indicate that the highly localized states derived from the defects of nitrogen doped carbon nanotube with divacancy (4ND-CNxNT) contribute to strong Sc and Ti bindings, which prevent metal aggregation. Comparison of the H2 adsorption capability of Sc over Ti-decorated 4ND-CNxNT shows that Ti cannot be used for reversible H2 storage due to its inherent high adsorption energy. The Sc/4ND-CNxNT possesses favorable adsorption and consecutive adsorption energy at the local-density approximation (LDA) and GGA level. Molecular dynamics (MD) study confirmed that the interaction between molecular hydrogen and 4ND-CNxNT decorated with scandium is indeed favorable. Simulations indicate that the total amount of adsorption is directly related to the operating temperature and pressure. The number of absorbed hydrogen molecules almost logarithmically increases as the pressure increases at a given temperature. The total excess adsorption of hydrogen on the (Sc/4ND)10-CNxNT arrays at 300 K is within the range set by the department of energy (DOE) with a value of at least 5.85 wt%.

Tuning hydrogen storage of carbon nanotubes by mechanical bending: theoretical study

The effects of mechanical bending on tuning the hydrogen storage of titanium functionalised (4,0) carbon nanotube have been assessed using density functional theory calculations with reference to the ultimate targets of the US Department of Energy (DOE). The assessment has been carried out in terms of physisorption, gravimetric capacity, projected densities of states, statistical thermodynamic stability and reaction kinetics. The Ti atom binds at the hollow site of the hexagonal ring. The average adsorption energies (−0.54 eV) per hydrogen molecule meet the DOE target for physisorption (−0.20 to −0.60 eV). The curvature attributed to the bending angle has no effect on the average adsorption energies per H2 molecule. With no metal clustering, the system gravimetric capacities are expected to be as large as 9.0 wt%. The reactions of the deformed (bent) carbon nanotube have higher probabilities of occurring than those of the un-deformed carbon nanotube. The Gibbs free energies, enthalpies and entropies meet the ultimate targets of the DOE for all temperatures and pressures. The closest reactions to zero free energy occur at (378.15 K/2.961 atm.) and reverse at (340 and 360 K/1 atm.). The translational component is found to exact a dominant effect on the total entropy change with temperature. Favourable kinetics of the reactions at the temperatures targeted by DOE are reported regardless of the applied pressure. The more preferable thermodynamic properties assigned to the bending nanotube imply that hydrogen storage can be improved compared to the nonbending nanotube.

Methane Storage in Nanoporous Media as Observed via High-Field NMR Relaxometry

The storage properties of methane gas in Vycor porous glass (5.7 nm) are characterized in a wide pressure range from 0.7 MPa-89.7 MPa using Nuclear Magnetic Resonance (NMR). We demonstrate the capability of high field NMR relaxometry for the determination of the methane gas storage capacity and the measurement of the Hydrogen Index, to a high degree of accuracy. This helps determine the excess gas in the pore space which can be identified to exhibit Langmuir properties in the low pressure regime of 0.7 MPa to 39.6 Mpa. The Langmuir model enables us to determine the equilibrium density of the monolayer of adsorbed gas to be 8.5% lower than that of liquid methane. We also identify the signatures of multilayer adsorption at the high pressure regime from 39.6 Mpa to 89.7 Mpa and use the Brunauer-Emmet-Teller (BET) theory to determine the number of adsorbed layers of methane gas. We show how these measurements help us differentiate the gas stored in the Vycor pore space into free and adsorbed fractions for the entire pressure range paving way for similar applications such as studying natural gas storage in gas shale rock or hydrogen storage in carbon nanotubes.

분자 모사를 이용한 탄소나노튜브의 수소 흡착 현상 분석

탄소나노튜브의 수소 저장소로써의 가능성을 평가하기 위한 분자 모사를 수행하였다. 일정한 온도와 압력에서 Grand canonical Monte Carlo 방법을 적용하여 탄소나노튜브에 수소가 흡착된 평형 상태를 구현하였다. Lennard-Jones 퍼텐셜 모델로부터 탄소나노튜브와 수소 분자 간 상호 작용 에너지를 계산 한 결과에 의하면 수소 분자는 나노튜브 외부보다 내부에 많은 양이 흡착되는 반면 흡착 강도는 외부가 높은 것으로 나타났다. 여러 가지 온도와 압력에 대해 흡착율을 검토하였으며, 200 K와 200 bar의 저온 고압 조건에서 약 2.5wt%의 흡착율을 나타내었다. Molecular simulation was performed to evaluate the possibility of hydrogen storage of carbon nanotubes. The equilibrium state of hydrogen adsorbed on carbon nanotubes was simulated by grand canonical Monte Carlo method at constant temperature and pressure. The interaction energy between hydrogen molecule and carbon nanotube was calculated by Lennard-Jones potential model. According to the interaction energy calculated, more hydrogen molecules were adsorbed on the inside than the outside of nanotubes. Whereas the adsorption strength was higher outside than inside. Adsorption capacity was investigated for various temperature and pressure. The maximum capacity of carbon nanotube for hydrogen storage was 2.5wt% at 200 K and 200 bar.

Designing novel nanoporous architectures of carbon nanotubes for hydrogen storage

A multi-technique theoretical approach was used to investigate hydrogen storage in a three-dimensional diamond-like architecture composed by interconnected carbon nanotubes (CNT). This is achieved with nodes formed by four nanotubes joined together by the inclusion of heptagonal rings placed appropriately. This novel nanoporous material, named Super Diamond has, by design, tunable pore size and exhibit large free volume and surface area, which can reach the values of 95% and 2535 g/m2 respectively. The interaction and the adsorption properties of this material with hydrogen were studied thoroughly via ab-initio and Grand Canonical Monte Carlo simulations. Our results show that a large pore Super Diamond can surpass the gravimetric capacity of 20% at 77 K and can reach the high value of 8% at room temperature.

Chemisorption, physisorption and hysteresis during hydrogen storage in carbon nanotubes

The question of chemisorption versus physisorption during hydrogen storage in carbon nanotubes (CNTs) is addressed experimentally. We utilize a powerful measurement technique based on a magnetic suspension balance coupled with a residual gas analyzer, and report new data for hydrogen sorption at pressures of up to 100 bar at 25 °C. The measured sorption capacity is less than 0.2 wt.%, and there is hysteresis in the sorption isotherms when multi-walled CNTs are exposed to hydrogen after pretreatment at elevated temperatures. The cause of the hysteresis is then studied, and is shown to be due to a combination of weak sorption – physisorption – and strong sorption – chemisorption – in the CNTs. Analysis of the experimental data enables us to calculate separately the individual hydrogen physisorption and chemisorption isotherms in CNTs that, to our knowledge, are reported for the first time here. The maximum measured hydrogen physisorption and chemisorption are 0.13 wt.% and 0.058 wt.%, respectively.

Carbon Nanotubes Used for Renewable Energy Applications and Environmental Protection/Remediation: A Review

Carbon nanotubes are surprisingly ubiquitous in their use for renewable energy applications as well as for environmental protection and remediation. Hence, this is the motivation for the current review, to investigate into their usefulness. The characteristic properties of these nanotubes are a result of their large surface areas, and their unique mechanical, electrical, and chemical properties, and in no small part, due to its relatively easy manufacturability. Research has been done using carbon nanotubes for hydrogen storage, although it does not seem logical that carbon nanotubes would be very useful for this purpose. Carbon nanotubes used for solar collectors are used mainly for their improved thermal and electrical conductivities. Organic solar cells do not have a long life since they deteriorate in the sun. Research into long-lasting, yet inexpensive organic solar cells is an active area, and should continue to be so for some time. Carbon nanotubes are activated by certain chemicals. They may be used to react with solids, liquids, and gases. Hence, they are employed for waste water treatment, liquid, and gaseous cleanup. They may be used to remove metals as well as life pathogens. As the number of new pollutants and pathogens entering the environment multiply, research should continue to study the use of carbon nanotubes with regards prevention and remediation.

Hydrogen Storage in Carbon Nanotubes Prepared by Using Copper Nanoparticles as Catalyst

carbon nanotubes were synthesized by pyroysis method using copper nanoparticles as catalyst. The structure, phase composition and hydrogen storage capacity were investigated by TEM, XRD spectra and Electrochemical System. The results show that the diameter of carbon nanotubes is 200-500nm, The P-C-T curve of adsorbing hydrogen of samples was measured in the pressure up to 12 MPa at room temperature. we show that a SWNT can strongly adsorb up to 8-wt% hydrogen. These results advance our fundamental understanding of dissociative adsorption of hydrogen in nanostructures and suggest new routes to better storage and catalyst materials.

Hydrogen storage in carbon nanotubes with Ni nanoparticles by electrochemical

In this paper, the electrochemical hydrogen storage in nanocomposite materials was studied. Multi-Walled Carbon Nanotubes (MWCNTs) electrode was prepared by mixing with special composite. The optimum ratio of MWCNTs was estimated 30-70% (w/w) in the composite material. MWCNTs were synthesized by Chemical vapor deposition (CVD). The nanocomposite was homogenized by microwave. Cyclic voltammetry (CV) was applied to study the behavior of electrode. Ni nanoparticles were electrodeposited on working electrodes via dualpulse method. Voltammograms indicated that, Ni nanoparticles have electrocatalytic effect on hydrogen storage capacity.

H2 adsorption mechanism in Mg modified multi-walled carbon nanotubes for hydrogen storage

Multi-walled carbon nanotubes (MWCNTs) with diameter of about 50 nm were synthesized using thermal chemical vapor deposition. We have investigated the influence of Mg doping to the MWCNTs on its hydrogen storage property. TEM micrographs showed that Mg was attached to the MWCNTs and discontinuous arrangement of the carbon walls was recognized in the MWCNTs. According to XPS and BET analyses, the surface functional groups and pore size of the Mg-MWCNTs are increased by interactions between the Mg and the MWCNT’s outer walls. The electrochemical discharging curves of the MWCNTs and Mg-doped MWCNTs revealed that the hydrogen storage capacity was 363 and 450 mAhg−1, respectively. Volumetric technique determined that the hydrogen storage capacity of the MWCNTs and Mg-MWCNTs was 0.7 and 1.5 wt%, respectively. There are likely a couple of mechanism for Mg metal that used as dopant to pure MWCNTs, one involves increasing of adsorption binding energy and desorption temperature due to increasing defect sites (oxygen functional groups), while the second explains by electron transfer from metal atoms to carbon atoms resulting in a considerable increase in both the adsorption binding energy and desorption temperature.