Lithium decoration of boron-doped hybrid fullerenes and nanotubes as a novel 3D architecture for enhanced hydrogen storage: A DFT study

A three dimensional (3D) dumbbell-like nanostructure composed by interconnected fullerenes and nanotubes with Lithium decoration and boron-doping (37Li@C₁₃₉B₃₁) has been proposed in virtue of density functional theory (DFT) and first-principles molecular dynamics (MD) simulations which shows excellent geometric and thermal stability. First-principles calculations are performed to investigate the hydrogen adsorption onto the 37Li@C₁₃₉B₃₁. The results indicate that B substitution can improve the metal binding and the average binding energy of 37 adsorbed Li atoms on the C₁₃₉B₃₁ (2.79 eV) is higher than the cohesive energy of bulk Li (1.63 eV) suppressing the clustering. Meanwhile, the H₂ storage gravimetric density of 178H₂@37Li@C₁₃₉B₃₁ reaches up to 15.9 wt% higher than the year 2020 target from the US department of energy (DOE). The average adsorption energy of H₂ molecules falls in a desirable range of 0.18–0.27 eV. Moreover, grand canonical ensemble Monte Carlo (GCMC) simulations reveal that at room temperature the hydrogen gravimetric density (HGD) adsorbed on 37Li@C₁₃₉B₃₁ reaches up to 11.6 wt% at 100 bars higher than the DOE 2020 target. Our multiscale simulations indicate that our proposed nanostructure provides a promising medium for hydrogen storage.     

DFT study of hydrogen storage on the metallic decoration of boron substitution on zeolite templated carbon vacancy

This work reports DFT calculations for the assessment of metallic decoration of boron substitution Zeolite Templated Carbon vacancy for hydrogen adsorption. The boron substitution on Zeolite Templated Carbon vacancy is characterized by the formation of pentagonal and heptagonal rings. Moreover, the boron substitution can be considered as a promising way for hydrogen storage, this way boron substitution is used on Zeolite Templated Carbon vacancy in order to create an active site for metallic decoration. Once that we develop a Boron substitution on Zeolite Templated Carbon vacancy, the decoration with Lithium, Sodium, and Calcium atoms is also carried out. The analysis reveals that the Na decoration has the best performance for hydrogen storage. The results show that boron substitution on Zeolite Templated Carbon vacancy decorated with 3 Sodium atoms can adsorb up to fifteen hydrogen molecules (5 hydrogen molecules per Sodium atom), this gives a gravimetric storage capacity of 6.55 % wt., which is enough for meeting DOE gravimetric targets. In addition, the average binding energies and adsorption energies are calculated in the range 0.2298–0.2144 eV/H₂, which constitute desirable energies for hydrogen adsorption. Besides, the hydrogen adsorption process is carried out by electrostatic interaction between the Na cation and the induced H₂ dipole. The calculation performed in this work reveals that the boron substitution on Zeolite Templated Carbon vacancy decorated with Na atoms is a good candidate as a medium for hydrogen storage.     

Enhancing hydrogen storage on carbon nanotubes via hybrid chemical etching and Pt decoration employing supercritical carbon dioxide fluid

Acidic etching and Pt particle decoration were applied to modify the hydrogen absorption behavior of carbon nanotubes (CNTs). Two different acidic solutions, namely H₂SO₄/HNO₃ and FeSO₄/H₂SO₄/H₂O₂, were used for etching treatment. A novel electroless deposition process, incorporating supercritical CO₂ (sc-CO₂) fluid, was used to decorate finely-dispersed nano-sized Pt particles on CNTs. The hydrogen storage capacities of various modified CNTs were measured by using a high pressure thermal gravimetric microbalance (HPTGA). The experimental results showed that acidic etching could increase the surface defect density and lead to open-up of the caps of CNTs, resulting in an increase in the active adsorption site for physical sorption of H_2. The electroless deposition of nano-Pt particles on CNTs, using conventional electrolyte, could promote chemical sorption of hydrogen via spillover mechanism. By employing sc-CO₂ bath, the Pt particle size became much finer and more uniformly distributed on the surfaces of CNTs, giving rise to a high hydrogen storage capacity. When a hybrid process including sc-CO₂ Pt decoration following acidic etching was applied to modify CNTs, a substantial enhancement of hydrogen storage capacity (about 2.7 wt%) was observed.     

A DFT study of hydrogen adsorption on Pt modified carbon nanocone structures: Effects of modification and inclination of angles

The adsorption of hydrogen molecule on Pt modified carbon nanocone (CNC) structures was investigated by density functional method. Pt atom was modified by both doping and decorating on the structures with 180⁰, 240⁰ and 300⁰ inclination angles of the CNC. The interactions of the hydrogen molecule on the ring and top sites of these modified structures were explored. Effect of doping and decorating of Pt atom on CNC structures has been also investigated. The adsorption enthalpy and Gibbs free energy values of the structure formed by doping the Pt atom at the ring are −118.4 and −85.3 kJ/mol, respectively. With the increase of the angle of inclination, the hydrogen interaction decreased at the ring and increased at the top. According to the results of this study, it is predicted that CNCs modified with Pt atom can be a promising hydrogen storage material under ambient conditions.     

Hydrogen storage performance of platinum supported carbon nanohorns: A DFT study of reaction mechanisms,thermodynamics, and kinetics

Platinum (Pt) is one of a robust hydrogen dissociative catalyst. However, the migration of dissociated hydrogens from Pt nanoparticles to carbon supports such as graphene and carbon nanotube are energetically unfavorable reactions. To enhance the hydrogen storage via migration mechanism, carbon nanohorn is applied as a support for Pt nanoparticles (Pt and Pt₄). The H₂ storage performance of Pt and Pt₄ supported on the mono-vacancy carbon nanohorn (vNH) has been investigated by using density functional theory calculations. The Pt and Pt₄ firmly deposit at the vacancy site through the three strong Pt–C bonds with binding energies about ?7.0 eV, which can prevent the metal desorption and migration. The mechanism of H₂ storage starts with H₂ adsorption followed by H₂ spillover reaction. The calculation results reveal that the supported Pt nanoparticles are the active sites for H₂ dissociative adsorption while the high curvature surface of carbon nanohorn is the active area for accommodating the migrated H atoms from the spillover reaction. Remarkably, the hydrogen spillover reactions over Pt– and Pt₄-supported on vNHs in this study are spontaneous at room temperature with highly exothermic reaction energy. The fundamental understanding obtained from this study is beneficial for further design and synthesis of high-performance materials for H₂ storage applications.     

Adsorption of hydrogen molecule on alkali metal-decorated hydrogen boride nanotubes: A DFT study

Adsorption of Li, Na, and K atom on surfaces of armchair (5,5) and zigzag (10,0) hydrogen boride nanotubes (HBNTs) was investigated using the periodic-DFT method. It was found that the average diameter (5,5) HBNT is shorter than the (10,0) HBNT by 1.246 Å and the (5,5) HBNT is more stable than the (10,0) HBNT by 0.991 eV. Adsorption strength of the (5,5) HBNT on alkali metals was found to be higher than the (10,0) HBNT. Adsorption abilities of H₂ on the (5,5) HBNT and (5,5) HBNT are in the same order: Li > Na > K. The adsorption energies of H₂ on Li-, Na-, and K-(5,5) HBNTs are −0.242, −0.165, and −0.121 eV, respectively, and on Li-, Na-, and K-(10,0) HBNTs are −0.277, −0.168, and −0.094 eV, respectively. The Li-HBNTs, Li-(5,5) HBNT, and (10,0) HBNT are the highest adsorption abilities on H₂ adsorption and the most significant change of metal charges. Therefore, the Li-(5,5) HBNT and (10,0) HBNT used as H₂ storage materials were suggested.     

Vanadium carbide coating as hydrogen permeation barrier: A DFT study

Density functional calculations are used to investigate hydrogen (H) behaviors in vanadium carbide (VC). Molecular H₂ dissociation, atomic H diffusion and penetration are analyzed using the transition state theory. H₂ prefers to be close to the surface as physical adsorption, providing an environment conducive for further dissociation, and dissociates into atomic H adsorbed at the top C atom sites with co-adsorption state. The dissociation rate on the surface is mainly limited by the temperature-controlled activation energy barrier. The adsorptivity of atomic H by the surface tends to decrease as increasing of H coverage. For atomic H penetration through the surface, a significantly endothermic energy barrier and the low diffusion prefactor suggest that the main resistant effect of H permeation takes place at the surface. Energetic, vibrational, electronic consequences, and quantum effects on the H behaviors are discussed thoroughly. Our theoretical investigation indicates VC is a promising hydrogen permeation barrier.     

Experimental investigation of Pt membrane on ZrVFe hydrogen storage alloy for hydrogen elimination performance

Hydrogen safety is a primary obstacle to the widespread use of hydrogen energy, and the risk of hydrogen utilization can be avoided by eliminating unnecessary hydrogen immediately. Here we report a new kind of hydrogen elimination catalyst based on ZrVFe hydrogen storage alloy supported Pt. The chemical reduction temperature and the Pt loading have a great influence on the hydrogen elimination performance. When the reduction temperature is 60 °C and the Pt loading is 2 wt%, the ZrVFe/Pt catalyst exhibits excellent hydrogen elimination ability at 2–20 vol% hydrogen concentration, especially the efficiency of hydrogen elimination at 20 vol% hydrogen concentration is as high as 99%. The hydrogen adsorption capacity of the ZrVFe/Pt catalyst was 13 times higher than that of the commonly used metal carrier FeCrAl/Pt catalyst. This work paves a new direction for the design and on-going development of hydrogen elimination catalyst for hydrogen energy applications.     

Y-decorated MoS2 monolayer for promising hydrogen storage: A DFT study

The potential hydrogen storage performance of the constructed Y-decorated MoS₂ was investigated via first-principles density functional theory (DFT) calculations. The Y could be stably decorated on the MoS₂ monolayer with adsorption energy being ?4.82 eV, the absolute value of which was higher than the cohesive energy of bulk Y. The introduced H₂ interacted strongly with the Y-decorated MoS₂ with an elongated bond length and reasonable adsorption energy being 0.792 Å and ?0.904 eV, respectively. There would be four H₂ in maximum adsorbed and stored on the Y-decorated MoS₂ with average adsorption energy being ?0.387 eV. Moreover, the hydrogen gravimetric capacity of the MoS₂ with full Y coverage on each side could be improved to be 4.56 wt% with average adsorption energy being ?0.295 eV. Our study revealed that the MoS₂ decorated with Y could be a potential material to effectively store H₂ with promising gravimetric density.     

Investigation of the effect of oxygen-containing groups on the hydrogen adsorption behavior of CSCNTs using density functional theory

The hydrogen adsorption behavior of cup-stacked carbon nanotubes (CSCNTs) decorated by –CO, –OH and –COOH at the edge of conical graphene layer (CGL) is investigated using density functional theory (DFT). The results reveal that the edge of pristine CGL hardly adsorbs hydrogen molecule due to the positive potential. When oxygen-containing group is decorated, the negative potential of O atom adsorbs hydrogen molecule strongly and the adsorption energy increases from 5.19 to 5.58, 6.25 and 6.53 kJ/mol following the order of –COOH > –OH > –CO. When two –COOH are decorated next to each other, the equilibrium position of hydrogen molecule deviates from the extended surface of CGL in an angle of 38°. When they are decorated next but one, the deviation angle of hydrogen molecule is reduced to 12°, so that the adsorption surface is expanded and the steric hindrance is avoided.     

Li-decorated B2O as potential candidates for hydrogen storage: A DFT simulations study

Two-dimensional (2D) B₂O monolayer is considered as a potential hydrogen storage material owing to its lower mass density and high surface-to-volume ratio. The binding between H₂ molecules and B₂O monolayer proceeds through physisorption and the interaction is very weak, it is important to improve it through appropriate materials design. In this work, based on density functional theory (DFT) calculations, we have investigated the hydrogen storage properties of Lithium (Li) functionalized B₂O monolayer. The B₂O monolayer decorated by Li atoms can effectively improve the hydrogen storage capacity. It is found that each Li atom on B₂O monolayer can adsorb up to four H₂ molecules with a desirable average adsorption energy (E_ave) of 0.18 eV/H₂. In the case of fully loaded, forming B₃₂O₁₆Li₉H₇₂ compound, the hydrogen storage density is up to 9.8 wt%. Additionally, ab initio molecular dynamics (AIMD) calculations results show that Li-decorated B₂O monolayer has good reversible adsorption performance for H₂ molecules. Furthermore, the Bader charge and density of states (DOS) analysis demonstrate H₂ molecules are physically absorbed on the Li atoms via the electrostatic interactions. This study suggests that Li-decorated B₂O monolayer can be a promising hydrogen storage material.     

Pt doped (8,0) single wall carbon nanotube as hydrogen sensor: A density functional theory study

In this study, it has been investigated the use of Pt doped carbon nanotube for the hydrogen gas sensor at room temperature and compared with available experimental literature data. The WB97XD method with 6-31G(d,p) and LanL2DZ basis sets have been utilized. The charge distributions obtained for the structures show that charge transfer is occurred from the adsorbed hydrogen molecule to the Pt atom of carbon nanotube structure as an electron acceptor. The HOMO–LUMO gap of the Pt doped SWCNT decreased with the adsorption of hydrogen molecule. As a conclusion, the electrical conductivity of Pt doped (8,0) SWCNT cluster increased after a hydrogen molecule adsorption. Accordingly, Pt doped (8,0) SWCNT has potential for sensing of hydrogen gas. Theoretical (DFT) results are in well agreement with available experimental literature data that was reported a chip sensor loaded Pt-CNT gave highest response coefficient for H₂ gas sensing.     

Graphene pillared with hybrid fullerene and nanotube as a novel 3D framework for hydrogen storage: A DFT and GCMC study

A new-type 3D pillared graphene framework with hybrid fullerene and nanotube pillars (PGF-hFN) has been created depended on density functional theory (DFT) and first-principles molecular dynamics simulations (MD). It is proved to have excellent thermal structural stability. The average adsorption energy of Li is 2.77 eV much higher than the metal cohesive energy excluding lithium aggregation problem. From DFT calculations, for Li-decorated B-doped PGF-hFN, the hydrogen gravimetric density (HGD) is as high as 12.92 wt% and the according volumetric uptake is 96.4 g/L with an average adsorption energy of 0.195 eV per H₂. Further grand canonical Monte Carlo (GCMC) simulations predict 7.2 wt% in excess HGD and 53.8 g/L in excess volumetric hydrogen density at near ambient temperature (233 K) and 100 bars with the ideal adsorption enthalpy which have exceeded the 2020 the U.S. Department of Energy (DOE) ultimate target for mobile applications. Our multiscale theoretical simulations indicate this new pillared structure should be a promising carrier accessible for sorption of hydrogen molecules.     

A DFT study on the hydrogen storage performance of MoS2 monolayers doped with group 8B transition metals

The adsorption of hydrogen (H₂) molecules on MoS₂ monolayers doped with Fe, Co, Ni, Ru, Rh, Pd, Os, Ir or Pt was calculated via first-principle density functional theory (DFT). The H₂ was found to interact most strongly with the MoS₂ doped with Os with a higher adsorption energy of ?1.103 eV. Investigations of the adsorptions of two to five H₂ molecules on Os-doped MoS₂ monolayers indicate that there are at most four H₂ interacting stably with the substrate with a promising average adsorption energy of ?0.792 eV. Molecular dynamics simulations also confirmed that the four H₂ molecules can still be reasonably adsorbed and stored on the Os-doped MoS₂ monolayer with a comparable average adsorption energy of ?0.713 eV at 300 K. This study indicates that MoS₂ monolayer doped with Os is a promising substrate to interact strongly with H₂ and can be applied to effectively store H₂ at room temperature.     

Interferents for hydrogen storage on a graphene sheet decorated with nickel: A DFT study

In the present work, the decoration of a graphene sheet with nickel is considered as a hydrogen storage material by means of density functional theory calculations. A number of factors relevant for the handling and operation of this material were analyzed. This includes the interaction with potentially interfering chemicals, hydride formation and the hydrogen storage capacity. The present results show that unless the access of oxygen to the surface is restricted, its strong bond to the decorated systems will preclude the practical use for hydrogen storage. In the best case, the energy required to replace an adsorbed oxygen molecule by hydrogen is of the order of 1.7 eV, something that indicates the severe problem that the presence of oxygen represents for this type of systems.     

Effect of transition metal (Cu and Pt) doping/ co-doping on hydrogen gas sensing capability of graphene: A DFT study

Carbon nano-materials are found to demonstrate good hydrogen gas sensing capability and researchers are trying their modified derivatives for enhanced sensitivity. Studies have confirmed improvement in sensing performance of graphene when doped with N or Si or Sb. However, effect of the doping of graphene with transition metals of comparable size on its hydrogen sensing properties has not yet been studied. In the present study, we investigated the sensitivity of pristine graphene, Pt-doped graphene; Cu-doped graphene and Pt–Cu co-doped graphene surface towards hydrogen molecule adsorption utilizing density functional theory (DFT) by ab initio method. The adsorption energies for the optimized geometries have been calculated to probe the suitability and effectiveness of the modified graphene structures for Hydrogen sensing. In addition, the electronic properties for instance charge transfer analysis, band gap and density of states have also been taken into consideration. The reactivity of graphene surface for hydrogen adsorption was found to be greatly enhanced with Pt–Cu co-doped graphene surface as demonstrated by the adsorption energies and electronic properties.     

A DFT study on production of hydrogen from biomass-derived formic acid catalyzed by Pt–TiO2

Production and storage of hydrogen from biomass component by using efficient catalysts, it can finely maintain the future energy of the world and reduce human dependence on fossil fuels. Hydrogen production mechanism via formic acid decomposition on the TiO₂ anatase (101) and Pt–TiO₂ surfaces in the solvent (water) and gaseous conditions performed by density functional theory (DFT) calculation. Regarding to the proposed routes, decomposition reaction of formic acid on TiO₂ surface incline to be followed by second route in the water which is acceptable in terms of energy. Decomposition reaction of formic acid on Pt–TiO₂ surface prefers to do it via first route (rotation around CO bond of formic acid) in solvent conditions. Furthermore, adsorption energy and geometric changes of formic acid on TiO₂ anatase (101) and Pt–TiO₂ surface in gaseous and solvent conditions were clearly studied.     

First-principles study on hydrogen storage by graphitic carbon nitride nanotubes

First-principles calculations based on density functional theory were carried out to investigate the hydrogen storage capacity of graphitic carbon nitride nanotubes. Graphitic carbon nitride nanotubes could be attractive hydrogen sorbent for two reasons: firstly, its porous structure allows easy access of hydrogen into the interior of the nanotubes; and secondly, the doubly bonded nitrogen at its pore edges provides active sites for either the adsorption of hydrogen (chemically and physically), or functionalization with metal catalysts. Our calculations show that an isolated nanotube can uptake up to 4.66 wt. % hydrogen, with an average overall hydrogen adsorption energy of about −0.22 eV per H atom. In the form of a bulk bundle, the hydrogen storage capacity is enhanced due to the increased availability of space among the tubes. We predict that the hydrogen storage capacity in the bundle is at least 5.45 wt. %. Importantly, hydrogen molecules can easily access the tube’s interior due to the low energy barrier (∼0.54 eV) for their passage through the pores, indicating a fast uptake rate at relatively low pressure and temperature. Our findings show that graphitic carbon nitride nanotubes should be applicable to practical hydrogen storage because of the high gravimetric capacity and fast uptake rate.