Synthesis,characterization of hexagonal boron nitride nanoparticles decorated halloysite nanoclay composite and its application as hydrogen storage medium

In the emerging front of research, much attention is focused on the usage of hydrogen as a promising alternative energy carrier that can potentially replace fossil fuels. Conversely, the realization of hydrogen as an energy carrier becomes impounded since the light weight and compact hydrogen storage materials are still prerequisites for hydrogen fuel cell technology. In the present study, the performance of nanoclay composites composed of acid treated halloysite clay nanotubes (A-HNTs) and hexagonal boron nitride nanoparticles (h-BN) are investigated towards hydrogen storage. where facile ultrasonic approach was adopted. The prepared A-HNT–h-BN nanoclay composites subjected to various characterization techniques such as X-ray Diffraction (XRD), micro–Raman Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), UV–Visible Diffuse Reflectance Spectroscopy (DRS), Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray Spectroscopy (EDX) and High Resolution Transmission Electron Microscopy (HRTEM) with Selected Area Transmission Electron Diffraction (SAED). The presence of h-BN nanoparticles at the surface of A-HNTs can be seen from HRTEM images and these findings are supported by XRD, FTIR and Raman results. Hydrogen adsorption studies are performed using Sieverts-like hydrogenation setup. A 2.88 wt% of hydrogen storage capacity and 100% desorption were achieved for the A-HNT–5wt% h-BN nanoclay composite at 50 °C. The adsorbed hydrogen possess the average binding energy of 0.33 eV, which lies in the recommended range (0.2–0.4 eV) for fuel cell applications. So it is expected that A-HNT–h-BN nanoclay composites will serve as a better hydrogen storage material for fuel cell applications in the near future.     

Superior hydrogen storage capacity of Vanadium decorated biphenylene (Bi+V): A DFT study

Herein, the hydrogen storage competency of vanadium-decorated biphenylene (Bi+V) has been investigated using Density Functional Theory simulations. The metal atom interacts with biphenylene with a binding energy value of −2.49 eV because of charge transfer between V 3d and C 2p orbitals. The structure and electronic properties are studied in terms of adsorption energy values, the spin-polarized partial density of states (PDOS), band structure plots, and charge transfer analysis. The Kubas-type interactions lead to average hydrogen adsorption energy values of −0.51 eV/H₂ which fulfills DOE-US criteria (0.2–0.7 eV/H₂). The diffusion energy barrier value of 1.75 eV lowers the chances of metal clustering. The complex binds 5H₂ on each V-atom resulting in a storage capacity of 7.52 wt% with an average desorption temperature of 595.96 K. The ab-initio molecular dynamics (AIMD) and phonon dispersions validates structural integrity at higher temperatures suggesting the excellent storage properties of this material at room temperature.     

Hydrogenation properties of MgH2- x wt% AC (x=0, 5, 10, 15) nanocomposites

Magnesium is considered as a promising candidate for hydrogen storage due to its high storage capacity (theoretical value ~ 7.6 wt%). Nanocomposites of Magnesium hydride and activated charcoal (AC) were prepared using ball milling method. These nanocomposites were characterized by XRD, TGA, DSC and SEM techniques. The TGA analysis show that the MgH₂-5 wt% AC nanocomposite exhibits dehydrogenation capacity of 7.45 wt% (which is very close to the storage capacity of MgH₂) and starts release of hydrogen at 140 °C temperature. The results from the Kissinger plot from DSC result showed that the activation energy for hydrogen desorption of MgH₂ with 5 wt% AC was reduced compared to those of as-received.     

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.     

Computational evaluation of Ca-decorated nanoporous CN monolayers as high capacity and reversible hydrogen storage media

Developing novel materials with high-capacity and reversible properties for storing hydrogen (H₂) is crucial for energy treatments. We here investigated comprehensively the H₂ storage performance of the Ca-decorated g-CN (Ca@CN) monolayers using first-principles calculations. The Ca atoms can be uniformly decorated into the center of the pores of g-CN monolayers without aggregation. The Ca@CN monolayer has an average H₂ adsorption energy of around 0.163–0.228 eV as well as high H₂ storage capacity of 10.1 wt%. The stabilities of the H₂ adsorption systems are confirmed by high hardness and low electrophilicity. The temperature of desorption is anticipated to be near the room temperature and ideal for fuel cell devices. The thermodynamic analysis along with desorption temperature reveal that the Ca@CN monolayer has promising potentials as reversible and high capacity hydrogen storage materials (HSM), which will motivate experimental efforts to synthesize the high-efficient HSM.     

Li-decorated double vacancy graphene for hydrogen storage application: A first principles study

Lithium decoration is an effective strategy for improving the hydrogen adsorption binding energy and the storage capacity in carbon nanostructures. Here, it is shown that Li-decorated double carbon vacancy graphene (DVG) can be used as an efficient hydrogen storage medium by means of Density Functional Theory (DFT) based calculations. The Li binding energy in DVG is 4.04 eV, which is much higher than that of pristine graphene. A maximum of four hydrogen molecules adsorb on Li decorated on one side of DVG and this leads to a gravimetric storage capacity of 3.89 wt% with an average adsorption binding energy of 0.23 eV/H₂. When Li is decorated on both sides of DVG, the gravimetric storage capacity reaches 7.26 wt% with a binding energy of 0.26 eV/H₂ which shows that desorption would take place at ambient conditions.     

Hydrogen storage performance of lithium borohydride decorated activated hexagonal boron nitride nanocomposite for fuel cell applications

A safe and cost effective material for hydrogen storage is indispensable for developing hydrogen fuel cell technology to reach its greater heights. The present work deals with hydrogen storage performance of lithium borohydride decorated activated hexagonal boron nitride (LiBH₄@Ah-BN) nanocomposite. where a facile chemical impregnation method was adopted for the preparation of LiBH₄@Ah-BN nanocomposite. The prepared nanocomposite was subjected to various characterization techniques such as X-ray Diffraction (XRD), Micro-Raman Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDX), Brunauer–Emmett–Teller (BET) Studies, CHNS-Elemental Analysis and Thermo Gravimetric Analysis (TGA). From BET studies, it is confirmed that, there is an enhancement in the specific surface area of LiBH₄@Ah-BN nanocomposite (122 m²/g) compared to Ah-BN (70 m²/g). The hydrogen storage ability was examined using a Sieverts-like hydrogenation setup. An excellent hydrogen storage capacity of 2.3 wt% at 100 °C was noticed for LiBH₄@Ah-BN nanocomposite. The TGA study indicates the dehydrogenation profile of stored hydrogen in the range of 110–150 °C. The binding energy of stored hydrogen (0.31 eV) lies in recommended range of US-DOE 2020 targets for fuel cell applications. The present investigation demonstrates the preparation of LiBH₄@Ah-BN nanocomposite based hydrogen storage medium which has remarkable cycling stability and hydrogen storage capacity. Hence these desirable traits make LiBH₄@Ah-BN nanocomposite as a potential hydrogen storage candidate for fuel cell applications in near future.     

Nanostructured hydrogen storage materials prepared by high-energy reactive ball milling of magnesium and ferrovanadium

Hydrogen storage nanocomposites prepared by high energy reactive ball milling of magnesium and vanadium alloys in hydrogen (HRBM) are characterised by exceptionally fast hydrogenation rates and a significantly decreased hydride decomposition temperature. Replacement of vanadium in these materials with vanadium-rich Ferrovanadium (FeV, V80Fe20) is very cost efficient and is suggested as a durable way towards large scale applications of Mg-based hydrogen storage materials. The current work presents the results of the experimental study of Mg–(FeV) hydrogen storage nanocomposites prepared by HRBM of Mg powder and FeV (0–50 mol.%). The additives of FeV were shown to improve hydrogen sorption performance of Mg including facilitation of the hydrogenation during the HRBM and improvements of the dehydrogenation/re-hydrogenation kinetics. The improvements resemble the behaviour of pure vanadium metal, and the Mg–(FeV) nanocomposites exhibited a good stability of the hydrogen sorption performance during hydrogen absorption – desorption cycling at T = 350 °C caused by a stability of the cycling performance of the nanostructured FeV acting as a catalyst. Further improvement of the cycle stability including the increase of the reversible hydrogen storage capacity and acceleration of H₂ absorption kinetics during the cycling was observed for the composites containing carbon additives (activated carbon, graphite or multi-walled carbon nanotubes; 5 wt%), with the best performance achieved for activated carbon.     

High-capacity hydrogen storage in Li-decorated (AlN)n (n = 12, 24, 36) nanocages

The capability of Li-decorated (AlN)_n (n = 12, 24, 36) nanocages for hydrogen storage has been studied by using density functional theory (DFT) with the generalized gradient approximation (GGA). It is found that each Al atom is capable of binding one H₂ molecule up to a gravimetric density of hydrogen storage of 4.7 wt% with an average binding energy of 0.189, 0.154, and 0.144 eV/H₂ in the pristine (AlN)_n (n = 12, 24, 36) nanocages, respectively. Further, we find that Li atoms can be preferentially decorated on the top of N atoms in (AlN)_n (n = 12, 24, 36) nanocages without clustering, and up to two H₂ molecules can bind to each Li atom with an average binding energy of 0.145, 0.154, 0.102 eV/H₂ in the Li_n(AlN)_n (n = 12, 24, 36) nanocages, respectively. Both the polarization of the H₂ molecules and the hybridization of the Li-2p orbitals with the H-s orbitals contribute to the H₂ adsorption on the Li atoms. Thus, the Li-decorated (AlN)_n (n = 12, 24, 36) nanocages can store hydrogen up to 7.7 wt%, approaching the U.S. Department of Energy (DOE) target of 9 wt% by the year 2015, and the average binding energies of H₂ molecules lying in the range of 0.1–0.2 eV/H₂ are favorable for the reversible hydrogen adsorption/desorption at ambient conditions. It is also pointed out that when allowed to interact with each other, the agglomeration of Li-decorated (AlN)_n nanocages would lower the hydrogen storage capacity.     

Hydrogen uptake of manganese oxide-multiwalled carbon nanotube composites

Hydrogen uptake of pristine multi-walled carbon nanotubes is increased more than three-fold at 298 K and hydrogen pressure of 4.0 MPa, upon addition of hydrogen spillover catalyst manganese oxide, from 0.26 to 0.94 wt%. Simple and convenient in situ reduction method is used to prepare Mn-oxide/MWCNTs composite. XRD, FESEM, and TEM demonstrates nanostructural characterization of pristine MWCNTs and composite. TGA analysis of Mn-oxide/MWCNTs composites showed a single monotonous fall related to MWCNTs gasification. Enhancement of hydrogen storage capacity of composite is attributed to spillover mechanism owing to decoration of Mn-oxide nanoparticles on outer surface of MWCNTs. Hydrogen uptake follows monotonous dependence on hydrogen pressure. Oxide-MWCNTs composite not only shows high hydrogen storage capacity as compared to pristine, but also exhibit significant cyclic stability upon successive adsorption–desorption cycles.     

Ameliorated microstructure and hydrogen absorption/desorption properties of novel Mg–Ni–La alloy doped with MWCNTs and Co nanoparticles

Based on the positive influence of carbon materials and transition metals, a new type of Mg-based composites with particle size of ～800 nm has been designed by doping hydrogenated Mg–Ni–La alloy with multi-walled carbon nanotubes (MWCNTs) and/or Co nanoparticles. The microstructures, temperature related hydrogen absorption/desorption kinetics and dehydrogenation mechanisms are investigated in detail. The results demonstrate that MWCNTs and Co dispersedly distribute on the surface of Mg–Ni–La particles after high-energy ball milling due to powders’ repeated cold welding and tearing. The experimental samples exhibit improved hydrogen storage behaviors and the addition of MWCNTs and Co can further accelerate the de-/hydriding kinetics. For instance, the Mg–Ni–La–Co sample can absorb 3.63 wt% H₂ within 40 min at 343 K. Dehydrogenation analyses demonstrate that the positive effect of MWCNTs is more obvious than that of Co nanoparticles for the experimental samples. The addition of MWCNTs and Co leads to the average dehydrogenation activation energy of experimental samples decreasing to 82.1 and 84.5 kJ mol^?1, respectively, indicating a significant decrease of dehydrogenation energy barriers. In addition, analyses of dehydrogenation mechanisms indicate that the rate-limiting steps vary with the addition of MWCTNs and Co nanoparticles.     

Graphitic carbon nitride (g-C3N4) decorated with Yttrium as potential hydrogen storage material: Acumen from quantum simulations

With the aid of the state-of-the-art Density Functional Theory simulations, triazine-like graphitic carbon nitride or g-C₃N₄ (abbreviated as gCN hereafter) nanosheet decorated with Y has been explored for reversible hydrogen storage applications in light fuel cell vehicles. The Y atom is found to bind strongly with gCN (binding energy ～ ?6.85 eV), can reversibly store 9 H₂ with an average adsorption energy of ?0.331 eV/H₂, an average desorption temperature of 384.24 K, and a storage capacity of 8.55% by weight, optimum for fuel cell application as prescribed by the Department of Energy. The bonding of Y on gCN involves a charge transfer from Y 4d orbitals to C and N 2p orbitals, whereas the adsorption of H₂ is due to Kubas interactions involving net charge transfer from Y 4d orbital to H 1s orbital. We have computed the diffusion energy barrier for Y atoms as 3.07 eV, which may prevent metal-metal clustering. Further, ab-initio molecular dynamics simulation has been performed to check the structural stability of the present system. The system is found to be stable at 500 K with different concentrations of Y doping. The present system with the appropriate average adsorption energy per H₂, suitable desorption temperature, and structural stability at higher temperatures is promising for onboard light fuel cell applications.     

Yttrium doped covalent triazine frameworks as promising reversible hydrogen storage material: DFT investigations

Through Density Functional Theory (DFT) simulations, we have explored the possibility of yttrium (Y) doped Triazine (Covalent Triazine Frameworks i.e., CTF-1) to be a promising material for reversible hydrogen storage. We have found that Y atom strongly bonded on Triazine surface can adsorb at the most 7H₂ molecules with an average binding energy of ?0.33 eV/H₂. This boosts the storage capacity of the system to 7.3 wt% which is well above the minimum requirement of 6.5 wt% for efficient storage of hydrogen as stipulated by the US Department of Energy (DoE). The structural integrity over and above the desorption temperature (420 K) has been entrenched through Molecular Dynamics simulations and the investigation of metal-metal clustering has been corroborated through diffusion energy barrier computation. The mechanism of interactions between Y and Triazine as well as between H₂ molecules and Y doped Triazine has been explored via analyses of the partial density of states, charge density, and Bader charge. It has been perceived that the interplay of H₂ molecules with Y on Triazine is Kubas-type of interaction. The above-mentioned analysis and outcomes make us highly optimistic that Y doped Triazine could be employed as reversible hydrogen storage material which can act as an environmentally friendly alternate fuel for transport applications.     

Improved hydrogen adsorption of ZnO doped multi-walled carbon nanotubes

Hydrogen storage is still one of the most important problems to improve hydrogen energy usage widespread. New materials capable of storing hydrogen with high efficiency must be introduced to overcome this problem. In recent years, addition of metals or inorganic compounds to multiwalled carbon nanotubes (MWCNTs) has been generally used for hydrogen uptake studies to enhance adsorption property of the nanotubes. In this study, Zinc oxide (ZnO) nanoparticles doped MWCNTs (ZnO-MWCNTs) have been produced as new reversible hydrogen storage materials, and we have investigated characterization of ZnO-MWCNTs by XRD, SEM, TGA, TEM and BET analyses. The functionalized MWCNTs and ZnO doped MWCNTs were subjected to hydrogenation step by dynamic gas sorption analyser under pressure of 5–50 bar. The hydrogen uptake capacities of the materials under different pressures were measured gravimetrically. It was indicated that by controlling the pressures for hydrogenation of ZnO-MWCNTs induces the spillover of ZnO nanoparticles in the layer of MWCNTs which in return with high hydrogen adsorption capacity. Consequently, the hydrogen adsorption of the functionalized MWCNTs (f-MWCNTs) and the ZnO-MWCNTs were achieved to be 1.05 wt% and 2.7091 wt% under pressure of 50 bar as maximum.     

Novel permeable material “yttrium decorated zeolite templated carbon” for hydrogen storage: Perspectives from density functional theory

The hydrogen storage capacity of a novel permeable material viz Yttrium (Y) decorated zeolite templated carbon (ZTC) has been investigated using ab-initio DFT based simulations. The study reveals that each Y atom bonded on ZTC can attach at the most of 7H₂ molecules with average binding energy of ?0.35 eV/H_2. The gravimetric hydrogen storage capacity of ZTC with full decoration of Y atom comes about to 8.61 wt% which is sufficiently higher than the limit of 6.5 wt% set by the energy department of the United States of America. The desorption temperature of the system is 437 K. The stability of the structure over such an elevated temperature has been ensured via molecular dynamics (MD) simulations. The stability of the structure at room temperature and presence of sufficient energy barrier for the diffusion of Y atom signifies that the chances of metal-metal clustering are negligible. It has been discerned that it is the Kubas interaction which plays the key role in the interaction between Y and H₂ molecules. The outcomes show that ZTC adorned with Y is a capable material for hydrogen storage which will inspire the instrumentalists to fabricate ZTC based fuel cell device.     

Enhancement of hydrogen storage capacity on co-functionalized GaS monolayer under external electric field

Hydrogen storage properties of co-functionalized 2D GaS monolayer have been systematically investigated by first-principles calculations. The strength of the binding energy of hydrogen (H₂) molecules to the pristine GaS surface shows the physisorption interactions. Co-functionalized GaS sheet by Li, Na, K and Ca atoms enhanced the capacity of binding energies of hydrogen and strength of hydrogen storage considerably. Besides, DFT calculations show that there is no structural deformation during H₂ desorption from co-functionalized GaS surface. The binding energies of per H₂ molecules is found to be 0.077 eV for pristine GaS surface and 0.064 eV–0.37 eV with the co-functionalization of GaS surface. Additionally, in the presence of applied external electric field enhanced the strength of binding energies and it is found to be 0.09 eV/H₂ for pristine GaS case and 0.19 eV/H₂ to 0.38 eV/H₂ for co-functionalized GaS surface. Among the studied GaS monolayer is found to be the superior candidate for hydrogen storage purposes. The theoretical studies suggest that the electronic properties of the 2D GaS monolayer show the electrostatic behavior of hydrogen molecules which confirms by the interactions between adatoms and hydrogen molecules before and after hydrogen adsorption.     

Theoretical study on the structural evolution and hydrogen storage in NbHn (n = 2–15) clusters

Niobium hydrides are attractive superconductors. Exploring the formation process of niobium hydrides is essential to elucidate the mechanism of superconductivity. One of the key issues is to clarify the atomic stacking patterns of Nb and H atoms, i.e., the structural evolution of Nb–H clusters. Here, the low-energy structural isomers of NbH_n (n = 2–15) clusters are determined using the CALYPSO method combined with density functional theory calculations. Geometries were fully optimized at the B3LYP/LANL2DZ/6–311++G(d) level of theory to determine global minimum structures for each size. The results indicate that NbH₁₃ is the most stable cluster in this size range. The 4d atomic orbital of Nb and the hydrogen 1s atomic orbital participate largely to the internal binding of the NbH₁₃ cluster. They hydrogen storage density and adsorption energy of this cluster are calculated to be 12.4 wt% and 2.58 eV, respectively. The high hydrogen storage density, suitable hydrogen adsorption energy, and high stability of NbH₁₃ shows promise as a hydrogen storage material. These results provide fundamental information for further design of metal hydrogen storage materials.     

High-capacity hydrogen storage in zirconium decorated zeolite templated carbon: Predictions from DFT simulations

The hydrogen (H₂) storage capacity of Zirconium (Zr) decorated zeolite templated carbon (ZTC) has been investigated using sophisticated density functional theory (DFT) simulations. The analysis shows that the Zr atom gets bonded with ZTC strongly with binding energy (BE) of ?3.92 eV due to electron transfer from Zr 4d orbital to C 2p orbital of ZTC. Each Zr atom on ZTC can attach 7H₂ molecules with average binding energy of ?0.433 eV/H₂ providing gravimetric wt% of 9.24, substantially above the limit of 6.5 wt% set by the DoE of the United States of America. The H₂ molecules are involved via Kubas interaction with Zr atom, which involves the charge transfer between Zr 4d orbital and H 1s orbital with interaction energy higher than physisorption but lower than chemisorption. The structural integrity of the system is confirmed via molecular dynamics (MD) simulations at room temperature and at highest desorption temperature of 500 K. We have investigated the chances of metal clustering by computing diffusion energy (E_D) barrier for the movement of Zr atom, and we obtained via calculation, we can infer that the presence of E_D barrier of ～2.36 eV may prevent the possibility. As the system ZTC has been synthesized, Zr doped ZTC is stable, existence of sufficient diffusion barrier prevents the clustering and adsorption energy and wt% of H₂ are within the range prescribed by DoE, we feel that Zr decorated ZTC can be fabricated as promising hydrogen storage material for fuel cell applications.