Synthesis and characterization of porous HKUST-1 metal organic frameworks for hydrogen storage

Hydrogen storage capacity has been investigated on a copper-based metal organic framework named HKUST-1 with fine structural analyses. The crystalline structure of HKUST-1 MOF has been confirmed from the powder X-ray diffraction and the average particle diameter has been found about 15–20 μm identified by FE-SEM. Nitrogen adsorption isotherms show that HKUST-1 MOF has approximately type-I isotherm with a BET specific surface area of 1055 m²g⁻¹. Hydrogen adsorption study shows that this material can store 0.47 wt.% of H₂ at 303 K and 35 bar. The existence of Cu (II) in crystalline framework of HKUST-1 MOF has been confirmed by pre-edge XANES spectra. The sharp feature at 8985.8 eV in XANES spectra represents the dipole-allowed electron transition from 1s to 4p_xy. In addition, EXAFS spectra indicate that HKUST-1 MOF structure has the Cu–O bond distance of 1.95 Å with a coordination number of 4.2.     

Li-decorated porous graphene as a high-performance hydrogen storage material: A first-principles study

Development of novel carbon-based nanoporous materials with high reversible capacity and excellent cycling stability is a hot topic in the field of hydrogen delivery and storage. In this work, first-principles calculations are carried out to discuss the hydrogen storage properties of Li-decorated porous graphene (Li-PG). The binding energies, electronic structures, storage capacities of hydrogen on different sites are investigated in details. The computational results show that with the increase of lithium doping concentration, the electron concentration of donor atoms exceeds the N_c value, and as a consequence, the PG changes from the p-type semiconductor to the n-type degenerate semiconductor. The maximum hydrogen adsorption configurations of H1a-H'1b and H2a-H'2b systems are obtained, and the average binding energy of per H₂ molecule is 0.245 eV and 0.263 eV, respectively. Furthermore, ab inito MD simulation results show that the H1-H'1 and H2-H'2 systems can hold up to sixteen and fifteen H₂ molecules, which corresponds to a hydrogen storage capacity of 10.89 wt% and 10.79 wt% at T = 300 K (no external pressure), respectively.     

Melaleuca bark based porous carbons for hydrogen storage

Typical porous carbons were obtained from waster biomass, melaleuca bark activated by potassium hydroxide (KOH), and characterized by XRD, SEM, TEM, FTIR, XPS and N₂-sorption. The different samples with tunable morphologies and texture were prepared by controlling synthesis reaction parameters. The resulting samples demonstrate both high surface area (up to 3170 m² g⁻¹) and large hydrogen storage capacity (4.08 wt% at 77 K and 10 bar), implying their great potential as hydrogen storage materials.     

Lithium hydrazide as a potential compound for hydrogen storage

The Metal–N–H system for hydrogen storage has been developed in recent years and is considered to be a promising solution. Here we report a potential compound for hydrogen storage, LiNHNH₂, which is a white solid with 8.0 mass% theoretical hydrogen content and can be synthesized from anhydrous hydrazine and n-butyllithium in diethyl ether. The thermodynamic behaviours and hydrogen storage properties of this compound were firstly investigated and are discussed in this paper. We demonstrate the decomposition pathway of LiNHNH₂ and reveal that an alkali metal hydride such as LiH can significantly increase the hydrogen desorption from LiNHNH₂. Moreover, LiNHNH₂ can also be used for destabilizing other hydrogen storage systems owing to its instability.     

Exfoliated MoS2 with porous graphene nanosheets for enhanced electrochemical hydrogen evolution

Porous graphene (P-rGO) was synthesized from graphene oxide (GO) via a one-pot calcination method with CO₂ as an activation agent at 800 °C. Due to the special porous structure, the surface area of P-rGO can be increased to ～759 m²/g. The P-rGO was then used as a support to incorporate with chemical exfoliated molybdenum disulfide (MoS₂) for the fabrication of MoS₂/P-rGO composite. Compared to bulk MoS₂, the exfoliated MoS₂ is in the 1T phase with a metallic property and smaller charge transfer resistance, thus has a better activity in electrochemical hydrogen evolution reaction (HER). The HER activity of 1T MoS₂ could be further increased after the combination with P-rGO. The overpotential of 1T MoS₂/P-rGO was only ～130 mV vs. RHE, and the corresponding Tafel slope was ～75 mV Dec^?1. The special porous structure and good electric conductivity of P-rGO decrease the charge transfer resistance of the composite without sheltering too many active sites of MoS₂, thus leading to the enhanced HER activity. As an efficient noble metal free HER catalyst, the 1T MoS₂/P-rGO has great potential for large-scale hydrogen production.     

Novel porous carbons synthesized from polymeric precursors for hydrogen storage

In this work, porous carbons were prepared from polymeric ion-exchangeable resin by a chemical activation method in order to obtain novel hydrogen storage materials, and the adsorption characteristics of the porous carbons were investigated. The textural properties were studied by BET and D–R methods with adsorption isotherms. The hydrogen storage behaviors of the porous carbons at 298 K and 100 bar were studied using a PCT apparatus. In the observed post-activation result, the hydrogen storage capacity was markedly improved. However, it was also found that the total amount of adsorption was not proportional to the specific surface area of the adsorbates. This indicates that hydrogen storage could be a function not only of specific surface area or total pore volume but also of microporevolume fraction or the average pore size of adsorbents.     

Addition of transition metals to lithium intercalated fullerides enhances hydrogen storage properties

We report an innovative synthetic strategy based on the solid state reaction of fullerene C₆₀ with lithium-transition metals alloys (platinum and palladium), which provides transition metal-decorated lithium intercalated fullerides, with improved hydrogen storage properties. Compounds with Li₆Pt_0.11C₆₀ and Li₆Pd_0.07C₆₀ stoichiometry were obtained and investigated with manometric/calorimetric techniques which showed an 18% increase of the final H₂ absorbed amount with respect to pure Li₆C₆₀ (5.9 wt% H₂) and an improved absorption process kinetic. The absorption mechanism was investigated with X-rays diffraction which allowed to identify the formation of the hydrofullerides. Scanning Electron Microscopy was applied to gain information on transition metal distribution and detected the presence of platinum and palladium aggregates which are shown to perform a surface catalytic activity towards hydrogen molecule dissociation process.     

Catenated metal-organic frameworks: Promising hydrogen purification materials and high hydrogen storage medium with further lithium doping

Based on the first-principles derived force fields and grand canonical Monte Carlo simulations, we find that the catenated metal-organic frameworks outperform the noncatenated structures, in terms of H₂ separation from other gases (CH₄, CO and CO₂) and H₂ adsorption by Li doping. A system utilizing IRMOF-11 (or IRMOF-13) for hydrogen separation and Li-doped IRMOF-9 for hydrogen storage is therefore proposed, with hydrogen uptake of 4.91 wt% and 36.6 g/L at 243 K and 100 bar for Li-doped IRMOF-9, which is close to the 2017 DOE target. It is promising to find appropriate microporous materials for hydrogen purification and storage at ambient conditions with structure catenated.     

Improved design of metal-organic frameworks for efficient hydrogen storage at ambient temperature: A multiscale theoretical investigation

A multiscale theoretical technique is used to examine the combination of different approaches for hydrogen storage enhancement in metal-organic frameworks at room temperature and high pressure by implementation lithium atoms in linkers. Accurate MP2 calculations are performed to obtain the hydrogen binding sites and parameters for the following grand canonical Monte Carlo (GCMC) simulations. GCMC calculations are employed to obtain the hydrogen uptake at different thermodynamic conditions. The results obtained demonstrate that the combination of different approaches can improve the hydrogen uptake significantly. The hydrogen content reaches 6.6 wt% at 300 K and 100 bar satisfying DOE storage targets (5.5 wt%).     

SANS characterization of porous magnesium for hydrogen storage

Porous magnesium was produced through the thermal decomposition of various additives in an effort to increase hydrogen storage capacity. Samples were characterized using SANS and different theoretical models were applied to the results and discussed. The polydisperse self-assembled (PSA) model was found to best represent the scattering from these materials as this model incorporates the polydispersity of the pores and allows for variations in structure factor. Pure magnesium produced using the same thermal method absorbed a negligible amount of hydrogen, and hydrogen uptake was found to increase with increasing porosity as determined using the PSA model. Maximum hydrogen uptake (1.3%) was found when 0.3% Cs₂CO₃ and 0.5% Ni were combined as an additive during thermal treatment. In addition, the development of porosity was found to promote hydrogen desorption at lower temperatures. SANS represents an indispensible method by which to characterize materials and the PSA model described in this work has the potential to be extremely useful in the characterisation of porous metallic systems.     

Degradation of biomass components to prepare porous carbon for exceptional hydrogen storage capacity

Porous carbon has been constructed in various strategies for hydrogen storage. In this work, a simple-effective strategy was proposed to transform sustainable biomass into porous carbon by degrade partial lignin and hemicellulose with Na₂SO₃ and NaOH aqueous mixture. This method collapses the biomass structure to provide more active sites, and also avoid the generation and accumulation of non-porous carbon nanosheets. As a result, the as-prepared sample possesses high specific surface area (2849 m² g^?1) and large pore volume (1.08 cm³ g^?1) concentrating almost completely on micropore. Benefit to these characteristics, the as-prepared sample exhibits appealing hydrogen storage capacity of 3.01 wt% at 77 K, 1 bar and 0.85 wt% at 298 K, 50 bar. The isosteric heat of hydrogen adsorption is as high as 8.0 kJ mol^?1, which is superior to the most biochars. This strategy is of great significance to the conversion of biomass and the preparation of high-performance hydrogen storage materials.     

A study on the hydrogen storage capacity of Ni-plated porous carbon nanofibers

In this study, we prepared highly porous carbon-nanofiber-supported nickel nanoparticles as a promising material for hydrogen storage. The porous carbons were activated at 1050 °C, and the nickel nanoparticles were loaded by an electroless metal-plating method. The textural properties of the porous carbon nanofibers were analyzed using N₂/77 K adsorption isotherms. The hydrogen storage capacity of the carbons was evaluated at 298 K and 100 bar. It was found that the amount of hydrogen stored was enhanced by increasing nickel content, showing 2.2 wt.% in the PCNF-Ni-40 sample (5.1 wt.% and 6.4% of nickel content and dispersion rate, respectively) owing to the effects of the spill-over of hydrogen molecules onto the metal–carbon interfaces. This result clearly indicates that the presence of highly dispersed nickel particles can enhance high-capacity hydrogen storage.     

Transition metal decorated covalent triazine-based frameworks as a capacity hydrogen storage medium

From ab initio density functional theory (DFT) calculations, the structural stability and hydrogen adsorption capacity of transition metal (TM, TM = Sc, Ti, V, Cr, Mn) decorated covalent triazine-based framework (CTF) are discussed. It is found that by calculation, these TM atoms can adsorb on the CTF sheet without clusters. The Sc, Ti, V, Cr and Mn decorated CTF are predicated to bind five, four, three, three and two of hydrogen molecules. We found that Sc and Ti decorated CTF are suitable candidates for effective reversible hydrogen storage at near ambient condition, whereas V, Cr and Mn decorated CTF are not promising materials due to too large average bind energies per hydrogen molecule.     

Electronic properties and hydrogen storage application of designed porous nanotubes from a polyphenylene network

Based on a polyphenylene network, a series of porous graphene nanotubes (PGNTs) are created and optimised via density functional theory calculations. The calculated band dispersion of the two-dimensional porous graphene can be tuned by rolling it into nanotube form. To explore the energy application of PGNTs, we studied H₂ adsorptions on metal (Li, Ca, and Na) decorated structures of PGNTs as well as B-substituted PGNTs. The results indicate that both the curvature effect and B substitution can strengthen the metal binding and prevent the metal atoms from clustering. Particularly for H₂ adsorption, modification of the electronic property by the curvature effect is beneficial to provide more accessible space, leading to much higher adsorption energies of H₂ on PGNTs than that on planar porous graphene, which is promising for the practical application of hydrogen storage.     

High hydrogen storage capacity of rice hull based porous carbon

A kind of porous carbon with high specific surface area (approximately 4000 m²/g) was prepared from rice hull through carbonization and sodium hydroxide activation. The effects of preparation parameters on the characteristics of the porous carbon were studied. The properties of these porous carbon samples were investigated by X-ray diffraction and scanning electron microscope (SEM) and Fourier transform infrared spectroscopy. The rice hull based porous carbon exhibits high hydrogen storage capacity of 7.7 wt% at 77 K and 1.2 MPa.     

Effect of nitrogen induced defects in Li dispersed graphene on hydrogen storage

As a candidate for hydrogen storage medium, Li decorated graphene with experimentally realizable nitrogen defects was investigated for geometric stability and hydrogen capacity using density functional theory (DFT) calculations. Among the three types of defective structures, it is expected that Li metal atoms are well dispersed on the graphene sheets with pyridinic and pyrrolic defects without clustering as the bond strength of Li on pyridinic and pyrrolic N-doped graphene layers is higher than the cohesive energy of the Li metal bulk. The two stable structures were found to exhibit hydrogen uptake ability up to three H₂ per Li atom. The binding energies of the hydrogen molecules for these structures were in the range of 0.12–0.20 eV/H₂. These results demonstrate that a Li/N-doped graphene system could be used as a hydrogen storage material.     

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.     

Enhanced room-temperature hydrogen storage capacity in Pt-loaded graphene oxide/HKUST-1 composites

Series of Pt-loaded graphene oxide (GO)/HKUST-1 composites were synthesized by the reaction between Pt@GO and precursors of HKUST-1. The parent materials and composites have been characterized by powder X-ray diffraction (XRD), Infrared (IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and gas adsorption analyzer. The XRD and IR analysis showed that the incorporation of Pt@GO did not prevent the formation of HKUST-1 units. SEM, TEM and EDS results revealed that Pt nanoparticles were well-dispersive and anchored tightly into composites. Meanwhile, the percentage of Pt@GO has an obvious effect on morphologies, crystallinities and surface areas of composites. More importantly, the significant enhancement of hydrogen storage capacity at ambient temperature for the composite with low Pt@GO content can be ascribed to the hydrogen spillover mechanism in such system.