Hydrogen storage properties of highly cross-linked polymers derived from chlorinated polypropylene and polyethylenimine

Highly cross-linked polymer derived from chlorinated polypropylene (CPP) grafted with polyethylenimine (PEI) was synthesized by hydrothermal amination reaction. The influence of different reaction conditions on the structure and properties of highly cross-linked polymer was investigated. The structures of the polymers named CPP-g-PEI were characterized by Fourier transform infrared (FT-IR) spectroscopy, elemental analysis (EA), ¹³C solid-state NMR (¹³C NMR), thermogravimetric analysis (TG), scanning electron microscopy (SEM), transmission electron microscope (TEM), powder X-ray diffraction (PXRD) and nitrogen sorption technique. CPP-g-PEI had honeycomb-like pores with an average size of between 5.37 and 13.54 nm and was thermally stable up to 250 °C. CPP-g-PEI was amorphous porous polymer with some spherulites. The N content of CPP-g-PEI increased and the Cl content of CPP-g-PEI decreased after hydrothermal amination reaction. The hydrogen storage properties of different CPP-g-PEI samples were determined by a hydrogen storage analyzer. Among all samples, hydrogen storage capacity of CPP-g-PEI at 100 °C and triethylamine solvent (CPP-g-PEI-2) achieved the highest hydrogen uptake 11.26 wt% at 77 K, 5 MPa. In addition, OH⁻ type CPP-g-PEI (CPP-g-PEI_OH−) exhibited a hydrogen uptake of 2.47 wt% at 300 K, 5 MPa. BET specific surface area of the sample was not directly associated with hydrogen storage capacity. Hydrogen adsorption enthalpy of CPP-g-PEI-2 was calculated by the Arrhenius equation to be 38.79 kJ/mol and the adsorption process of CPP-g-PEI was investigated to be reversible physical adsorption.     

Hydrogen storage properties of the novel crosslinked UiO-66-(OH)2

Metal organic frameworks (MOF) are a type of nanoporous materials with large specific surface area, which are especially suitable for gas separation and storage. In this work, we report a new approach of crosslinking UiO-66-(OH)₂ to enhance its hydrogen storage capacity. UiO-66-(OH)₂ was synthesized using hafnium tetrachloride (HfCl₄) and 2, 5-dihydroxyterephthalic acid (DTPA) through a canonical modulated hydrothermal method (MHT), followed by a post-synthesis modification, which is to form a crosslinking structure inside the porous structure of UiO-66-(OH)₂. During the modification process, the phenolic hydroxyl groups on the UiO-66-(OH)₂ reacted with methanal, and HCl aqueous solution and triethylamine served as catalyst (the products denoted as UiO-66-H and UiO-66-T, respectively). Powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), ¹³C nuclear magnetic resonance spectroscopy (¹³C NMR) proved that the crosslinking was formed. The BET specific surface area and the average adsorption pore size of UiO-66-H and UiO-66-T significantly increased after modification. The hydrogen storage capacity of UiO-66-H reached a maximum of 3.37 wt% (16.87 mmol/g) at 77 K, 2 MPa. Hydrogen adsorption enthalpy of UiO-66-T was 0.986 kJ/mol, which was higher than that of UiO-66-(OH)₂ (0.695 kJ/mol). This work shows that UiO-66-(OH)₂ is a promising candidate for potential application in high-performance hydrogen storage.     

Integration of hydrogenation and dehydrogenation based on dibenzyltoluene as liquid organic hydrogen energy carrier

The heat transfer oil dibenzyltoluene (DBT) offered an intriguing approach for the scattered storage of renewable excess energy as a novel Liquid Organic Hydrogen Carrier (LOHC). The integration of hydrogenation and dehydrogenation in H0-DBT/H18-DBT pairs demonstrated that the feasibility of hydrogenation and dehydrogenation reaction conducted in one reactor with the same catalyst, which would be proposed to simplify the hydrogen storage process. The optimal reaction temperature based on the inhibition of ring opening and cracking was investigated combined with the ¹H NMR analysis. Meanwhile, the ideal catalyst 3 wt% Pt/Al₂O₃ for high hydrogen storage efficiency was screened out. Cycle tests of hydrogenation and dehydrogenation integration reaction had shown that the hydrogen storage efficiency was 84.6% after five cycle tests. The integration of hydrogenation and dehydrogenation reaction based on DBT exhibited the ideal thermal stability, which demonstrated its potential as a reversible H₂ carrier.     

Micro-mechanism study on the effect of O2 poisoned ZrCo surface on hydrogen absorption performance

Hydrogen storage alloys are usually susceptible to poisoning by O₂, CO, CO₂, etc., which decreases the hydrogen storage property sharply. In this paper, the adsorption characteristics of oxygen on the ZrCo(110) surface were investigated, and the effect of oxygen occupying an active site on the surface on the hydrogen adsorption behavior was discussed. The results show that the dissociation barrier of H₂ is increased by more than 26% after O occupies the active sites on the ZrCo(110) surface, and the probability of H₂ adsorption and dissociation decreases significantly. The adsorption energy of H atoms on the O–ZrCo(110) surface decreased by 18–56%, and the adsorption stability of H decreased. In addition, H atom diffusion on the surface and into bulk are prevented with higher reaction energetic barriers by O occupying active sites. Eventually, the ability of the ZrCo surface to adsorb hydrogen is seriously reduced.     

Remarkable isosteric heat of hydrogen adsorption on Cu(I)-exchanged SSZ-39

Hydrogen storage capacity on Cu(I)-exchanged SSZ-39 (AEI), -SSZ-13 (CHA) and Ultra stable-Y (US–Y, FAU) at temperatures between 279 K and 304 K are investigated. The gravimetric hydrogen storage capacity values reaching 83 μmol H₂ g⁻¹ (at 279 K and 1 bar) are found to be comparable with the highest adsorption capacity values reported on metal-organic frameworks. The volumetric hydrogen storage capacity values; on the other hand, are found to be more than three times of those reported on metal-organic frameworks (0.57 g/L on Cu(I)-SSZ-39 at 1 bar and 296 K vs. ca. 0.18 g/L on Co₂(m-dobdc) at 1 bar and 298 K (Kapelewski MT, Runčevski T, Tarver JD, Jiang HZH, Hurst KE, Parilla PA et al. Record High Hydrogen Storage Capacity in the Metal-Organic Framework Ni₂(m-dobdc) at Near-Ambient Temperatures. Chem Mater 2018; 30:8179–89)). The isosteric heat of adsorption values are calculated to be between 80 kJ mol⁻¹ and 49 kJ mol⁻¹ on Cu(I)-SSZ-39 and between 22 kJ mol⁻¹ and 15 kJ mol⁻¹ on Cu(I)-US-Y indicating H₂ adsorption mainly at Cu(I) cations located at the eight-membered rings on Cu(I)-SSZ-39 and at six-membered rings on Cu(I)-US-Y. Hydrogen adsorption experiments performed at 77 K showed higher adsorption capacity values for Cu(I)-SSZ-39 at 1 bar, but Cu(I)-US-Y showed potential for hydrogen storage at higher pressure values.     

Plumbene: A next generation hydrogen storage medium

Plumbene, a recently discovered 2D material, has been examined for hydrogen storage. First principles calculations have been performed to investigate the hydrogen adsorption on pristine plumbene monolayer. The hydrogen molecule prefers to adsorb on three adsorption sites, i.e. H (hollow-site), T (top-site) and B (bond-site), of plumbene surface with desired adsorption energy. The adsorption energy is highest (−149 meV) at hollow site and lowest (−104 meV) at bond site. One side hydrogen decorated plumbene exhibit 3.37 wt% Hydrogen Gravimetric Density (HGD). Whereas 6.74 wt% (HGD), with the average adsorption energy of −117 meV/H_2, has been achieved in both side hydrogen decorated plumbene monolayer. Applied electric field can effectively controls the adsorption and desorption processes. Positive electric field makes the adsorption strong while the negative electric field results in weakening of hydrogen adsorption. It means electric field act as a switch to store and release hydrogen with good control and usage selectivity. Present study reveals that the plumbene is a strong candidate for hydrogen storage to meet the desired target of HGD suggested by U.S. Department of Energy by the year 2021.     

Pd‐Ni/Cd loaded PPy/Ti composite electrode: Synthesis,characterization, and application for hydrogen storage

A wide compositional range of Pd‐Ni/Cd on polypyrrole (PPy)‐modified Ti plates (Pd‐Ni/Cd/PPy/Ti) was fabricated via electrochemical deposition. The hydrogen absorption properties of the prepared Pd‐Ni/Cd/PPy/Ti electrodes were evaluated using cyclic voltammetry and chronoamperometry in acidic media. The optimal Pd₃₆‐Ni₇/Cd₅₇/PPy/Ti electrode achieved a hydrogen storage capacity of 331.3 mC cm^?2 mg^?1 and an H/Pd ratio of 0.77. The enhancement of the hydrogen storage was attributed to a synergistic effect between the Pd‐Ni/Cd catalysts. The surface morphology, crystallinity, and chemical composition of the Pd‐Ni/Cd/PPy/Ti electrode were characterized using scanning electron microscope (SEM), X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS), respectively. Hydrogen spillover occurred on the trimetallic catalysts, and secondary hydrogen spillover occurred on the PPy/Ti support. The enhanced hydrogen sorption capacity was due to both the synergistic effect of the trimetallic catalysts and the assistance of PPy, making Pd‐Ni/Cd/PPy/Ti a promising hydrogen storage material.     

Importance of clay-H2 interactions for large-scale underground hydrogen storage

Underground hydrogen storage is considered an option for large-scale green hydrogen storage. Among different geological storage types, depleted oil/gas fields and saline aquifers stand out. In these cases, hydrogen will be prevented from leaking back to the surface by a tight caprock seal. It is therefore essential to understand hydrogen interactions with shale-type caprocks. To this end, natural pure montmorillonite clay was exposed to hydrogen gas at different pressures (0–50 bar) and temperatures (77, 195, 303 K) to acquire data on its adsorption capacity related to UHS and caprock saturation. Montmorillonite was chosen because of its large specific surface area enabling quantification of the adsorption process. Hydrogen adsorption was successfully fitted with a Langmuir isotherm model and yielded small partition coefficients indicating that hydrogen does not preferentially adsorb to the clay surface. Adsorption on montmorillonite goes back to weak physisorption as inferred from minor negative changes in the enthalpy of reaction (−790 J/mol), derived from an Excel Solver approach to the van't Hoff equation. Based on own as well as literature values, adsorption capacities, which were originally reported as mol/kg or wt%, are recast as hydrogen volume adsorbed per specific surface area (μL/m²). The acquired range is surprisingly narrow, with values ranging from 3 to 6 μL/m², and indicates the normalised volume of hydrogen that can be expected to remain in the shale-type caprock after injected hydrogen migrated upwards through the porous reservoir. This ‘residual’ caprock saturation with hydrogen can be further restrained by considering the geothermal gradient and its effect on the molar volume of hydrogen. The experimental results presented here recommend injecting hydrogen deeper rather than shallower as pressure and temperature work in favour of increased storage volumes and decreased hydrogen loss through clay adsorption in the caprock.     

Adsorption and compression contributions to hydrogen storage in activated anthracites

We prepared activated carbons (ACs) that are among the best adsorbents for hydrogen storage. These ACs were prepared from anthracites and have surface areas (S_BET) as high as 2772 m² g⁻¹. Anthracites activated with KOH presented the highest adsorption capacities with a maximum of 5.3 wt.% at 77 K and 4 MPa. Non-linearity between hydrogen uptake at 77 K and pore texture was confirmed, as soon as their S_BET exceeded the theoretical limiting value of (geometrical) surface area, i.e., S_BET > 2630 m² g⁻¹. We separated adsorption and compression contributions to total hydrogen storage. The amount of hydrogen stored is significantly increased by adsorption only at moderate pressure: 3 MPa and 0.15 MPa at 298 and 77 K, respectively. Hydrogen adsorption on ACs at high pressure, above 30 MPa at 298 K and 8 MPa at 77 K, has not interest because more gas can be stored by simply compression in the same tank volume.     

Fundamentals of hydrogen storage processes over Ru/SiO2 and Ru/Vulcan

Hydrogen adsorption and desorption over Ru/SiO₂ and Ru/Vulcan are investigated in terms of hydrogen storage and release characteristics by both dynamic and static experiments. Ru particle dispersions as a function of metal loading were determined by HR-TEM and volumetric chemisorption experiments. Vulcan was more accommodating for spillover hydrogen than SiO₂. High Ru dispersions, i.e., small particle sizes, favored the amount of hydrogen spillover to Vulcan, as revealed by temperature programmed desorption (TPD) of hydrogen. TPD of hydrogen under He flow experiments over Ru/SiO₂ and Ru/Vulcan materials revealed a low temperature process (up to 200 °C) attributed to desorption of weakly bound hydrogen from Ru metal surface. A high temperature process (above 450 °C) was attributed to diffusion of hydrogen from the support to the Ru particle and desorption at the Ru sites. Hydrogen adsorbs strongly on Ru metal, as indicated by the initial heats of H₂ adsorption measured as 100 kJ/mol over 1 wt% Ru/Vulcan by adsorption calorimetry. At higher coverages, heat of adsorption of hydrogen was measured as 10 kJ/mol. Low heat of adsorption of hydrogen at high coverages indicate multilayer weak adsorption of hydrogen over the storage material, which can desorb at lower temperatures.     

Hydrogen adsorption properties of Ag decorated TiO2 nanomaterials

In this work, we present the synthesis of Ag doped TiO₂ materials. The products are characterized by powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, nitrogen adsorption, and hydrogen adsorption. The Ag/TiO₂ materials exhibit 3.65 times higher in hydrogen adsorption capability compared with the non-doped TiO₂ materials thank to the existence of Ti³⁺ species, which are Kubas-type hydrogen adsorption centers, and the Ag nanoparticles which provide spillover effects. We believe that this is the first time that both Kubas-type adsorption and spillover are exploited in the design of novel hydrogen storage materials.     

Stabilized Li-decoration and enhanced hydrogen storage on reduced graphene oxides

Hydrogen storage properties of Li-decorated graphene oxides containing epoxy and hydroxyl groups are studied by using density functional theory. The Li atoms form Li₄O/Li₃OH clusters and are anchored strongly on the graphene surface with binding energies of −3.20 and −2.84 eV. The clusters transfer electrons to the graphene substrate, and the Li atoms exist as Li⁺ cations with strong adsorption ability for H₂ molecules. Each Li atom can adsorb at least 2H₂ molecules with adsorption energies greater than −0.20 eV/H₂. The hydrogen storage properties of Li-decorated graphene at different oxidation degrees are studied. The computations show that the adsorption energy of H₂ is −0.22 eV/H₂ and the hydrogen storage capacity is 6.04 wt% at the oxidation ratio O/C = 1/16. When the O/C ratio is 1:8, the storage capacity reaches 10.26 wt% and the adsorption energy is −0.15 eV/H₂. These results suggest that reversible hydrogen storage with high recycling capacities at ambient temperature can be realized through light-metal decoration on reduced graphene oxides.     

Hydrogen storage on cation-decorated biphenylene carbon and nitrogenated holey graphene

Hydrogen storage on cation-decorated biphenylene carbon (BPC) and nitrogenated holey graphene (C₂N) layered materials are addressed by dispersion-corrected density functional theory calculations. Maximum storage capacity and adsorption energy of a gas-phase H₂ monolayer adsorbed on both sides of (Li⁺, Na⁺, Mg²⁺, Ca²⁺)-doped layers are investigated. We find that cations distribute homogeneously on BPC and C₂N with a maximum densities of 1.9 and 1.7 ion/nm², respectively. The H₂ adsorption on cation-decorated BPC shows binding energies that vary from ?0.14 to ?0.26 eV/H₂, depending on whether the cation is single or double charged, where the storage capacity are calculated to be around 10 wt%. Whereas, for cation-doped C₂N, the H₂ binding energies vary from ?0.11 to ?0.31 eV/H₂, with storage capacity between 7.3 and 8.8 wt%. Our results suggest that cation-doped C₂N is the most stable material, providing both reversibility and high capacity for hydrogen storage at operational conditions.     

Grand canonical Monte Carlo simulations of hydrogen adsorption in carbon aerogels

Hydrogen storage plays a fundamental role in the future hydrogen energy system, and carbon aerogel is one of the most potential hydrogen storage materials because of its high gravimetric and volumetric density on hydrogen adsorption. In this paper, the amorphous structure of carbon, obtained by a numerical simulation process by using the molecular dynamic and Monte Carlo methods, as well as the primary unit method, was intercepted as a sphere structure for numerical annealing to build a carbon nanosphere, which serves as the basic unit to reconstruct the carbon aerogel's skeleton by the Diffusion Limited Cluster Aggregation (DLCA) method. The hydrogen adsorption in carbon aerogel was simulated by using the self-coding parallel grand canonical Monte Carlo (GCMC) method. The influences of particle diameter, density, temperature, pressure, and specific surface area on the hydrogen adsorbing capacity in carbon aerogel were analyzed in detail. The results showed that the carbon aerogel's hydrogen storage capacity with a specific surface area of 2680 m²/g could reach 4.52 wt % at 77 K and 3.0 MPa.     

Electrochemical study of hydrogen diffusion behavior in Mg2Ni-TYPE hydrogen storage alloy electrodes

Hydrogen diffusion behavior in Mg₂Ni-type hydrogen storage alloy electrodes was characterized by using both potentiostatic polarization method, based on a spherical diffusion model, and electrochemical impedance spectroscopy (EIS) technique. The values of the diffusion coefficients of hydrogen in Mg₂Ni and Mg_1.9V_0.1Ni_0.8Al_0.2 are 1.2×10⁻¹¹ ∼ 1.57×10⁻¹⁰ and 3.1 ∼ 7.6×10⁻⁹ cm²/s, respectively. The values of diffusion coefficients decline notably with the increase in depth of discharge (DOD). The decay rate of diffusion coefficient in Mg₂Ni with DOD is much quicker than that in Mg_1.9V_0.1Ni_0.8Al_0.2. The experimental results suggested that the substitutions of V and Al for Mg and Ni in Mg₂Ni could significantly improve the hydrogen diffusion performance in this alloy and thus substantially increase discharge capacity of the electrode. © 1998 International Association for Hydrogen Energy     

Hydrogen adsorption on graphene,hexagonal boron nitride,and graphene-like boron nitride-carbon heterostructures: A comparative theoretical study

The results of DFT and ab initio calculations of the hydrogen physisorption on graphene, hexagonal boron nitride (h-BN), and a graphene-like boron nitride-carbon heterostructure (GBNCH) are discussed. PBE-D3, B3LYP-D3 as well as MP2 methods were employed in calculating the adsorption energies (Ea) of a hydrogen molecule to the appropriate structure and the optimal distances between them. Six adsorption sites were examined, and it is demonstrated that the ‘hollow’ sites are favorable for hydrogen adsorption. It was established that GBNCH exhibits increased Ea values in comparison with graphene and h-BN. Hydrogen adsorption isotherms at different temperatures were obtained using grand canonical Monte-Carlo simulations, and it was shown that GBNCH reveals advanced adsorption properties in comparison with its counterparts. The usage of GBNCHs for hydrogen storage is also discussed.     

Pore-scale imaging of hydrogen displacement and trapping in porous media

Hydrogen can act as an energy store to balance supply and demand in the renewable energy sector. Hydrogen storage in subsurface porous media could deliver high storage capacities but the volume of recoverable hydrogen is unknown. We imaged the displacement and capillary trapping of hydrogen by brine in a Clashach sandstone core at 2–7 MPa pore fluid pressure using X-ray computed microtomography. Hydrogen saturation obtained during drainage at capillary numbers of <10^?7 was ～50% of the pore volume and independent of the pore fluid pressure. Hydrogen recovery during secondary imbibition at a capillary number of 2.4 × 10^?6 systematically decreased with pressure, with 80%, 78% and 57% of the initial hydrogen recovered at 2, 5 and 7 MPa, respectively. Injection of brine at increasing capillary numbers up to 9.4 × 10^?6 increased hydrogen recovery. Based on these results, we recommend more shallow, lower pressure sites for future hydrogen storage operations in porous media.     

Investigation of graphene oxide-hydrogen interaction using in-situ X-ray diffraction studies

Hydrogen is one of the alternatives as clean fuel for our growing demands for energy. However, its storage for practical applications is a challenge due to low energy density. The interaction mechanism between the hydrogen gas and the host involved plays a vital role to explore its potential application as hydrogen storage material. So, in the present work, we have studied the interaction of Graphene oxide with hydrogen gas at different pressures varying from 70 mbar to 900 mbar at room temperature using reliable in-situ X-ray diffraction technique. XRD patterns showed that the hydrogen gas induced strain up to ～6.3% in GO films for 1% and 10% hydrogen atmosphere. The interaction mechanism was studied qualitatively using Raman spectroscopy and Fourier transform infra-red (FTIR) spectroscopy. Elastic recoil detection analysis (ERDA) technique was employed to determine the concentration of hydrogen in GO film which increased from ～1.7 × 10²² atoms/cc (for pristine GO) to ～ 9.5 × 10²² atoms/cc after exposing to 100% hydrogen environment at 900 mbar pressure.     

Simulation of hydrogen thermal desorption and stability titanium hydrides TiHx

Hydrogen behavior in metals and alloys is of great importance since the hydrogen-metal systems used for absorption of nuclear radiation in thermonuclear energy production. Titanium hydride (TiH²) employed widely as a material for hydrogen storage due to its high capacity for hydrogen isotopes.The hydrogen thermal desorption of titanium hydrides with different concentrations is studied by density functional theory methods for determining the cohesion energy of H in TiH_x as a function of the hydrogen concentration, and stability TiH_x sample with high-level H is determined. For macro-kinetic simulation of hydrogen behavior in TiH_x we use the open hydrodynamic package OpenFOAM. Using such simulations, we can model the hydrogen thermal desorption under the action of an ion beam.     

Hydrogen uptake of high surface area-activated carbons doped with nitrogen

Three activated carbons (ACs) having apparent surface areas higher than 2500 m²/g were doped with nitrogen by treatment with urea at 623 K under air flow. Nitrogen contents as high as 15.1 wt.% were obtained, but resulting in decreased surface areas and pore volumes. Hydrogen storage capacities of ACs before and after nitrogen doping were measured at 77 K and up to 8 MPa. After doping, the hydrogen uptake was lower due to the corresponding decrease of surface area. Statistical, ANOVA, analysis of the relevancy of surface area and nitrogen content on hydrogen storage at 77 K was carried out, taking into account our data and those data available in the open literature. We concluded that surface area controls hydrogen adsorption and nitrogen content is not a relevant parameter.