Molecular dynamics simulation of H2 in amorphous polyethylene system: H2 diffusion in various PE matrices and bubbling during rapid depressurization

Polyethylene (PE) is a candidate liner material for Type IV storage devices. In this case, all-atom molecular dynamics simulations are employed to study the properties of Polyethylene with the presence of H₂, including tensile properties, glass transition, diffusion in different PE and bubbling during rapid depressurization. The presence of H₂ deteriorates the polyethylene matrix's tensile performance and decreases the glass transition temperature. The branch, side chain and small molecules promote the diffusion of H₂ in the amorphous region by introducing more free volume below Tg. With a sufficient length, the length of polymer chain has minor effect on the diffusion of H₂. Graphene, as a 2D reinforcement, could decrease the diffusion of H₂ but suffers from poor interfacial bonding. Finally, H₂ bubble(s) formed from the over-saturated H₂ molecule and were observed in both the exclusive and free volume and stabilised at low pressure during rapid depressurization. According to the result obtained in this work, branchless HDPE is expected to give superior performance while the viscosity, which is important during processing, could be tailored by molecular weight. Processing technique leads to orientation is preferred, such as injection moulding.     

Raman spectroscopy study of molecular hydrogen solubility in water at high pressure

We have measured the Raman spectra of gaseous molecular hydrogen dissolved in liquid water at room temperature and as a function of pressure. Vibrational spectra of molecular hydrogen have been clearly detected. Band intensities and profiles have been carefully measured using, for calibration purposes, the water OH stretching band. From the measured intensities of the Raman band, we have obtained the behavior of hydrogen concentration in the liquid water, as a function of the gas partial pressure. The observed behavior is presented and compared to Henry’s law predictions. Additionally, we present a detailed analysis of the spectral band features from which important information on the interaction of hydrogen with water molecules could be derived.     

Modification of COF-108 via impregnation/functionalization and Li-doping for hydrogen storage at ambient temperature

Post-modification approaches such as Li-doping, impregnation, and functionalization are promising methods to enhance H₂ adsorption in metal–organic frameworks (MOFs) and covalent-organic frameworks (COFs). In this work, we propose a two-step method to modify COF-108 with the aim to enhance its hydrogen storage capacity at ambient temperature. First, we geometrically modified COF-108 through C₆₀ impregnation or aromatic ring grafting. Subsequently, we surface doped the modified COF-108 with Li atoms. COF-108 is the lightest 3D crystalline material ever reported and it is a promising H₂ storage material. Our grand canonical Monte Carlo (GCMC) simulations demonstrated that the combination of Li-doping with C₆₀ impregnation or aromatic ring grafting can potentially increase the volumetric H₂ adsorption capacity of COF-108 to reach a total H₂ adsorption capacity close to the U.S. DOE target. One of the Li-doped C₆₀-impregnated (Li₆C₆₀) COF-108 (with 8 Li₆C₆₀ moieties impregnated) showed an absolute H₂ uptake beyond the 2010 DOE target (45.6 mg/g and 28.6 g/cm³) at 233 K and 100 bar. Impregnation of C₆₀ and/or grafting of aromatic rings not only increased the density of doped Li in the modified COF-108 but also created more overlapped potential interaction with H₂, which resulted in higher number of H₂ adsorption sites per unit volume as compared to the unmodified material.     

The optimal adsorption pathway of H2 molecules on Ti-Acetylene/ ethylene compounds: A DFT study

Ti-Acetylene/Ethylene complexes were used to be considered as a potential high capacity hydrogen storage media by physisorption. Here, special attentions have been paid to the optimal adsorption pathway of H₂ molecules on TiC₂H₂/TiC₂H₄ compounds by using CCSD(T) and B3LYP functionals. An interesting result is that some most stable configurations of TiC₂H₂(nH₂)(n = 1–7) complexes are not the structures coordinated by H₂ molecules but plausible hydrogenation intermediates. Based on the potential energy profiles and MD simulations, the optimal adsorption pathway is considered as TiC₂H₂(T) → 1b → 2c → 2b → 2a → 3b → 3a → 4a → 5a → 5b → 6d → C₂H₆ + Ti(H₂)₅ for TiC₂H₂ and TiC₂H₄(1c) → 2a → 3b → 3a → 4a → 5a → 5b → 6d → C₂H₆+Ti(H₂)₅ for TiC₂H₄. It indicates that the adsorptions of H₂ molecules on TiC₂H₂/TiC₂H₄ contain chemisorption and physisorption. The product C₂H₆+Ti(H₂)₅ exhibits 14 wt% uptake of H₂, which is completely consistent with the experimental results.     

Evaluating the competitiveness and uncertainty of offshore wind-to-hydrogen production: A case study of Poland

Offshore wind is currently the most rapidly growing renewable energy source on a global scale. The increasing deployment and high economic potential of offshore wind have prompted considerable interest in its use for hydrogen production. In this context, this study develops a Monte Carlo-based framework for assessing the competitiveness of offshore wind-to-hydrogen production. The framework is designed to evaluate the location-based variability of the levelised cost of hydrogen (LCOH) and explore the uncertainty that exists in the long-term planning of hydrogen production installations. The case study of Poland is presented to demonstrate the application of the framework. This work provides a detailed analysis of the LCOH considering the geographical coordinates of 23 planned offshore wind farms in the Baltic Sea. Moreover, it presents a comparative analysis of hydrogen production costs from offshore and onshore wind parks in 2030 and 2050. The results show that hydrogen from offshore wind could range between €3.60 to €3.71/kg H₂ in 2030, whereas in 2050, it may range from €2.05 to €2.15/kg H₂.     

Calculation of CO2, CH4 and H2S solubilities in aqueous electrolyte solution at high pressure and high temperature

This paper reports an investigation into the characterisation of liquid-vapor electrolyte solutions at high pressure and high temperature,A procedure to enable calculations of methane,carbon dioxide and hydrogen sulphide solubilities in brines(0-6m.) for temperature from 25 to 350℃ and for pressures from 1 to 1800 bar is presented.The model is based on Helgeson,Kirkham and Flowers modified equations of state(HKF)and on the semi-empirical interaction model introduced by Pitzer,HKF modified equations of state are used to calculate the reference fugacity of gas species,and the Pitzer ionic interaction model is used to calculate the activity coefficient of dissolved species(i.e.ionic or neutral).The efficiency of the combination of the two models is confirmed by several comparisons with data in the literature.     

Experimental and numerical study of the laminar burning velocity of NH3/H2/air premixed flames at elevated pressure and temperature

Ammonia (NH₃) is a carbon-free fuel that shows great research prospects due to its ideal production and storage systems. The experimental data of the laminar burning velocity of NH₃/H₂/air flame at different hydrogen ratios (X_H2 = 0.1–0.5), equivalent ratios (φ = 0.8–1.3), initial pressures (P = 0.1–0.7 MPa), and initial temperatures (T = 298–493 K) were measured. The laminar burning velocity of the NH₃/H₂/air flame increased upon increasing the hydrogen ratios and temperature, but it decreased upon increasing the pressure. The equivalent ratio of the maximum laminar burning velocity was only affected by the proportion of reactants. The equivalence ratio value of the maximum laminar burning velocity was between 1.1 and 1.2 when X_H2 = 0.3. The chemical reaction kinetics of NH₃/H₂/air flame under four different initial conditions was analyzed. The less NO maximum mole fraction was produced during rich combustion (φ > 1). The results provide a new reference for ammonia as an alternative fuel for internal combustion engines.     

A study of the methanation of carbon dioxide on Ni/Al2O3 catalysts at atmospheric pressure

The hydrogenation of carbon dioxide producing methane and CO has been investigated over Ni/Al₂O₃ catalysts. The as prepared catalysts have been characterized by XRD and Temperature Programmed Reduction. Spent catalysts have been characterized by XRD and Field Emission SEM. Catalytic activity needs the presence of Ni metal particles which may form in situ if the Ni loading is higher than that needed to cover the alumina surface with a complete monolayer. If Ni content is lower, pre-reduction is needed. Catalysts containing very small Ni particles obtained by reducing moderate loading materials are very selective to methane without CO formation. The larger the Ni particles, due to higher Ni loadings, the higher the CO production. Cubic Ni metal particles are found in the spent catalysts mostly without carbon whiskers. The data suggest that fast methanation occurs at the expense of CO intermediate on the corners of nanoparticles interacting with alumina, likely with a “via oxygenate” mechanism.     

Two-state reaction guaranteed high efficiency hydrogen production in Sn+H2O reaction: A preliminarily theoretical study based on single molecule model

The Sn + H₂O reaction is important in both hydrogen production through solar thermochemical redox cycles and investigations like the treatment of nuclear reactors or flame inhibition. Based on single molecule model, this work systematically explores its possible reacting channels in different spin multiplicities at CCSD(T)//DFT level of theory to reveal the underlined mechanism for its reported efficient hydrogen production. It is found that the singlet and triplet potential energy surfaces cross each other during the water attacking process, which makes the hydrogen production channel in the singlet state energetically favored. Quantitative calculations about the possibility of surface crossing and spin inversion with respect to minimum energy crossing point, spin-orbit coupling coefficient and intersystem crossing probability confirm that the optimal reacting pathway involves the two-state reaction scenario. This special reactive pattern makes hydrogen production not only possible but also efficient. Analysis of the equilibrium constant of reactive channels and their variation with temperature reveals the performance of two-state reaction channel agrees well with reported data range and nontrivial temperature dependence.     

Separation of H2/CH4 gas mixture through graphenylene membrane with functionalized nanopore: A computational study

Using molecular dynamics (MD) simulations, we investigated the performance of graphenylene membrane with functionalized nanopore in the H₂/CH₄ separation. In the present work, we studied the impact of functionalized nanopore, system temperature (298, 323, and 348 K), applied difference pressure (up to 2 MPa), and feed composition on the H₂/CH₄ separation performance. The passage of gas molecules across the nanopore was monitored within the simulations, and the permeance was determined under applied conditions. The results revealed that the size of gas molecules and its interaction with the membrane nanopore are two important factors in the separation performance of H₂/CH₄ gas mixture. It is also found that H₂ molecules can easily pass through the studied membranes, whereas no CH₄ molecule was seen in the permeate side, which confirms the ultrahigh selectivity of H₂ over CH₄. Furthermore, the maximum H₂ permeance of 1.95 × 10⁵ GPU through the pore 1 was obtained at 1.5 MPa, which was higher than that of 1.93 × 10⁵ GPU through pore 2. The results also demonstrated that the system temperature doesn't have any effect on the membrane performance. To this end, the permeance of H₂ molecules through the studied membranes obviously increased with raising the ration of H₂ molecules in the feed composition. Due to high selectivity and permeance, the graphenylene membrane with functionalized nanopore is expected to have promising applications in hydrogen separation from H₂/CH₄ mixed gas.     

High pressure DSC study of hydrogen sorption in MgH2/graphite mixtures: Effects of sintering and oxidation

Hydrogen absorption and desorption properties of ball milled Mg and Mg/graphite materials were analyzed by high pressure differential scanning calorimetry. The influence on hydrogen sorption kinetics of different graphite distribution, oxygen poisoning and magnesium sintering was studied. The Mg/graphite mixture with graphite distributed in the bulk showed better kinetics than the material with graphite located on the surface and Mg without additive. The effect of sintering and oxygen poisoning was a progressive storage capacity loss, due to a kinetic limitation in the case of sintering, and due to irreversible magnesium oxidation in the case of poisoning. The mixtures with graphite exhibited more resistance toward oxygen contamination, particularly in the case where graphite was primarily located on the surface compared to the material with graphite well dispersed in the bulk.     

A comparative study of the role of additive in the MgH2 vs. the LiBH4-MgH2 hydrogen storage system

The objective of the present work is the comparative study of the behaviour of the Nb- and Ti-based additives in the MgH₂ single hydride and the MgH₂ + 2LiBH₄ reactive hydride composite. The selected additives have been previously demonstrated to significantly improve the sorption reaction kinetics in the corresponding materials. X-Ray Diffraction (XRD), X-Ray Absorption Spectroscopy (XAS), X-Ray Photoelectron Spectroscopy (XPS) and Electron Microscopy (TEM) analysis were carried out for the milled and cycled samples in absence or presence of the additives. It has been shown that although the evolution of the oxidation state for both Nb- and Ti-species are similar in both systems, the Nb additive is performing its activity at the surface while the Ti active species migrate to the bulk. The Nb-based additive is forming pathways that facilitate the diffusion of hydrogen through the diffusion barriers both in desorption and absorption. For the Ti-based additive in the reactive hydride composite, the active species are working in the bulk, enhancing the heterogeneous nucleation of MgB₂ phases during desorption and producing a distinct grain refinement that favours both sorption kinetics. The results are discussed in regards to possible kinetic models for both systems.     

The effect of driving cycles and H2 production pathways on the lifecycle analysis of hydrogen fuel cell vehicle: A case study in South Korea

This study focuses on the simulation and analysis on the fuel economy of a hydrogen fuel cell vehicle, data collection and modeling to estimate greenhouse gas emission during its lifecycle. Since regenerative braking is a velocity related process, a car which is equipped with it can be significantly affected by the driving cycle. Therefore, the influence of five driving patterns on the fuel economy of a FCEV is investigated. Further prediction of life cycle emission is carried out by several hydrogen production pathways. The results indicate that the mileage of this FCEV for 1 complete charging can be extended by as much as 7% in fast shift driving mode with energy recovery of 30% during braking. The results also prove that hydrogen produced by natural gas in an on-site manner can reduce the lifecycle emission by more than 50%, comparing to that by Naphtha.     

A thermodynamic analysis of the SO2/H2SO4 system in SO2-depolarized electrolysis

The hybrid sulfur thermochemical cycle has been proposed as a means to produce efficiently massive quantities of clean hydrogen using a high-temperature heat source like nuclear or solar. The cycle consists of two steps, one of which is electrolytic. The reversible cell potential for this step and, hence, the resulting operating potential will depend on the concentrations of dissolved SO₂ and sulfuric acid at the electrode. To understand better how these are related as functions of temperature and pressure, an Aspen Plus phase equilibrium model using the OLI Mixed Solvent Electrolyte physical properties method was employed to determine the activities of the species present in the system. These activities were used in conjunction with the Nernst equation to determine the reversible cell potential as a function of sulfuric acid concentration, temperature and pressure. A significant difference between the reversible and actual cell potentials was found, suggesting that there may be considerable room for reducing the operating potential.     

The effects of the dimethylether bridging moiety in the H-cluster of the Clostridium pasteurianum hydrogenase on the mechanism of H2 production: A quantum mechanics/molecular mechanics study

[Fe–Fe]-hydrogenases are naturally occurring metalloenzymes that catalyze the reversible production of H₂ from two protons and two electrons. [Fe–Fe]-hydrogenases found in two species – Clostridium pasteurianum (CpI) and Desulfovibrio desulfuricans (DdH) – were shown with x-ray crystallography to have active sites that are very similar, although several atoms that bridge the dithiolate ligand were unresolved. In earlier work, we employed density functional theory (DFT) within a QM/MM method to investigate two previously proposed mechanisms of hydrogen production by DdH and CpI hydrogenases. In one mechanism (I), a CO ligand bridging two Fe atoms in the active site rotates to a terminal position while in the other (II) the CO bridge remains intact throughout the catalytic cycle. We previously assumed that the active sites for the two hydrogenases were identical; each had a dimethylamine bridging moiety, whose basicity is important for Mechanism II. Our overall conclusion, taking into consideration an energy comparison for the two mechanisms and activation energies for the CO-unbridging step in Mechanism I, was that Mechanism II was favored for both hydrogenases. In this paper, we extend our previous work to show that Mechanism II is favored over Mechanism I even if the bridging moiety in CpI hydrogenase is dimethylether, a significantly weaker base than dimethylamine, providing further support for Mechanism II even though experimental verification of the bridging moiety for the CpI H-cluster is lacking.     

Maximizing the hydrogen photoproduction yields in Chlamydomonas reinhardtii cultures: The effect of the H2 partial pressure

Photoproduction of H₂ gas has been examined in sulfur/phosphorus-deprived Chalmydomonas reinhardtii cultures, placed in photobioreactors (PhBRs) with different gas phase to liquid phase ratios (V_g.p./V_l.p.). The results demonstrate that an increase in the ratio stimulates H₂ photoproduction activity in both algal suspension cultures and in algae entrapped in thin alginate films. In suspension cultures, a 4× increase (from ∼0.5 to ∼2) in V_g.p./V_l.p results in a 2× increase (from 10.8 to 23.1 mmol l⁻¹ or 264–565 ml l⁻¹) in the total yield of H₂ gas. Remarkably, 565 ml of H₂ gas per liter of the suspension culture is the highest yield ever reported for a wild-type strain in a time period of less than 190 h. In immobilized algae, where diffusion of H₂ from the medium to the PhBR gas phase is not affected by mixing, the maximum rate and yield of H₂ photoproduction occur in PhBRs with V_g.p./V_l.p above 7 or in a PhBR with smaller headspace, if the H₂ is effectively removed from the medium by continuous flushing of the headspace with argon. These experiments in combination with studies of the direct inhibitory effect of high H₂ concentrations in the PhBR headspace on H₂ photoproduction activity in algal cultures clearly show that H₂ photoproduction in algae depends significantly on the partial pressure of H₂ (not O₂ as previously thought) in the PhBR gas phase.