Research on hydrogen permeability of polyamide 6 as the liner material for type Ⅳ hydrogen storage tank

As the liner material of type IV hydrogen storage tank, polymer is restricted in commercial application due to its high hydrogen permeability. In this paper, for the first time, the suitability of polyamide 6 (PA6) filled with lamellar inorganic components (LIC) as the hydrogen storage tank liner is comprehensively investigated, including thermal and mechanical properties, morphology and structure, rheology, and the hydrogen permeability under various temperature (−10 °C, 25 °C, 85 °C) and pressure (25 MPa, 35 MPa, 50 MPa) conditions. The results show that comparing with PA6, the thermal and processing properties of LIC/PA6 have been improved, the tensile strength, bending strength and bending modulus of LIC/PA6 are increased by 36%, 17% and 12%, respectively. Especially, the hydrogen permeability of LIC/PA6 is decreased by 3–5 times which meets the requirements specified by the hydrogen tank standard. The research work provides a theoretical basis and reference for the preparation and selection of high barrier liner materials in the future.     

Cryosorption storage of gaseous hydrogen for vehicular application – a conceptual design

A conceptual design for the cryosorption storage of gaseous hydrogen in activated carbon for vehicular application has been presented. In this work, a novel concept for the storage/discharge of hydrogen has been proposed. This system ensures faster filling and gradual release of hydrogen on demand. These two features are important for making onboard hydrogen storage effective for small cars. Numerical models for adsorption and desorption half cycles are presented. Assuming that the pressurisation and depressurisation are occurring adiabatically, transient analysis has been done to critically study the effective hydrogen storage capacity of activated carbon. The amount of activated carbon required to store hydrogen for travelling a specific distance has been computed.     

Lumped parameter simulation for charge–discharge cycle of cryo-adsorptive hydrogen storage system

As a renewable energy source, the hydrogen energy receives widespread concerns. Many efforts have been devoted to the commercial application of hydrogen energy. However, the hydrogen storage technology remains one of the primary bottlenecks. A lumped parameter model is developed for the cryo-adsorptive hydrogen storage system. The variational isosteric heat of adsorption based on Dubinin–Astakhov isotherm of adsorption is successfully used for cryo-adsorption model. Lumped parameter simulation is made for charge–discharge cycle of adsorptive hydrogen storage system at cryogenic temperature by Matlab/Simulink. The change of liquid–gaseous interface of nitrogen is considered in the lumped parameter model to improve the simulation accuracy. The lumped parameter model is applied for modeling different processes and well validated by cryo-adsorption experiments. The lumped pressure and the lumped temperature during charge–discharge cycle predicted by Simulink are compared with the two dimensional simulation results by Comsol. Furthermore, the effect of the charge flow rate on the performance of the hydrogen storage system is systematically analyzed. This model provides a feasible approach for the optimization of the cryo-adsorptive hydrogen storage system.     

Role of atomic hydrogen supply on the onset of CO2 methanation over La–Ni based hydrogen storage alloys studied by in-situ approach

Mechanochemical CO₂ methanation reactions using LaNi₅ and LaNi_4.6Al_0.4 hydrogen storage alloy powders were investigated by the in-situ monitoring of the gas pressure change during ball-milling. Methane generation begins when the H₂ partial pressure drops due to the H-uptake by the powder. Phase transition occurred in the sample after milling for 15 min and 224 min, with separate metallic Ni, La-oxide and La-hydroxide phases observed. Methane generation continued even after this phase separation. Our results imply that the formation of La-hydroxide at the surface and sub-surface contributed to methane generation during ball-milling. A comparison of LaNi₅ and LaNi_4.6Al_0.4 suggests the amount of hydrogen stored in the hydrogen storage powder dominates the timing of the onset of the methane generation.     

Advances on materials design and manufacture technology of plastic liner of type Ⅳ hydrogen storage vessel

The growing demand for type IV hydrogen tanks with long life, lightweight, high hydrogen storage density characteristics has posed new issues for liners. The paper discusses the causes of liner failure in terms of hydrogen permeation, thermal instability, and mechanical damage, as well as a focused analysis of alternative material optimization strategies. Through a detailed investigation of aggregate state structures, formulations and processes, the principles of material modification, primarily inorganic functional filler/polymer filler filling composite and laminated orientation, and their enhancing effects are sorted out. Besides, the benefits and drawbacks of blow molding, injection and welding, and the rotating technique, which were employed by some manufacturers are contrasted in the article, for overcome the problematic molding of hollow plastic liners with metal BOSS structures. This text will be a valuable resource for material exploitation as well as efficient and reliable molding of various liners.     

Ternary compounds in the magnesium–titanium hydrogen storage system

Mg–Ti–H samples were mechano-chemically synthesized by ball milling in argon atmosphere or under elevated hydrogen pressure. The detailed reaction mechanism during hydrogen release and uptake during continuous cycling was investigated by in-situ synchrotron radiation powder X-ray diffraction (SR-PXD) experiments. The thermal behaviour of the samples and hydrogen desorption properties were examined by simultaneous thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and mass spectrometry (MS) measurements. A ternary Ti–Mg–H compound with a fcc lattice form during mechano-chemical sample preparation in hydrogen atmosphere using metal powders, but not using metal hydrides as reactants. The amount of β-MgH₂ increases during the first hydrogen absorption cycle at 300 °C at the expense of the high-pressure polymorph, γ-MgH₂ and the amount of β-MgH₂ remain constant during the following hydrogenations. This study reveals that the ternary compound tends to absorb increasing amounts of magnesium in the dehydrogenated state during cycling. A strong coupling between the amounts of magnesium in the ternary Ti–Mg–H phase and the formation of magnesium and magnesium hydride during hydrogen release and uptake at 300 °C is observed. The composition and the amount of the Ti–Mg–H phase appear to be similar in the hydrogenated state. Fast absorption–desorption kinetics at 300 °C and lower onset temperatures for hydrogen release is observed for all investigated samples (lowest onset temperature of desorption T_on = 217 °C).     

Thermodynamic development and design of a concentrating solar thermochemical water-splitting process for co-production of hydrogen and electricity

A concentrating solar plant is proposed for a thermochemical water-splitting process with excess heat used for electricity generation in an organic Rankine cycle. The quasi-steady state thermodynamic model consisting of 23 components and 45 states uses adjustable design parameters to optimize hydrogen production and system efficiency. The plant design and associated thermodynamic model demonstrate that cerium oxide is suitable for thermochemical water-splitting cycles involving the co-production of hydrogen and electricity. Design point analyses at 900 W/m² DNI indicate that a single tower with solar radiation input of 27.74 MW and an aperture area of 9.424 m² yields 10.96 MW total output comprised of 5.55 MW hydrogen (Gibbs free energy) and 5.41 MW net electricity after subtracting off 22.0% of total power generation for auxiliary loads. Pure hydrogen output amounts to 522 tonne/year at 20.73 GWh/year (HHV) or 17.20 GWh/year (Gibbs free energy) with net electricity generation at 14.52 GWh/year using TMY3 data from Daggett, California, USA. Annual average system efficiency is 38.2% with the constituent hydrogen fraction and electrical fraction being 54.2% and 45.8%, respectively. Sensitivity analyses illustrate that increases in particle loop recuperator effectiveness create an increase in hydrogen production and a decrease in electricity generation. Further, recuperator effectiveness has a measurable effect on hydrogen production, but has limited impact on total system efficiency given that 81.1% of excess heat is recuperated within the system for electricity generation.     

Effect of para–ortho conversion on hydrogen storage system performance

We present a study of the effects of para–ortho conversion on performance of an adsorption-based hydrogen storage system using finite element methods implemented in COMSOL Multiphysics 4.3a platform. The base model which does not take into account the para–ortho conversion is validated using the experimental data of Maxsorb activated carbon measured with a test bench at room and cryogenic temperatures. The validated model is subsequently applied to simulate the storage system filled with MOF-5 and then extended to investigate the effects of endothermic para–ortho conversion of hydrogen isomers on storage and thermal performances during hydrogen charging/discharging cycle for four inlet temperatures, 35, 50, 77 and 100 K. Our results show that the endothermic conversion reduces the system temperature and increases the net storage capacity. The temperature changes due to the different heat sources are used to investigate the effect of conversion on the temperature reduction. The adsorbed and gas phase masses in the storage system with and without conversion at the end of the charging time are used to determine the effect of conversion on the storage system capacity. Even though the conversion is more significant at low temperature (35 K), the gains are larger at high temperature (100 K).     

Integration of hydrogenation and dehydrogenation system for hydrogen storage and electricity generation – simulation study

The present study combines methylcyclohexane dehydrogenation and toluene hydrogenation systems to produce steam for power generation. Methylcyclohexane dehydrogenation requires heat input, which has been accomplished using heat, released from toluene hydrogenation system, and heat exchange with steam, produced from the steam generator. The integration of these systems results in the generation of 5 MW electricity, which is used to run the electrolysis unit. The overall process does not require an extra source of energy, decreasing the external utility requirement. Both the systems have been investigated against various catalysts for the selection of best catalyst, thus enhancing overall process efficiency. The study has been carried out using Aspen HYSYS v 9. Aspen Energy Analyzer v 9 has been used to do the energy analysis of the system. Overall plant costing has been carried out using Aspen Economic Analyzer v 9.     

Effect of carbon addition on hydrogen storage behaviors of Li–Mg–B–H system

Various carbon additives were mechanically milled with LiBH₄/MgH₂ composite and their hydrogen storage behaviors were investigated. It was found that most of the carbon additives exhibited prominent effect on the host material. Among the various carbon additives, purified single-walled carbon nanotubes (SWNTs) exhibited the most prominent effect on the kinetic improvement and cyclic stability of Li–Mg–B–H system. Results show that LiBH₄/MgH₂ composite milled with 10 wt.% purified SWNTs additive can release nearly 10 wt.% hydrogen within 20 min at 450 °C, which is about two times faster than that of the neat LiBH₄/MgH₂ sample. On the basis of hydrogen storage behavior and structure/phase investigations, the possible mechanism involved in the property improvement upon carbon additives was discussed.     

Seasonal storage of electricity by hydrogen in benzene–water system

The use of hydrogen in benzene–water system which combines water electrolysis and hydrogenation in a polymer electrolyte cell was carried out as a means for seasonal storage of electricity. Gas diffusion electrodes were effective in improving coupled reactions of electrochemical benzene hydrogenation and water electrolysis. The reaction kinetics for the electrochemical hydrogenation process using gas diffusion electrodes was investigated by evaluating current efficiency and reaction rate. The results showed that the rate of hydrogen evolution was higher than the rate of benzene hydrogenation and the apparent activation energy of hydrogen evolution was lower than that of benzene hydrogenation. As the electrode potential increased, the hydrogen evolution rate increased. The benzene hydrogenation reaction rate reached a maximum at −0.8 V electrode potential, then decreased slightly. The current efficiency, however, reached its maximum at −0.7 V. Modifying electrodes by adding 0.2 wt% polyethylene glycol (PEG6000) reduced the mass transfer resistance of organic phase (cyclohexane/benzene) and improved the hydrogenation reaction rate.     

Evaluation of thermodynamic parameters for hydrogen in the storage device ST-90®

The thermodynamic parameters such as partial molar enthalpy (ΔH_H), partial molar entropy (ΔS_H), and partial molar excess entropy (ΔS^E_H) of the dissolved hydrogen in the hydrogen storage unit ST-90^® containing 18.6 kg of misch metal based AB₅ alloy are evaluated based on the calculation of Sieverts constant and from Clausius–Clapeyron equation. The partial molar enthalpy at infinite dilution (ΔH⁰_H) and the partial molar excess entropy at infinite dilution (ΔS^E,0_H) have been obtained from the dependence of and on the hydrogen concentration. The nature of metal-hydrogen and hydrogen interactions are also evaluated for the three single phases namely α, β and γ. The hydrogen–hydrogen interaction is attractive in the α phase and repulsive in the β and γ phases. For the mixed phases α+β and β+γ, it is very difficult to predict the nature of the interactions either as attractive or repulsive.     

Development of hydrogen absorption–desorption experimental test bench for hydrogen storage material

A volumetric experimental set-up used for measuring hydrogen absorption–desorption characteristics of hydrogen storage material will be presented. Although the experimental set-up is mainly employed to do hydrogen absorption–desorption cycling (including pressure cycling and thermal cycling) measurement automatically, it also can incidentally provide general measurements such as pressure-composition-temperature (P–C–T) curves and kinetics measurements in manual way in the ranges of 0.004–12 MPa and 213–773 K. The experimental set-up can be used to investigate the influence of hydrogen absorption–desorption cycles to hydrogen storage properties of material. The leakage rate of the whole experimental set-up was evaluated systemically. The usability and reliability of the experimental set-up were checked with LaNi₅ and Pd/K (kieselguhr).     

Study and design of a hybrid wind–diesel-compressed air energy storage system for remote areas

Remote areas around the world predominantly rely on diesel-powered generators for their electricity supply, a relatively expensive and inefficient technology that is responsible for the emission of 1.2 million tons of greenhouse gas (GHG) annually, only in Canada [1]. Wind–diesel hybrid systems (WDS) with various penetration rates have been experimented to reduce diesel consumption of the generators. After having experimented wind–diesel hybrid systems (WDS) that used various penetration rates, we turned our focus to that the re-engineering of existing diesel power plants can be achieved most efficiently, in terms of cost and diesel consumption, through the introduction of high penetration wind systems combined with compressed air energy storage (CAES). This article compares the available technical alternatives to supercharge the diesel that was used in this high penetration wind–diesel system with compressed air storage (WDCAS), in order to identify the one that optimizes its cost and performances. The technical characteristics and performances of the best candidate technology are subsequently assessed at different working regimes in order to evaluate the varying effects on the system. Finally, a specific WDCAS system with diesel engine downsizing is explored. This proposed design, that requires the repowering of existing facilities, leads to heightened diesel power output, increased engine lifetime and efficiency and to the reduction of fuel consumption and GHG emissions, in addition to savings on maintenance and replacement cost.     

Improvement of Mg–Al alloys for hydrogen storage applications

In the context of energy carrier, storage of hydrogen is one of the key challenges for research today. The group of Mg-based hydrides stands as a promising candidate for competitive hydrogen storage with high reversible hydrogen capacity.     

An investigation of the borohydride oxidation reaction on La–Ni-based hydrogen storage alloys

In this study, LaNi_4.7Sn_0.2Cu_0.1 metal hydride alloys, with and without surface deposits of Pt, are investigated as electrocatalysts for the borohydride oxidation reaction (BOR) in alkaline media. Results obtained for LaNi_4.78Al_0.22 and LaNi_4.78Mn_0.22 are used for comparison. It is observed that wet exposition to hydrogen or sodium borohydride lead to some hydriding of the metal hydride alloy particles, particularly that with a coating of Pt. In the presence of borohydride ions, the hydrided charged alloys present more negative potentials for the (boro)hydride oxidation process, and these enhancements are significantly larger for the Pt-coated material. In the potential range of interest, the results demonstrate considerable activity for the BOR, but just for the alloy with Pt. In the presence of borohydride ions in the solution there is a continuous hydriding the alloy during the discharge of the metal hydride electrode. Differential electrochemical mass spectrometry (DEMS) measurements showed that there is formation of H₂, either by hydrolysis or by partial oxidation of the borohydride ions, but in the absence of Pt the hydrolysis process is quite slow.     

The effect of particle size on the electrode performance of Ti–V-based hydrogen storage alloys

The effect of particle size ranging from 100 mesh to below 500 mesh on the electrochemical properties of _{Ti0.8Zr0.2V2.7Mn0.5Cr0.8Nix}(x=0.75,1.75)${\mathrm{Ti}}_{0.8}{\mathrm{Zr}}_{0.2}{\mathrm{V}}_{2.7}{\mathrm{Mn}}_{0.5}{\mathrm{Cr}}_{0.8}{\mathrm{Ni}}_x(x=0.75,1.75)$ hydrogen storage alloy electrodes was investigated. SEM observation on the surface of the alloy electrodes after charge/discharge cycles revealed that the abilities of anti-pulverization and anti-corrosion of the x=0.75$x=0.75$ alloy were much lower than those of the x=1.75$x=1.75$ alloy. For both of the two alloys, the electrode performance is affected markedly by the particle size. With the increase of the initial particle size, the initial discharge capacity of the alloy electrode decreases and the pulverization of the alloy particles aggravates, especially for the particles of the x=0.75$x=0.75$ alloy with size larger than 400 mesh, the size of which was minimized obviously compared with their initial size. However, the maximum discharge capacity and the cycling stability almost do not correlate to the initial particle size but relate with their actual particle size. As the actual particle size decreases, the maximum discharge capacity increases and the cycling stability declines.     

Flexibility improvement evaluation of hydrogen storage based on electricity–hydrogen coupled energy model

To achieve carbon neutrality by 2060, decarbonization in the energy sector is crucial. Hydrogen is expected to be vital for achieving the aim of carbon neutrality for two reasons: use of power-to-hydrogen (P2H) can avoid carbon emissions from hydrogen production, which is traditionally performed using fossil fuels; Hydrogen from P2H can be stored for long durations in large scales and then delivered as industrial raw material or fed back to the power system depending on the demand. In this study, we focus on the analysis and evaluation of hydrogen value in terms of improvement in the flexibility of the energy system, particularly that derived from hydrogen storage. An electricity–hydrogen coupled energy model is proposed to realize the hourly-level operation simulation and capacity planning optimization aiming at the lowest cost of energy. Based on this model and considering Northwest China as the region of study, the potential of improvement in the flexibility of hydrogen storage is determined through optimization calculations in a series of study cases with various hydrogen demand levels. The results of the quantitative calculations prove that effective hydrogen storage can improve the system flexibility by promoting the energy demand balance over a long term, contributing toward reducing the investment cost of both generators and battery storage and thus the total energy cost. This advantage can be further improved when the hydrogen demand rises. However, a cost reduction by 20% is required for hydrogen-related technologies to initiate hydrogen storage as long-term energy storage for power systems. This study provides a suggestion and reference for the advancement and planning of hydrogen storage development in regions with rich sources of renewable energy.     

Influence of Cr on the hydrogen storage properties of Ti-rich Ti–V–Cr alloys

In the present work, we studied the effects of Cr on the crystal structures and hydrogen storage properties of ternary alloys, Ti_0.7V_0.3−xCr_x and Ti_0.8V_0.2−xCr_x. Metal–hydrogen interactions were characterised by Thermal Desorption Spectroscopy (TDS) and in situ Synchrotron X-ray diffraction (SR-XRD). All initial alloys crystallise with body-centred cubic (BCC) crystal structures formed as solid solutions of V and Cr in Ti. Upon hydrogenation, the dihydrides (Ti,V,Cr)H₂ with face-centred cubic (FCC) structures are formed. An increase in the Cr content leads to systematic changes in the structure and hydrogenation behaviours. The changes include (a) contraction of the unit cells for the initial alloys and for the corresponding dihydrides; (b) slower hydrogen absorption kinetics and an increase in the incubation period for hydrogenation; (c) a decrease in the thermal stability of the saturated hydrides; and (d) a reduction in the apparent activation energy of hydrogen desorption. In situ SR-XRD and TDS studies of the FCC Ti–V–Cr hydrides indicated that their decomposition consists of five individual desorption events.