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Transitioning to a sustainable energy future necessitates innovative storage solutions for renewable energies, where hydrogen (H₂) emerges as a pivotal energy carrier for its low emission potential. This paper explores unlined rock caverns (URCs) as a promising alternative for underground hydrogen storage (UHS), overcoming the geographical and technical limitations of UHS methods like salt rock caverns and porous media. Drawing from the experiences of natural gas (NG) and compressed air energy storage (CAES) in URCs, we explore the viability of URCs for storing hydrogen at gigawatt-hour scales (>100 GWh). Despite challenges such as potential uplift failures (at a depth of approximately less than 1000 m) and hydrogen reactivity with storage materials at typical conditions (below temperatures of 100°C and pressures of 15 MPa), URCs present a flexible, scalable option closely allied with green hydrogen production from renewable sources. Our comprehensive review identifies critical design considerations, including hydraulic containment and the integrity of fracture sealing materials under UHS conditions. Addressing identified knowledge gaps, particularly around the design of hydraulic containment systems and the interaction of hydrogen with cavern materials, will be crucial for advancing URC technology. The paper underscores the need for further experimental and numerical studies to refine URC suitability for hydrogen storage, highlighting the role of URCs in enhancing the compatibility of renewable energy sources with the grid. • Detailed exploration of unlined rock cavern (URC) technology. • Analysis of URCs' potential for large-scale hydrogen storage. • Insights from historical use of URCs in compressed gas storage. • Examination of the opportunities and challenges in using URCs for hydrogen storage. [ABSTRACT FROM AUTHOR]

The paper is devoted to the development of a device for protecting facilities with turn-to-turn insulation, namely transformers and wind generators in order to increase the reliability of operation of electrical power systems, renewable energy installations and energy storage systems. The paper presents the results of experimental studies of the parameters of a prototype frequency-dependent device, as well as an assessment of the effectiveness of suppression of high-frequency surge voltages by the proposed device. The results of four groups of measurements are shown, which were compared with each other and with the results of previously showed computer simulations. The high efficiency of the proposed device when influencing the slope and amplitude of short high-frequency transients is shown. It is indicated that the parameters proposed earlier in the simulation allow the device to be used effectively. A brief analysis of alternative methods and means of protection is provided, and the prospects for using the device as protective equipment for wind power plants are also considered. [ABSTRACT FROM AUTHOR]

In order to meet the hydrogen refueling demand of fuel cell vehicles and reduce the cost of HRS operation process, it is necessary to study the hydrogen refueling process of cascade hydrogen storage system of hydrogen refueling station. In this paper, a thermodynamic model of the hydrogen refueling process for fuel cell vehicles is established, and the effect of the variation of these thermodynamic parameters on the specific energy consumption and utilization rate of the hydrogen refueling process is investigated in terms of the pressure ratio and capacity of the hydrogen storage tank, which is the core of the hydrogen refueling station, consisting of multiple hydrogen storage tanks. The results show that the specific energy consumption and hydrogen utilization of the hydrogen refueling station decreases as the ratio of the nominal pressure of the medium-pressure stage to the nominal pressure of the high-pressure stage increases over the course of the pressure ratio change. In addition, the capacity variation is only slightly changed as a result of the pressure ratio variation. Therefore, the lowest ratio of specific energy consumption can be found by fixing the utilization rate and by changing the pressure ratio. For example, in this paper, if the total mass of hydrogen in the station is 600 kg and the hydrogen utilization rate is required to be not less than 12 %, the optimal pressures for each level are 50.2 MPa, 65 MPa and 86.7 MPa. • A thermodynamic model of the hydrogen filling process for fuel cell vehicles is established. • The pressure ratio and capacity of cascade hydrogen storage systems were analyzed. • Specific energy consumption and hydrogen utilization are used as evaluation indicators. • The optimal pressures for each level are 50.2 MPa, 65 MPa and 86.7 MPa. [ABSTRACT FROM AUTHOR]

Using the WIEN2k code, first-principles simulations of ZrXH 3 (X = Zn, Cd) hydride perovskites are performed to determine their hydrogen storage properties. The purpose of this study is to investigate their structural, optoelectronic, hydrogen storage, mechanical and thermoelectric properties. The structural analysis demonstrates their stability through the heat of formation along with desorption temperature and shows that these compositions belong to the orthorhombic space group Cmcm (no.63). The band structure and density of states are estimated for electronic characteristics, indicating the metallic nature of both compositions. Analysis of elastic properties such as elastic constants, Pugh's ratio, bulk modulus, Poisson's ratio, and anisotropy factor are explored to determine the mechanical stability of these compositions and demonstrate their suitability as a transport medium in hydrogen storage systems even at higher pressure. To study the optical behavior of the perovskites under consideration for hydrogen storage applications, the dielectric parameters, dielectric constants, refractive index, optical conductivity, absorptivity, and energy loss function are studied. The present paper represents the initial theoretical effort toward future exploration of these materials for hydrogen storage applications. [Display omitted] Using the WIEN2k code, first-principles simulations of ZrXH 3 (X = Zn, Cd) hydride perovskites are performed to determine their hydrogen storage properties. The purpose of this study is to investigate their structural, optoelectronic, hydrogen storage, mechanical and thermoelectric properties. The structural analysis demonstrates their stability through the heat of formation along with desorption temperature and shows that these compositions belong to the orthorhombic space group Cmcm (no.63). The band structure and density of states are estimated for electronic characteristics, indicating the metallic nature of both compositions. Analysis of elastic properties such as elastic constants, Pugh's ratio, bulk modulus, Poisson's ratio, and anisotropy factor are explored to determine the mechanical stability of these compositions and demonstrate their suitability as a transport medium in hydrogen storage systems even at higher pressure. To study the optical behavior of the perovskites under consideration for hydrogen storage applications, the dielectric parameters, dielectric constants, refractive index, optical conductivity, absorptivity, and energy loss function are studied. The present paper represents the initial theoretical effort toward future exploration of these materials for hydrogen storage applications. • Stability of ZrXH 3 (X = Zn, Cd) hydride perovskites is confirmed by Enthalpy of formation. • ZrXH 3 (X = Zn, Cd) hydride perovskites have high value of decomposition temperature. • The gravimetric hydrogen storage capacities comes out to be 1.89 % and 1.46 % respectively. • Metallic behavior is reveled by electronic structure of these hydrides. [ABSTRACT FROM AUTHOR]

Due to the extra evaporation loss caused by the ortho-para hydrogen conversion (OPHC) during the storage and transportation of liquid hydrogen (LH 2), the initial concentration of ortho-hydrogen (o-H 2) plays an important role in the large-scale safe operation and utilization of LH 2. However, there are very limited studies focusing on clarifying the impact of the OPHC on thermal behaviors of LH 2 tanks. In light of this, this paper establishes and develops an extended thermal multi-zone model that couples the OPHC process with the mass and energy conservation equations of the ullage and liquid for an LH 2 tank. With the help of the model, a thermodynamic analysis of the pressurization rate is performed to obtain the dominant parameter that evaluates the effect of the initial o-H 2 concentration on the pressure build-up process. The results indicate that the interfacial mass transfer rate caused by the OPHC is the dominant parameter accounting for more than 90% of the effect of all parameters on the pressurization rate during a 10-day process with an initial liquid fill ratio of 90% and a heat leakage of 40 W. Additionally, the effect of the initial o-H 2 concentration on the optimal liquid fill ratio is discussed in this paper. The results indicate that when the initial o-H 2 concentration changes from 0.2% to 10%, the optimal liquid fill ratio decreases from 82.5% to 74%. The present work provides theoretical support and guidance for controlling the o-H 2 concentration to realize the long-term and high-efficiency storage of LH 2. • Modeling of transient ortho-para hydrogen conversion (OPHC) for LH 2 tanks. • Thermodynamic analysis coupled with OPHC on LH 2 storage is conducted. • Interfacial mass transfer by OPHC determines the pressure rise in LH 2 tanks. • Initial concentration of o-H 2 reduces the optimized liquid fill ratio of tanks. [ABSTRACT FROM AUTHOR]

To explore more possibilities for hydrogen economy, Mg-based alloys containing long period stacking ordered (LPSO) phase for solid-state hydrogen storage deserve attention. In this paper, indium (In) element is adopted to alter the de/hydrogenation abilities of Mg–Y–Zn alloys. The relationship between microstructural features and hydrogen storage behaviors of Mg 95 Y 3 Zn 2- x In x (x = 0, 1 and 2 at.%) alloys are discussed in detail. Indium element can modify the morphology of LPSO phase and more Mg interfaces are obtained. LPSO phase cannot be generated when Zn is completely replaced by In element; instead α-Mg grains and eutectic phase (Mg + MgYIn) the constitute the In 2 alloy. Element In benefits the activation process of the alloys in this paper, which helps the alloy particles to be hydrogenated quickly in the first hydrogenation. Specifically, 1 at.% In substitution for Zn accelerates dehydrogenation and the dehydrogenation temperature reduces by 11 °C. The benefits of In element for dehydrogenation behaviors mainly come from increased Mg grain boundaries, larger MgH 2 lattice constants with weaker Mg–H bonds, uniformly distributed nanoscale YH 2 /YH 3 phase. • Indium can modify the morphology of LPSO phase with rough boundaries. • Indium substitution for Zn increases the MgH 2 cell volume, weakening Mg–H bonds. • Nanosized YH 2 and Indium alloying synergistically reinforce the hydrogen desorption. [ABSTRACT FROM AUTHOR]

Hydrogen is crucial in the forthcoming low-carbon energy systems offering the potential to reduce CO 2 emissions and its versatility to be utilized across diverse energy sectors. Precise assessment of hydrogen thermo-physical characteristics is vital for the effective design and execution of numerous processes encompassing hydrogen production, transportation, storage, and utilization. In this paper, various distinct machine learning (ML) approaches, namely extreme gradient boosting (XGBoost), Random Forest (RF), Adaptive boosting (AdaBoost), and Light gradient boosting machine (LightGBM) were implemented to estimate thermo-physical properties, namely thermal conductivity, density, viscosity, and diffusivity in water based on pressure and temperature variables. For this purpose, comprehensive experimental data points covering a broad range of pressures and temperatures were acquired from the literature. The results demonstrated a strong agreement between the predictions generated by all proposed techniques and the experimental data. Furthermore, XGBoost yielded a root mean square error (RMSE) of 0.0085, 2.1548, 0.3343, and 1.5308 for the estimation of thermal conductivity, density, viscosity, and diffusivity, respectively, demonstrating superior accuracy in predicting all outcomes. In the sensitivity evaluation, it was observed that temperature, with absolute relevancy factor 0.88, 0.54, 0.246, and 0.92 had the most significant influence on the hydrogen thermo-physical properties in the order mentioned above. Furthermore, the trend analysis of the model indicated that all thermo-physical properties of hydrogen experience positive effects from temperature and pressure, except for density, which decreases as temperature increases. The leverage technique confirmed the statistical validity of both the experimental dataset used for modeling and the model's development. This study's results provide the efficient design and secure operation of hydrogen storage, refueling stations, transportation infrastructure, and production facilities. [Display omitted] • Hydrogen holds great importance in the forthcoming low-carbon energy. • XGBoost, RF, AdaBoost, and LightGBM are utilized for modeling the thermo-physical properties of hydrogen. • XGBoost demonstrates its superior accuracy in predicting thermal conductivity, density, viscosity, and diffusivity. • Temperature has the most significant influence on the hydrogen thermo-physical properties. [ABSTRACT FROM AUTHOR]

The paper describes a new method for determining the energy efficiency of the life cycles of wind farms by the aggregated data of energy costs. The rationale for the use of aggregated data to determine energy costs during the life cycle of the wind farms is given. The classification of wind turbines and wind farms elements by the parameters and technical characteristics of the elements with subsequent division into groups for which aggregated data of energy costs are determined is given. Within the framework of the method have been developed an algorithm for determining energy costs on the production of elements of wind turbines and wind farms and formulas for their calculation during the life cycle of wind farms. In order to test the method, energy cost was calculated during the life cycle for two wind farms with wind turbines that differ parameters and technical characteristics of the elements and their energy efficiency was determined. It has been shown that the use of a hydrogen storage unit as part of a wind turbine makes it possible to efficiently use energy during down periods and increase the efficiency of the installation by 25–30%. It is noteworthy that a wind-hydrogen farm allows not only to accumulate excess energy during lean periods, but also to save the resource of wind turbines. When the energy reserve in the hydrogen battery reaches close to full, part of the wind turbines of the wind-hydrogen farm can be automatically temporarily stopped in a given order. This technology can provide an extension of the warranty service life for each wind turbine. [ABSTRACT FROM AUTHOR]

Mackinawite FeS is the most common corrosion product in the early stage of steel in H 2 S environment and also has an effective catalysis for hydrodesulfurization, hydrogen release reactions and heavy metal ion removal since its high specific surface area and reactive surface like other van der Waals materials. In this paper, ab initio molecular dynamics (AIMD) is used to study the interactions between small molecules (H 2 S, H 2 O and H) and FeS at 300 K. The calculation results show that the primary dissociation of H 2 S only occurs on the FeS(111) surface and H 2 S is chemically adsorbed on the (011) and (100) surfaces but physically adsorbed on the (001) surface. It will dissociate and generate H atoms when different amounts H 2 S or H 2 O molecules appear in the interlayer of FeS, in which H 2 S is more prone to dissociation. The dissociated H atoms will be "captured" by Fe/S atoms in mackinawite FeS, leading to the shrink of layer. Moreover, H atoms could combine into H 2 , which suggests that layered FeS has great potential for hydrogen generation. The diffusion coefficient of H atoms in mackinawite FeS layer is estimated about 1.67 × 10−8 m2/s. These findings have significant meaning for application of mackinawite FeS in corrosion science, hydrogen generation, hydrogen storage and other fields. • Visually show the adsorption, dissociation and diffusion of wet H 2 S on different mackinawite surface. • Clarify the effect when different molecules (H 2 S, H 2 O, H) appear in the interlayer of FeS. • Demonstrate the barrier properties of layered mackinawite to H atoms. • Give new insights into the application of mackinawite in hydrogen production and storage. [ABSTRACT FROM AUTHOR]

Energy hubs (EHs) represent a pivotal paradigm in achieving optimal resource utilization across various energy domains. This paper presents an advanced framework for the optimal management of a smart island, leveraging the synergies within the water-electricity nexus. By integrating diverse resources, including electricity, water, heat, and hydrogen, the proposed EH model aims to meet the multifaceted demands of consumers on the island. To enhance operational efficiency, this study delves into the nuanced impacts of key EH components, elucidating their roles in meeting demand profiles and minimizing operational costs. Formulated as a mixed integer linear programming (MILP) model, the EH optimization problem is addressed using the GAMS optimization tool. The overarching objective is to fulfill consumer demand while concurrently optimizing resource utilization, considering factors such as storage degradation costs and emissions from fossil-fuel-based units. In addition to strategic optimization, this study pioneers a novel approach to stochastic parameter forecasting, integrating convolutional neural networks (CNNs) and long-short-term memory networks (LSTMs). By harnessing the capabilities of these advanced forecasting techniques, the EH model can anticipate dynamic changes in demand patterns with heightened accuracy and precision. The empirical results underscore the transformative potential of the proposed EH framework, showcasing significant reductions—up to 30%—in emission costs. Moreover, the study underscores the pivotal role of EHs as enablers for scaling up renewable energy penetration, offering a robust foundation for sustainable energy transitions in island communities and beyond. Additionally, implementing a load-shifting demand response program can lower total costs by approximately $257 per day, offering significant savings for EHs over extended periods. [Display omitted] • Modeling a mixed integer linear programming for energy management of an energy hub. • Comprehensive study on hydrogen and electric storage systems. • Uncertainty modeling using convolutional and long short-term memory networks. • Modeling water–electricity nexus to meet water and electricity demand. [ABSTRACT FROM AUTHOR]

Hydrogen energy is one of promising non-polluting and renewable energy sources. In this paper, we present a first principal study of hydrogen storage in pure C 60 fullerene cage and Stone-Wales (SW) defective C 60 cages using density functional theory (DFT) with applying both the exchange functional B3LYP and the dispersion correction wb97xd at 6–31+g(d,2p) basis set. In addition, the counterpoise correction is applied, and the basis set superposition error is calculated. The calculations underscore that the hydrogenation binding energy of C 60 cages occurs through an endothermal process for C 60 H in with a hydrogen binding energy of 0.09 eV and through an exothermal process for C 60 H out , C 60 SW 66 H out , and C 60 SW 65 H out , cages with hydrogen binding energies of −2.17 eV, −2.96 eV, and −2.20 eV, respectively. Remarkably, for the first time, the intermediate hydrogen binding energy is found inside C 60 SW 66 H in fullerene, and C 60 SW 65 H in fullerene cages with energies of −0.26 eV and −0.81 eV, respectively. The hydrogen adsorption inside the cavity of C 60 SW 66 fullerene cage is thermodynamically possible below 289.8 K and entire pressure range considered. Our results highlight, for the first time, that the endohedral cavity of C 60 SW 66 is a promising new medium for hydrogen storage due to its binding energies (−0.26 eV) and its hydrogen storage weight percentage (5.3%) that are close to the optimal conditions specified by DOE for commercial use. In addition, this study opens up a new discovery of Stone-Wales defective C 60 fullerene for further endohedral cavity applications. • New insight into endohedral cavity of Stone Wales C 60 SW 66 is reported. • For the first time, a new promising medium for hydrogen storage inside cavity of C 60 SW 66 is proved. • Binding energies of −0.26 eV and hydrogen storage weight percentage up to 5.3% are achieved inside the cavity of C 60 SW 66. • This study opens a new discovery of the SW defective C 60 fullerene for further endohedral cavity applications. [ABSTRACT FROM AUTHOR]

Magnesium-based materials are favored by researchers because of their high hydrogen storage capacity, but they cannot be put to daily use because of their more demanding reaction conditions. Recently, the method to improve the hydrogen storage performance of MgH 2 by catalyst doping has been widely investigated. In this paper, Co 3 O 4 catalysts were prepared by homogeneous precipitation method. It was demonstrated that the Co 3 O 4 catalyst could effectively improve the hydrogen storage performance of MgH 2. According to the experimental results, the dehydrogenation onset temperature of the MgH 2 +15 wt% Co 3 O 4 composite was about 200 °C, which was about 130 °C lower than that of pure MgH 2 , and the amount of dehydrogenation was 6.26 wt%. The dehydrogenation activation energy of the MgH 2 +15 wt% Co 3 O 4 composite was reduced to 89.13 kJ/mol, which was about 45.7% lower than that of pure MgH 2. After complete dehydrogenation, the composites started to absorb hydrogen at 50 °C with 6.2 wt%, while the activation energy of reabsorption was also reduced to 47.97 kJ/mol. After 10 cycles of MgH 2 +15 wt% Co 3 O 4 composites, the hydrogen storage capacity of MgH 2 could still be maintained at 99%, which indicated that it had good cycling stability. It was confirmed by various characterizations that Co 3 O 4 was uniformly distributed on the MgH 2 matrix after ball milling. After the first reaction, Co 3 O 4 was converted to CoO, which was uniformly attached to the Mg/MgH 2 surface and stabilized during the cycling process, continuing to provide active sites for hydrogen. The hydrogen storage composite MgH 2 +Co 3 O 4 was prepared in this study, and Co 3 O 4 was uniformly distributed on the MgH 2 matrix. In the first hydrogen release process, Co 3 O 4 is gradually converted to CoO, and then in the hydrogen absorption process, hydrogen enters Mg. During the cycle, the CoO is in a stable state and evenly dispersed on the Mg/MgH 2 surface, continuing to provide an active site for hydrogen. [Display omitted] • Co 3 O 4 with good air adaptation performance is applied to MgH 2 system. • Composites started to release H 2 at 200 °C and could start to absorb H 2 at 50 °C. • The activation energy of de/hydrogenation was significantly reduced for composites. [ABSTRACT FROM AUTHOR]

The importance of the energy transition and the role of green hydrogen in facilitating this transition cannot be denied. Therefore, it is crucial to pay close attention to and thoroughly understand hydrogen storage, which is a critical aspect of the hydrogen supply chain. In this comprehensive review paper, we have undertaken the task of categorising and evaluating various hydrogen storage technologies across three different scales. These scales include small-scale and laboratory-based methods such as metal-based hydrides, physical adsorbents, and liquid organic hydrogen carriers. Also, we explore medium and large-scale approaches like compressed gaseous hydrogen, liquid cryogenic hydrogen, and cryocompressed hydrogen. Lastly, we delve into very large-scale options such as salt caverns, aquifers, depleted gas/oil reservoirs, abandoned mines, and hard rock caverns. We have thoroughly examined each storage technology from technical and maturity perspectives, as well as considering its techno-economic viability. It is worth noting that development has been ongoing for each storage mechanism; however, numerous technical and economic challenges persist in most areas. Particularly, the cost per kilogramme of hydrogen for most current technologies demands careful consideration. It is recommended that small-scale hydrogen storage technologies such as metal hydrides (e.g., MgH 2 , LiBH 4) need ongoing research to enhance their performance. Physical adsorbents have limited capacity except for activated carbon. Some liquid organic hydrogen carriers (LCOHs) are suitable for medium-scale storage in the near term. Ammonia-borane (AB), with its high gravimetric and volumetric properties, is a promising choice for medium-scale storage, pending effective dehydrogenation. It shows potential as a hydrogen carrier due to its high storage capacity, stability, and solubility, surpassing DOE targets for storage capabilities. Medium-scale storage, utilising compressed gas cylinders and advancements in liquefied and cryocompressed hydrogen storage, requires cost reduction measures, and a strategic supply chain. Large-scale storage options include salt caverns, aquifers, and depleted gas/oil reservoirs, with salt caverns offering pure hydrogen, need further techno-economic analysis and deployment projects to mature, but storage costs are reasonable, ranging mostly from €0.25/kg to €1.5/kg for location specific large-scale options. • Comprehensive review of hydrogen storage technologies from small to very large scale. • Metal hydride MgH 2 shown to be economically viable with storage at €2.8 per kg. • Ammonia-borane (AB) offers promising medium-scale hydrogen storage potential. • Technological advancements are enhancing compressed gas hydrogen storage systems. • Large-scale hydrogen storage costs vary between €0.25 and €1.58 per kg. [ABSTRACT FROM AUTHOR]

This paper addresses the urgent need for efficient hydrogen storage methods in the context of combating climate change and transitioning to sustainable energy sources. Among various storage options, LiBH 4 is highlighted for its high volumetric and gravimetric energy densities, critical factors in determining its suitability for energy applications. However, challenges arise due to its high thermolysis temperature, which poses difficulties, especially in applications like automotive use where high temperatures are required. The commercial viability of LiBH 4 remains a significant obstacle due to the nascent stage of chemical hydride technology and the absence of large-scale production facilities. Environmental concerns also loom large, as the production of LiBH 4 relies on extensive mining of lithium and boron, known for their environmental impact. Furthermore, the economic feasibility of LiBH 4 as a hydrogen storage medium is questioned, given the substantial portion of total expenses attributed to hydrogen costs, affecting all methods except those based on fossil fuels or electricity. Nevertheless, there is optimism that with technological advancements and improved infrastructure, the costs associated with LiBH 4 and hydrogen storage overall may decrease over time. In conclusion, while LiBH 4 presents promising energy density characteristics, its practical implementation faces challenges such as high production costs, environmental concerns, and technological limitations. Overcoming these obstacles is crucial for realizing a sustainable and carbon-free energy landscape driven by hydrogen. • LiBH 4 shows promise for high energy density storage but faces obstacles high production costs and environmental concerns. • A comprehensive decision matrix analysis showcases the strengths and weaknesses of various hydrogen storage options. • LiBH 4 may find applications in small-scale personal storage due to its safety and energy density. [ABSTRACT FROM AUTHOR]

Hydrogen is considered a truly clean energy source with great potential for replacing fossil fuels. However, the special physical and chemical properties of this source make large-scale, safe, and efficient storage challenging, thus limiting its widespread use. Consequently, an underground hydrogen storage system inspired by underground methane storage and CO 2 geological sequestration has been proposed, and it is increasingly becoming a focus of research. Depleted oil reservoirs are ideal sites for such systems. Nevertheless, research on these types of underground hydrogen storage systems is limited to a few feasibility assessments, and the hydrogen seepage laws in reservoirs with residual oil are not well understood. In this paper, a study was conducted involving mathematical modeling and numerical simulation of underground hydrogen storage, which was converted from the SSZ low-permeability depleted oil reservoir in Bohaiwan Basin, eastern China, to reveal the seepage patterns between hydrogen and complicated in situ fluids (oil, gas, and water). First, a comprehensive analysis was conducted using numerous rock samples and experimental data to identify the composition, genesis, and distribution patterns of the sandstone reservoir, detailing its internal pore structure and fluid distribution postdepletion characteristics. Then, the hydrogen seepage properties in the presence of oil films in the three main throat types of low-permeability sandstone were analyzed, and corresponding mathematical models of the different throats were established. Finally, a numerical simulation of underground hydrogen storage was conducted to assess the impacts of various parameters, such as injection speed, reservoir heterogeneity, and residual oil saturation, on hydrogen seepage. The planar and vertical diffusion patterns of hydrogen were clarified, and the key factors affecting the efficiency of underground hydrogen storage were analyzed, offering suggestions for the establishment of stable and efficient underground hydrogen storage systems. • Selection and description of typical low-permeability reservoirs for UHS. • Mathematical model establishment for hydrogen percolation in porous rock. • Numerical simulation of the storage process of hydrogen. • Percolation laws of hydrogen in rock porous. [ABSTRACT FROM AUTHOR]

Hydrogen possesses a lot of potential as a renewable source of energy due to its high energy density and positive impact on the environment. It is expected to play a substantial role in various long-term applications. Considerable research effort has been directed toward identifying suitable materials for electrochemical hydrogen storage (EHS), including graphene-based materials. Graphene's exceptional properties, such as high electrical and thermal conductivity, electrochemical activity, chemical stability, and structural flexibility, make it an ideal candidate for hydrogen storage. This paper, given the profound importance of graphene in EHS and the existing knowledge gap regarding recent developmental trends and research directions, identifies current worldwide research advancements in graphene-based EHS and the impact of the modification on overall effectiveness by conducting a comprehensive search of literature published within the past five years. It presents a comprehensive comparison of various graphene-based materials, including doped graphene structures, metal hydride-graphene composites, graphene quantum dots, and graphene-alloy composites. It also outlines the main opportunities and obstacles of graphene-based materials in EHS research according to the investigated studies and provides insights and recommendations for forthcoming research in this area. [Display omitted] • Electrochemical hydrogen storage is an effective method of hydrogen storage. • Recent advancements in graphene-based electrochemical hydrogen storage were explored. • Graphene is an ideal candidate for electrochemical hydrogen storage. • Graphene modification has a significant impact on electrochemical hydrogen storage. • Insights and recommendations for future research in this field are presented. [ABSTRACT FROM AUTHOR]

The shared energy storage system is recognized as a promising business model for the coordinated operation of integrated energy systems (IES) to improve the utilization of energy storage and the consumption of renewable energy. As the hydrogen energy gradually receives more attention, this paper constructs the structure of a hybrid hydrogen energy storage system shared by an IES alliance in a dynamic pricing mode. A bi-level optimization model for the shared hybrid hydrogen energy storage system (SHHESS) is proposed to optimize the capacity configuration decisions and the pricing strategy jointly. The upper level determines the capacity and dynamic price of SHHESS with maximum profits and the lower level obtains the optimal operation of the IES alliance minimizing the total operation costs. The proposed model is solved by an improved PSO-GA algorithm and CPLEX solver. Finally, numerical tests are conducted in different scenarios. The results show that the hybrid energy storage system improves the daily profits of SHHESS by 70.3% and 5.44%, and reduces the renewable energy curtailment by 80.93% and 48.92% respectively compared to the battery-only and hydrogen-only systems. Additionally, the daily operation cost of the IES alliance is 35.2% lower than the individual operation scenario. The proposed model confirms the feasibility and superiority of the hybrid hydrogen energy storage system in a sharing business mode. • Design an interactive structure of a shared hybrid hydrogen energy storage system. • Propose a bi-level planning optimization framework for shared hybrid hydrogen energy storage. • The dynamic price of energy storage sharing service is optimized. • Determine the optimal operation strategy of the integrated energy system alliance. • Propose a hybrid method combining an improved PSO-GA and CPLEX optimizer. [ABSTRACT FROM AUTHOR]

This paper proposes a multi-objective framework for sustainable scheduling of hybrid hydrogen-power systems. In the proposed model, the microgrid system incorporated renewable energy systems, battery energy storage systems, non-renewable resources, power-to-hydrogen, hydrogen-to-power, demand response programs, and hydrogen storage systems to present a highly flexible structure in the energy systems. The purpose of the proposed model is to provide a complete operation mechanism for the daily scheduling of microgrids considering environmental, economic, and sustainable problems. To this end, a stochastic three-objective optimization model is proposed to consider the intermittent behavior of renewable generation, loads, and market prices and simultaneously tries to minimize the carbon emission, total cost, and peak loads. The peak load reduction is important because it increases the reliability, renewable energy integration, power quality, and reduced cost of reserve capacity. Therefore, a min-max approach is presented to reduce the peak load in the proposed model. Also, the hydrogen-to-power and power-to-hydrogen resources are integrated as flexible resources to increase the efficiency of microgrids during operation scheduling. The proposed model is evaluated on a standard case study and the numerical results show the multi-objective model reduces the carbon emission by 28.05 kg and increases the load factor by 6.26%, respectively. • Description of a multi-objective problem that integrates electricity and hydrogen. • Proposing an enviro-economic model to reduce carbon emission and operating cost. • The proposed model significantly uniforms the load profile by min-max approach. • Hydrogen storage tank and DR programs are considered to increase the flexibility. [ABSTRACT FROM AUTHOR]

World is presently facing major challenges in energy industry to reduce or replace greenhouse gases (CO 2 , CH 4 , NO x etc.) emissions to net zero in the coming decades while decreasing the reliance on traditional fossil fuels. In the current scenario, hydrogen (H 2) appears to be an excellent alternative energy source to meet the criteria. Storage of H 2 over a long period of time in large quantities poses a significant challenge for its widespread uses. In order to overcome this issue, the idea of using large-scale depleted underground hydrocarbon reservoirs, salt caverns, underground aquifers, etc. is considered to be a suitable option for underground hydrogen storage. However, underground storage of H 2 for a longer time period comes up with a potentially high microbial activity where H 2 can be utilized in the microbial metabolism and converted into undesirable gases like CH 4 and H 2 S which in turn, damage the porous medium due to clogging, acid formation, and corrosion activity. This review paper explores the various scientific challenges during large-scale H 2 storage in porous medium to facilitate the global H 2 economy. Moreover, a detailed description of the effect of subsurface environment conditions such as pressure, temperature, pH, and salinity on microbes is included in this study. In addition to this, steps to counter microbial activity in stored H 2 monitoring and mitigation approaches are also discussed in this article. • Underground hydrogen storage and its mechanism are discussed. • Effect of microorganisms on stored hydrogen and porous media properties comprehensively reviewed. • The impact of microbial activity on subsurface storage environment conditions. • Monitoring and mitigation strategies to counter microbial activities comprehensively reviewed. • Latest treatment proposition of microbial activities and role of biocides in underground hydrogen storage discussed. [ABSTRACT FROM AUTHOR]

Modern energy systems are large distributed systems and, as a rule, contain energy storage systems and, in particular, hydrogen batteries and hydrogen production systems. The use of hydrogen for energy transportation has recently been actively studied in a number of scientific projects. To ensure continuous operation of instrumentation and control equipment on long hydrogen pipelines (gas and cryogenic), it is important to ensure constant autonomous power supply to these systems. This can be solved using micromechanical energy microgeneration systems for the uninterrupted operation of various sensors, which are installed in large numbers on almost all elements of the structure and infrastructure. In addition, an important area of scientific research is the revision of the concepts and appearance of traditional devices of modern renewable energy: windmills, solar cells, turbines, etc. Fundamentally new energy devices are on the agenda, capable of recovering mechanical energy of any power and supplying it to the consumer in the form of a given specific energy flow. Collection of chaotically distributed natural energy of the environment (mechanical energy in the form of: vibrations, acoustic vibrations, wave energy, gusts of wind, tornadoes, precipitation, vibrations of the earth's crust, etc.), as well as collection of dissipated energy from artificial sources (iron and automobile highways, airstrips, spaceports, production facilities, etc.) with the help of mechanical microgenerators will allow the recovery and conversion of mechanical energy of various powers, including low power, into a universal energy carrier - hydrogen. Mechanical vibrations of artificial origin are of particular interest due to their widespread use for domestic and industrial purposes in a wide range of vibrations. The energy of mechanical vibrations can be collected and converted into electrical energy using piezoelectric, electromagnetic, triboelectric or electrostatic (capacitive) energy converters. Electrostatic microelectromechanical energy converters are considered the most promising among other energy converters, since their manufacturing processes are based on standard technology for the production of integrated circuits and microelectromechanical systems. Energy conversion by an electrostatic converter is carried out due to an external mechanical force that does work against the force of attraction of the charged electrodes of a variable capacitor. To transfer the received electrical energy to the load of the consuming device, the electrostatic converter is connected to the corresponding electrical circuits (conditioning circuits). Such a system as a whole is a kind of microgenerator or energy collector. Microenergy flow recovery systems integrated into large energy systems will ensure the collection and recovery of significant amounts of energy for remote energy consumers. At the same time, the concept of a distributed mechanical energy recovery system is quite simple: a mechanical energy receiver - a converter into electrical energy - a preliminary electrical storage device - an energy distributor - an electric energy accumulator - an electrolyser - a hydrogen accumulator - a fuel cell. To optimize the operation of the working circuit, including preliminary electrical systems for energy storage and conversion: capacitors and electric energy accumulators, electrolyzers; To ensure their durability and reliability, flexible automatic control of electrical power distribution is necessary. The real work was done to solve that problem. In addition, for extended and large power facilities it is important to ensure widespread sensory control of system parameters. At the same time, if all sensors receive power from an autonomous energy-generating device, then the costs of creating extended communications for instrumentation will be sharply reduced. In addition, the reliability of the control system will significantly increase. The results of studying operation features of a kinetic microgenerator with reduced output voltage are presented. The performance of a multi-stage modified Bennet doubler is compared to a system including a two-stage modified Bennet doubler and a diode-capacitor voltage divider. It is shown that with an increase of the number of stages in the modified Bennet doubler, the conversion of mechanical energy into electrical energy becomes less and less efficient. At the same time, for achieving the maximum energy accumulation rate (power), a two-stage power amplifier based on the Bennet doubler is preferable. It is established that when analyzing the operation of a diode-capacitor voltage divider, it is necessary to take into account the intrinsic (reverse) capacitances of the discharging diodes affecting the divider operation significantly. The divider behavior features while changing the load resistance and the intrinsic capacitances of the discharge diodes are found and analyzed. Analytical expressions linking the main characteristics of the microgenerator as a whole with the parameters of the electronic components used are derived. It is shown that for expanding the range of the "correct" division of the divider, it is necessary to use discharge diodes with minimal intrinsic capacitances, and also that connecting a load to the Bennet doubler as a voltage divider changes the permissible capacitance modulation depth of the variable capacitor. This paper examines the concepts of creating large energy-generating flows based on arrays of micromechanical energy converters placed on optimal energy-efficient receiving surfaces and analyzes the issues of cryogenic production, storage, consumption and transportation of hydrogen. Stationary and mobile cryogenic storage systems for hydrogen are considered. Much attention is paid to the safety of large cryogenic and gas hydrogen systems. [ABSTRACT FROM AUTHOR]

Renewable energy production through electrolysis of water to obtain "green hydrogen" has gained interest as a clean energy storage option. However, integrating variable renewable energy resources into the grid poses challenges to maintaining energy balance and stability. In this paper, a hybrid energy storage system combining short-term battery energy storage system and long-term hydrogen-based energy storage system is proposed for an isolated DC microgrid with a structure similar to a hydrogen refueling station. Passivity-Based Control (IDA-PBC) is utilized for power converters regulation, ensuring global stability based on Lyapunov theory while accounting for the nonlinear characteristics of the physical system. The control strategy is designed to ensure a reliable supply of electrical energy to the loads, preserve the quality of electrical variables in the network, and secure the safe operation of system components. Additionally, to safeguard devices from overvoltage, a Sliding Mode Reference Conditioning loop (SMRC) is proposed. It intervenes only when there is a potential risk of exceeding predefined boundaries. Simulations results under demanding conditions demonstrate the effectiveness of incorporating hydrogen energy storage systems with IDA-PBC and SMRC for this class of problems. • An isolated MG with H2 storage, typical structure of a refueling station, was modeled. • The IDA-PBC ensures the stability of the nonlinear and complex MG. • SMRC ensures overvoltage protection in the bus. • The control confirms that H2 storage integrated with RES contributes to MG stability. [ABSTRACT FROM AUTHOR]

Hydrogen energy, characterized by its high calorific value and sustainability, represents a secondary clean energy source. It is predominantly stored, transported, and utilized through pipeline networks. However, a comprehensive optimization approach for the design for the ground pipeline network of hydrogen storage is currently lacking. This paper embarks on a systematic exploration of the layout, station type and parameter design for the ground pipeline network of hydrogen storage. Addressing various application perspectives, the study constructs two distinct pipeline network structures: the Star-Star Global Optimization Model (SSGO-Model) and the Star-Tree Global Optimization Model (STGO-Model). Three cases are discussed under six different constraint scenarios. These scenarios focus on layout optimization, variable capacity layout optimization, and the overall optimization of layout and parameters. An overall optimization strategy is proposed to solve the models. A detailed analysis of the iteration process, layout schemes, station and pipeline constraints, investment, and flow parameters of the pipeline network in the optimization results is presented. Through systematic analysis, the correctness and effectiveness of the model are verified, demonstrating the variability of optimization results under different topological structures and constraint conditions. Moreover, when conducting integrated optimization, the total investment is minimized, proving its superiority. The findings demonstrate the applicability of these models in guiding the construction for the ground pipeline network of hydrogen storage, thereby fostering the advancement of hydrogen storage technology. Concurrently, this research contributes significantly to the development of hydrogen energy, offering strategic insights and practical solutions for its efficient deployment. • Integrated optimization model for hydrogen storage ground pipeline network. • The model considers layout, station type and parameter design. • Overall optimization strategy is proposed. • Three cases verify optimization model. [ABSTRACT FROM AUTHOR]

This paper proposes an experimental and numerical study of the hydrogen storage properties of the Ni 0.6 Mg 0.4 Fe 2 O 4 compound. Firstly, the sol-gel method was used to synthesize the compound Ni 0.6 Mg 0.4 Fe 2 O 4. Second, the synthesized compound's morphological and structural properties were ascertained using X-ray and SEM techniques. Third, the experimental hydrogen adsorption's kinetics and isotherms were carried out. At last, the experimental hydrogen adsorption isotherms were compared to a mathematical model based on the formalism of statistical physics. With the use of this model, it was possible to ascertain the following: on the one hand, the stereographic parameters involved in the adsorption process, such as the number of receptor sites (n 1 and n 2), their density (N m1 and N m2), as well as the energy parameters (P 1 and P 2) and the energies of adsorption for each type of site (ΔE ads1 and ΔE ads2). On the other hand, the thermodynamic functions that regulate the hydrogen adsorption reaction, such as the internal and Gibbs energies, as well as the entropy versus temperature and pressure. Ni 0.6 Mg 0.4 Fe 2 O 4 has a significant hydrogen storage capacity (0.15 wt %) at moderate temperatures. The numerical results showed that hydrogen is inserted into two types of interstitial sites via an exothermic process. [Display omitted] • Synthesis, morphology, and structural analysis of a compound Ni 0.6 Mg 0.4 Fe 2 O 4. • Investigative analysis of the Ni 0.6 Mg 0.4 Fe 2 O 4 compound's hydrogen storage characteristics. • Assessment of the hydrogen adsorption isotherms and kinetics in the Ni 0.6 Mg 0.4 Fe 2 O 4 compound. • A mathematical model based on statistical physics is used to validate experimental data. • Determination of the steric parameters and thermodynamic functions governing the adsorption reaction. [ABSTRACT FROM AUTHOR]

Hydrogen energy storage systems (HESS) play an essential role in Microgrid (MG) systems to address the inherent generation characteristics of renewable energy sources. Also, the integration of Demand Response (DR) into the Energy Management System (EMS) of a renewable-based Multi-Microgrid (MMG) can lead to substantial technical and economic benefits. This paper proposes a modified optimization algorithm for optimizing MMG Energy Management (EM). The proposed algorithm is a modified version of the Student Psychology-Based Optimization (SPBO) technique called Modified Student Psychology-Based Optimization (MSPBO). This modification aims to improve issues such as slow convergence, low solution accuracy, lack of diversity, and getting stuck in local optima. The proposed MSPBO method incorporates a local escape operator and a collaborative student class to achieve a better balance between exploiting known solutions and exploring new possibilities. The MSPBO algorithm is applied to address the EM challenge within a MMG context. Considering the integration of renewable sources as Wind turbines and solar photovoltaic and the HESS, the EM problem is formulated as a two-stage multi-objective optimization: minimizing the operating cost of conventional generators and power transactions cost in addition to the cost of HESS, while maximizing operator benefits and peak load reduction. This multi-objective problem is tackled using a hybrid ε-lexicography–weighted-sum approach that avoids the need for normalization. The performance of the proposed MSPBO is evaluated using CEC 2017 benchmark test functions, utilizing various statistical measures such as best, average, worst, rank, and standard deviation (SD) of fitness values, along with Wilcoxon's rank-sum test. The MSPBO technique is compared with other optimization algorithms for these test functions, highlighting its efficiency and adeptness in achieving a harmonious trade-off between exploiting known solutions and exploring new ones. Furthermore, the MSPBO method is applied to solve two case studies. In Case 1, which involves a single stage with conventional demand response optimization, the results achieved using MSPBO are benchmarked against other optimization techniques, revealing its superior efficacy in addressing the EM challenge. In Case 2, a more complex two-stage multi-objective problem is tackled using MSPBO, and the assessment of the integration of HESS in the MMG is evaluated. In the second stage, there is a notable enhancement in peak load reduction percentage (PRP), from 13.9% to 16.13% without the HESS and from 12.68% to 16.46% with the integration of HESS. [ABSTRACT FROM AUTHOR]

Distribution feeder reconfiguration (DFR) in distribution systems can enhance operating conditions by reducing losses and improving voltage indices. This paper introduces a dual-stage risk-based framework that concurrently tackles day-ahead reconfiguration and microgrid scheduling within the distribution network. To control the negative aspects of uncertainties, the proposed framework integrates energy storage systems (ESS/HSS) and demand response programs (DRPs) at the network level, enhancing adaptability. The initial stage of the proposed model employs the AC power flow model, utilizing loss and voltage deviation functions as objective benchmarks for network reconfiguration. The scheduling is meticulously executed per interval, deriving optimized structures under diverse scenarios with the aid of a case reduction technique (CRT) to streamline solutions. The ultimate solution employs the grey wolf optimization (GWO) algorithm and CPLEX solver in the first and second stages respectively. Outcomes from applying this approach to the adjusted 118-bus network manifest improved operational conditions and voltage quality through reconfiguration. Impressively, the integration of ESS/HSS and DRPs yields a substantial 22.34% reduction in total operating costs, a conclusion substantiated by the numerical findings. Furthermore, by leveraging the CRT, a remarkable 56.17% reduction in problem-solution time is achieved. [Display omitted] • Investigating the impact of losses and voltage deviations on network performance. • Introducing a two-stage risk-based framework to determine the optimal topology. • Finding solutions to the micro-grids planning problem with the distribution network reconfiguration. • Adopting a case reduction method to lessen time demand required for solving the day-ahead planning problem. • Investigating the effect of demand response programs on the voltage characteristics and losses of the system. [ABSTRACT FROM AUTHOR]

Large-scale underground hydrogen storage can replace fossil fuel power generation and balance long-term and short-term energy consumption. There is still a lack of research on the quantitative evaluation of hydrogen saturation in hydrogen storage formations. By constructing a sandstone hydrogen storage reservoir model for numerical simulation of gas-water identification, a method for qualitative and quantitative evaluation of hydrogen saturation and hydrogen density in reservoirs is found. Monitor the change of hydrogen saturation in the reservoir, master the storage status of hydrogen, and enrich the hydrogen injection plan. In this paper, the RPM-formation model is established by combining the pulse neutron logging technology and the Monte Carlo method. The relationship between the capture gamma count ratio the hydrogen density and the hydrogen saturation under different porosity conditions is simulated. The effect of formation water salinity and shale content on the relationship between the count ratio and porosity. The results show that under the same porosity condition, the counting ratio increases with the increase of hydrogen density, and increases or decreases with the increase of hydrogen saturation under different hydrogen densities. The salinity and shale content of the formation water affect the count ratio. Based on the simulation data, the evaluation model of hydrogen saturation is established, the influence of shale content and formation water salinity is analyzed and corrected, the capture gamma ratio chart is constructed, and the method of qualitative and quantitative evaluation of the reservoir is found, which provides a logging method for monitoring the change of hydrogen saturation in different components of underground hydrogen storage formation. [Display omitted] • The simulation process of pulsed neutron logging is realized by Monte Carlo method. • The qualitative evaluation of reservoir gas-bearing property is realized by using Rcapture. • An evaluated model was established to quantify reservoir hydrogen saturation. • A correction chart corrects shale content and formation water salinity. • The research results can assist in optimizing the hydrogen injection scheme. [ABSTRACT FROM AUTHOR]

To address the pressing need for sustainable energy solutions, hydrogen has emerged as a "zero-emission" energy source with vast potential in diverse sectors like manufacturing, transportation, and electricity generation. However, the realization of a hydrogen economy hinges on the development of safe and stable technologies and materials for hydrogen storage and transport. This paper presents a comprehensive review of the latest advancements in hydrogen storage systems, with a particular focus on porous materials. Notably, porous carbon materials derived from biomass waste have garnered attention due to their exceptional qualities. These include abundant and easily accessible raw materials, simplified production processes, adjustable characteristics, cost-effectiveness, low mass density, high specific surface area and porosity, structural diversity, and sustainable regeneration. These attributes position them as promising candidates for further exploration in hydrogen storage devices, particularly for achieving high H2 uptake capacities. The feasibility of utilizing both plant- and animal-based biomass porous carbons is examined, encompassing activated porous carbons, heteroatom doped porous carbons, and their composites, as pivotal components for the development of porous carbon storage devices. The synthesis and characterization of each form, along with their respective hydrogen storage capacities, are highlighted. While each material exhibits promise, it is important to note that they do present certain technological drawbacks. Addressing these limitations through further research and development is crucial to unlocking their full potential for future applications in the burgeoning hydrogen economy. [Display omitted] • Unique features of Biomass-derived carbon materials for hydrogen storage capacity. • Critical overview and key lessons from non-biomass derived materials. • Carbon materials from organic waste bridge hydrogen storage to the future economy. • Biomass-based carbon materials are signalling a need for further investigation. [ABSTRACT FROM AUTHOR]

Hydrogen as a fuel of the future for mobile applications has the potential to increase energy efficiency and reduce emissions significantly (Groos et al., 2023 [1]). A main focus to enable hydrogen powered aviation is the efficient storage onboard (Prewitz et al., 2023 [2] ; Verstraete et al., 2010 [3] ; Prewitz et al., 2020 [4]). Especially the storage volume is a major challenge because of the rather low volumetric energy density of compressed or either liquified hydrogen in comparison with kerosene (Hassan et al., 2021 [5] ; Stetson et al., 2014 [6] ; Troeltsch et al., 2020 [7]). Glass capillaries have a high strength, also their geometry and low hydrogen permeability make them a suitable micro pressure tank (Prewitz et al., 2018; Veziroglu et al., 2003 [8] ; Meyer-Scherf, 2015 [9]). By combining glass capillaries and carbon fibers in a polymer matrix, a material composite could be developed that is both a structural element, contributing to load bearing, and a hydrogen tank at the same time. The synergetic use of the structure as storage could be a solution to tackle the problem of the increased required storage volume for hydrogen powered aviation. This paper presents a theoretical micromechanical analysis, the design and manufacturing process of the composite material, and the experimental results of tensile testing conducted on a glass capillary hybridized carbon fiber reinforced plastic (GCRP). The aim is to determine the influence of the glass capillary content on the tensile strength and tensile modulus of the GCRP. • Development of carbon fiber and glass capillary hybrid structural hydrogen storage. • Multipurpose utilization and potential synergetic effects could save weight. • Tensile mechanical properties shows degradation with increasing capillary fraction. [ABSTRACT FROM AUTHOR]

In order to search for good hydrogen storage materials, the structural, optoelectronic and hydrogen storage properties of double perovskites KNaMg 2 F 6-x H x and KNaAe 2 H 6 (Ae = Be, Mg, Ca) have been studied by first-principles calculations based on density functional theory in this paper. All the negative formation energies demonstrate the thermodynamic stability of these materials. Except for KNaBe 2 H 6 , the rest of the materials are wide-band gap semiconductors or insulators. The gravimetric storage capacity of KNaMg 2 F 6-x H x increases with the introduction of hydrogen and reaches a maximum of 5.19 wt% at x = 6. Meanwhile, the KNaBe 2 H 6 exhibits the best storage capacity of 8.57%. The favorable desorption temperature for stable KNaMg 2 H 6 material is 470.4 K, which is feasible in actual application. As the concentration of hydrogen increases, the electronic bandgap of KNaMg 2 F 6-x H x decreases gradually due to its electron conduction band moving to a lower energy range. The bond population analysis indicates that there is a mixture of ionic and covalent bonds in the studied materials. These materials are all ultraviolet absorber, and a red-shift can be observed in the absorption edge due to the variation of bandgap. • Double perovskites are introduced as the novel hydrogen storage materials. • Hydrogen substitution improves the stability and optoelectronic performance of double perovskites. • All materials exhibit wide band gaps as well as high ultraviolet absorption. • Stable KNaMg 2 H 6 material possesses ideal desorption temperature of 470.4 K and gravimetric storage capacity of 5.19 wt%. [ABSTRACT FROM AUTHOR]

In this paper, certain issues envisaged in the framework of development of design methodology for intelligent autonomous distributed hybrid power complexes (ADHPC) with green hydrogen and energy storage, functioning in grid mode and in the mode of interaction with the global (national) grid (GN) have been solved. Depending on their energy deficit or surplus, relative to the global grid, ADHPCs can operate as a load or as an energy source, respectively, as follows: based on the analysis of the energy balance management process in the ADHPC, a reasonable choice of the structure of the system of accumulation and distribution of power flows (SADCF) was made from the point of view of increasing the reliability of its functioning and ensuring the physical feasibility of the energy balance management process in this structure, i.e. keeping the actual power consumption of the consumers close to the required rated power at each given time t. This is achieved by including a condenser connected to the SADCF system on its assembly and distribution bus and a storage system BS with double-level ((BS1, BS2), double-circuit ((BS1(1), BS1(2)), (BS2(1), BS2(2))) structure, whereby: BS1of the level 1 - to manage the capacity balance in the SADCF under normal ADHPC regime and the variation of green hydrogen and consumption capacities within their confidence intervals assessed at the design stage; BS2 of the level 2 - to coordinate ADHPC and GN modes of operation and to control, together with BS1 of the level 1, GN, diesel generator (DG), the power balance in the SADCF when the ADHPC fails and when RES and consumption power are outside their confidence intervals; alternating charge/discharge operation of the parallel circuits will extend the life of the BS system; – a comprehensive definition of optimal ADHPC system situational energy balance management task is formulated. [ABSTRACT FROM AUTHOR]

Renewable hydrogen is considered as one of the key technologies that may be needed to fully decarbonise our economies, providing the high-temperature heat, fuels and feedstock that might not be possible to electrify. Several pilot projects are underway, and some assessments of the economics of green hydrogen have been published. However, most of them have assessed the costs of producing renewable hydrogen in large-scale, grid-connected units. Another option, pointed by many as a robust strategy in the early stages, is to produce hydrogen locally, in "hydrogen valleys", to serve industrial demand. In this paper, the economics of the different technical configurations and strategies that might be used for this decentralised, variable-demand option are analysed, accounting for the impact that a non-constant operation may cause on the operational efficiency of electrolysers, and for the potential benefits of local hydrogen storage. Our results show that when hydrogen demand is variable, production costs are higher compared to the constant demand case, due to the higher electrolyser size required. Electricity price optimization plus hydrogen storage can be a valuable option in some cases, although the cost benefit is negligible (about 1%) unless price volatility in the market increases with higher RES shares, or investment costs decrease significantly. Sourcing electricity exclusively from a dedicated renewable power plant can only become competitive if electricity market prices rise as observed recently or triggered by increasing CO 2 prices. • Different production strategies are compared to minimise H 2 production costs. • Faraday efficiency increases costs for variable electricity generation. • Electricity price optimization is best for H2 valleys, although compression costs may change this. • Direct H 2 production from renewable plants is not competitive with current prices. [ABSTRACT FROM AUTHOR]

Metal borohydrides exhibit remarkable hydrogen storage capabilities. Nevertheless, the practical application of metal borohydrides as onboard hydrogen storage materials is constrained owing to their elevated hydrogen release temperatures, limited reversibility, and sluggish kinetics. This paper presents an overview of the current research advancements concerning the hydrogen storage capacity of metal borohydrides and the measures employed to improve their properties, encompassing ionic substitution, nano-methods, catalytic doping, and the construction of composite systems. Lastly, this article scrutinizes the challenges and prospects associated with metal borohydrides, proposes methodologies to augment their hydrogen storage capabilities, and furnishes guidelines for further research on metal borohydrides and the broader hydrogen storage domain. • Hydrogen storage is the major barrier to the widespread adoption of hydrogen energy. • Storage via metal borohydrides results in high capacities. • Borohydrides face difficulty in stability and reversibility. • Storage targets must be achieved through various modification methods. [ABSTRACT FROM AUTHOR]

The low thermal conductivity of hydrogen storage materials significantly limits the reaction rate of hydrogen storage and release in metal hydrides reactors. In present paper, a heat transfer fluid channel was designed by topology optimization method to enhance the heat transfer performance and increase the hydrogen storage and release rates. Firstly, a series of channel structures were obtained through two-dimensional topology optimization, then they were embedded into metal hydride reaction beds by three-dimensional reconstruction. The hydrogen storage and release performance of different reaction beds were analyzed, the most effective bed structure was derived and compared with the finned bed. The results show that the hydrogen storage and release time of the designed fluid channel reaction bed is 31.5% and 24.4% less than the finned bed. Lastly, the hydrogen storage and release performance of the designed reaction bed under different operating conditions were examined. The appropriate operation conditions were derived: for hydrogen storage, hydrogen pressure of 1.0 MPa, HTF inlet velocity of 0.25 m s−1 and inlet temperature of 293 K; for hydrogen release, hydrogen pressure of 0.1 MPa, HTF inlet velocity of 0.25 m s−1 and inlet temperature of 363 K. Moreover, the reaction bed designed by topology optimization has obvious advantages and shows better hydrogen storage and release performance compared to finned reactors under various operating conditions. • A reactor structure for hydrogen storage is obtained by topology optimization. • The absorption and desorption time of optimized reactor is 31.5% and 24.4% less than the finned reactor. • The appropriate operation conditions for hydrogen storage and release are obtained. • The optimized reactor has better performance than finned reactors under various conditions. [ABSTRACT FROM AUTHOR]

Nowadays, renewable energy sources are integral to programs for the development of electric power systems. It is established that modern renewable generation units and energy storage systems utilize power electronic-based interfaces, such as voltage source converters, to convert power. On the one hand, the utilization of a voltage source converter provides certain advantages, such as the absence of a direct link to the network, the ability to operate on all quadrants of the PQ diagram, and the possibility of connecting renewable generation units to a weak network. On the other hand, the widespread use of renewable generation units utilizing voltage source converters reduces the overall inertia of the electric power system. However, excessive use of power electronic converters in the network leads to a significant increase in harmonic pollution, thereby introducing fresh challenges to ensuring safe and stable operation of the electric power system. To ensure the dependable operation of an electric power system with renewable energy sources units and energy storage systems based on the voltage source converter, it is essential to update the control system of the voltage source converter to meet the requirements for traditional generation as part of the electric power system. This paper presents the outcome of the power oscillation damping controller application implemented in the voltage source converter, which enhances the electric power system's stability. [ABSTRACT FROM AUTHOR]

In this paper, the numerical calculation model of salt cavern hydrogen storage was established based on the proposed salt cavern hydrogen storage in a bedded salt mine in Jiangsu Province of China. The effects of the minimum internal pressure, maximum internal pressure, average internal pressure and injection-production rate on the stability and tightness of the storage were explored respectively. The results revealed that: (1) The volume shrinkage rate and the plastic zone distribution of the surrounding rock decreased with the increase of the minimum internal pressure, and increased with the decrease of the maximum internal pressure. (2) When the depth of salt cavern is around 1700 m , its long-term stability cannot meet the requirements according to the traditional standard of 0.3–0.8 times of the vertical stress at the cavern roof. It is therefore suggested that the minimum internal pressure of the storage should be increased to 0.4 times of the vertical stress at the cavern roof. (3) The tightness evaluation indexes, including leak range, pore pressure distribution of hydrogen, and cumulative leakage of hydrogen in surrounding rock, all increased with the increase of average pressure and amplitude of internal pressure. (4) Under the same average internal pressure and injection-production frequency, the greater the injection-production rate (the amplitude of internal pressure), the smaller the cumulative leakage rate is. Therefore, increasing the injection-production rate is beneficial to the storability of the hydrogen storage. • Different internal pressures are set to study the stability and tightness of the salt cavern for hydrogen storage. • Raising the minimum internal pressure can enhance the stability of the salt cavern. • The amplitude of internal pressure is the key factor affecting the tightness of the salt cavern. • The selection of internal pressure for hydrogen storage should take into account the effects of multiple factors. [ABSTRACT FROM AUTHOR]

The establishment of a prediction model for the hydrogen absorption state of a solid-state hydrogen storage device is crucial for its practical application. In this paper, a solid-state hydrogen storage device filled with AB 2 hydrogen storage alloy is investigated. The experimental data are obtained by controlling the hydrogen absorption temperature and hydrogen absorption rate respectively. The Broyden-Fletcher-Goldfarb-Shanno algorithm (BFGS) is used to fit the solid-state hydrogen storage device experimental data based on the Richards model, and Linear Regression, Gradient Descent and Artificial Neural Network algorithms are used to predict the parameters of the Richards model. It is confirmed that the Linear Regression model has the best prediction effect after verified by the test set, with coefficients of determination R2 ≥ 0.96. This study provides an effective way to predict the hydrogen absorption state of solid-state hydrogen storage devices quickly. • The effects of temperature and rate on hydrogen absorption process of solid-state hydrogen storage device are studied. • Richards model is used to fit the hydrogen absorption curve shaped as an S-type. • The prediction model of hydrogen absorption process of the device is established. • Three machine learning algorithms are applied to establish the prediction model. [ABSTRACT FROM AUTHOR]

Solid-state hydrogen storage technology is currently the most economical, reliable, safe, and volumetrically efficient storage method. Unfortunately, whether physically or chemically adsorbed hydrogen storage, a single hydrogen storage material cannot be used as a medium for real-life applications. Among them, magnesium-based alloys have the highest mass density for storing hydrogen among metal-based alloys, while porous materials with physical adsorption properties have become a research hotspot for combining with metal hydrogen storage materials since they have the advantages of high specific surface area, low cost, abundant unsaturated active sites, exceptionally high porosity, adjustable pore size and structure, and tunability of composition. Hence, this paper intends to provide the readers with an overview and elucidation of the catalytic effects and mechanisms of metal-organic frameworks and carbon-based porous materials (activated carbon, carbon nanofibers, and carbon nanotubes) in improving the kinetic and thermodynamic properties of Mg/MgH 2. The results demonstrated that MOFs and carbon-based porous materials act as catalysts, co-catalysts, inhibitors of grain agglomeration and sintering, and layered scaffolds in Mg/MgH 2 , respectively. The rational design of the Mg/MgH 2 composite system was also prospected by comparing the advantages and disadvantages of these modification methods. To contribute a feasible idea and solution for the production of solid-state hydrogen storage materials with a high capacity for storing hydrogen, low cost, good hydrogen absorption/desorption kinetics, and excellent cycling stability for application in real industry and life. • Porous materials reduce sintering and agglomeration of Mg/MgH 2 particles. • Porous materials can serve as hierarchical scaffolds for nanoscale MgH 2. • Porous materials enhance the dissociation/recombination rate of H 2. • Porous materials improve cyclic stability of MgH 2. [ABSTRACT FROM AUTHOR]

The first principle of calculation is a computational technique based on quantum mechanics that may precisely determine the ground-state electronic structure and associated mechanical and thermodynamic characteristics of solid materials. This study explains the history of first-principles development, calculation techniques, and the use of ultra-soft pseudopotential in hydrogen storage materials based on an inquiry and analysis of the findings of previous research. This paper primarily reviews the research progress of first principles in improving two-dimensional hydrogen storage materials, metal-organic framework materials, alkali metal-base composite hydrides, and metal-base hydrogen storage materials in order to speculate on the hydrogen storage mechanisms of materials. It is possible to estimate the location of hydrogen adsorption in a material by computing its electronic structure, band structure, electron density, and lattice vibration. This information is then used to compute the hypothetical new hydrogen storage material. Finally, the direction of first-principles computing in hydrogen storage materials is anticipated. • The research progress of DFT in predicting and simulating new hydrogen storage materials is introduced. • The merits and demerits of the application of DFT in solid hydrogen storage and its future development direction are pointed out. [ABSTRACT FROM AUTHOR]

This paper investigates an innovative study on the performance of a hybrid condensing boiler-fuel cell micro-cogeneration system for single residential applications. It combines experimental and dynamic numerical investigations including renewable energy for green hydrogen production and solid storage. Basing on the hourly measurements for a typical winter day, a dynamic model was developed and validated against different home heating need. Highlighting the influence home energy needs on fuel cell operating mode, it shows that single homes with low energy demand led to reduce the fuel cell's yearly operation below 50 %. In low-energy homes, a reduction in fuel cell size led to an increase in yearly operation to 60-70 % and achieved a 55 % electrical coverage rate. The integration of metal hydride hydrogen solid storage, powered by renewable sources, is emphasized. This setup increases heat demand, influencing fuel cell operation. In winter season, fuel cell operated for an average of 611 h, compared to 61 h in summer. System efficiency averaged 91 % annually, peaked at 95 % in summer, and sustained 93 % when both FC and condensing boiler were switched on. [Display omitted] • Modeling of a hybrid Boiler-Fuel Cell MCHP system for residential energy management. • Calibration of the FC-MCHP model using experimental data from a real MCHP unit. • Electrical and thermal coverage of the FC-MCHP unit with green hydrogen production and storage under different scenarios. • Strategies for optimal hydrogen consumption in in residential application. • Impact of solid-state hydrogen storage on FC-MCHP consumption and thermal management. [ABSTRACT FROM AUTHOR]

As a non-material-based compression means, the ionic liquid compressor is drawing attention in hydrogen storage, where the advantages of ionic liquid and hydraulic drive systems are combined. However, the existence and motion of ionic liquids lead to a complex gas-liquid interaction in the hydrogen cylinder, which further influences the thermodynamic behaviour of the compressor. The trajectory of the piston is a critical factor affecting the ionic liquid motion and gas compression process, thus a proper trajectory is required to improve compressor performance. In this paper, 9 different piston trajectories are proposed, under which the multi-phase flow and thermodynamic feature of the compressor were investigated by the numerical simulations combined volume of fluid (VOF) and image process methods. Liquid level stability was defined and adopted as one key performance index for the thermodynamic characteristics. Results showed that the highest value of mean liquid level stability was found as 0.739 in the case with the trajectory of T8. When the piston trajectory was T8, the maximum hydrogen product was obtained as 0.48 g with the ionic liquid discharged of 4.80 g. The optimal trajectory was identified considering the liquid level stability, the delivered mass and the energy consumption. • 9 different piston trajectories are proposed for the investigation. • Liquid level stability is defined as the performance index of the compressor. • VOF and image process methods are adopted to obtain liquid level stability. • Compressor performance is investigated under 9 piston trajectories. • The optimal piston trajectory is obtained based on the analysis. [ABSTRACT FROM AUTHOR]

In this paper, a novel ammonia-hydrogen-electricity cogeneration system is developed. To mitigate the cost associated with hydrogen storage and transportation in later stages, the proposal is to utilize high-temperature ammonia production instead of conventional hydrogen production. A comparative analysis between ammonia and transportation for hydrogen is conducted to assess cost efficiencies. To improve the system efficiency, a supercritical CO 2 Brayton cycle is applied as the power generation cycle. This choice exhibits superior parameter compatibility with the system compared to the Rankine cycle. The study scrutinizes the impacts of different energy utilization sequences and varying process parameters of the power generation cycle on the system's performance to ascertain the most optimal configuration. The results indicate that the Brayton cycle is more suitable for integration with the nuclear-IS thermochemical hydrogen production system, significantly enhancing the power generation capacity of the ammonia-hydrogen-electricity cogeneration system. These improvements result in 18.8 % increase in power generation efficiency and a 9.3 % boost in overall energy efficiency of the system. Subsequent to this enhancement, the system attains an impressive energy efficiency of 47.0 % along with a system exergy efficiency of 63.4 %. This study introduces an innovative approach for optimizing and enhancing the energy efficiency of a cogeneration system by employing nuclear energy as a high-temperature heat source for hydrogen (ammonia) production. • A novel ammonia-hydrogen-electric cogeneration system is developed. • The system bolsters efficiency by 9.3 % through a synergistic Brayton cycle coupling. • Conducted an assessment and comparison of the transportation and storage expenses associated with hydrogen and ammonia. [ABSTRACT FROM AUTHOR]

Hydrogen, known for its renewable nature, high energy utilization efficiency, and clean combustion, holds significant importance as a component in future energy systems. However, the development of an economical, safe, and efficient method for hydrogen storage remains a formidable challenge. In recent decades, researchers have made significant progress in achieving reversible hydrogen absorption and release using various metal hydrides. Among them, magnesium hydride (MgH 2) has attracted considerable attention for its high energy density, low cost, and good reversibility. Nevertheless, the high hydrogen absorption and desorption temperature, sluggish kinetic properties, and poor cycling performance of MgH 2 remain as the bottlenecks for its practical application. To mitigate these deficiencies, significant research efforts have been focused on the development of carbon-based materials as a means of preparing multifunctional materials. Carbon-based materials have demonstrated great potential in facilitating synergistic modification strategies, such as nanosizing, catalytic effects, and spatial confinement, which have been proven effective in enhancing the hydrogen storage performance of MgH 2. In this paper, we present a comprehensive overview of various carbon-based materials, highlighting their unique properties and their contribution to improving hydrogen storage within MgH 2 matrices. To be specific, we have been systematically reviewed the synergistic impacts of carbon materials, metal-organic frameworks, transition metal carbides (MXenes), and their respective composites on enhancing the hydrogen storage performance of MgH 2. Additionally, this study underscores the benefits of utilizing multifunctional carbon-based materials as modifiers for MgH 2 and proposes potential avenues for academic research. [Display omitted] • The properties and benefits of various carbon-based materials has been comprehensively reviewed. • Carbon-based materials and their roles in improving the hydrogen storage of MgH 2 have been thoroughly investigated. • The promise of multifunctional carbon-based materials as modifiers for MgH 2 is highlighted. • The future directions of carbon-based materials in hydrogen storage are discussed. [ABSTRACT FROM AUTHOR]

Multi-layer wound cylindrical shells are the preferred structures for storage vessels working in high pressure and hydrogen atmosphere. However, they are susceptible to external blast loads from accidental hydrogen explosions. In order to study the response of such structures under external blast loading, a numerical model was developed, which combined a thermo-viscoplastic constitutive model and a fluid-structure coupling approach, and was subjected to external blast loads of different TNT equivalency weights. The strain responses and initial velocity fields of the structure were analyzed. A rigid-plastic theoretical model was also developed to calculate the maximum displacement of the inner shell and was compared with the simulation results. Moreover, the axial velocity vibration histories and dominant frequencies at different locations of the steel belts were numerically obtained. In addition, four vibration modes of the steel belts were presented in this paper. Furthermore, strain growth was observed in the high-frequency vibration area, and the possible reasons for the strain growth were analyzed and discussed in detail. The results will be useful for predicting the deformation modes of such multi-layer wound cylindrical shell structures under the risk of external hydrogen explosions. • Blast wave propagation and dynamic structural response were coupled together. • Maximum deformation of inner shell was calculated by rigid-plastic modal solution. • Vibration pattern and frequency of outer shell were revealed. • Superposition of vibrations with high frequencies causes strain growth. [ABSTRACT FROM AUTHOR]

Hydrogen storage cylinder is an important component in high-pressure gaseous hydrogen (HPGH 2) storage system, and plays a key role in hydrogen-powered transportation including land vehicles, ships and aircrafts. Over the past decade, the number of hydrogen fuel cell vehicles (HFCVs) has rapidly increased worldwide. In order to promote the application of hydrogen storage cylinder, guide its design, manufacture, inspection and testing, a series of regulations, codes and standards have been issued. The Chinese national standard, GB/T 42612, for type IV hydrogen storage cylinders has also been issued. This paper first gives a brief overview to these regulations, codes and standards. Furthermore, the specifications including scope, category, filling cycles, service life, materials, design, manufacture, qualification tests and periodic inspections are analyzed and compared. Issues about evaluation method for hydrogen compatibility of non-metallic materials, welded joints of plastic liner, joint between boss and liner are also discussed. Notably, the performance requirements in GB/T 42612 are generally in accordance with the international ones, but the requirements of materials, design and manufacture are more detailed. • The regulations, codes and standards for on-board high-pressure hydrogen storage cylinders are compared. • An in-depth analysis of scope, category, filling cycles, service life, materials, design, manufacture, etc. is provided. • The requirements for materials, design and manufacture in GB/T 42612 are more detailed than the others. • NDT methods for welded joints of plastic liner and joints between plastic liner and metal boss need to be developed. • Effective periodic inspection methods other than visual inspection need to be further researched. [ABSTRACT FROM AUTHOR]

The cost of hydrogen production from environmentally friendly energy resources is a primary barrier to fully realizing a hydrogen economy. Therefore, a detailed analysis of hydrogen production costs from various sustainable routes is required. This paper presents a comparative economic study of hydrogen production using several nuclear reactors integrated with electrolysis hydrogen production methods. The Hydrogen Economic Evaluation Program (HEEP) software is used for comparing hydrogen production using different technologies. The HEEP tool was developed by International Atomic Energy Agency (IAEA) and offers comprehensive data for the different nuclear power plants, hydrogen production processes, and various storage and transportation options. The current study utilizes HEEP capabilities to evaluate the cost of nuclear hydrogen production and compare it with non-nuclear sources. Furthermore, it considers the cost of hydrogen storage and transportation options. The reactors considered are Advanced Pressurized Water Reactor (APWR) and High Temperature Gas-cooled Reactor (HTGR) to power low- and high-temperature electrolyzers. In addition, the costs of hydrogen produced using electricity from grid, solar, and wind are evaluated and compared with that of nuclear plants. It is found that the cost of hydrogen production and storage using Compressed Gas (CG) from an APWR plant is 8.2 $/kg for a plant capacity of 360 MWe; the cost is reduced to 6.06 $/kg when the capacity increased to 1117 MWe. It is also found that HTGR integrated with HTSE can produce hydrogen at 3.51 $/kg, which is slightly lower than the case of using the grid electricity, which costs 3.55 $/kg. • Studied costs of electrolysis hydrogen production using APWR and HTGR at different scales. • Compared costs of hydrogen production using nuclear, solar, wind, and grid electricity. • Considered additional costs for compression, liquefaction, and metal hydride storage options. • Evaluated and compared vehicle and pipeline transportation costs for 500 km. [ABSTRACT FROM AUTHOR]

Hydrogen storage vessels in hydrogen refueling stations are densely arranged, so high-speed fragments generated by explosion accidents may endanger adjacent vessels. It is of great significance to explore the dynamic responses and damage modes of hydrogen storage vessels under impact loads to promote the intrinsic safety development of hydrogen storage vessels. In this paper, a finite element analysis model is developed for simulating the dynamic responses of vessels under the impact of fragments. The influences of the number of winding layers, impact velocity, fragment mass, and fragment shape are investigated. The results show that fragment impact is a kind of local damage behavior with two typical stages of hitting and rebounding. The impact resistance of vessels increases with the number of winding layers. Impact velocity and fragment mass are positively related to deformation and damage. Conical fragments have stronger damage abilities, while spherical fragments cause greater deformation. [Display omitted] • The dynamic response and damage modes of vessels under impact were investigated. • The impact resistance of vessels increases with the number of winding layers. • Different factors have different effects on the damage and deformation of vessels. • System energy is mainly converted into internal energy. [ABSTRACT FROM AUTHOR]

In this paper hydrogen sorption properties of Mg–V multilayer thin films are studied. Thin films are synthesized by means of RF magnetron sputtering. Further modification of material is done using low energy H ion irradiation. The hydrogen sorption properties and kinetics are assessed using TOF-ERDA, in situ optical microscopy coupled with TDS, and TEM analysis. The results of TOF-ERDA indicate full hydrogenation of samples, although the presence of oxygen throughout the film is observed. It corresponds to the formation of MgO, also confirmed by EELS results with hydride plasmon peak hindered by MgO peak. Hydrogenation causes severe damage to the surface of the film and fragmentation of the V layer. TDS and optical analysis indicate lower desorption temperatures for thinner films. The desorption onset does not depend on defects concentration. The kinetic analysis further shows that the apparent activation energy for the thinner film is two times lower. • Mg/V sandwich multilayer thin films are synthesized by RF magnetron sputtering. • The results of TOF-ERDA indicate full hydrogenation of samples. • Apparent activation for desorption depends on thickness. • TDS indicates lower desorption temperatures for thinner films. [ABSTRACT FROM AUTHOR]

With the extensive utilization of fossil fuels, environmental concerns have been growing. Hydrogen-powered vehicles (HPVs) as well as hydrogen refueling stations (HRSs) are expected to proliferate to alleviate the pollution. In order to promote the economic valibity of HRSs, this paper proposes an optimal scheduling model for distributed HRSs to maximize HRSs' revenue during a day. HRSs serves both the mobility sector with fuel individually and the power system with reserve demand response collaboratively. The elaborated operating of electrolysers and relaxed control of hydrogen storage are involved to enhance practicability and flexibility of the scheduling. Considering that this model has multiple variables, intractable high-dimension nonlinear constraints, a transfer multi-agent reinforcement learning algorithm is developed. The algorithm consists of two parts: the one is the multi-agent optimization method by transforming multi-decision optimization into a multi-agent optimization; the other is to transfer the empirical knowledge of the source task to reinforcement learning according to the similarity between the source task and the target task, making it cut down the blindness of exploration and accelerate convergence. Numerical studies reveal that participating in the reserve services market collaboratively increases overall revenues of HRSs by up to 32.90%, and the computation time is sharply shortened by approximately 34 times compared to the basic reinforcement learning. • A joint operation model of distributed HRSs is proposed to lift revenue by 32.90%. • Relaxed control of hydrogen storage is utilized to minimize service deviation. • An evolutionary transfer reinforcement learning shortens solving time by 34 times. [ABSTRACT FROM AUTHOR]

This paper aims at the development and validation of a computational fluid dynamic (CFD) model for simulations of the refuelling process through the entire equipment of the hydrogen refuelling station (HRS). The absence of such models hinders the design of inherently safer refuelling protocols for an arbitrary combination of HRS equipment, hydrogen storage parameters, and environmental conditions. The CFD model is validated against the complete process of refuelling lasting 195s in Test No.1 performed by the National Renewable Energy Laboratory (NREL). The test equipment includes high-pressure tanks of HRS, pressure control valve (PCV), valves, pipes, breakaway, hose, and nozzle all the way up to three onboard tanks. The model accurately reproduced hydrogen temperature and pressure through the entire line of HRS equipment. A standout feature of the CFD model, distinguishing it from simplified models, is the capability to predict temperature non-uniformity in onboard tanks, a crucial factor with significant safety implications. • CFD model of refuelling through the entire HRS equipment reproduced NREL Test No.1. • Complete hydrogen refuelling process of 195 s simulated in 2 days on 32-core CPU. • The model can be used to design fuelling protocols for HRS with any equipment. [ABSTRACT FROM AUTHOR]

Underground hydrogen storage has been the subject of extensive research recently. Hydrogen diffusion coefficient into brine critically affects hydrogen loss. However, the available data pertain to hydrogen diffusivity in pure water or NaCl solutions, with rare interpretations of temperature and salinity effects. In this paper, molecular dynamics simulations at realistic conditions were conducted to calculate these coefficients in various brines, particularly those containing divalent salts. The results indicate lower diffusivities at higher salinities and lower temperatures, the value being 7.29 × 10−9 m2/s at 323 K, increasing to 10.2 × 10−9 m2/s at 353 K for 1 molal NaCl solution. The diffusion coefficient decreases up to 38 % as the salinity increases from 1 to 5 molal. Besides, hydrogen diffusivity in MgCl 2 solution is up to 60 % smaller than in NaCl solutions at the same molality. Radial distribution functions and hydrogen bond analyses confirm the results. This research provides new data for estimating hydrogen loss in aquifers or water-saturated caprocks. [Display omitted] • The diffusion coefficient of hydrogen in brine is calculated at actual UHS conditions. • The simulation results are validated using literature data. • The impacts of salinity and temperature on the diffusivities are evaluated. • The hydrogen diffusivity in MgCl 2 and NaCl solutions are compared. • A mathematical model to predict hydrogen diffusivity in NaCl solution is presented. [ABSTRACT FROM AUTHOR]