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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]

The world is still largely dependent on oil and natural gas for its energy requirements which are harmful to the environment; therefore, it is high time that we look for alternative technologies for our growing energy needs. One such emerging area is fuel cell technology which produces clean energy in the form of electrical power. Integrating a Metal Hydride Hydrogen Storage (MHHS) system with a fuel cell can help increase energy efficiency. The heat dissipated during hydrogen absorption in MHHS can be used in other applications. In this paper, energy and exergy analysis of a fuel cell-based integrated system is performed. The system presents a Reversible Proton Exchange Membrane Fuel Cell capable of working in dual modes, i.e., as an Electrolyser as well as a fuel cell. The MHHS and Vapour Absorption Refrigeration System (VARS) are coupled with a reversible fuel cell for hydrogen storage and cooling applications, respectively. While working in the fuel cell mode, maximum efficiency of 47.84% is evaluated at 80 °C. The system efficiency with and without the VARS system at 80 °C was 73.29% and 47.84%, respectively. On the contrary, in the electrolyzer mode, the maximum efficiency comes out to be 85.65%. The use of the MHHS system for hydrogen storage results in excess heat release, and as a result, the overall efficiency of the electrolyzer was increased to 94.05%. • Thermodynamic integration of PEMFC with MHHS and VARS is performed. • Effect of key parameters on fuel cell system performance is investigated. • System energy and exergy efficiency of 73.3% and 59.5% respectively are reported. • The proposed system can achieve maximum electrolyzer efficiency of 85.65%. • Maximum cooling output from vapour absorption system is found to be 60.56 kW. [ABSTRACT FROM AUTHOR]

Designing self-sufficient renewable energy systems is becoming a key issue in the energy sector due to modern energy goals. Due to the variability of renewable energy sources, very often it is necessary to adopt hybrid configurations of renewable energy systems and advanced energy storage to achieve self-sufficiency. However, the adoption of complex and novel systems, including technologies as photovoltaic, wind turbines, biomass gasifiers, hydrogen energy storage, must to be founded on a comprehensive analysis of the system operation under different conditions and its energy and economic performance in the investigated case study. Therefore, the aim of the present paper is carry out a comprehensive feasibility analysis of a novel hybrid renewable energy system achieving a high self-sufficiency level. The system integrates a wind turbine and photovoltaic panels to match the energy load of a tourist resort in Agkistro, Greece. Energy exceeding the load is directed to the energy storage system based on the battery and hydrogen tank. As backup energy source, a wood gasifier is used. The investigation is performed by means of a numerical model developed in TRNSYS software allowing one to simulate dynamically the system and to assess its energy and economic performance. The goal achieved during the simulation of the system was to ensure at least 97% of energy demand from renewable sources. Moreover, a parametric analysis of the storage system is presented. It is found that payback period of the installation varies in the range between 11 and 15 years, for systems configurations allowing to satisfy 90–98% of the users energy yearly demand from renewables. The achieved results allows one to evaluate the feasibility of the proposed system from both an energy and economic point of view. • Island energy systems in Greece. • Hybrid energy system with both battery and hydrogen energy storage. • 97% reduction of energy produced from fossil fuels with 30% of energy curtailed. • Parametric study concerning sizes of the energy storage. [ABSTRACT FROM AUTHOR]

The majority of research in the carbon-based nanomaterials (CNMs) field has concentrated on the classification and synthesis of CNMs, with relatively few studies focusing on CNMs' roles in photocatalytic hydrogen production. CNMs have proven their potential as an effective addition to the appeal of photocatalytic hydrogen evolution because of their superior chemical and physical properties. This paper explores the recent advancements in photocatalytic hydrogen (H 2) production utilizing CNMs. As evidenced in the literature, carbon quantum dot (CQD)-sensitized titanium dioxide (TiO 2) can demonstrate to have a photocatalytic hydrogen generation activity of 472 mol g−1 h−1 and 1458 mol g−1 h−1 without and with loading metal co-catalyst (Pt). The optimum catalyst, 0.4 CQD/CdS, contributes to the highest H 2 production rate of 309 mmol g−1 h−1 (apparent quantum yield of 32.6%), which is 1.5 times greater than that of bare CdS. This would significantly accelerate the hydrogen production process. There are still challenges to reaching maximum photocatalytic hydrogen production, including low hydrogen storage. The overall price of hydrogen produced via photocatalysis is also higher because of the energy needed to store the hydrogen. Even though the problem is not directly related to the usage of CNMs, this restriction generates uncertainty and limits commercial investment. Given the rising demand for energy and the trend toward green power, it is recommended that extensive industrial uses of photocatalytic hydrogen produced by employing CNMs be investigated for better and more sustainable energy frameworks. • Recent advances in photocatalytic H 2 production are investigated utilizing CNMs. • The optimum catalyst, 0.4 CQD/CdS can produce the highest H 2 at 309 mmol g−1 h−1. • CQD-sensitized TiO 2 can generate 1458 mol g−1 h−1 photocatalytic hydrogen with Pt. • Photocatalytic H 2 production using CNMs should be investigated for industrial use. [ABSTRACT FROM AUTHOR]

Green hydrogen, proposed as a sustainable alternative for conventional fuels, has gained utmost importance due to its reduced carbon footprint and potential application in maintaining balance between energy generation and demand. Utilization of hydrogen-based systems are challenged by cost effective storage methods. Bio-hydrogen storage technologies using cryogenic and adsorptive methods are discussed in this review paper, along with their operating conditions and storage capacities. An analysis of operational challenges and recent advancements in hydrogen storage techniques is presented. With a storage pressure of 70 MP, cryogenic hydrogen is almost twice as dense as compressed hydrogen. Technical challenges such as material cost and explosion risk can be addressed by hydrogen adsorption on activated carbon active sites. Maximum hydrogen storage capacity are reported by activated carbon obtained from Chitosan (6.77 wt%), Bamboo (6.6 wt%) and African palm shell (6.5 wt%) at 77 K and 4–20 Mpa. Further, nanotechnology approaches are presented in detail for increasing hydrogen storage capacity in pristine Si and Mg. The future perspectives in terms of technological, and economic aspects are discussed. • Detailed review on hydrogen storage methods is presented. • Role of cryogenics and adsorptive media are discussed. • The comparative performance of various methods is tabulated. • Existing research gap and future perspectives are analyzed. [ABSTRACT FROM AUTHOR]

This paper discusses the technical and economic feasibility of a renewable energy-based system, aimed to replace the traditional diesel engines implemented on a pushed and pusher bulk carrier barge. This barge has a challenging navigational route in the Nile River from Alexandria to Aswan and vice versa. It is scheduled to complete 30 trips annually while carrying 850 tons/trip. The system is based on photovoltaic panels, and was selected with its excess energy to be stored primarily in the form of H 2 gas through electrolysis, and batteries (i.e. Power to Gas technology) to be later converted back to electrical energy through fuel cells. Hence, an operation algorithm was formulated to optimize the performance of the system by defining operating modes that use solar energy, hydrogen energy, batteries, or hybrid energy coming from multiple sources that result in an internal rate of return (IRR) of 15.1% and overall efficiency of 57.9%. This high efficiency is due to the nature of water current that flows from south to north of Egypt, therefore, causing a significant reduction in power demand in the trip from Aswan to Alexandria that requires 11,980 kW h, compared to the trip from Alexandria to Aswan that requires 21,064 kW h. • Zero emission solution combining solar energy, hydrogen generation and fuel cell propulsion for a barge in Nile River. • Preparation to achieve the 7th goal of sustainable development ensuring green propulsion in Nile River cargo transport. • Efficient use of natural resources, solar energy and water current from south to north of Egypt. • Integrating electrolizer, fuel cell, solar energy pv, batteries, and hydrogen storage to form an autonomous barge. [ABSTRACT FROM AUTHOR]

Precooling technology is a widely used method for increasing the flight speed of turbojet engines. To solve the problems of oversized fuel tank and engine performance degradation caused by the low density of hydrogen fuel, a new precooled engine cycle based on hydrogen production technology from ammonia cracking is proposed. To evaluate the engine performances, a thermodynamic model and a test platform are established. The study shows that the test heat sink of ammonia is 4.12 MJ at 620.5 °C, and the upper boundaries of heat sink and hydrogen production rate of ammonia are higher than other chemical fuels. Besides, the optimized fuel ratio is set to 2.0, and the best compressor pressure ratio could be obtained at the point with the highest engine performances Further, the maximum flight Mach number of precooled engine is Ma 4.69, and compared with GE90 and J-58 engines, the carbon emission of precooled engine could be reduced by 94.15% and 72.95% respectively. Moreover, by increasing the cold storage degree, the engine performance can be further improved especially at high pressure ratio. Overall, the research of this paper is hopeful to provide a new idea and necessary theoretical support for the development of high-performance supersonic aero-engine. • A new precooled engine cycle based on hydrogen production technology is proposed. • The test heat sink of ammonia reaches 4.12 MJ at 620.5 °C. • The maximum flight Mach number of precooled engine is Ma 4.69. • The carbon emission of precooled engine could be reduced by 94.15%. • The method to improve the engine performances through clod storage is also proposed. [ABSTRACT FROM AUTHOR]

Economical hydrogen storage and transportation contribute to hydrogen energy utilization. In this paper, for economically distributing hydrogen from the hydrogen plant to the terminal hydrogen refueling station, considering the daily hydrogen demand and transportation distance, firstly a comprehensive techno-economic analysis of the point-to-point hydrogen storage and transportation system based on compressed gas hydrogen (GH), liquid hydrogen (LH), pipeline hydrogen (PH), and liquid organic hydrogen carriers (LOHC) is investigated, respectively. The optimal economical point-to-point energy storage and transportation modes under various transportation distance and daily hydrogen demand are obtained. Then the economic analysis of different hydrogen storage and transportation modes under 1-to-N hydrogen storage and transportation scenario is conducted, which can significantly decrease the cost of LH storage and transportation mode. To step further, the 1-to-N relay hydrogen storage and transportation scenario is constructed to improve the applicability and reduce the unit cost. The economic analysis of 14 kinds of feasible combinations of hydrogen storage and transportation modes is systematically assessed. Regarding to the transportation distance and daily hydrogen demand, the optimal economical 1-to-N relay energy storage and transportation modes are identified. This study may contribute to rationally design and application for economic hydrogen storage and transportation systems. [Display omitted] • The economics of point-to-point hydrogen storage and transportation scenario is investigated. • The economics of the 1-to-N hydrogen storage and transportation scenario is analyzed. • 1-to-N relay hydrogen storage and transportation scenario is constructed to improve economic applicability. • 1-to-N relay hydrogen storage and transportation scenarios may exhibit obvious economic advantage. [ABSTRACT FROM AUTHOR]

Variable Renewable Energy Sources are crucial for decarbonizing industries and efficient energy storage. Hydrogen storage technologies are limited in their large-scale capabilities. PtL technology can synthesize alternative fuels like methanol, which can be used in existing energy infrastructures to produce liquid fuel. The paper presents an innovative approach for utilizing in-situ thermal energy, using a hot reservoir rock (HRR) system for methanol synthesis at high temperature and pressure in an underground large-scale natural reservoir reactor. This approach aims to integrate renewable energy technologies into a single energy generation and fuel production system, including the direct utilization of renewable sources. Solutions from the oil and gas industry can be adapted to this action, such as continuous injection, alternate injection, separate injection, or chemical flooding. Conventional geothermal reservoirs, HDR systems, and depleted hydrocarbon reservoirs can be used as "underground reactors". However, it was also noted that there are challenges, such as catalyst distribution and the complexity of reservoir pore space. • Reservoir rock as a geochemical reactor for underground in-situ e-methanol synthesis. • Synergy between energy storage, CCUS, e-methanol production, and geothermal energy. • Effective use of surplus renewable energy with hydrogen technologies. • Risk reduction related to chemical processing and high environmental neutrality. • Use of resources related to the oil and gas industry for the energy transition. [ABSTRACT FROM AUTHOR]

In a 100% renewable energy scenario, power generation fluctuates, requiring management and control of this generation. Storage is presented as a solution to regulate production discontinuity. In particular, seasonal storage can compensate for long-term fluctuations and serve as a necessary complement to short-term storage management. Due to the potential role of hydrogen in the decarbonization of energy production systems, this research attempts to analyse the levelized cost of storage (LCOS) of this energy carrier as a solution to long-term electricity requirements. The research focuses on the analysis of the total Power-to-Power (P2P) process cost, all factors affecting the input of electricity up to the output of electricity after the conversion of the hydrogen are considered. A transformation of the surplus electricity to hydrogen through a PEM electrolyzer is proposed in this paper. This hydrogen would be stored seasonally in salt caverns. Finally, a gas-to-energy transformation using gas turbines or fuel cells is contemplated. The analysis presents highly competitive results in terms of cost, demonstrating the system's competitiveness and potential: the turbine powered by 100% hydrogen solution appears to be more cost effective than the fuel cell solution: 0.207€/kWh and 0.284€/kWh respectively. Hydrogen storage presents itself as the most cost-effective long-term alternative in the near future, even better than pumped hydro, compressed air or batteries. • LCOS: Levelized Costs of Storage for a large-scale and long-term system. • The use of hydrogen as an energy carrier to store electrical energy from renewable sources at large scale. • Long-term storage of hydrogen in salt caverns. • Transformation of stored hydrogen into electricity through turbine and fuel cells. [ABSTRACT FROM AUTHOR]

In renewable-based microgrids, intermittency caused by some energy sources highlights the important role of energy storage systems. Nowadays, hydrogen and thermal energy storage are expected to play key roles in grid-scale applications, for facilitating effective penetration of clean energy sources. This paper, through a multilevel control framework for the energy management of a renewable and reversible solid oxide based microgrid, develops medium level controls accounting for the dynamic behaviour of storage systems. The storage systems considered are a hydrogen storage tank and a thermal energy storage based on phase change material technology. In particular, the proposed algorithm is helpful in the microgrid design phase as well as for clearly assessing high-level energy management strategies, since dynamic and transient behaviours of tanks during both charging and discharging phases are validated. In this way, top-level energy management strategies can be further refined and optimized in addition to a techno-economic design being pursued, primarily through shrinking the initial sizes of storages and thereby achieving significantly lower initial capital costs. For the analyzed microgrid, its feasibility is demonstrated by reducing by as much as 40% the size of the hydrogen tank and by up to 20% the energy capacity of the thermal storage. Finally, the proposed medium level control in a multilevel algorithm framework for a hydrogen-based microgrid is also seen to be fruitful for avoiding waste energy, which can be beneficial against the background of distributed energy systems acting in virtual power plants. • An rSOC-microgrid relying on renewables and innovative storages (i.e., HST and PCM-TES). • Multilevel control strategy checking storages resiliency in terms of energy satisfaction. • HST and TES sub-models considering transient phases for charging and discharging. • Scenario analyses aimed at optimizing both energy and economic aspects of energy storages. [ABSTRACT FROM AUTHOR]

This paper introduces a Techno-Economic Assessment (TEA) on present and future scenarios of different energy storage technologies comprising hydrogen and batteries: Battery Energy Storage System (BESS), Hydrogen Energy Storage System (H 2 ESS), and Hybrid Energy Storage System (HESS). These three configurations were assessed for different time horizons: 2019, 2022 and 2030, under both on-grid and off-grid conditions. For 2030, a sensitivity analysis under different energy scenarios was performed, covering other trends in on-grid electric consumption and prices, CO 2 taxation and the evolution of hydrogen technology prices from 2019 until 2030. The selected case study is the Research Park Zellik (RPZ), a CO 2 -neutral sustainable Local Energy Community (LEC) in Zellik, Belgium. The software HOMER (Hybrid Optimisation Model for Electric Renewable) has been selected to design, model and optimise the defined case study. The results showed that BESS was the most competitive when the electric grid was available among the three possible storage options. Additionally, HESS was overall more competitive than H 2 ESS-only, regardless of the grid connection mode. Finally, as per HESS, hydrogen was proved to play a complementary role when combined with batteries, enhancing the flexibility of the microgrid and enabling deeper decarbonisation by reducing the electricity bought from the grid, increasing renewable energy production and balancing toward an island operating mode. • Assessment of hybrid energy storage systems for future energy scenarios. • Sensitivity analysis with different technical, economic, and environmental KPIs. • Analysis of the effects of the connection and capacity access to the electric grid. • Application to a real case study: a CO2-neutral Local Energy Community. [ABSTRACT FROM AUTHOR]

Hydrogen is seen as a key energy vector in future energy systems due to its ability to be stored in large volumes for long periods, providing energy flexibility and security. Despite the importance of storage in hydrogen's potential role in a zero-carbon energy system, many techno-economic analyses fail to adequately model different storage methods in hydrogen supply chains, often ignoring storage requirements altogether. Therefore, this paper uses a data-driven techno-economic analysis (TEA) tool to examine the effect of storage size and cost on three different 2030 hydrogen supply chain scenarios: wind-based, solar-based, and mixed-source grid electrolysis. For varying storage sizes and specific capital costs, the overall levelised cost of hydrogen (LCOH), including production, storage, and delivery to a constant demand, varies significantly. The LCOH ranges from €3.90–12.40/kgH 2 , €5.50–12.75/kgH 2 , and €2.80–15.65/kgH 2 for the wind-based, solar-based, and mixed-source grid scenarios respectively, with lower values for scenarios with low-cost storage. This highlights the critical role of low-cost hydrogen storage in realising the energy flexibility and security electrolytic hydrogen can provide. • Techno-economic analysis tool examines the effect of storage on hydrogen production. • Wind-based, solar-based, and grid electricity-based electrolysis scenarios examined. • Production only cost of hydrogen decreases by up to 35% with increasing storage size. • Up to 56 days of storage required to supply renewable hydrogen at a constant hourly rate. • Overall cost of renewable hydrogen in 2030 varies from €2.80–15.65/kgH 2. [ABSTRACT FROM AUTHOR]

Hydrogen is a promising energy source for resolving the world's energy demands without releasing pollution, but storing hydrogen poses a significant challenge. Carbon materials such as activated carbon (AC), carbon nanotubes (CNT), carbon nanofibers (CNF), carbon nano-onions (CNOs) and graphene are potential substrate materials for hydrogen storage through physisorption/chemisorption due to their large surface areas and the ability to bind hydrogen. We investigate the hydrogen storage capacity of CNOs synthesized through thermal chemical vapour deposition using acetylene in this paper. SEM and XRD analysis revealed that the CNOs are spherical and comprised 18 shells at 850 °C and 7 shells at 1000 °C. However, the CNO interlayer thickness increased from 3.42 to 3.58 A0, which has a significant impact on the physisorption process. Functionalized CNOs were studied for their hydrogen storage capacities at 77 K and 1.5 atm, demonstrated a hydrogen storage capacity of 18.2%. The BET measurements revealed that the CNOs samples have a surface area of 642 m2/gm and FTIR showed a significant increase in –OH and –CH bond vibrations. Desorption studies of hydrogen reveal primarily two stages. The removal of hydrogen from CNO requires a first-stage activation energy of 6 kJ/mol and a second-stage activation energy of 127 kJ/mol, confirming the presence of both physiosorbed and chemisorbed hydrogen. This study found that hydrogen storage capacity of CNOs is extremely promising, and has a potential for mobile applications. • The hydrogen storage capacity of synthesized CNOs was determined. • The functional groups are determined using FTIR analysis. • The number of shells, carbon atoms, interlayer thickness are calculated by XRD. • The hydrogen desorption kinetics are investigated using Coat's-Redfern's method. [ABSTRACT FROM AUTHOR]

This paper presents a novel energy management strategy (EMS) to control a wind-hydrogen microgrid which includes a wind turbine paired with a hydrogen-based energy storage system (HESS), i.e., hydrogen production, storage and re-electrification facilities, and a local load. This complies with the mini-grid use case as per the IEA-HIA Task 24 Final Report, where three different use cases and configurations of wind farms paired with HESS are proposed in order to promote the integration of wind energy into the grid. Hydrogen production surpluses by wind generation are stored and used to provide a demand-side management solution for energy supply to the local and contractual loads, both in the grid-islanded and connected modes, with corresponding different control objectives. The EMS is based on a hierarchical model predictive control (MPC) in which long-term and short-term operations are addressed. The long-term operations are managed by a high-level MPC, in which power production by wind generation and load demand forecasts are considered in combination with day-ahead market participation. Accordingly, the hydrogen production and re-electrification are scheduled so as to jointly track the load demand, maximize the revenue through electricity market participation and minimize the HESS operating costs. Instead, the management of the short-term operations is entrusted to a low-level MPC, which compensates for any deviations of the actual conditions from the forecasts and refines the power production so as to address the real-time market participation and the short time-scale equipment dynamics and constraints. Both levels also take into account operation requirements and devices' operating ranges through appropriate constraints. The mathematical modeling relies on the mixed-logic dynamic (MLD) framework so that the various logic states and corresponding continuous dynamics of the HESS are considered. This results in a mixed-integer linear program which is solved numerically. The effectiveness of the controller is analyzed by simulations which are carried out using wind forecasts and spot prices of a wind farm in center-south of Italy. • Design of control algorithms for islanded and grid-connected microgrids. • Development of hierarchical MPCs to target long-term and short-term operations. • Tracking the load demand and maximizing the revenue via electricity markets. • Minimization of the HESS operational costs. [ABSTRACT FROM AUTHOR]

Liquid Organic Hydrogen Carriers (LOHCs) feature a highly variable rate of hydrogen release if held at constant pressure and temperature, but in real-life applications hydrogen release must be controlled to match end-user demand. The aim of this paper is to provide an overall assessment of LOHC systems' controllability, within a general framework regardless of the specific application field. Hydrogen discharge can be controlled through the reactor pressure and temperature; thus, a PI controller is introduced acting on three control variables independently: discharge pressure; thermal fluid inlet temperature; thermal fluid mass flow rate. A quantile analysis is performed on the uncontrolled hydrogen release: practical values of the energy-to-power ratios for LOHC systems are 2–6 h. A normalised release time is introduced to assess the efficiency of the control system. Temperature control leads to the best results, with an efficiency higher than 90% for the entire load range, while pressure control leads to satisfactory performance only at low loads. The mass flow rate control is the least effective, with efficiencies always below 80%. Sensitivity analysis highlights the temperature control strategy as the best fit to enhance controllability across the whole power range. Pressure control presents a more variable trend. • Liquid Organic Hydrogen Carriers release hydrogen at highly variable flow rates • Flow rate control systems are required to meet end-user demand • Control variables: discharge pressure, thermal fluid inlet temperature and flow rate • Heat transfer fluid inlet temperature provides the most effective control • Very good controllability expected with synergic pressure and temperature controls [ABSTRACT FROM AUTHOR]

As a promising candidate for accident-tolerant fuel (ATF) cladding materials, FeCrAl alloys are susceptible to hydrogen embrittlement (HE) under high-temperature radioactive water environments. Understanding the HE mechanism of FeCrAl is crucial, and studying H 2 dissociative adsorption can provide valuable insights since it is the first step in the HE processes. In this paper, we investigated the H 2 dissociative adsorption on Fe (110) and FeCrAl (110) surfaces using first-principles calculations based on Density Functional Theory (DFT). Our results indicate that the decomposition of H 2 molecules on FeCrAl (110) surfaces is significantly affected by surface elemental effects compared to Fe (110) surfaces. Specifically, Al atoms weaken both the H 2 decomposition and the H binding strength of Al-containing sites. Cr atoms decrease the decomposition tendency of H 2 in certain configurations, but Cr aggregation enhances the binding strength of H atoms on Cr-containing sites. The mechanism underlying the Al/Cr weakening effects on H 2 decomposition is due to the charge deficiency through alloying. Our findings have generalized implications for studying the interactions between iron-based alloys and hydrogen in various applications such as hydrogen storage, transportation, and prevention. • The strength of H 2 –Fe/Cr/Al interactions follow the order: H 2 –Al < H 2 –Cr < H 2 –Fe. • Al atoms have strong weakening effect on H 2 dissociation compared to Fe. • Cr atoms have slight weakening effect on H 2 dissociation compared to Fe. • The Cr aggregation can enhance H 2 –Cr interaction & H binding strength. • The weakening effects of Al & Cr on H 2 dissociation are caused by the charge deficit of Al & Cr after alloying with Fe. [ABSTRACT FROM AUTHOR]

This paper established a two-dimensional axisymmetric model with a marine high-pressure hydrogen storage tank as the research object. Using numerical simulation, the effects of different aspect ratios, inlet diameters, and inlet pipe lengths on the temperature rise of the hydrogen storage tank during the filling process were studied. As the L/D ratio of the hydrogen storage tank increases, the momentum of the hydrogen gas reaching the bottom of the tank gradually decreases, making it easier to form localized high-temperature regions. For a hydrogen storage tank with an L/D of 6.0, the difference between the maximum and average temperature at the end of filling was 155.85 K. In contrast, the temperature difference of the tank with an L/D of 3.6 was only 32.81 K. In addition, the inlet pipe delivers the hydrogen deep into the tank and reduces the obstructing effect of the existing hydrogen in the tank on the newly filled hydrogen. For smaller L/D hydrogen storage tanks, the inlet pipe may backfire and create a high-temperature zone at the shoulder of the tank. In contrast, for larger L/D hydrogen storage tanks, a suitable length of inlet pipe can deliver the hydrogen deep into the tank. This will enhance the gas flow inside the tank, facilitating heat exchange and avoiding the formation of localized high-temperature areas at the bottom of the tank. However, excessively long inlet pipes can also lead to high-temperature areas on the shoulders. At a specific charge mass flow rate, the lower the inlet diameter, the higher the hydrogen flow rate. The larger flow rate helped promote uniform hydrogen mixing in the tank and made it challenging to form localized high-temperature regions. • Effects of L/D ratio, inlet diameter and length on filling process are studied. • The inlet pipe lengths have different effects on cylinder with different L/D. • A suitable length of inlet tube can effectively reduce the hydrogen temperature. • Some recommendations are given to optimize the design of hydrogen storage tank. [ABSTRACT FROM AUTHOR]

In this paper, the hydrogen storage properties of the MmNi 4.6 Al 0.4 and MmNi 4.6 Fe 0.4 compounds are compared experimentally and theoretically. The experimental curves of the activation process, experimental isotherms of absorption and the Van't Hoff's plot were first investigated. Following that, a theoretical model is contrasted with the experimental data. The mathematical equations of this model contain parameters, such as the number of hydrogen atoms per site (n 1 , n 2), the densities of the receiving sites (N 1m , N 2m), and the energy parameters (P 1 , P 2). All these parameters are obtained by numerically adjusting the experimental data. Depending on the applied temperature, the relevant parameters of the suggested model were identified and described. Entropy, internal energy, and other thermodynamic variables that govern the absorption reaction were all calculated and displayed as a function of pressure and temperature. • Measurement of hydrogen absorption isotherms by MmNi 4.5 Al 0.4 and MmNi 4.6 Fe 0.4 compounds. • Validation of experimental data by a mathematical model using statistical physics. • Determination of the steric parameters governing the absorption reaction. • Calculation of the thermodynamic functions of the absorption reaction. [ABSTRACT FROM AUTHOR]

The paper emphasizes the significance of sustainable energy solutions centered around electric vehicles (EVs). This involves Electric Intelligent Parking Lots (IPLs) that are interconnected with Renewable Energy Sources (RES) and Hydrogen Storage Systems (HSS) to achieve both technical and environmental goals. The study introduces a probabilistic approach to managing HSS-based energy in IPLs, employing the Probabilistic Two-Point Estimate Method (TPEM) to consider variables like sun radiation, temperature, wind speed, and IPL load. The Honey Badger Algorithm (HBA) is employed for optimization, striving to minimize operational costs related to energy distribution while maximizing profits by exploring revenue opportunities within the IPL system. This strategy enhances energy management and intelligent EV charging in IPLs, improving efficiency and economic viability. The approach is tested in a standard IPL environment integrated with RES and load demand, showcasing its successful technical and financial outcomes. Results reveal a 7.8 % profit increase from renewable resources and an additional 4.89 % when uncertainties are factored in. Ultimately, the proposed energy management framework utilizing HSS and RES integration proves effective in achieving objectives, with the potential for greater profitability through renewable resource incorporation and uncertainty consideration. • Optimal energy management framework proposed for electric vehicle integration in intelligent parking lots. • Simulation of efficient charging and discharging strategy in an IPL for electric vehicles. • Impact of renewable sources integration (wind and solar) on IPL efficiency and revenue generation. • Uncertainty analysis of renewable sources and load demands in IPL using two-point estimation method. • Smart integration of renewable sources, hydrogen storage, and electric vehicle charging for optimal operation of IPL. [ABSTRACT FROM AUTHOR]

After a natural disaster, electrical grids might go into a self-healing mode to restore service and reconnect any customers that lost power. In the self-heal system, the fast operation and restoring the critical loads (CLs) during a fault by available resources can increase the flexibility and resilience of the network. In addition to renewable energy sources and electric vehicles (EVs) storage devices, the hydrogen storage system and the process of converting hydrogen into electric energy by micro-gas turbine (MGT) have been modeled in order to assess the impact of this storage system in electrical loads restoration in critical conditions. Self-healing functionality is enhanced by using alternative and novel energy sources. In such a situation, how to interact with the stochastic nature of network components will be challenging. This paper formulates the optimal service restoration (SR) problem using chance-constrained Adaptive Distributionally Robust Optimization (ADRO) to address the ambiguities introduced by the uncertain parameters. A tri-level robust optimization model is developed such that the optimal switching in the network until clearing the fault is determined at the upper level, and the maximization of the SR based on the load demand values is determined at the lower level. The proposed method is demonstrated by simulation results on the modified Civanlar test system. In an equal operating condition and considering β = 3, it can be seen that the initial hydrogen State of the Tank (SoT) by 50 % can improve the load restoration by 7.5 % compared to the uncharged hydrogen tank. By increasing the initial SoT to the nominal value (10 Kg), the load restoration can increase to 13.2 %. [Display omitted] • Customized hydrogen into electric energy conversion model is developed in the energy management field. • Each uncertain parameter is considered ambiguous in the manner that follows an unknown but bounded distribution. • EVs, PHEVs, flexible loads, and the coordinated operation of the hydrogen-to-power system are all taken into account simultaneously. • A tri-level MILP model is formulated to determine the service restoration schedule. • CVaR is employed to effectively deal with the uncertainty of the parameters. [ABSTRACT FROM AUTHOR]

Subsurface hydrogen storage would be one of the main possible solutions for a successful energy transition in the future of world energy. However, hydrogen gas is an electron donor which may lead to microbial activity when storing hydrogen in the subsurface. Methanogenesis, acetogenesis, and sulfate reduction are the primary biological reactions that can lead to hydrogen loss through biochemical processes. This paper presents a novel bio-geochemical modelling approach which considers the kinetics of microbial reactions as well as the equilibrated geochemical reactions in the context of underground hydrogen storage. The findings demonstrate that the type of mineralogy and formation water composition may greatly influence biochemical reactions and thus potentially the storage/recovery performance of hydrogen. This study provides a detailed comparison and analysis of the behaviour occurring in calcite, dolomite, and quartz systems assuming the North Sea seawater composition as the in-situ brine. It is found that dolomite is the least favourable mineralogy in terms of hydrogen loss and hydrogen sulfide production, while calcite and quartz are better suited in a seawater-rich environment. • The interplay between biochemical and geochemical reactions during UHS is studied. • There is a strong interplay between biochemical and geochemical reactions. • Small concentrations of sulfate may lead to dangerous level of gas toxicity. [ABSTRACT FROM AUTHOR]

Magnesium-based hydrogen storage alloy has become one of the most promising hydrogen storage alloy materials due to its high hydrogen storage capacity, lightweight and abundant resources. However, the practical application of MgH 2 for hydrogen storage is still impeded by its slow kinetics and high temperature of hydrogen absorption and desorption. In this paper, the literature on the modification of alloys in recent years is summarized, and the methods to improve the properties of magnesium-based hydrogen storage alloys are briefly discussed. The research progress of transition metal-based materials and light metals to improve the kinetic and thermodynamic properties of magnesium-based hydrogen storage alloys is reviewed mainly from the classification of metal substitution method, catalytic method and light metal complexation method. By comparing the differences and characteristics of each modification method, the development direction of preparation methods of magnesium-based hydrogen storage alloys is analyzed and prospected. The first two methods mainly improve the kinetic performance by reducing the activation energy of the reaction of the magnesium-based material, while the third method is to reduce the particle size of the magnesium-based material to the nanometer level, which can greatly reduce the reaction enthalpy change during the hydrogen absorption and desorption process of the alloy, thereby reducing the hydrogen absorption temperature of the magnesium-based material. • The property improved incriminate forming a solid solution and constructing a hydrogen pump. • The alloy kinetic property the are improved by expanding the contact area between H and alloy. • The physical adsorption of hydrogen by carbon-based materials acts as a hydrogen pump. • The complex cooperates with the catalyst to clearly improve the hydrogen storage property. [ABSTRACT FROM AUTHOR]

The superabsorbent polymer (SAP) of the disposable diaper, which could serve as a substrate for pathogen growth, was valorized into nanostructured carbon through chemical activation for electrochemical hydrogen storage. The Box-Behnken experimental design was employed to elucidate the effects of activation conditions. Optimization results show that activation temperature and KOH:SAPC molar ratio had a greater impact on the textural and morphological characteristics of the nano-activated carbon. The best electrode material exhibited a surface area of 2552 m2/g, a total pore volume of 1.28 cm³/g, a total micropore volume of 0.871 cm³/g, and a pore size of 1.32 nm. The galvanostatic charge/discharge curves indicate that only higher current densities of 1 and 2 A/g could achieve a faster release of stored hydrogen in approximately 4 min. The best material stored hydrogen mainly through the electric double-layer mechanism, and the specific capacity reached 1878 mAh/g (6.60 wt% of H 2), which ranks among the best-reported hydrogen storage capacities with activated carbon. • Diaper waste was used as a sustainable precursor to prepare activated carbon. • Abundant micropores and high surface area allowed high hydrogen storage capacity. • Higher current density achieved faster release of adsorbed hydrogen atoms. • The mechanism of hydrogen storage is mainly electric double layer. [ABSTRACT FROM AUTHOR]

Underground hydrogen storage in depleted hydrocarbon reservoirs and aquifers has been proposed as a potential long-term solution to storing intermittently produced renewable electricity, as the subsurface formations provide secure and large storage space. Various phenomena can lead to hydrogen loss in subsurface systems with the key cause being the trapping especially during the withdrawal cycle. Capillary trapping, in particular, is strongly related to the hysteresis phenomena observed in the capillary pressure/saturation and relative-permeability/saturation curves. This paper address two key points: (1) the sole impact of hysteresis in capillary pressure on hydrogen trapping during withdrawal cycles and (2) the dependency of optimal operational parameters (injection/withdrawal flow rate) and the reservoir characteristics, such as permeability, thickness and wettability of the porous medium, on the remaining hydrogen saturation. To study the capillary hysteresis during underground hydrogen storage, Killough [1] model was implemented in the MRST toolbox [2]. A comparative study was performed to quantify the impact of changes in capillary pressure behaviour by including and excluding the hysteresis and scanning curves. Additionally, this study investigates the impact of injection/withdrawal rates and the aquifer permeability for various capillary and Bond numbers in a homogeneous system. It was found that although the hydrogen storage efficiency is not considerably impacted by the inclusion of the capillary-pressure scanning curves, the impact of capillary pressure on the well properties (withdrawal rate and pressure) can become significant. Higher injection and withdrawal rates does not necessarily lead to a better performance in terms of productivity. The productivity enhancement depends on the competition between gravitational, capillary and viscous forces. The observed water upconing at relatively high capillary numbers resulted in low hydrogen productivity. highlighting the importance of well design and placement. [Display omitted] • Buoyancy plays a significant role on UHS performance. • A dimensionless number analysis to study the influence of injection/withdrawal schemes on UHS performance. • Capillary pressure scanning curves did not significantly affect the hydrogen saturation distribution. • Water upconing limits the UHS performance at high flow rates. • Interplay between Bond and capillary numbers should be considered for UHS. [ABSTRACT FROM AUTHOR]

The sluggish de/hydrogenation kinetics and stable thermodynamics of magnesium hydride (MgH 2) are unfavorable for its large-scale application. Herein, the medium-entropy alloy CrCoNi nanosheets were synthesized and remarkably enhanced the low-temperature hydrogen storage performance of MgH 2. Surprisingly, the initial dehydrogenation temperature of 9 wt% CrCoNi modified MgH 2 was greatly reduced from 325 °C to 195 °C, a drop of 130 °C compared to non-additive MgH 2. Also, the MgH 2 –CrCoNi composite released 4.84 wt% hydrogen at 300 °C even in 5 min and absorbed 3.19 wt% hydrogen at 100 °C within 30 min (3.2 MPa). The calculated de/rehydrogenation activation energy were reduced by 45 and 55 kJ mol−1, respectively. Further cyclic kinetics investigation indicates that the 9 wt%-CrCoNi doped MgH 2 still presented good stability after 20 cycles, losing only 0.36 wt% hydrogen capacity. The XRD pattern validated that CrCoNi remained stable during the cyclic reaction process. Besides, the uniformly distributed CrCoNi nanosheets were in tight contact with the MgH 2 surface, providing abundant catalytic active sites and low-energy barrier diffusion channels. Under synergistic catalysis, the H atoms are rapidly absorbed and released across the Mg/MgH 2 interface, resulting in excellent kinetic properties. Briefly, this paper provides new references and inspirations to design efficient polymetallic catalysts for hydrogen storage materials. • CrCoNi nanosheets were prepared via a facile wet chemical ball milling method. • The de/hydrogenation performance of 9 wt% CrCoNi modified MgH 2 was greatly enhanced. • The synergistic effect of Cr, Co and Ni elements played a key role in the catalysis on MgH 2. [ABSTRACT FROM AUTHOR]

The increasing heterogeneity and scalability of the Internet of everything, especially, the Energy Internet (EI), is a prompt for novel engineering paradigms. The current infrastructure of hardware technologies besides the available software stack is becoming obsolete for handling the advanced requirements of the smart energy ecosystem. Accordingly, software definitions of the Internet of Things (IoT) stack functions are gaining interest to provide more flexible and scalable implementations. This paper investigates a sophisticated softwarization explicit hybrid model predictive control strategy for energy storage facility systems through the accessor design pattern. This strategy is presumed to support and facilitate the integration of higher-level analytic and control functionalities within the IoT stack at edges and nodes. Simulation is conducted with the Ptolemy II software to evaluate the execution semantics of the proposed strategy. In addition, real-time experiments on a lab-scale hydraulic tank process with both abrupt and gradual commands test scenarios showed the efficiency and reliability of the accessor-based controllers for achieving the control objectives for the benchmark storage facility with an abstract implementation. The analysis shows that this process can serve as a benchmark to mimic the charge and discharge cycles of storage elements in EI ecosystems. • A new paradigm for hydrogen energy storage interfacing within energy Internet ecosystems is proposed and investigated. • An actor-oriented approach is applied for implementing real-time control systems of hydrogen storage. • Software-defined model predictive control is implemented within a Node.js accessor host. • A benchmark process is developed as an emulator for hydrogen energy storage to evaluate the accessors design pattern. [ABSTRACT FROM AUTHOR]

This paper highlights the hydrogen storage performance of surface oxidized LiBH 4 (Lithium borohydride) system incorporated with NiO nanostructures under 250 °C. Surface oxidized LiBH 4 system was impregnated with hydrothermally synthesized mesoporous NiO nanorods (NiONR) and NiO nanoplates (NiONP) using simple ultrasonication method. Hydrogen sorption and desorption studies has been investigated for LiBH 4 /NiONR and LiBH 4 /NiONP systems for the first time. The Brunauer-Emmett-Teller results showed that the specific surface area of NiONR, NiONP, LiBH 4 /NiONR and LiBH 4 /NiONP systems were 77.92, 88.12, 96.67 and 101.65 m2/g, respectively. Hydrogenation followed by isothermal dehydrogenation at 250 °C revealed that the LiBH 4 /NiONR and LiBH 4 /NiONP systems released ∼3.44 wt% and 4.02 wt% of hydrogen respectively in 60 min. Using the Kissinger's relation, the activation energy (E a) was calculated as 69.28 and 63.23 kJ/mol for LiBH 4 /NiONR and LiBH 4 /NiONP systems, respectively. The dehydrogenation rate of LiBH 4 /NiONP system was found to be greater than that of LiBH 4 /NiONR system due to its large surface area and lower activation energy. The reported results revealed that nickel oxide nanostructures incorporated surface oxidized LiBH 4 systems provide new opportunities for the solid-state hydrogen storage applications. [Display omitted] • Hydrogen sorption/desorption studies were investigated for the LiBH 4 /NiO systems. • The surface area of LiBH 4 /NiONR and LiBH 4 /NiONP are 96.7 and 101.6 m2/g respectively. • LiBH 4 /NiONP and LiBH 4 /NiONR desorb 4.0 and 3.4 wt% of hydrogen at 250 °C in 1 h. [ABSTRACT FROM AUTHOR]

To design and optimize the thermal management of metal hydride (MH) tank, high-fidelity model (HFM) composed of numerous partial differential equations, is often adopted to capture the spatial evolution of key parameters accurately. However, computational difficulties raise in dealing with such nonlinear interconnections for system-level simulation. Therefore, the model reduction of MH system has drawn much attention aiming at the trade-off between accuracy and computational cost. In this paper, a hybrid modeling method which integrates advantages of the state-space model (SSM) and HFM, is proposed and applied for the model reduction of MH tank. In particular, four data-driven matrices are introduced to improve the model accuracy. The results show that the root mean square errors of the average temperature between hybrid reduced model (HRM) and HFM are 0.0399 K and 0.1989 K respectively for the cases without and with thermal management. In addition, the HRM is able to capture dynamic characteristic under perturbed input variables with a relative error of temperature within 0.4%, indicating great potential for system-level simulation. What's more, the analysis of predominant pole derived from the state matrices of different thermal managements, reveals that the expanded graphite has superior effect on the adjustment time extension compared with fins, while the fins have distinct advantages in heat transfer enhancement at the cost of volumetric hydrogen storage density. • A hybrid modeling method combining state-space model and data-driven correction is proposed. • The reduced model of MH tank shows great agreement with HFM under various operation parameters. • The accuracy of reduced model has also been verified for the MH tank with thermal management and perturbed variables. • The effect of thermal management on the dynamic characteristic of MH tank is summarized. [ABSTRACT FROM AUTHOR]

In this paper, a new two-dimensional B 6 N 6 monolayer is investigated as a type of promising material for hydrogen storage. The average binding energy between Lithium and BN monolayer will be significantly increased from 0.80 eV to 2.42 eV and the metal agglomeration is also effectively avoided by the substitution of one nitrogen atom with one carbon atom. We use Density functional computations to check the hydrogen adsorption properties and find up to ten hydrogen molecules will be adsorbed on the double side Lithium decorated BNC monolayer with the adsorption energy of per H 2 from 0.19 eV to 0.27 eV. The maximum storage gravimetric capacity of hydrogen can reach to 11.1 wt%. Meanwhile, the molecular dynamics (MD) calculations confirm that the 10H 2 @Li-decorated BNC structure is still thermodynamic stable. In addition, the simulation results of Grand Canonical Monte Carlo (GCMC) further prove that the hydrogen gravimetric density (HGD) is expected to reach to 7.48 wt% at room temperature (298 K). • C-doping can avoid Li clustering and enhance hydrogen adsorption. • The binding energy of Li-decorated B 6 N 5 C 1 nanosheet can reach 2.42 eV. • The hydrogen storage capacity achieves to 11.1 wt% by DFT calculation. • Dreiding force field parameters are fitted and GCMCs is employed. [ABSTRACT FROM AUTHOR]

In this paper we investigate the nature of hydrogen diffusion in substoichiometric TiC using simulations. Specifically, we examine how well connected the carbon structural vacancies are in TiC x using percolation theory and how many structural carbon vacancies are connected to the surface of TiC x. This provides direct insight into the number of sites available for hydrogen storage and the interconnected nature of the carbon vacancy network. We also compute the binding energies and migration energies of hydrogen in TiC x using density functional theory. This is conducted over a range of carbon concentrations from nearly stoichiometric TiC to Ti 2 C and includes the differences in vacancy ordering. We find that the migration energy of hydrogen in TiC x generally decreases with carbon loss and is associated with the tetrahedral interstices near them but that the binding energy of hydrogen to TiC x is independent of carbon concentration. Furthermore, we show that this migration path can occur through the tetrahedral interstices, which is influenced by local carbon concentration. These results also demonstrate the vacancy ordered R 3 ¯ m Ti 2 C structure does not possess any more superior ability to store or transport hydrogen than the F d 3 ¯ m Ti 2 C structure. • Hydrogen insertion in TiC x should occur for carbon concentrations below TiC 0.7. • The energy barriers for hydrogen diffusion drop with carbon concentration. • Hydrogen diffusion occurs from carbon vacancy to tetrahedral interstice. • It is easier to diffuse hydrogen into ordered F d 3 ¯ m Ti 2 C than R 3 ¯ m Ti 2 C. [ABSTRACT FROM AUTHOR]

The paper presents large eddy simulations (LES) model of two-phase (liquid-gas) hydrogen behaviour during pressurised tank venting. The results of simulations are compared against published experiment on flash-boiling of liquid hydrogen (LH2) in a large-scale tank of 7.622 m height, 2.3 m internal diameter, filled with LH2 to 6.248 m (80% tank filling) at pressure 321.8 kPa gauge. The volume-of-fluid model is applied for tracking phases and Lee's model is used to simulate evaporation and condensation. The effect of various Lee's model evaporation-condensation coefficients on the process dynamics is assessed. The simulations are compared against experimental pressure dynamics monitored at the venting pipe and experimental temperature measured by thermocouples in gaseous and liquid phases during the first 15 s of venting. The LES model reasonably predicts physical phenomena during depressurisation of LH2 storage tank, including the pressure recovery phenomenon, LH2 level and temperature dynamics in the tank. • LES model of two-phase hydrogen behaviour in LH2 tank during release is presented. • The flash-boiling phenomenon in large-scale 30 m3 vertical tank is simulated. • The model reproduced the pressure recovery phenomenon. • Unsteady boiling at thermometer surface is reason of temperature drop and recovery. [ABSTRACT FROM AUTHOR]

In this paper, we report the effect of adding the rare earth element lanthanum on the hydrogen storage properties of TiFe synthesized by mechanical alloying (MA). A remarkable improvement was observed in the first hydrogenation (activation) of La-added TiFe. Milling led to the refinement of the crystallite size of the TiFe alloy leading to nanocrystallinity. The formation of a stable hydride phase LaH 3 facilitated heterogeneous nucleation and acted as a gateway for the hydrogenation of the TiFe phase. No change in thermodynamics was observed for the rare earth-added TiFe compared to pure TiFe reported in the literature. The microstructure revealed a uniform distribution of the elements. However, La was completely immiscible with the TiFe alloy-a conclusion drawn from the thermodynamics study of the sample. Also investigated was pure TiFe synthesized by MA and arc melting to compare these two synthesis methods. • TiFe added with rare earth lanthanum was synthesized by mechanical alloying. • Uniform distribution of elements without the additive getting alloyed to TiFe. • Achieved remarkable improvement in the activation of the La-added TiFe. • No change in thermodynamics of the lanthanum-added TiFe compared to pure TiFe. • Highly stable LaH 3 phase facilitated heterogeneous nucleation and acted as a gateway for hydrogenation. [ABSTRACT FROM AUTHOR]

In this paper, three optimisation methods are used to determine the parameters of a commercial metal hydride hydrogen tank, considered as a grey box in which the thermophysical parameters are unknown. These parameters are essential for the development of energy management strategies and the study of tank ageing. A model of the hydride tank containing an AB 5 intermetallic was developed and experimentally validated. An absorption test campaign of the studied tank was carried out to collect data necessary for the optimisation algorithms. A comparative study was carried out in accordance with the speed of convergence and precision between the three stochastic optimisation methods: Particle Swarm Optimisation (PSO), Genetic Algorithm (GA) and Differential Evolution (DE). The results of the simulation of the storage system using the parameters determined by the algorithms show a remarkably close agreement with the experimental data, with a maximum error of 2.1%. • Innovative proposal for the determination of parameters of a metal hydride hydrogen tank. • Experimental test for the static characterization of a metal hydride tank for hydrogen storage. • An experimentally verified mathematical model for the hydrogen storage system is put forth. • Validation with experimental data and three stochastic optimisation methods: PSO, GA and DE. [ABSTRACT FROM AUTHOR]

In recent years, two-dimensional materials with larger specific surface area and more active sites have been widely designed as hydrogen storage materials. In this paper, we investigate and clarify the hydrogen storage performance of Mg-decorated g-C 6 N 7 (Mg@g-C 6 N 7) monolayer using first-principles calculations. By calculating the binding energy, we find that the most stable configuration for the Mg atom is at the holey site bonded with two N atoms (denoted as N1) in monolayer g-C 6 N 7. A modification effect of the Mg atom enhances the activity of g-C 6 N 7 monolayer. The ideal theory storage gravimetric density of the Mg@g-C 6 N 7 monolayer is up to 10 wt% with the average adsorption energy of −0.178 eV/H 2. Furthermore, the physical mechanism of H 2 molecules adsorbed on monolayer Mg@g-C 6 N 7 is theoretically explored. We find that orbital interactions and electrostatic interactions exist between Mg2+ cation and the 1st to 4th H 2 molecules, while only strong electrostatic interactions make the 5th to 10th H 2 molecules bind onto the Mg2+ cation. The effects of temperature and pressure on the hydrogen storage performance are also investigated, and the results show that the hydrogen adsorbed structures of Mg@g-C 6 N 7 are stable at room temperature under mild pressure. [Display omitted] • Metal Mg was applied to decorate monolayer g-C 6 N 7. • The activity of g-C 6 N 7 monolayer is enhanced due to modification effect of Mg atom. • Mg-decorated g-C 6 N 7 monolayer exhibits a high hydrogen storage capacity of up to 10 wt%. [ABSTRACT FROM AUTHOR]

In this paper, Mg 2.3 Y 0.1 Ni + x wt.% graphene (x = 1, 3, 5, 7) composite hydrogen storage alloys were fabricated by mechanical ball milling of Mg 2.3 Y 0.1 Ni alloy powder and graphene. The experimental results show that the phases of the composite alloy consist mainly of Mg 2 Ni, Mg, MgNi 2 and Ni 3 Y phases, and graphene tends to be distributed at the edges of the alloy, increasing the phase boundary resulting from the contact between the C-boundary and the Mg 2.3 Y 0.1 Ni alloy, providing more channels for the diffusion of H 2. In which 7 wt.% of graphene is added, the gestation period of the composite alloy completely disappears. And the ball-milled alloy with 3 wt.% graphene at different temperatures has the highest hydrogen uptake in 2 min and the highest hydrogen release in 10 min. At 573 K, the composite alloy has a hydrogen absorption capacity of 3.251 wt.% H 2 in 2 min and reaches 90.21% of the maximum hydrogen absorption, while it is able to release 3.389 wt.% H 2 in 10 min and reaches 99.04% of the maximum hydrogen release. And the composite alloy with 3 wt.% graphene has the smallest dehydrogenation activation energy. The absolute value of the enthalpy change is reduced from 60.1 kJ/mol to 54.8 kJ/mol, and the desorption enthalpy change is reduced from 73.4 kJ/mol to 67.5 kJ/mol. • Addition of graphene increases the phase boundary of the composite alloy. • Graphene lowers the reaction barrier of the alloy with hydrogen. • Graphene improves the kinetics of hydrogen absorption/release of the alloy. • Graphene reduces the thermodynamic stability of composite alloys. [ABSTRACT FROM AUTHOR]

The perovskite-type hydride compounds are potential candidate materials in the field of hydrogen storage. This paper presents a systematical study of XTiH 3 (X = K, Rb, Cs) using density functional theory. The analysis of formation energy, elastic properties and phonon dispersion curves indicate that all the studied materials are thermodynamically, mechanically and dynamically stable. By analyzing the B/G ratio, it is determined that these compounds are brittle materials. The electronic properties reveal that the XTiH 3 compounds exhibit semi-metallic characteristics. The charge transfer characteristics of these compounds were analyzed using Bader partial charges. Moreover, the thermodynamic characteristics of these compounds were investigated and the dependence of their free energy, entropy and heat capacity on the temperature were analyzed. Finally, the gravimetric hydrogen storage capacities of KTiH 3 , RbTiH 3 and CsTiH 3 were calculated to be 3.36, 2.22 and 1.65 wt%, respectively. The hydrogen desorption temperatures of KTiH 3 , RbTiH 3 and CsTiH 3 were found to be 209 K, 161 K and 107 K, respectively. To our knowledge, this study represents the very first investigation of XTiH 3 compounds and offers valuable references to this hydrogen storage material. [Display omitted] • XTiH 3 (X = K, Rb, Cs) perovskite have been investigated using first-principles. • XTiH 3 perovskite exhibit thermodynamic, mechanical and dynamical stability. • The gravimetric hydrogen storage capacity is found to be 3.36 wt% for KTiH 3. [ABSTRACT FROM AUTHOR]

In a Sieverts apparatus, the poor heat transfer performance of a sample cell leads to inaccuracy in kinetics test of hydrogen storage materials. Consequently, the analysis of heat transfer of the reaction process in the sample cell is essential. However, it is difficult for traditional detection methods to track the physical and chemical dynamic changes in the sample cell. In this paper, the finite element method was used to simulate the reaction process in the sample cell. A two-dimensional numerical model was designed to characterize the hydrogen absorption process in order to investigate the link between the heat transfer performance of the sample cell and the reaction kinetics. It was found that the reaction kinetics would be close to the intrinsic kinetics of the materials as its amount decreased. However, the decreased amount of hydrogen storage materials had a restricted effect on the increase of the reaction rate. The relevant amount of hydrogen storage material was recommended based on the comprehensive analysis of this study. In addition, the improvement of the thermal conductivity of the MH reaction bed and sample cell material improved the heat transfer performance to a certain extent. Finally, the relationship among the amount of hydrogen storage material, thermal conductivity and absorption time was established through the simulation analysis, which provided some schemes for optimizing the reaction kinetics testing accuracy of Sieverts apparatus. • The heat transfer performance of sample cell was simulated. • A numerical model describing the reaction process was developed. • The factors affecting the reaction kinetics were analyzed. • Some optimization schemes were proposed. [ABSTRACT FROM AUTHOR]

This paper presents the energy management of flexi-renewable energy hubs in electric and thermal networks based on the market clearing price model and participation of hubs in the energy market. Renewable sources include wind sources and bio-waste units, where the latter simultaneously plays a role in electrical and thermal energy generation. Hydrogen and thermal storage are used as a source of flexibility in the hub. The proposed scheme has a two-level formulation. Its upper level considers the participation of hubs in the energy market. It maximizes the expected profit of energy hubs by observing the operational constraints of power sources and storage devices (in the form of a hub) and the hub's flexibility limitation. The lower-level problem presents the market clearing price model. In this problem, the expected operation cost of the generation units in the electric and thermal networks is minimized subject to satisfying the constraints of the optimal power flow of the mentioned networks. The Karush-Kuhn-Tucker method provides a single-level formulation of the scheme. Also, stochastic optimization is adopted to model the uncertainties of load and renewable power to examine the flexibility of energy hubs accurately. Finally, by evaluating the numerical results obtained from different study cases, the scheme can improve the operating conditions of energy networks and obtain optimal flexibility and economic conditions for energy hubs. The hydrogen storage device next to the thermal storage device can achieve 100% flexibility conditions for the hubs. Storage devices can enhance the economic status of renewable hubs by about 9.2%. The energy management of flexi-renewable hubs improves energy networks' operational and economic status by 21–24% and 8.8% compared to power flow studies. • Investigating impact of flexi-renewable EHs on the energy price and social welfare. • Considering the market clearing price model for the energy market. • Using hydrogen and heat storage devices in EH to improve the flexibility of EHs. • Modeling of CHP-based BUs for generation of electrical and thermal energy. • Modeling of economic, operation and flexibility indicators in EMS. [ABSTRACT FROM AUTHOR]

The transition from fossil fuels to renewable energy sources is seen as an essential step toward a more sustainable future. Hydrogen is being recognized as a promising renewable energy carrier to address the intermittency issues associated with renewable energy sources. For hydrogen to become the "ideal" low or zero-carbon energy carrier, its storage and transportation shortcomings must be addressed. This paper will provide the current large-scale green hydrogen storage and transportation technologies, including ongoing worldwide projects and policy direction, an assessment of the different storage and transportation methods (compressed hydrogen storage, liquid hydrogen, blending hydrogen into natural gas pipelines, and ammonia as green hydrogen carrier), as well as economic factors that influence the viability of large-scale green hydrogen storage and transportation. The results of our study highlight several significant findings concerning the cost, challenges, and potential advancements in the green hydrogen storage and transportation field. Our analysis demonstrates that the cost associated with storing and transporting green hydrogen is anticipated to decrease over time due to technological advancements and economies of scale being achieved. However, the commercialization of this technology requires addressing challenges related to storage methods, transportation modes, efficiency optimization, and technology adoption. For example, our research highlights the need for thorough technical and economic evaluations of using salt caverns for hydrogen storage. The efficiency of hydrogen storage and transportation utilizing existing infrastructure, such as storage tanks and natural gas pipelines. By elucidating these aspects, our research contributes valuable insights that can guide future endeavors toward achieving a sustainable and economically viable green hydrogen industry. • Role of government support in green hydrogen storage remains crucial. • Different storage and transportation methods is analyzed and compared. • Cost of hydrogen is expected to decrease for economies of scale. [ABSTRACT FROM AUTHOR]

In this paper, a two-layer hierarchical control strategy for an isolated DC microgrid with a hybrid energy storage system is considered. The DC microgrid studied is composed of a short-term battery energy storage system, long-term hydrogen-based energy storage system and renewable energy resources. The proposed control strategy, combines concepts of Interconnection and Damping Assignment Passivity-Based Control (IDA-PBC) as a primary level and Model Predictive Control (MPC) as a supervisory level. The IDA-PBC layer guarantees a correct power balance and ensures global stability according to Lyapunov theory, considering the non-linear behavior of the physical system. On the other hand, the MPC layer calculates the reference signals for the primary level, ensuring null stationary error in the desired variables. As known, it is important to keep the electrolyzer, the fuel cell and the batteries in a safe operating mode to increase their useful life and guarantee the quality of the hydrogen produced. In this sense, the benefits of MPC are exploited by considering system constraints in the controller design. The main objective of the two-layer control strategy is to ensure the supply of electrical energy to the loads and quality in the electrical variables of the network. Representative simulation results under demanding conditions verify the effectiveness of combining IDA-PBC and MPC for this class of problems. • An isolated MG with H2 storage, typical structure of a refueling station, was modeled. • The hierarchical control strategy successfully combines IDA-PBC and MPC techniques. • The IDA-PBC ensures the stability of the nonlinear and complex MG. • Supervisor MPC ensures zero stationary error and safe operating mode of the MG. • The control confirms that H2 storage integrated with RES contributes to MG stability. [ABSTRACT FROM AUTHOR]

This paper presents a framework for the efficient design and evaluation of a standalone hybrid renewable energy system (HRES) to meet the energy requirements of a rural community in the north-eastern region of Nigeria. The proposed microgrid system incorporates solar photovoltaic, wind turbines, biomass gasifier, fuel cell, and Battery storage. The sizing of each component is determined through the utilization of real local meteorological data and the load demand over a year, employing the Levy flight-salp swarm algorithms (LF-SSA). The optimization objective is to minimize the annualized system cost (ASC) of the HRES, while also considering the reliability constraint of Loss of power supply probability (LPSP). The comparative outcomes demonstrate that the LF-SSA surpasses other examined algorithms, namely the salp swarm, genetic algorithm, and HOMER software by achieving substantial cost savings of $29033, $50796, $191771 respectively in relation to the proposed HRES. The result further shows that, the LF-SSA provides the lowest LCOE of $0.933162/kWh, in contrast to SSA at $0.947737/kWh, GA at $0.958660/kWh, and HOMER at $1.075351/kWh. Additionally, the results indicate that the implemented Energy Management System (EMS) has successfully facilitated the establishment of an environmentally friendly and cost-effective energy system. • An efficient energy storage system is essential for managing intermittent energy supply. • The fuel cell can generate DC power by combining hydrogen with oxygen. • The amount of power generated by a PV panel depends on temperature and solar radiation intensity. • Deterministic rule-based controllers operate based on pre-defined rules. • Energy Management System coordinate the flow of power between different components. [ABSTRACT FROM AUTHOR]

On the path to a net-zero-carbon economy, large-scale energy storage will be an essential part of a renewable energy system. Hydrogen generated from renewable or zero-carbon sources has significant potential as an energy storage medium, by allowing for long-duration and high-capacity energy storage. At the volumes anticipated, however, underground storage systems will likely be essential. Much like the current natural gas system, underground hydrogen storage would provide a safe and cost-effective complement to smaller surface storage infrastructure. Recently, there has been significant interest in the possibility of converting existing gas storage systems to hydrogen storage, though many uncertainties exist in such a process. This paper explores the reservoir dynamics of natural gas/hydrogen gas mixtures and the resulting impacts on storage conversion and gas deliverability. Two specific topics are addressed. First, a novel viscosity model for hydrogen-containing gas mixtures is developed, which shows better agreement with experimental measurements than the widely-used Lohrenz-Bray-Clark model. Second, detailed reservoir simulations are used to investigate cost-effective injection/withdrawal strategies for converting a natural gas storage system to one that stores hydrogen/natural-gas blends. The critical role of buoyancy and gravity override is described, and recommendations are made regarding key reservoir characteristics and injection strategies for managing this behavior. • This study focuses on the conversion of an operational natural gas storage field to hydrogen storage. • A novel viscosity model is developed for hydrogen-containing gas mixtures. • Reservoir simulations evaluate the effect of geologic and engineering parameters on composition and rate of recovered gas. • Gravity segregation significantly influences the severity of fluctuations in the produced gas composition. [ABSTRACT FROM AUTHOR]

The safety of hydrogen directly affects the use of hydrogen refueling stations and public acceptance of hydrogen energy. This paper presented a methodology for the optimal design of the minimum height, width, and safety distance of the firewall of the hydrogen refueling station under various leakage pressures. The obtained relationship between distances and different hydrogen storage pressures is essential for directing the design of hydrogen refueling stations and firefighters to carry out the rescue. Results from numerical simulation showed that the firewall should be 2 m taller than the leakage hole to prevent the hydrogen jet fire from spreading back. The distance before and behind the firewall presented a linear relationship with the leakage pressure. The specific safe distances behind the firewall were 8.4, 8.5, 9.2, and 9.3 m. The firewall width exhibited a non-linear relationship with the leakage pressure. The specific values were 2.5 m for 35 or 45 MPa and 3 m for 70 or 90 MPa. • Methodology for the optimal design of firewalls in hydrogen refueling stations is determined. • The firewall should be 2 m higher than the leakage hole. • Firewalls can deflect flames and prevent them from spreading behind walls. • The distance before and behind the firewall increases with the increase of hydrogen storage pressures. [ABSTRACT FROM AUTHOR]

Hydrogen, as a clean energy source, has been widely used in the automotive industry. However, considering the difficulties of hydrogen storage and transportation, the in-situ production process has received increasing attention. In this paper, a hydrogen production system for dimethyl ether self-heating steam reforming is proposed, using a spiral tube reactor in which the oxidation of dimethyl ether occurs in the spiral tube, and the exothermic oxidation of dimethyl ether is used to provide heat for the dimethyl ether steam reforming hydrogen production reaction. A numerical model of the hydrogen production system for dimethyl ether self-heating reforming is developed, the model is simulated and analyzed, the accuracy of the model is verified through experiments, the influence of various parameters and on the system is analyzed, and the system is optimized. The results show that the proposed system can solve the problems of high energy consumption, low hydrogen yield and difficult reaction control faced by traditional autothermal reforming hydrogen production, and the system can achieve 87.79% dimethyl ether conversion rate, 84.94% hydrogen yield and 85.94% system thermal efficiency. [Display omitted] • Designed a self-heating hydrogen production reaction system for dimethyl ether reforming. • Derive the numerical model and control equation inside the reactor. • Effect of oxygen-to-ether ratio on reforming hydrogen production system is studied. • Effect of steam-to-ether Ratio on reforming hydrogen production system is studied. • Effect of reaction temperature on reforming hydrogen production system is studied. [ABSTRACT FROM AUTHOR]

Cryogenic supercritical hydrogen storage technology is a high-density physical hydrogen storage method, which is a highly promising hydrogen storage approach. However, existing research has mainly focused on the development of storage devices for cryogenic supercritical hydrogen, with limited research on the cooling process of supercritical hydrogen. Therefore, a novel cooling process for cryogenic supercritical hydrogen production based on helium expansion cycle with liquid nitrogen (LN 2) pre-cooling is proposed in this paper. In this process, after being compressed and cooled in multiple stages, the feed hydrogen is pre-cooled by LN 2. Then, cryogenic supercritical hydrogen (10 MPa, −235.15 °C, 63.36 g/L) is obtained by helium multi-stage expansion refrigeration. The process is simulated by Aspen HYSYS and optimized by genetic algorithm (GA) to obtain lower specific energy consumption (SEC). Thermodynamic analyses are conducted to evaluate the process. And compared with the conventional hydrogen liquefaction process, the results show that the proposed process is reasonable and superior. The SEC 0 , figure of merit (FOM), and the total exergy loss of the system are 5.432 kWh/kg H2 , 43.88%, and 289.69 kW respectively. This study indicates that the proposed process has significant implications for the hydrogen industry and provides valuable information for cryogenic supercritical hydrogen storage systems. • A novel high-density cryogenic supercritical hydrogen storage system is proposed. • Twelve key variables in the process are optimized to reduce the energy consumption. • The process has higher exergy efficiency than conventional LH 2 plants. • The volume storage density of hydrogen can reach 63.36 kg/m3 in the system. [ABSTRACT FROM AUTHOR]

Nitrogen heterocyclic organics are promising hydrogen storage carriers with the advantage of being capable of large-scale transportation over long distances using existing oil and gas facilities. However, traditional methods for the hydrogenation and dehydrogenation of organic hydrogen carriers usually require high temperature and pressure conditions and external hydrogen supplies, which hinder their large-scale applications, as well as having certain safety risks. In this paper, a reversible electrochemical hydrogen storage system using quinoxaline as a hydrogen carrier was developed with potential for use at room temperature and atmospheric pressure. Experiments revealed that the hydrogenation conversion of quinoxaline reached 95% within 120 min at −0.20 V vs. RHE, and the dehydrogenation conversion of 1,2,3,4-tetrahydroquinoxaline reached 100% within 30 min at 1.30 V vs. RHE. This means that the system achieved quick and efficient reversible hydrogen storage. The Pd/NF dual-function electrode prepared by spontaneous redox reaction still showed high catalytic activity after 8 cycles, indicating its good long-term stability. The proton donor in the electrochemical hydrogenation process of quinoxaline was water, which completely eliminates the safety risk from the use of external hydrogen. This work provides a simple and reliable strategy for efficient hydrogen storage using nitrogen heterocyclic organics. [Display omitted] • The hydrogenation conversion of quinoxaline reached 95%. • The optimum dehydrogenation conversion of 1,2,3,4-tetrahydroquinoxaline was 100%. • Pd/NF electrode was operated as a dual-function electrocatalyst. • Efficient reversible hydrogen storage was achieved at 25 °C and atmospheric pressure. • The H∗ required for the electrochemical hydrogenation of quinoxaline came from H 2 O. [ABSTRACT FROM AUTHOR]