Thermodynamic analysis of low-temperature and high-pressure (cryo-compressed) hydrogen storage processes cooled by mixed-refrigerants

Cryo-compressed hydrogen (CcH₂) is a promising hydrogen storage method with merits of high density with low power consumption. Thermodynamic analysis and comparison of several CcH₂ processes are conducted in this paper, under hydrogen storage conditions of 10–100 MPa at 60–100 K. Mixed-refrigerant J-T (MRJT), nitrogen/neon reverse Brayton (RBC) and hydrogen expansion are employed for cooling hydrogen, respectively. Combined CcH₂ processes such as MRJT + neon-RBC are proposed to reach higher CcH₂ density at lower temperatures (<80 K). It was indicated that the specific power consumptions (SPC) of MRJT processes are obviously lower than those of nitrogen/neon-RBC or hydrogen expansion processes. For a typical storage condition of 50 MPa at 80 K, MRJT CcH₂ process could achieve hydrogen density of 71.59 kg m^?3, above liquid hydrogen. While its SPC of 6.42 kWh kg^?1 is about 40% lower than current dual-pressure Claude hydrogen liquefaction processes (10.85 kWh kg^?1).     

Hydrofluoroolefin-based mixed refrigerant for enhanced performance of hydrogen liquefaction process

Hydrogen has the highest gravimetric energy density of all fuels; however, it has a low volumetric energy density, unfavorable for storage and transportation. Hydrogen is usually liquefied to meet the bulk transportation needs. The exothermic interconversion of its spin isomers is an additional activity to an already energy-intensive process. The most significant temperature drop occurs in the precooling cycle (between ?150 °C and up to ?180 °C) and consumes more than 50% of the required energy. To reduce the energy consumption and improve the exergy efficiency of the hydrogen liquefaction process, a new high-boiling component, Hydrofluoroolefin (HFO-1234yf), is added to the precooled mixed refrigerant. As a result, the specific energy consumption of precooling cycle reduces by 41.8%, from 10.15 kWh/kg_LH2 to 5.90 kWh/kg_LH2, for the overall process. The exergy efficiency of the proposed case increases by 43.7%; however, the total equipment cost is also the highest. The inflated cost is primarily due to the added ortho-to-para hydrogen conversion reactor, boosting the para-hydrogen concentration. From the perspective of bulk storage and transportation of liquid hydrogen, the simplicity of design and low energy consumption build a convincing case for considering the commercialization of the process.     

Hydrogen storage materials for hydrogen and energy carriers

Hydrogen storage technology is essentially necessary to promote renewable energy. Many kinds of hydrogen storage materials, which are hydrogen storage alloys, inorganic chemical hydrides, carbon materials and liquid hydrides have been studied. In those materials, ammonia (NH₃) is easily liquefied by compression at 1 MPa and 298 K, and has a highest volumetric hydrogen density of 10.7 kg H₂/100 L. It also has a high gravimetric hydrogen density of 17.8 wt%. The theoretical hydrogen conversion efficiency is about 90%. NH₃ is burnable without emission of CO₂ and has advantages as hydrogen and energy carriers.     

Analysis and assessment of partial re-liquefaction system for liquefied hydrogen tankers using liquefied natural gas (LNG) and H2 hybrid propulsion

Boil-off gas (BOG) is inevitable on board liquefied hydrogen tankers and must be managed effectively, by using it as fuel, re-liquefying it or burning it, to avoid cargo tank pressure issues. This study aims to develop a BOG re-liquefaction system optimized for l60,000 m³ liquefied hydrogen tankers with an LNG and hydrogen hybrid propulsion system. The proposed system comprises hydrogen compression and helium refrigerant sections with 2 J–Brayton cascade cycles. Cold energy recovery from the fuels and feed BOG exiting the cargo tanks was used. The system exhibits a coefficient of performance (COP) of 0.07, a specific energy consumption (SEC) of 3.30 kWh/kg_LH2, and exergy efficiency of 74.9%, with the hydrogen BOG entering the re-liquefaction system at a feed temperature of −220 °C. The theoretical COP and SEC values at ideal conditions were 0.09 and 2.47 kWh/kg_LH2, respectively. The effects of varying the hydrogen compression pressure, inlet temperature of the hydrogen expander, feed hydrogen temperature and helium compression pressure were investigated. Additionally, the LNG-to-hydrogen fuel ratio was adjusted to satisfy the Energy Efficiency Design Index (EEDI) Phase 2 and 3 emission requirements.     

Micro-cogeneration based on solid oxide fuel cells: Market opportunities in the agriculture/livestock sector

Bio-waste embeds an extraordinary renewable potential, and it becomes a source of energy savings when transformed into a valuable resource, like biogas. Cogeneration (CHP) from biogas employing high-temperature Solid Oxide Fuel Cells (SOFCs) scores a high sustainability level, thanks to improved environmental and energy performances. The synergy between the niche market of small/micro biogas producers and SOFCs might act as a springboard to open market opportunities for both SOFC commercialization and business upgrade of small farms. However, local regulations, waste management, renewable energy subsidies and, above all, availability of eligible sites, determine real chances for on-the-ground implementation.Through a detailed analysis of the application scenario, this research aims at investigating opportunities for the experimentation of SOFC–CHP in small biogas plants and identifying the possible bottlenecks for future deployment. When it becomes relevant, energy conversion of livestock (especially cattle and swine) and agriculture waste requires SOFC modules from 10 kW_e to 35 kW_e. This is in line with the current status of SOFC suppliers. Moreover, considering the fuel cell market roll-out, the average levelized cost of electricity is expected to decrease from 0.387 €/kWh to 0.115 €/kWh, when electricity is produced from livestock waste available on-site.     

Planning of micro-combined heat and power systems in the Portuguese scenario

High efficiency cogeneration is seen by the European Commission as part of the solution to increase energy efficiency and improve security of supply in the internal energy markets. Portuguese residential sector has an estimated technical market potential of around 500 MW_e for cogeneration of <150 kW_e in size. Additionally, in Portugal there is a specific law for power production in low voltage, where at least 50% of the produced electric energy must be own consumed and the maximum power delivered to the power utility should be less than 150 kW_e. Therefore, generic application tools cannot be applied in this regard. In this work, we develop the MicroG model for planning micro-CHP plants in agreement with the Portuguese energy legal framework. The model is able to design, evaluate and optimize from the techno-economic point of view any micro-CHP plant. MicroG appeals to some data bases, such as micro-cogeneration technologies and power consumption profiles that are also described. In addition, a practical case on a gym is considered to show all the functionalities of the model. The developed model has proven to be extremely useful from the practical point of view. This model could help the development of the micro-CHP Portuguese market, which in turns contributes to accomplish the targets of Kyoto protocol and EU cogeneration Directive. Other improvements to MicroG model can be made in order to enlarge the range of application to other micro-cogeneration technologies and to accomplish with the CO₂ emissions trading.     

Effect of hydrogen nanobubble addition on combustion characteristics of gasoline engine

Hydrogen is an attractive energy source for improving gasoline engine performance. In this paper, a new hydrogen nanobubble gasoline blend is introduced, and the influence of hydrogen nanobubble on the combustion characteristics of a gasoline engine is experimentally investigated. The test was performed at a constant engine speed of 2000 rpm, and engine load of 40, 60, and 80%. The air-to-fuel equivalence ratio (λ) was adjusted to the stoichiometric (λ = 1), for both gasoline, and the hydrogen nanobubble gasoline blend. The results show that the mean diameter and concentration of hydrogen nanobubble in the gasoline blend are 149 nm and about 11.35 × 10⁸ particles/ml, respectively. The engine test results show that the power of a gasoline engine with hydrogen nanobubble gasoline blend was improved to 4.0% (27.00 kW), in comparison with conventional gasoline (25.96 kW), at the engine load of 40%. Also, the brake specific fuel consumption (BSFC) was improved, from 291.10 g/kWh for the conventional gasoline, to 269.48 g/kWh for the hydrogen nanobubble gasoline blend, at the engine load of 40%.     

Modelling of an HTPEM-based micro-combined heat and power fuel cell system with methanol

A fuel cell-based combined heat and power system using a high temperature proton exchange membrane fuel cell has been modelled. The fuel cell is fed with the outlet hydrogen stream from a methanol steam reforming reactor. In order to provide the necessary heat to this reactor, it was considered the use of a catalytic combustor fed with methanol. The modelling aims to fit the hydrogen production to the demand of the fuel cell to provide 1 kW_e, maintaining a CO concentration always lower than 30,000 ppm. A system with 65 cells (45.16 cm² cell area) stack operating at 150 °C and hydrogen utilization factor = 0.9 (with O₂/methanol ratio = 2 at combustor; H₂O/methanol ratio = 2 and temperature = 300 °C at reformer) needed a total methanol flow of 23.8 mol h⁻¹ (0.96 L h⁻¹) to reach 1 kW_e, with a system power efficiency (LHV basis) ca. 24% and a CHP efficiency over 87%. The ability to recycle the non-converted hydrogen from the fuel cell anode to the combustor and to use the heat produced at the fuel cell for obtaining hot water increased the global energy efficiency.     

Plug-in hybrid fuel cell vehicles market penetration scenarios

The main objective of this research is to analyze the impact of the market share increase of hydrogen based road vehicles in terms of energy consumption and CO₂, on today's Portuguese light-duty fleet. Actual yearly values of energy consumption and emissions were estimated using COPERT software: 167112 TJ of fossil fuel energy, 12213 kton of CO₂ emission and 141 kton of CO, 20 kton of HC, 46 kton of NO_x and 3 kton of PM. These values represent 20–40% of countries total emissions. Additionally to base fleet, three scenarios of introduction of 10–30% fuel cell vehicles including plug-in hybrids configurations were analysed. Considering the scenarios of increasing hydrogen based vehicles penetration, up to 10% life cycle energy consumption reduction can be obtained if hydrogen from centralized natural gas reforming is considered. Full life cycle CO₂ emissions can also be reduced up to 20% in these scenarios, while local pollutants reach up to 85% reductions. For the purpose of estimating road vehicle technologies energy consumption and CO₂ emissions in a full life cycle perspective, fuel cell, conventional full hybrids and hybrid plug-in technologies were considered with diesel, gasoline, hydrogen and biofuel blends. Energy consumption values were estimated in a real road driving cycle and with ADVISOR software. Materials cradle-to-grave life cycle was estimated using GREET database adapted to Europe electric mix. The main conclusions on CO₂ full life cycle analysis is that light-duty vehicles using fuel cell propulsion technology are highly dependent on hydrogen production pathway. The worst scenario for the current Portuguese and European electric mix is hydrogen produced from on-site electrolysis (in the refuelling stations). In this case full life cycle CO₂ is 270 g/km against 190 g/km for conventional Diesel vehicle, for a typical 150,000 km useful life.     

Application of hydrides in hydrogen storage and compression: Achievements,outlook and perspectives

Metal hydrides are known as a potential efficient, low-risk option for high-density hydrogen storage since the late 1970s. In this paper, the present status and the future perspectives of the use of metal hydrides for hydrogen storage are discussed. Since the early 1990s, interstitial metal hydrides are known as base materials for Ni – metal hydride rechargeable batteries. For hydrogen storage, metal hydride systems have been developed in the 2010s [1] for use in emergency or backup power units, i. e. for stationary applications.With the development and completion of the first submarines of the U212 A series by HDW (now Thyssen Krupp Marine Systems) in 2003 and its export class U214 in 2004, the use of metal hydrides for hydrogen storage in mobile applications has been established, with new application fields coming into focus.In the last decades, a huge number of new intermetallic and partially covalent hydrogen absorbing compounds has been identified and partly more, partly less extensively characterized.In addition, based on the thermodynamic properties of metal hydrides, this class of materials gives the opportunity to develop a new hydrogen compression technology. They allow the direct conversion from thermal energy into the compression of hydrogen gas without the need of any moving parts. Such compressors have been developed and are nowadays commercially available for pressures up to 200 bar. Metal hydride based compressors for higher pressures are under development. Moreover, storage systems consisting of the combination of metal hydrides and high-pressure vessels have been proposed as a realistic solution for on-board hydrogen storage on fuel cell vehicles.In the frame of the “Hydrogen Storage Systems for Mobile and Stationary Applications” Group in the International Energy Agency (IEA) Hydrogen Task 32 “Hydrogen-based energy storage”, different compounds have been and will be scaled-up in the near future and tested in the range of 500 g to several hundred kg for use in hydrogen storage applications.     

Thermal conductivity measurements of magnesium hydride powder beds under operating conditions for heat storage applications

One of the major issues of the change in energy politics is the storage of renewable energy in order to facilitate a continuous energy supply to the grid. An efficient way to store energy (heat) is provided by the usage of Thermochemical Energy Storage (TES) in metal hydrides. Energy is stored in dehydrogenated metal hydrides and can be released by hydrogenation for consumption. One prominent candidate for high temperature (400 °C) heat storage is magnesium hydride. It is a well-known and investigated material which shows high cycling stability over hundreds of cycles. It is an abundant material, non-toxic and easy to prepare in bigger scales. One of the major drawbacks for heat storage applications is the low heat transfer capability of packed beds of magnesium hydrides. In this work we present results of effective thermal conductivity (ETC) which were measured under hydrogen pressure up to 25 bar and temperatures up to 410 °C in order to meet the operating conditions of magnesium hydride as a thermochemical heat storage material. We could show that the effective thermal conductivity of a magnesium hydride – hydrogen system at 410 °C and 25 bar hydrogen increases by 10% from 1.0 W m⁻¹ K⁻¹ to 1.1 W m⁻¹ K⁻¹ after 18 discharging and charging cycles. In dehydrogenated magnesium hydride this increase of the thermal conductivity was found to be at 50% from 1.20 W m⁻¹ K⁻¹ to 1.80 W m⁻¹ K⁻¹ at 21 bar hydrogen. These data are very important for the design and construction of heat storage tanks based on high temperature metal hydrides in the future.     

Optimal heat recovery during polymer electrolyte membrane electrolysis

The severe reduction in the available fossil fuel resources highlights the need to make more use of renewable energy resources (RER), such as solar photovoltaic (PV) modules, wind turbines, hydro-turbines, etc. Hydrogen (H₂) may be seen as a possible alternative fuel which can be produced from renewable energy, as mentioned and a promising contender in the energy storage domain. A hydrogen electrolyser harnesses the energy produced by the RER, in order to produce H₂, which could be stored in its current form to be used at a later stage to generate electrical energy, by means of a fuel cell.In this paper, an optimal switching control of a solid polymer electrolyte membrane water electrolyser (PEMWE) water heating system is presented, in which actual historic exogenous data obtained from a weather station in the considered area is used as inputs for the established model.The main aim of this paper was to develop an optimal control model, which maximizes the removal of the undesired heat from the PEMWE and transferring it to the hot water storage tank (HWST), whilst ensuring sufficient hydrogen is being produced.Simulations of the optimal switching control of a PEMWE water heating system was conducted successfully with the SCIP (Solving Constrained Integer Programs) solver in the optimization toolbox in MATLAB.The optimal switching control model yields a daily energy consumption of 49.85 kWh by the PEMWE compared to an energy consumption of 48.86 kWh by the standard PEMWE system (baseline). The optimal switching control model resulted in 2.51 kg of hydrogen compared to 2.56 kg which is produced by the standard PEMWE system. Moreover, the optimal control model recovered 1.03 kWh of heat successfully which is transferred to the HWST.The optimal control model development and implementation for a PEMWE to maximize the thermal energy recovery from the PEMWE to the HWST whilst ensuring stable H₂ production are presented as one of the main contributions to the study.Secondly, by recovering the generated heat from the PEMWE, the time period for the membrane to degrade to a thickness of 50% could be prolonged by 0.68 years, after which the membrane degradation occurs non-linearly.     

Data results and operational experience with a solar hydrogen system

A solar hydrogen system is presented able to provide uninterrupted 200 W_e power to an isolated application. It is composed of a photovoltaic generator, a battery set, an electrolyser, a metal-hydride system for hydrogen storage and a fuel cell. Batteries are charged with the photovoltaic array and the fuel cell, and discharged with the electrolyser and the application load. The fuel cell switches on when the state of charge of the batteries is low, until they are recovered to a predetermined level. The electrolyser produces H₂ at 30 bar, enough to feed directly the metal hydrides, avoiding pressurization steps. Metal hydrides work under pressure control in the temperature range 0–40 °C. Kinetics of absorption–desorption of hydrogen is observed as an important limiting aspect for this kind of storage. The system is able to convert about 6–7% of total solar energy irradiated in 1 year. Results and evaluation after 1-year operation are shown. Energy management is found to be a critical issue to improve the behavior of the system.     

Economic analysis and optimal design of hydrogen/diesel backup system to improve energy hubs providing the demands of sport complexes

Energy crisis has led the communities around the world to use energy hubs. These energy hubs usually consist of photovoltics, wind turbines and batteries. Diesel generators are usually used in these systems as backup system. In this research, for the first time, an attempt is made to replace the traditional diesel only backup system with hydrogen only system and combined hydrogen and diesel backup system in hybrid photovoltaic and wind turbine energy systems. After introducing the available energy modeling tools and methods, explaining over advantages and disadvantages of each one, HOMER software was selected for this research. The simulations of this research show that using the traditional diesel generator as the backup system of the energy hub, creates a low cost system with the net present cost (NPC) of 2.5 M$ but also produces the highest amount carbon emission which is equal to 686 tons/year. The results of this study also indicate the hybrid renewable energy system which is supported by the hydrogen only backup system has the highest net present cost (NPC) and initial capital cost but reduces the maximum amount of carbon. The calculated NPC and carbon production of the energy hub using hydrogen only backup system are equal to 4.39 M$ and 55,205, respectively. On the other hand, the combined hydrogen/diesel backup system has reduced NPC compared with the hydrogen only backup system. The CO₂ production of this system is also lower than the diesel only backup system. The calculations indicate that the NPC and CO₂ production of the combined backup system are 3.53 M$ and 511,695 kg/yr. By comparing advantages and disadvantages of all 3 scenarios, the micro grid which uses the combined diesel/hydrogen backup system is selected as the most optimal system. The sensitivity analysis of the selected system shows that fluctuations of inflation rate along with the fluctuations of both fuel cells and electrolyzers capital cost do not affect the net present cost (NPC) considerably. On the other hand, fluctuations of capital cost of the main components like wind turbines affect the NPC much more than the others. If the inflation rate drops from 15% to 14% and wind turbine capital cost multiplier reduces from 1 to 0.8, the NPC value will drop by the value of 300,000 $.     

Application of atmospheric pressure microwave plasma source for hydrogen production from ethanol

In contrast to conventional technologies of hydrogen production like water electrolysis or coal gasification we propose a method based on the atmospheric pressure microwave plasma. In this paper we present results of the experimental investigations of the hydrogen production from ethanol in the atmospheric pressure plasma generated in waveguide-supplied cylindrical type nozzleless microwave (915 MHz and 2.45 GHz) plasma source (MPS). Argon, nitrogen and carbon dioxide were used as a working gas. All experimental tests were performed with the working gas flow rate Q ranged from 1500 to 3900 NL/h and absorbed microwave power P_A up to 6 kW. Ethanol was introduced into the plasma as vapours carried with the working gas. The process resulted in the ethanol conversion rate greater than 99%. The hydrogen production rate was up to 210 NL[H₂]/h and the energy efficiency was 77 NL[H₂] per kWh of absorbed microwave energy.     

Investigation of photovoltaic-hydrogen power system for a real house in Turkey: Hydrogen blending to natural gas effects on system design

In the study, the effects of hydrogen mixing studies at the rate of 20% to the natural gas system which is an ongoing study in Turkey, on the photovoltaic system (PV) is investigated using a real house consumption. Providing the annual electrical energy consumption (1936,83  kWh) and 20% of natural gas consumption (62,4 m³) of a real house with hydrogen is included in the study. A PV-hydrogen system is theoretically investigated to provide the energy required for hydrogen production from solar panels. Hydrogen blending effects on PV size, capacity usage, and carbon footprint are analyzed. Thus, the contribution was also made to the “green hydrogen” works and reduction of the carbon footprint of the house. It was found that the required hydrogen for electricity can be provided 52,5 m² solar panel area and 14,28% increase in this area and installed power can provide an amount of hydrogen that need for 20% hydrogen blending to the natural gas system. The overall system capacity usage decreased when the system is used for 20% hydrogen blending to the natural gas system. The carbon footprint of the house was decreased by 67,5%. If the hydrogen has not been blended with 20% natural gas, this ratio would have been 59,2%.     

Lithium metal hydrides (Li2CaH4 and Li2SrH4) for hydrogen storage; mechanical,electronic and optical properties

Hydrogen storage is a critical step for commercialisation of hydrogen consumed energy production. Among other storage methods, solid state storage of hydrogen attracts much attention and requires extensive research. This study rationally and systematically designs novel solid state hydrides; Li₂CaH₄ (GHD is obtained as −6.95 wt %) and Li₂SrH₄ (GHD is obtained as −3.83 wt %) using computational method. As a first step, we suggest and predict crystal structures of solid state Li₂CaH₄ and Li₂SrH₄ hydrides and look for synthesizability. Then, the mechanical stabilities of hydrides are identified using elastic constants. Both hydrides fulfil the well-known Born stability criteria, indicating that both Li₂CaH₄ and Li₂SrH₄ are mechanically stable materials. Several critical parameters, bulk modulus, shear modulus, Cauchy pressures, anisotropy factors of hydrides and bonding characteristics are obtained and evaluated. Furthermore, electronic and optical band structures of hydrides are computed. Both Li₂CaH₄ and Li₂SrH₄ have indirect bands gaps as 0.96 eV (Г-U) and 1.10 eV (Г-R). Thus, both materials are electronically semiconducting. Also, Bader charge analysis of hydrides have been carried out. Charge density distribution suggests an ionic-like (or polarized covalent) bonding interaction between the atoms.     

Clean syngas from small commercial biomass gasifiers; a review of gasifier development,recent advances and performance evaluation

Biomass gasification is a key opportunity to produce bio-renewable energy, replacing conventional fossil fuels. Nevertheless, its commercial development for hydrogen and syngas production has been hampered by a range of intractable issues. This review examines reported issues, comparing their impacts on the commerciality of large-scale and small-scale biomass gasification. The development of gasifiers is explored, and key indicators of performance discussed. A framework is developed to identify preferred selections of commercial gasifier technologies, using the key indicators to rank performance. Current commercial small-scale (70 kW_e–3 MW_e) gasifier technologies are reviewed confirming the dominance of derivatives of downdraft fixed bed gasifiers. The importance of this study is to highlight the success of commercial small-scale gasification systems, utilising their specific economic advantages over larger scale projects, and to encourage their further deployment while a framework is provided to rank gasifier designs to facilitate targeting of research and development efforts for maximum effectiveness.     

Assessment of biotic and abiotic graphite cathodes for hydrogen production in microbial electrolysis cells

Hydrogen represents a promising clean fuel for future applications. The biocathode of a two-chambered microbial electrolysis cell (biotic MEC) was studied and compared with an abiotic cathode (abiotic MEC) in order to assess the influence of naturally selected microorganisms for hydrogen production in a wide range of cathode potentials (from −400 to −1800 mV vs SHE). Hydrogen production in both MECs increased when cathode potential was decreased. Microorganisms present in the biotic MEC were identified as Hoeflea sp. and Aquiflexum sp. Supplied energy was utilized more efficiently in the biotic MEC than in the abiotic, obtaining higher hydrogen production respect to energy consumption. At −1000 mV biotic MEC produced 0.89 ± 0.10 m³ H₂ d⁻¹ m⁻³NCC (Net Cathodic Compartment) at a minimum operational cost of 3.2 USD kg⁻¹ H₂. This cost is lower than the estimated market value for hydrogen (6 USD kg⁻¹ H₂).     

Combined effects of molar ratio and ball milling energy on the phase transformations and mechanical dehydrogenation in the lithium amide-magnesium hydride (LiNH2 + nMgH2)(n = 0.5–2.0) nanocomposites

The phase transformations occurring as a function of the ball milling energy injected into the hydride system (LiNH₂ + nMgH₂), having molar ratios n = 0.5–2.0, have been thoroughly studied. The milling energy in a magneto-mill is estimated by a semi-empirical method. X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) measurements show that for the molar ratios n < 1.0 three new phases such as LiH, amorphous Mg(NH₂)₂ (a-Mg(NH₂)₂) and Li₂Mg(NH)₂ are formed during ball milling depending on the injected quantity of milling energy. Hydrogen is not released during milling when the LiH and a-Mg(NH₂)₂ hydrides are being formed whereas the formation of the Li₂Mg(NH)₂ hydride phase is always accompanied by a profound release of hydrogen. For the molar ratios n ≥ 1.0, at a low level of injected milling energy, the hydride phases formed are LiH and a-Mg(NH₂)₂. The latter reacts with MgH₂ during further milling to form the new phase MgNH whose formation is also accompanied by a profound release of hydrogen. Based on the experimental data we established an approximate hydride phase-injected milling energy diagram for various levels of injected milling energy and the molar ratios.