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e The schematic of hydrogen purification using metal hydrides; A. Absorption (mixed gases), B. Flushing (impure gases) and C. Desorption (pure hydrogen).
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Over two decades, research in the field of metal hydride based thermal machines has gained immense attention by the researchers of different fields. Because of its capability to store large volume of hydrogen per unit mass at near ambient condition, its utilization has been spread in numerous applications such as energy storage and other biological...
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... i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 8 ) 1 e2 7 attention due to their ease of operation, safety and also because of its economic niche [95]. Metal hydrides offer a high level purification of hydrogen providing the possibility of separation of hydrogen from the other mixed gases with simple reversible chemical reactions [96]. The advantage of metal hydrides is that the metal alloys absorb only hydrogen and they do not undergo any chemical reaction with other gases. One of the best quality of metal hydrides is the delivery of clean and pure hydrogen, irrespective of the input hydrogen quality, without any additional cost [97]. The sequence of processes involved in the separation and purification of hydrogen from the contaminated gases is shown in Fig. 2. The mixture of gases (hydrogen and other impurities) is sent into the MH reactor at certain absorption conditions (A). The metal alloy reacts with hydrogen and forms MH by releasing heat (exothermic reaction) while the other gases occupy the void space. After completion of absorption reaction, the gases in the reactor is flushed out (B), as it is present in voids, while the hydrogen remains in the bed. Finally, by utilizing available heat, the pure hydrogen can be desorbed from the bed (C). However, the ratio of hydrogen desorbed to absorbed may be comparatively less (75%e96%) and the impurities have gradual deteriorating effects on the performance of the sys- tem by slowing down the sorption reaction [98]. In general, the recovery rate of hydrogen from the MH reactor rises with in- crease in overall heat transfer coefficient, decreasing cooling fluid temperature and increasing supply pressure [99]. The integration of aluminum foam with metal alloy makes the system more effective for hydrogen purification, but the volumetric capacity of the hydride reactor reduces ...
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... they do not undergo any chemical reaction with other gases. One of the best quality of metal hydrides is the delivery of clean and pure hydrogen, irrespective of the input hydrogen quality, without any additional cost [97]. The sequence of processes involved in the separation and purification of hydrogen from the contaminated gases is shown in Fig. 2. The mixture of gases (hydrogen and other impurities) is sent into the MH reactor at certain absorption conditions (A). The metal alloy reacts with hydrogen and forms MH by releasing heat (exothermic reaction) while the other gases occupy the void space. After completion of absorption reaction, the gases in the reactor is flushed out ...
Citations
... Metal hydride-based thermal energy storage systems (MH-TESS) based on metal/alloy-hydrogen reactions have shown potential for a variety of applications ranging from domestic heating to industrial process heating [3][4][5]. Although MH were initially investigated for hydrogen storage, they have been found to be suitable for several thermal applications such as heating, cooling, thermal compression, and heat storage due to their endothermic and exothermic reactions [6][7][8][9][10][11][12]. The decomposition of MH into metal and hydrogen gas demands heat input, which is used to store the available heat, and the formation of MH, which involves an exothermic reaction, is used to deliver the stored heat. ...
Thermal energy storage using coupled metal hydride reactors is attractive because it offers several advantages such as one-time hydrogen loading, high thermal storage density, compactness and possibility of simultaneous heating and cooling. This study presents experimental investigations on a coupled metal hydride based thermal energy storage system. Based on compatibility criteria of hydrides described in this work, LaNi4.25Al0.75 for thermal energy storage and La0.75Ce0.25Ni5 for hydrogen storage were chosen. The study employed two novel cartridge type coupled reactors with enhanced heat transfer surfaces. The effects of heat source and ambient temperatures on the system performance were investigated. The study reveals that coupled hydride systems with suitable pairs of hydrides can deliver high energy storage capacities at good thermal efficiencies. The heat output of 227.7 kJ was achieved with a heat transfer rate of 130.7 W at 55.7 % efficiency. The hydrogen storage alloy exhibited good compatibility with the energy storage alloy with fast hydrogenation and dehydrogenation. It also produced a cooling effect of 171.8 kJ while desorbing hydrogen.
... Metal hydride-based hydrogen storage (MHHS) provides a viable alternative by safely storing hydrogen at near ambient conditions without potential energy leakage. hermic hydriding/dehydriding processes extend its additional usage as various thermal systems [2]. For near ambient operating conditions, LaNi5 (or similar AB5-type alloys) has been extensively studied by researchers for numerous applications, including hydrogen storage, thermal energy storage, purification and compression, etc. [2]. ...
... hermic hydriding/dehydriding processes extend its additional usage as various thermal systems [2]. For near ambient operating conditions, LaNi5 (or similar AB5-type alloys) has been extensively studied by researchers for numerous applications, including hydrogen storage, thermal energy storage, purification and compression, etc. [2]. ...
Considering world energy scenario and necessity to switch to renewables from conventional energy dependency, hydrogen has turned out to be one of the most suitable option for catering the energy needs almost in every energy consuming sectors. Metal Hydride Hydrogen Systems (MHHS) has turned out as a boon as energy solution because of its safe storage and near ambient operating conditions. The study reports experimental studies on 3.75 kg La0.7Ce0.1Ca0.3Ni5 based 41 embedded cooling tube (ECT) MH reactor with outer cooling jacket (OCJ) coupled to a fuel cell with controlled hydrogen discharge. The primary emphasis was given on the controlled hydrogen discharge to power 1 kW proton exchange membrane fuel cell (PEMFC) operating in the range of 30 to 50 °C. Hydrogen discharge at various desorption temperatures was investigated and was found that discharge temperature above 40 °C was enough for running 1 kW fuel cell. However, for lower discharge temperature (35 °C), the desorption pressure achieved could run only 0.5 kW fuel cell and the system was not suitable to be coupled with fuel cell for desorption temperature below 35 °C. The study also reports the numerical investigation carried out on the electrical power output and heat loss during fuel cell operation with respect to current density at varying temperature. It was observed that as the fuel cell temperature increased from 35 to 50 °C, the efficiency of conversion of electrochemical energy into power output increased from 39.8% to 43% at a current density of 0.8 A/cm 2. It was revealed about 1.3 kW of waste heat was rejected by a 1 kW fuel cell operating at a current density of 0.8 A/cm 2 and 50 °C. In addition, a 3.75 kg MH reactor required only 60-80 W of heat input to discharge hydrogen at a constant rate of 13 L/min (sufficient to run 1 kW fuel cell) for 36.3 min. This proved that only 16 % of total waste is enough to run a single reactor. Hence, multiple such reactors can be commissioned to power 1 kW fuel cell for longer duration.
... Hydrogen absorption is accompanied by heat release (exothermic), while heat energy is supplied during desorption (endothermic) to release hydrogen. MHHS are also utilized in various engineering applications such as hydrogen purification [3,4], hydrogen compression [5,6], thermal energy storage [7e9], and heating and cooling applications [10,11]. Developing an MHHS demands an appropriate choice of alloys, efficient reactor designs, and selecting optimum operating parameters. ...
The goal of the current study is to develop a dynamic model for forecasting the absorption and desorption behavior of metal hydride hydrogen system. The accuracy of the developed dynamic model is verified with the actual model. The effect of reactor diameter (10–25 mm), hydrogen supply pressure (5–20 bar) and desorption temperature (40–70 °C) on the accuracy of the temperature profile predicted by the dynamic model as compared to the actual model is investigated. The results showed that the percentage deviation of the dynamic model with actual model increase with the reactor diameter. The dynamic model predicted the average bed temperature during absorption with a maximum deviation of 4.32% (14 K) for a reactor of 25 mm diameter compared to the actual model. A maximum deviation of only 2.11% (6.32 K) was observed for the same reactor during desorption at 323 K. Further, the percentage deviation increases with the supply pressure and desorption temperature. Overall, it is observed that the slower the absorption/desorption, the better is the prediction accuracy of the dynamic model. On the other hand, the dynamic model is over 300 times faster than the actual, which saves computational time and cost. Furthermore, the dynamic model is extended for studying the coupled reactor system of a dual-stage metal hydride hydrogen compressor. Four alloy pairs are compared in terms of compression ratio, the amount of energy lost due to hysteresis, average hydrogen discharge rate, and isentropic efficiency. The comparison results suggested that an appropriate combination of AB5-AB2 type alloy is suitable for higher delivery plateau pressure, lower energy loss due to hysteresis, and a reasonable compression ratio.
... On the one hand, these MHs offer the highest volumetric storage densities possible. On the other hand, their gravimetric hydrogen storage capacity is too low to serve as a primary hydrogen storage system in aviation [4,5]. However, MHs enjoy an ongoing research emphasis due to their immense potential in engineering applications besides hydrogen storage [6]. ...
... However, MHs enjoy an ongoing research emphasis due to their immense potential in engineering applications besides hydrogen storage [6]. Some examples of those 'secondary' applications are hydrogen compression, purification and sensing as well as the use in optical or thermal systems [5,6]. This paper evaluates the potential of MHs in aviation. ...
... The properties of MHs enable multiple engineering applications. To generate an overview, those applications are classified in table I [5,6,8,9]. Not every of those applications offers reasonable use cases in aviation. ...
Hydrogen, used in a gas turbine or in fuel cells of electrified propulsion systems, is a promising energy carrier for future sustainable aviation. However, many challenges, like the storage of hydrogen or the thermal management, have to be tackled in the upcoming years. Metal hydrides, being one option to store hydrogen, are not only achieving high volumetric hydrogen storage densities, but also enable various auxiliary functions like high-power thermal applications or hydrogen compression. This study investigates potential use cases of metal hydrides in future hydrogen powered aviation. Hence, the possible applications of metal hydrides are presented. The following seven potential use cases for aviation are examined and evaluated: hydrogen emergency storage, cabin air-conditioning, thermal management of fuel cells, gas gap heat switches, hydrogen boil-off capture, onboard hydrogen compression and hydrogen safety sensors. The evaluation is performed by means of a weighted point rating. The results of this evaluation reveal the high potential of metal hydrides for hydrogen boil-off capture, hydrogen safety sensors and cabin air-conditioning. This study outlines, how metal-hydride-based components can contribute to the transition to future sustainable aviation.
... Those MHs form when the hydrogen reacts with metallic compounds. MHs offer the highest possible volumetric storage densities, while their gravimetric hydrogen storage capacity is too low to serve as a competitive primary hydrogen storage system in aviation [3,12]. ...
... In addition to hydrogen storage, MH reactors have demonstrated their suitability for high-power thermal applications [12,13]. MHs offer high thermal storage capacities of up to 2 000 kJ/kgMH and therefore are most suitable as an additional heat sink [12][13][14]. ...
... In addition to hydrogen storage, MH reactors have demonstrated their suitability for high-power thermal applications [12,13]. MHs offer high thermal storage capacities of up to 2 000 kJ/kgMH and therefore are most suitable as an additional heat sink [12][13][14]. Besides such an utilization as a thermal storage material, MH reactors (MHR) can also be used as a heat pump [12][13][14][15][16]. ...
... Apart from hydrogen storage, metal hydrides could be used for hydrogen compression, purification, thermal storage and other applications. In recent years research groups and companies focus on the cost-efficient scale-up of the metal hydride technologies, and the scale up issues include optimization of heat and mass transfer inside MH devices [2,5]. ...
... The most widely used on practice are AB 5 alloys based on LaNi 5 . Both La and Ni are partly substituted by other elements (mischmetal, Ce, etc. for La and Mn, Fe, Al, Co, Sm, etc. for Ni) to obtained desired thermodynamic and/or electrochemical properties. ...
... Studies have suggested various designs for hydrogen storage systems to facilitate effective heat transfer [14]. These designs are as diverse as the heat transfer enhancements themselves and include the addition of fins, cooling tubes, cooling coils, etc. [35,36]. Mellouli et al. [26,27,37] developed several mathematical models for detailed analysis of MH bed operations. ...
An Ansys Fluent–based model was constructed for simulating hydrogen storage and discharge from a large-scale metal hydride (MH) heat exchanger. The model's validity was initially verified in light of specific experimental data. Mass and heat transport processes inside the fixed bed during the absorption and desorption cycles were simulated for various hydrogen pressures and MH thermal conductivity. The findings were reported as average and special changes in the metal's bed temperature and hydrogen concentration. The hydrogenation (dehydrogenation) rate of the MH was improved when the applied charging (discharging) pressure was increased. However, even though it affected the thermal behavior of the reactor, the thermal conductivity of the MH did not affect the hydrogenation rate of the bed.
... The hydrogen storage capacity for these alloys varies between 1 and 3 wt%. Intermetallic alloys have been used for various applications, such as heat pumps, hydrogen sensors, compressors, catalysts, battery electrodes, purification of hydrogen, etc. [71,72]. They are generally defined as A x B y , as shown in. ...
h i g h l i g h t s g r a p h i c a l a b s t r a c t The importance of tunability of Metal hydrides are discussed. Summarized the effect of integrating carbon-based materials on Metal hydrides. Presented synthesizing strategies for Metal hydrides and carbon-based materials. Highlighted comparative summary of the characterization techniques. Available online xxx Keywords: High entropy alloys Intermetallic alloys Metal hydrides Nanoscale carbon materials Polymers Hydrogen storage a b s t r a c t Hydrogen-based economy has a great potential for addressing the world's environmental concerns by using hydrogen as its future energy carrier. Hydrogen can be stored in gaseous, liquid and solid-state form, but among all solid-state hydrogen storage materials (metal hydrides) have the highest energy density. However, hydrogen accessibility is a challenging step in metal hydride-based materials. To improve the hydrogen storage kinetics, effects of functionalized catalysts/dopants on metal atoms have been extensively studied. The nanostructuring of metal hydrides is a new focus and has enhanced hydrogen storage properties by allowing higher surface area and thus reversibility, hydrogen storage density, faster and tunable kinetics, lower absorption and desorption temperatures, and durability. The effect of incorporating nanoparticles of carbon-based materials (graphene, C60, carbon nanotubes (CNTs), carbon black, and carbon aerogel) showed improved hydrogen storage characteristics of metal hydrides. In this critical review, the effects of various carbon-based materials, catalysts, and dopants are summarized in terms of hydrogen-storage capacity and kinetics. This review also highlights the effects of carbon nanomaterials on metal hydrides along with advanced synthesis routes, and analysis techniques to explore the Please cite this article as: Desai FJ et al., A critical review on improving hydrogen storage properties of metal hydride via nanostructuring and integrating carbonaceous materials, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2023.04.029 effects of encapsulated metal hydrides and carbon particles. In addition, effects of carbon composites in polymeric composites for improved hydrogen storage properties in solid-state forms, and new characterization techniques are also discussed. As is known, the nanomaterials have extremely higher surface area (100e1000 time more surface area in m 2 /g) when compared to the bulk scale materials; thus, hydrogen absorption and desorption can be tuned in nanoscale structures for various industrial applications. The nanoscale tailoring of metal hydrides with carbon materials is a promising strategy for the next generation of solid-state hydrogen storage systems for different industries.
... Other types of H 2 separation membranes such as ionic liquids (ILs) and electrochemical H 2 pumping membranes are getting attention due to their high H 2 purification from mixtures of gases. ILs membranes are considered more suitable for the separation of (Muthukumar et al., 2018) Its hydrolysis suffers from sluggish kinetics in neutral aqueous solution (Ouyang et al., 2021a) To develop catalyst free systems; As difficulty and cost of recovering catalysts is huge (Ouyang et al., 2021a) 2. Mg-based alloys Mg-based alloys are easily available in low cost, and its hydrolysis to separate H 2 produces environmentally benign products (Ma et al., 2017) The addition of acid solution to dissolve magnesium hydro oxide in passive layers induces corrosion in reactors and hazards for users Mg(OH) 2 thermodynamic value is undesirable and low reaction kinetics need higher temperature, and the contamination of magnesium particles during dehydrogenation ...
Depleting energy resources, global warming and environmental problems associated with conventional fuels are serious global challenges of the modern world. The substitution of conventional energy resources with more efficient and sustainable resources is inevitable. In this scenario, hydrogen (H2) has emerged as the ultimate choice due to its superior characteristics such as low carbon emissions, cleanliness, and efficiency. However, for the successful implementation of making H2 as the next-generation fuel source, the hurdles of production, separation, and storage of H2 should be resolved. This paper summarizes the issues and challenges in the separation of H2 gas from various production streams by using available separation technologies. Different types of H2 separation technologies, including membranes, adsorption processes, metal hydrides, and cryogenic separation technologies, have been considered and discussed. The review encompasses the types, advantages, and disadvantages of each technology, followed by a detailed account of issues and challenges observed in each separation method. More attention has been given to membrane technology because it is the most promising technology for the production of high-purity H2. Finally, this review provides an outlook for future directions and developments in H2 separation technologies.
... Metal hydrides (MHs) are promising sorption materials for thermal energy storage, cooling, and heating applications [1,2]. They provide high energy density (as high as 2814 kJ/kg of hydride) and offer a wide range of operating temperatures. ...
The performance of a metal hydride (MH)-based TES system depends on its energy and power densities, i.e., the total energy storage capacity and the rate at which it can be charged/ discharged, which are highly influenced by reactor design and material properties. The present study focuses on design of the MH reactor by considering critical parameters such as discharging time, energy and power densities. Firstly, the discharging behavior of the tubular reactors is analyzed and compared. Secondly, an annular MH reactor is proposed to enhance the discharging power and reduce the discharging time of the tubular reactors. The results elucidated that the annular MH reactor reduced the discharging time of a 2.5-inch tubular reactor (i.e., 396 min) by 70%, with only a 16% reduction in energy storage density. The average specific discharge power of 2.5-inch tubular reactor is increased by ∼2.5 times with the annular MH reactor. Further, it is found that the number of reactors can be reduced with the annular MH reactor for the equivalent storage capacity and performance. Thirdly, performance of the annular MH reactor is evaluated by applying the conditions experienced by the reactors near the outlet section of a MH reactor array. Finally, radial fins are added to the annular MH reactor to reduce the discharging time for the reactors near the MH array outlet section. The proposed annular MH reactor with radial fins yielded a system-level gravimetric storage density of 560 kJ/kg, much higher than the present sensible and latent heat storage systems.
