Magnesium Hydride Synthesis via Hydrolysis
Ultrasonication is an efficient and simple method to produce magnesium hydride for hydrogen storage. Ultrasound accelerates the hydrolysis of magnesium and hydrogen in order to form magnesium hydride. In contrast to the conventional dissociative chemisorption process, ultrasonic hydrolysis of magnesium hydride runs at room temperature and ambient pressure. This makes the sono-chemical route easy, safe and readily available. High-performance ultrasound allows for the fast and efficacious production of large magnesium hydride bulks.
Magnesium Hydride for Hydrogen Storage
Magnesium hydride, MgH2, has drawn widely attention as option for hydrogen storage. Main benefits are its abundant resource, high performance, light weight, low-cost, and safety. In comparison to other hydrides usable for hydrogen storage, MgH2 has the highest hydrogen storage densities with up to 7.6 wt %. Hydrogen can be stored in Mg in the form of Mg-based metal hydrides. The process of MgH2 synthesis is known as dissociative chemisorption. A common method to produce Mg-based metal hydride from Mg and H2, is the formation at a temperature of 300–400°C and a hydrogen pressure of 2.4–40 MPa. The formation equation goes as following: Mg + H2 ⇌ MgH2
The high heat treatment comes with significant degradation effects of the hydrides, such as recrystallization, phase segregation, nanoparticles agglomeration etc. Furthermore, high temperatures and pressures make the formation of MgH2 energy-intensive, complex and thereby expensive. An alternative non-thermal and significantly more simple method is the ultrasonically promoted hydrolysis of magnesium hydride at room temperature and ambient pressure.
Ultrasonic Hydrolysis of Magnesium Hydride
Ultrasonication is well known for its capability to initiate and accelerate chemical reactions, to influence chemical pathways and to improve the overall efficiency of a reaction. The beneficial effects of low-frequency, high-power ultrasound on chemical reactions is known as sono-chemistry.
Power ultrasound is already applied to many heterogeneous reactions, catalyses and syntheses in R&D and industrial stage to increase yield, conversion rate and overall reaction efficiency. For the hydrolytic synthesis of magnesium hydride, sonication has been scientifically proven to be highly beneficial, too.
Sonication improves mass transfer thereby accelerating the reaction, and helps to overcome the thermodynamic and kinetics barriers. Thermal energy, i.e. heat, is required to drive the absorption /desorption hydrogenation processes in magnesium. The use of non-direct thermal energy sources such as power ultrasound is an efficient alternative in order to destabilize magnesium hydride.
The research group of Hiroi et al. (2011) investigated the effect of ultrasonication at various frequencies on the hydrolysis of magnesium hydride (MgH2). They found that low frequency ultrasound was the most efficient method in order to obtain a high conversion rate. The hydrolysis rate at low frequency sonication “reached as high as 76% in terms of the reaction degree at 7.2 ks at an ultrasonic frequency of 28 kHz. This value was more than 15 times the value obtained in the case of the non-sonicated sample, indicating an equivalent hydrogen density of 11.6 mass% on the basis of the weight of MgH2.”
The results revealed that ultrasound will enhance the hydrolysis reaction of MgH2 by increasing reaction rate constant due to the generation of radical and exfoliating the passive layer of Mg(OH)2 over the unreacted MgH2 due to the generation of large shear forces. (Hiroi et al. 2011)
Problem: Slow Hydrolysis of Magnesium Hydride
Promotion of MgH2 hydrolysis via ball milling, hot water treatment or chemical additives have been investigated, but were not found to enhance the chemical conversion rate in a significant manner. Regarding the addition of chemicals, chemical additives, such as buffering agents, chelators, and ion exchangers, which helped to prevent the formation of a passivating Mg(OH)2 layer, produced impurities in the post-Mg cycling process.
Solution: Ultrasonic Dispersing of Magnesium Hydride
Ultrasonic dispersing and wet-milling is a highly efficient technique to produce nano-sized particles and crystals with a very narrow distribution curve. By dispersing magnesium hydride evenly in nano-size, the active surface area becomes significantly enlarged. Furthermore, sonication removes passivating layers and increases mass transfer for superior chemical conversion rates. Ultrasonic milling, dispersing, deagglomeration and particle surface cleaning excel other milling techniques in efficiency, reliability and simplicity.
Ultrasonic Nanostructuring of MgH2
Nano-size / nano-structured magnesium-based structures such as MgH2 nanoparticles and nanofibres can be further enhanced by reducing the particle and grain size, thereby decreasing their hydride formation enthalpy ΔH. Ultrasonic nanostructuring is a highly effective technique that allows to change the thermodynamics of magnesium hydride without affecting the hydrogen capacity. The ultra-fine MgH2 nanoparticles exhibit a significantly improved hydrogen desorption capacity.
- Faster reaction
- Higher conversion rate
- Removal of passivating layers
- More complete reaction
- Increased mass transfer
- Higher yields
- Nanostructured MgH2
- Improved hydrogen sorption
High-Performance Ultrasonicators for MgH2 Hydrolysis
Sonochemistry – the application of power ultrasound to chemical reactions – is a reliable processing technology, which facilitates and accelerates the syntheses, catalytic reactions and other hetergeneous reactions. Hielscher Ultrasonics portfolio covers the full range from compact lab ultrasonicators to industrial sonochemical systems for all kind of chemical applications such as the hydrolysis of magnesium hydride and its nano-milling / nano-structuring. This allow us at Hielscher to offer you the most suitable ultrasonicator for your envisaged MgH2 synthesis. Our long-time experienced staff will assist you from feasibility tests and process optimisation to the installation of your ultrasonic system on final production level.
The small foot-print of our ultrasonic homogenizers as well as their versatility in installation options make them fit even into small-space processing facilities. Ultrasonic processors are installed worldwide in fine chemistry, petro-chemistry, and nano-material production facilities.
Batch and Inline
Hielscher’s sonochemical equipmment can be used for batch and continuous flow-through processing. Ultrasonic batch processing is ideal for process testing, optimisation and small to mid-size production level. For a producing large volumes of materials, inline processing might be more advantageous. A continuous inline mixing process requires a sophisticated setup – consisting in a pump, hoses or pipes and tanks -, but it is highly efficient, rapid and requires significantly less labour. Hielscher Ultrasonics has the most suitable sonochemical setup for your sono-synthesis reaction, processing volume and goals.
Ultrasonic Probes and Reactors for MgH2 Hydrolysis at Any Scale
Hielscher Ultrasonics product range covers the full spectrum of ultrasonic processors from compact lab ultrasonicators over bench-top and pilot systems to fully-industrial ultrasonic processors with the capacity to process truckloads per hour. The full product range allows us to offer you the most suitable ultrasonic homogenizer for your process capacity and production targets.
Ultrasonic benchtop systems are ideal for feasibility testing and process optimization. Linear scale-up based on established process parameters makes it very easy to increase the processing capacities from smaller lots to fully commercial production. Up-scaling can be done by either installing a more powerful ultrasonic unit or clustering several ultrasonicators in parallel. With the UIP16000, Hielscher offers the most powerful ultrasonic homogenizer worldwide.
Precisely Controllable Amplitudes for Optimum Results
All Hielscher ultrasonicators are precisely controllable and thereby reliable work horses in production. The amplitude is one of the crucial process parameters that influence the efficiency and effectiveness of sonochemical reactions All Hielscher Ultrasonics’ processors allow for the precise setting of the amplitude. Sonotrodes and booster horns are accessories that allow to modify the amplitude in an even wider range. Hielscher’s industrial ultrasonic processors can deliver very high amplitudes and deliver the required ultrasonic intensity for demanding applications. Amplitudes of up to 200µm can be easily continuously run in 24/7 operation.
Precise amplitude settings and the permanent monitoring of the ultrasonic process parameters via smart software give you the possibility to treat your reagants with the most effective ultrasonic conditions. Optimal sonication for an outstanding chemical conversion rate!
The robustness of Hielscher’s ultrasonic equipment allows for 24/7 operation at heavy duty and in demanding environments. This makes Hielscher’s ultrasonic equipment a reliable work tool that fulfils your chemical process requirements.
Highest Quality – Designed and Manufactured in Germany
As a family-owned and family-run business, Hielscher prioritizes highest quality standards for its ultrasonic processors. All ultrasonicators are designed, manufactured and thoroughly tested in our headquarter in Teltow near Berlin, Germany. Robustness and reliability of Hielscher’s ultrasonic equipment make it a work horse in your production. 24/7 operation under full load and in demanding environments is a natural characteristic of Hielscher’s high-performance mixers.
Hielscher Ultrasonics’ industrial ultrasonic processors can deliver very high amplitudes. Amplitudes of up to 200µm can be easily continuously run in 24/7 operation. For even higher amplitudes, customized ultrasonic sonotrodes are available.
The table below gives you an indication of the approximate processing capacity of our ultrasonicators:
|Batch Volume||Flow Rate||Recommended Devices|
|1 to 500mL||10 to 200mL/min||UP100H|
|10 to 2000mL||20 to 400mL/min||UP200Ht, UP400St|
|0.1 to 20L||0.2 to 4L/min||UIP2000hdT|
|10 to 100L||2 to 10L/min||UIP4000hdT|
|n.a.||10 to 100L/min||UIP16000|
|n.a.||larger||cluster of UIP16000|
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Literature / References
- Hiroi, Shun; Hosokai, Sou; Akiyama, Tomohiro (2011): Ultrasonic irradiation on hydrolysis of magnesium hydride to enhance hydrogen generation. International Journal of Hydrogen Energy, 36(2), 2011. 1442-1447.
- Xin Zhang; Yongfeng Liu; Zhuanghe Ren; Xuelian Zhang; Jianjiang Hui; Zhenguo Huang; Yunhao Lu; Mingxia Gao; Hongge Pan (2021): Realizing 6.7 wt% reversible storage of hydrogen at ambient temperature with non-confined ultrafine magnesium hydrides. Energy & Environmental Science, 2021.
- Brad W. Zeiger; Kenneth S. Suslick (2011): Sonofragmentation of Molecular Crystals. J. Am. Chem. Soc. 2011, 133, 37, 14530–14533.
Facts Worth Knowing
Advantages of Magnensium Hydride for Hydrogen Storage
- Ideal, balanced gravimetric
- Superior volumetric energy density
- Abundantly available
- Easy to handle (even in air)
- Direct reaction with water is possible
- Reaction kinetics can be tailored for specific applications
- High reaction and product safety
- Non-toxic and safe-to-use
- Environmentally friendly
What is Magnesium Hydride?
Magnesium hydride (MgH2; also known as magnesium dihydride) has a tetragonal structure and exhibits the form of a colourless cubic crystal or off-white powder. It is used as a hdyrogen source for fuel batteries below 10,000W. The hydrogen amount that is released by water is higher than 14.8wt%, which is significantly higher than the hydrogen amount released via a high pressure gas hydrogen storage tank (70MPa,~5.5wt%) and heavy metal hydrogen storage materials (<2wt%). Furthermore, magnesium hydride is safe and highly efficient, which turns it into a promising technology for efficacious hydrogen storage. Hydrolysis of magnesium hydride is used as supply hydrogen system in proton-exchange membrane fuel cells (PEMFC), which improve energy density of the system significantly. Solid / semi-solid Mg-H fuel battery systems with high-energy density are also in development. Their promising advantage is an energy density 3-5 times higher than that of lithium-ion batteries.
Synonyms: Magnesium dihydride, magnesium hydride (hydrogen storage grade)
Used as material for hydrogen storage
Molecular Formula: MgH2
Solubility: insoluble in normal organic solution