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 ■ Date: Sep 18, 2020
【Overview of Hydrogen Storage Technology in China 】
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As an energy storage medium, the essence of fuel cell is to convert between chemical energy and electrical energy through the oxidation of hydrogen. However, although the specific energy of hydrogen is large (142 MJ/kg, the highest of any practical fuel), its volumetric energy density is very low: only 12.1 MJ/m3 at 288.15 K and 1 atm.
As a bridge between hydrogen production and utilization, one of the key points of hydrogen storage technology is to increase the energy density of hydrogen. Yet other factors must be taken into consideration when evaluating the pros and cons of hydrogen storage technology, such as safety, transportation cost, difficulty of hydrogenation/dehydrogenation, etc.
In this article, we summarized the current status of several hydrogen storage technologies in China that have received widespread attention and give insights for future development of these storage technologies. 
(1) High-pressure gaseous hydrogen is currently the most mature and the mainstream method for hydrogen transportation in China
(2) Cryogenic hydrogen transportation has a relatively high hydrogen storage density and is in rapid development. The standardization work is ongoing, and civil cryogenic hydrogen projects are getting more attention. With the increase in the volume of hydrogen transported, its economy of scale will be highlighted.
(3) LOHC and Metallic Hydride are not yet commercialized.
- Some features of LOHC (easy to handle, easy to transport, chemically stable) make it not only promising medium for long-distance transport, but also for long-term storage.
- Although Metallic Hydride has some advantages (ambient storage condition), it is undeniable that more research should be done to overcome the drawbacks (low storage density, difficulty in dehydrogenation/dehydrogenation) before it can be manufactured and commercialized.
(4) In the future hydrogen energy industry system, we expect renewable energy production to replace industrial by-product hydrogen as a clean and high-quality hydrogen source. Under this vision, we look forward to transportation method suitable for higher hydrogen storage capacity and for longer distance.
【Introduction of different hydrogen storage technologies】
Commonly used hydrogen storage technologies mainly include physical, chemical hydrogen storage technologies.
  Physical hydrogen storage technology refers to a technology that store hydrogen simply by changing the physical storage conditions to increase the hydrogen density. This does not require a hydrogen storage medium, has lower cost, and the dehydrogenation process is relatively easy. High-pressure gaseous hydrogen and cryogenic hydrogen storage are two most typical physical hydrogen storage technologies in China (Figure 1).
  Chemical hydrogen storage technology is a technology that uses storage carrier to react with hydrogen under certain conditions to generate stable compounds (hydrogenation), and then changes the conditions to achieve hydrogen release (dehydrogenation). Current carriers include liquid organic hydrogen carrier (LOHC), metal hydride, liquid ammonia, etc.
Figure 1 Comparison of different hydrogen storage technologies 
1. Gaseous Hydrogen
By compressing with high pressure, hydrogen is compressed and charged into a hydrogen storage vessel. This hydrogen storage method is now the most commonly used and mature technology.
The materials for manufacturing hydrogen vessels have also gone through various generations and have formed different standards.
Type I—all-metal cylinders 全金属瓶
Type II—all-metal hoop-wrapped composite cylinders 金属内胆纤维环向缠绕气瓶 
Type III—fully wrapped composite cylinders with metallic liners 金属内胆纤维全缠绕气瓶 
Type IV—fully wrapped composite cylinders with nonload bearing nonmetallic liners 非金属内胆纤维全缠绕气瓶 
All-metel vessels (often steel) are commonly used for high-pressure gas compression storage with operating pressure as high as 700 bars. However, for hydrogen storage, steel is not a desirable material. It is because the diffusion of hydrogen into steel causes hydrogen embrittlement failure, especially when the vessels undergo frequent charge and discharge. In the case of rupture, steel fragments may cause serious injuries. Steel vessels are heavy and have low gravimetric storage density. Such problems can be resolved by using vessels made of composite materials comprised of polyethylene, or carbon fiber and epoxy resin with thin aluminum liner and by ameliorating the material wrapping methods.
These different type of vessels have different properties and thus would be used in differnt cases: According to different hydrogen application scenario, transportationstationary hydrogen storage and onboard hydrogen storage.
(1) For  stationary hydrogen storage and transportation storage
Two storage pressures are available according to downstream onboard storage pressure demand: 45MPa (supply to 35MPa tank) and 98MPa (supply to 70MPa tank). Instead of purchasing all high-pressure storage tanks, hydrogen station can minimize required compression pressures, compression time, and overall system cost by using cascade storage system: low (20-30 MPa), medium(30-40 MPa), and high (40+ MPa). Sometimes the hydrogen storage tube trailer is also used as in-station storage facility.
At present, there are two main types of high-pressure hydrogen storage containers in domestic hydrogen refueling stations (Figure 2):​
- Seamless tube (Type I storage vessel) : Most widely adapted storage vessel in HRS in China. Usually have 20MPa (both for transportation and stationary use, more common) and 45MPa (only for stationary use). 
- Stationary flat steel ribbon wound vessel​钢带错绕式储氢罐: domestically innitiated technology, China has completely independent intellectual property rights in the design and manufacturing of storage vessel. There usually have 45MPa (capacity can reach 20 m3) and 98MPa (capacity can reach 1 m3).
- Type III storage vessel: there are also 45MPa and 98MPa type. Compared with 20MPa seamless tube, higher storage pressure require less space and can bear more hydrogen. Yet due to technical constraints, only few companies are manufacturing type III storage vessels. More R&D work is still needed before it can be widely applied in China. Higher storage capacity in HRS is required as the local hydrogen demand increase, however, type III tank may replace type I tank which is the most commonly adapted in Chinese HRS.
Figure 2 Stationary storage in Hydrogen Refueling Stations
Reference: Public information, Summarized by Integral
(2) For onboard hydrogen storage
Type I and II cylinders are impractical for automotive applications where weight and volume play a critical role in defining the overall efficiency of the vehicle. As such, most recent efforts at developing high-pressure, compressed cylinders for light-duty vehicles has been devoted to Type III and IV cylinders. For both types, there are two working pressure: 35 MPa and 70Mpa. Although it is more widely used internationally type IV cylinder, type III cylinder still enjoys its market dominancy in China, especially for 35MPa tank (70MPa type III are currently under final process of testing validation, see Figure 3)
Figure 3 Current market player of type III storage tank in China
Reference: Public information, summarized by Integral
In contrast, since there was once an accident on type IV tank caused by the leakage of hydrogen gas and type IV tank was therefore forbidden to be sold in China. Also, other factors have confined the development of type IV tank. Heavy reliance on foreign suppliers, for instance, carbon fibers from Toray Industries, largely restricted the price and output of the tanks.
Nevertheless, type IV storage tank still has advantanges over type III tanks in many aspects. For example, it has less weight and longer lifetime. Some vessle failure could be avoided by using non-metallic meterials, such as hydrogen embrittlement. With the FCEV development, in the long term, hydrogen supply infrastructure gets more completely constructed in city center and FC passenger vehicles will start to grow in number. Higher weight-sensitivitiy of FC passenger vehicles will make type IV storage tank more favorable.
It was not until recently that the standardization work of type IV cylinder in China was re-picked up, which could be interpreted that the R&D and market development of type IV tank are still drawing attention from both academic and industry sides. 
Some market players have already shown business acumen and quick reaction towards this trend. Shenyang CLD (沈阳斯林达), which already led in type III hydrogen cylinders, exhibited their uncommercialized 70MPa type IV hydrogen storage vessle at the 5th FCVC (Fuel Cell Vehicle Congress) (Figure 4).
Figure 4 70MPa Type IV cylinder, exhibited by CLD
Reference: 5th FCVC Exhibition
2. Cryogenic Hydrogen
Compared with high-pressure gaseous hydrogen, cryogenic hydrogen storage has several advantages:
- Higher hydrogen storage capacity and lower storage pressure: can be adapted to larger hydrogen demand in the future as well as decrease the required hydrogen station size
- Higher hydrogen purity: can increase the life of fuel cells. Ithe liquefaction process, impurities will also be solidified, and the purity can thus be further improved. 
- Economic advantage in larger volume and long distance: For more details of economic calculation, please refer to our blog " Analysis of Hydrogen Tranportation Cost in China"
Currently the market demand for hydrogen used in FCEV hasn't been fully developed, hence the high production and transportation costs are still high. Therefore, most of the liquid hydrogen projects are for military use in China. For example, Hainan Wenchang rocket launching base, Xichang rocket launching base, etc. Civil liquid hydrogen market is in its very early stage and industry standard in commercial application is yet under developed (the first industry standard draft regarding liquid hydrogen production, storage and transportation safety was finally released in 2019 and currently under final evaluation process).
With the development in hydrogen and FCEV industry, hydrogen demand is expected to increase greatly. In addition, in face of hydrogen demand and supply imbalance in some region, the transportation of hydrogen from hydrogen-abundant region (e.g. renewable energy source provinces where excess of hydrogen will be generated) to demand region will also appear. The economies of scale will render the transportation via cryogenic hydrogen more attractive.
In China, currently there are basically two types of civil liquid hydrogen projects: 1) those undertaken by private enterprises and mainly for station use; 2) those undertaken by SOEs, mainly for energy management (scale-up projects using curtailed RE power) (Figure 5). The latter one has much larger capacity, they can be ten or hundred times larger than previous type of project. These serves as demostration projects, and take years to be fully commercialized.
Figure 5 List of civil liquid hydrogen projects 
Reference: Public information, summarized by Integral
【Major Player】Beijing Aerospace Testing Technology Research Institute (Institute 101) 北京航天试验技术研究所(101所)
Founded in 1958, it is China’s largest, most versatile and technologically advanced aerospace power research and test base. As research institute affiliated to CASC(航天科技), Institute 101’s strength is its testing ability of hydrogen energy equipment. For example, liquid hydrogen-related testing such as hydrogen combustion, diffusion and explosion experiments, etc.
As a leading player in liquid hydrogen for military use, Institute 101 is actively promoting "military-civilian integration" to promote the application of liquid hydrogen in the civilian field. According to Zhao Yaozhong's speech, their senior engineer at "International Conference on the Development of Hydrogen Energy and Fuel Cell Industry”, Institute 101 would offer their technology and experiences, including onboard liquid hydrogen supply system, hydrogen station development and verification, related hydrogen standards, etc for the promotion of liquid hydrogen technologies.
(For more information, see Hydropedia
【Major Player】Beijing Sinoscience Fullcryo Technology 中科富海
Founded in August 2016 with a registered capital of 131million RMB in Beijing, Fullcryo’s technology base was experts from Technical Institute of Physics and Chemistry, CAS and research achievements from national projects for key scientific equipment.
Fullcryo specializes in the R&D and manufacturing of large-scale cryogenic equipment with a working temperature below 20K and has developed full-set solution for hydrogen liquefaction, liquefied hydrogen storage and transport and hydrogen filling station to substantially reduce the hydrogen storage and transportation costs and further promote the large-scale application of hydrogen energy.
(For more information, see  Hydropedia
3. Carrier Technology: LOHC
The LOHC technology is based on the chemical bonding of hydrogen to liquid organic carriers (LOHC), which are mostly aromatic hydrocarbons or heterocyclic substances. The loading takes place via an exothermic hydrogenation reaction, the discharge via an endothermic dehydrogenation. In contrast to some other chemical hydrogen storage processes, these reactions are reversible. 
The carrier molecule is cycled between a loaded (LOHC+) and unloaded (LOHC-) state. The worldwide research and development work in the field of LOHC is based on different LOHC substances, such as dibenzyltoluene (Hydrogenious, Germany), benzene or toluene (Chiyoda, Japan) and N-Ethylcarbazole (Hynertech, China). 
Compared to other technologies, storage via LOHC has several advantages:
- Easy to handle: storage under ambient temperature and pressure, which greatly reduces the cost of handling hydrogen (without great liquefaction or gas compression cost).
- Easy to transport: using convetional chemicals, existing oil & chemicals infrastructure can be use for the storage and  transportation.
- Chemically stable: already converted to liquid chemical (loaded LOHC+), there is very minor loss by long term storage & long distance transport
Future operation of central LOHC hydrogenation plants are possible at locations where a large amount of curtailed RE-generated hydrogen is produced and stored in long term. Loaded LOHC+ can be transported via standard chemical tank trucks to the hydrogen refueling stations, which are equipped with a dehydrogenation system. There, the hydrogen can be produced when needed and then integrated into the existing hydrogen refueling station technology.
【Major Player】Hynertech 氢阳能源
Co-founded in 2014 by Prof. Hansong Cheng of China University of Geosciences (Wuhan) and his partners, Hynertech has developed state-of-the-art technology to store and transport hydrogen using LOHC technology. 
Hynertech stepped in advanced in the standardization work. It not only released its own corporate standards but also led in the drafting of association standard, such as that <Determination of hydrogen storage density of hydrogenated liquid organic hydrogen carrier - Water displacement method> that was officially released on 2020.5.
Hynertech's headquartered is in Wuhan, Hubei, which set its FCEV industry development plan with great ambition. As the demand for high-quality hydrogen keep increasing, Hubei will probably face insufficient hydrogen supply (by-product generated hydrogen). Under this situation, hydrogen generated from renewable energies from neighbor provinces would makeup this shortage and LOHC, with high storage density, low dissipation and large transportation volume, is considered high promising.
Therefor, Hynertech signed projects with Yidu government for the production of LOHC and with Southern Power Grid for the utilization of curtailed renewable hydropower in Yunnan and Sichuan provinces.
(For more information, see Hydropedia
4. Carrier Technology: Metallic Hydride
Metals or alloys can also be applied as carrier for the storage of hydrogen. In presence of a catalyst, hydrogen molecule is dissociated into atoms, which will then diffuse into the lattic of the metal and form metallic hydrides.
Light metals such as Li, Be, Na, Mg, B and Al, form a large variety of metal–hydrogen compounds. One reason they are especially interesting is due to their light weight, which might increase the gavimetric storage density. There are considerable researches on magnesium(Mg) and its alloys for onboard hydrogen storage due to their high hydrogen-storage capacity and low cost. Besides, the Mg-based hydrides possess good-quality functional properties, such as heat-resistance, vibration absorbing, reversibility and recyclability. In recent years, therefore, much attention has been paid to investigations on specific material properties of Mg alloys for the development of new functional materials.
The formed metal hydride leads to a solid-state hydorgen storage under moderate temperature and pressure, which gives them the important safety advantage over the gas and liquid storage methods. However, before the commercialization of metallic hydride as storage material, there are more things to be tackled:
- Unfavorable adsorption/desorption process: requires high temperature (200-500°C) , and has slow desorption kinetics. Many efforts has focused on Mg-based hydrides in recent years to reduce the desorption temperature and to fasten the re/dehydrogenation reactions. These can be accomplished to some extent by changing the microstructure of the hydride by ball-milling (mechanical alloying) with elements which reduce the stability of the hydrides and also by using proper catalysts to improve the absorption/desorption kinetics.
- Not high enough storage capacity: To date, rare earth-based material (rare earth metal, Ti, TiV system) is more mature in solid-state hydrogen storage. Among theses materials, TiMn-based material has already been applied in onboard hydrogen storage for FC buses. But as the metals have high atomic weight, the storage capacity is still in low level (~2.6%). To further increase the capacity, more efforts would be put on lightweight metal-based materials.
- High material cost: On the one hand, the raw material cost of hydrogen storage materials fluctuates greatly due to the price fluctuations of non-ferrous metal raw materials; on the other hand, the market for these materials is still small and hasn't been scaled up, which result in the higher manufacturing costs.
In view of the above-mentioned problems, it is particularly important to develop the R&D and application of reliable hydrogen storage materials.
【Major Player】H2Store 氢储 
H2 Store 上海氢储 (Shanghai) is a company that specializes in solid-state hydrogen storage technology. Its business covers the R&D, manufacturing and sales of solid-state hydrogen storage technology and products. It was jointly established on January 24, 2019, by Jiaotong University Hydrogen Science Center and Shanghai Hyfun 上海氢枫 Energy Technology as part of Hyfun's development strategy in upstream hydrogen storage and transportation.
H2 Store mainly uses Mg-based material as hydrogen storage carrier. In 2015, H2 Store has achieved 7.6wt% storage capacity, with a scaled production capacity of 20-50 ton/year and by 2018 they started officially use Mg-based metallic hydride in industrial hydrogen storage products. 
In 2019H2, H2 Store established H2 Store (Jiangsu) in Rugao, Jiangsu and invested 240 million RMB to set up a producion base for Mg-based hydrogen storage material. The project consists of two phases: Phase I is mainly for setting up R&D center and part of the production lines and Phase II will be capacity expansion. Phas I is expected to be completed by the end of 2020, after which the annual production capacity will reach 400 Mg-based solid-state hydrogen storage vehicles, 300 hydrogen storage tanks, and 200 sets of flexible hydrogen storage equipment.
【Comparison of different hydrogen storage technologies】
Figure 6 Comparison of different hydrogen storage technologies 
Reference: Integral Report
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