At present, the most common hydrogen storage technologies include high-pressure gaseous hydrogen storage, low-temperature liquid hydrogen storage, and solid-state hydrogen storage. Among them, high-pressure gaseous hydrogen storage technology is the most mature, relying on advantages such as low cost, fast hydrogen charging and discharging speed, low energy consumption, and simple structure, becoming the main hydrogen storage technology promoted in China.
In addition to the V type non liner fully composite gas cylinder that is still in its infancy, four types of hydrogen storage cylinders have entered the market application stage:
1. Type I all-metal gas cylinder: with a large capacity ratio, working pressure of 17.5-20MPa, low cost, and a small amount used for CNG trucks and buses;
2. Type II metal inner composite material circumferential winding gas cylinder: with a relatively large capacity, working pressure of 26-30MPa, metal inner liner (steel), medium cost, widely used in CNG vehicle gas cylinders;
3. Type III metal inner composite fully wound gas cylinder: with a relatively small capacity, working pressure of 30-70MPa, metal inner liner (steel/aluminum), high cost, lightweight market application, hydrogen fuel electric vehicle;
4. Type IV plastic inner liner composite material fully wound gas cylinder: with a small capacity ratio and a working pressure of 30-70MPa, the inner liner is made of materials such as polyamide (PA6), high-density polyethylene (HDPE), and polyester plastic (PET).
Type IV hydrogen storage cylinders have more advantages:
At present, Type IV hydrogen storage cylinders are widely used in foreign markets, while Type III hydrogen storage cylinders are mainly used in domestic commercial hydrogen storage.
We know that when hydrogen gas is greater than 30MPa, irreversible "hydrogen embrittlement" phenomenon occurs, that is, hydrogen corrodes the metal liner, leading to plastic failure of the metal, resulting in cracks and fractures. This situation may lead to hydrogen leakage, causing an explosion!
Moreover, there is a potential difference between the aluminum metal and the carbon fibers in the winding layer. If the aluminum liner comes into direct contact with the carbon fiber winding layer, it is also prone to corrosion. To prevent this situation, researchers added a corrosion layer of discharge couples between the inner liner and the winding layer, but this also increased the overall weight of the hydrogen storage cylinder, increasing logistics difficulty and cost.
It is necessary to fasten the "safety belt" when storing and transporting hydrogen energy.Compared to Type III, Type IV hydrogen storage bottles have greater advantages in terms of safety. Firstly, the non-metallic liner used in Type IV is composed of composite materials such as polyamide (PA6), high-density polyethylene (HDPE), and polyester plastic (PET). Among them, polyamide (PA6) has good mechanical properties such as tensile strength and impact resistance. Its melting temperature is high, but its hot deformation temperature is low, and its melting point can reach 220 ℃. High density polyethylene (HDPE) has good heat resistance and environmental cracking resistance, as well as high toughness and impact resistance. With the support of these plastic composite materials, Type IV hydrogen storage bottles have superior resistance to hydrogen embrittlement corrosion, longer service life, and greater safety advantages. Secondly, the quality of plastic composite materials is lighter, saving the weight of the metal liner and reducing logistics costs.
In June 2023, the national standard "Carbon fiber fully wound compressed hydrogen plastic inner liner gas cylinders for vehicles" jointly drafted by Zhejiang University, the Special Equipment Safety Supervision Bureau of the State Administration for Market Regulation, and other units was released. It will be officially implemented on June 1, 2024, further promoting the commercialization process of type IV hydrogen storage cylinders.
