High-pressure gaseous hydrogen storage is one of the key technologies under continuous development. Storage tanks are classified into five main types (I, II, III, IV, V), differing in materials, capacity, weight, and specific use. But where does this classification come from?
Although these terms are common in the industry, they are not directly specified in ISO regulations. However, ISO standards regulate the safety and design requirements for each tank type. Type I (metallic) tanks are covered by ISO 9809, Type II (partially wrapped) by ISO 11119-1, Type III (metal liner) by ISO 11119-2, and Type IV (polymeric liner) by ISO 11119-3 and ISO 11439. Type V tanks, still in development, are addressed by ISO/AWI TR 19884.
Type I Tanks: Strength and Durability
Type I tanks are the most traditional and are made entirely of metal, usually steel or aluminum. These tanks are primarily used for stationary storage due to their high weight, which limits their mobility applications. Their mechanical strength and durability are exceptional, making them very safe and reliable for containing hydrogen at working pressures between 200 and 250 bar.
Although their robustness is an advantage, they present efficiency drawbacks since their weight limits the amount of hydrogen stored per unit mass. With energy densities of approximately 200 bar of pressure, these tanks are suitable for applications where weight is not a critical factor, such as industrial plants or hydrogen stations, with a storage cost of around 1,000€/kg (unit cost of hydrogen storage). However, due to hydrogen adsorption and diffusion in metallic materials, it is necessary to implement controls to prevent phenomena such as hydrogen embrittlement, which could compromise the tank’s structural integrity.
Type II Tanks: Efficiency and Lightweight Design
Type II tanks are an evolution of metallic tanks, combining a partial fiberglass or carbon fiber wrap over a metal core (usually steel or aluminum). This design significantly reduces weight compared to Type I tanks, making them more viable for mobile applications.
These tanks operate at higher pressures, reaching up to 1,000 bar, with an energy density of approximately 0.9 kWh/kg. They offer a balance between strength and weight reduction. The external fiber wrap reinforces the tank, allowing for more hydrogen storage without significantly increasing weight. However, their energy density is still lower than that of more advanced types, and their cost is higher than Type I tanks due to the use of composite materials, with a unit hydrogen storage cost of approximately 1,500–2,000€/kg.
Type III Tanks: High Capacity for Mobility
Type III tanks represent a significant technological leap, as they feature a fully carbon fiber-wrapped aluminum inner liner. This hybrid structure allows operation at pressures of up to 700 bar, offering high storage capacity with considerably reduced weight.
With a higher energy density than Type II tanks at 1.5 kWh/kg, these tanks are ideal for mobility applications, such as hydrogen vehicles, where weight reduction is essential to improve range. Despite their advantages, Type III tanks are more expensive due to the extensive use of carbon fiber, with a hydrogen storage unit cost of around 2,000€/kg.
Type IV Tanks: The Best Option for Advanced Mobility
Type IV tanks represent the latest generation in high-pressure hydrogen storage. They feature a polymer inner liner (typically polyethylene) fully wrapped in carbon fiber. These are the lightest tanks and offer the best weight-to-storage capacity ratio, making them the preferred choice for mobility applications, especially in cars and trucks.
These tanks can withstand pressures of up to 700 bar and, due to their composition, are highly resistant to corrosion and hydrogen embrittlement. However, polymeric materials pose additional risks, such as hydrogen permeation, which can compromise safety if not properly controlled. Additionally, polymer swelling and degradation under pressure are challenges that must be addressed in the design. Despite these challenges, their energy density can reach 2 kWh/kg, and their lightweight nature makes them the best option for advanced mobile applications. However, their high cost, with a unit hydrogen storage price of 4,000€/kg, limits their use mainly to sectors with high investment capacity.
Type V Tanks: Under Development
Type V tanks are an emerging technology promising even greater weight reductions and storage capacity improvements. These tanks are made entirely of advanced composite materials, without the need for a metal or polymer liner. Although still in development, they are expected to withstand pressures even higher than 700 bar.
Antonio López García
12/03/2025
