What materials are in hydrogen fuel tanks?
Hydrogen fuel tanks used in vehicles are designed as lightweight, high‑pressure vessels built around a polymer inner liner and a strong composite outer shell. They typically operate at about 350 bar and, in some designs, at 700 bar, with safety devices and metal fittings integrated into the structure. The main materials work together to contain hydrogen safely while minimizing weight.
Core materials of the tank
The following list covers the key materials typically found in automotive hydrogen storage tanks.
- Inner liner: a polymer layer such as high-density polyethylene (HDPE) or alternative polymers like polyamide 12 (PA12) that provides a gas-tight barrier and hydrogen compatibility.
- Composite overwrap: carbon fiber reinforced polymer (CFRP), typically carbon fibers embedded in an epoxy resin, which supplies most of the vessel’s strength at a light weight.
- Resins and bonding agents: epoxy or other compatible resins that bind the carbon fibers and form the overwrap around the liner, plus bonding agents at interfaces.
- Outer protective jacket: additional polymer or CFRP skins for environmental protection and abrasion resistance, and sometimes thermoplastic outer surfaces.
- Metal end-fittings and hardware: aluminum or stainless steel end caps, flanges, and connection hardware that interface with valves and the vehicle’s high‑pressure system.
- Seals, gaskets, and O-rings: fluorinated elastomers (such as FKM/Viton) and PTFE-based seals chosen for chemical resistance and hydrogen compatibility.
These materials work together to hold hydrogen safely at high pressures, while keeping weight down and resisting hydrogen permeation and embrittlement.
Construction and safety features
Manufacturers assemble the tank through a multi-step process designed to ensure integrity under extreme pressures. The following steps outline typical production and safety considerations.
- Fabricate the polymer liner to exact inner dimensions, ensuring hydrogen-tightness and chemical compatibility.
- Apply the carbon-fiber overwrap by winding or laying CFRP sheets and curing the epoxy resin to form a strong, pressure-resistant shell.
- Add any outer jackets or protective coatings and perform surface finishing to protect against environmental exposure.
- Install end-fittings, valve assemblies, and safety devices such as pressure relief systems and sensors.
- Conduct rigorous testing, including high‑pressure leak checks, hydrostatic tests, and burst simulations to verify performance and safety margins.
Controlled manufacturing, quality assurance, and safety testing are essential given the volatility of hydrogen and the high pressures involved.
Inner liner materials
Details: HDPE liners are common because they offer strong chemical resistance to hydrogen, low permeability, and compatibility with the composite system. PA12 or other polyamides can be used for even lower hydrogen permeation and improved fracture resistance in some designs.
Composite overwrap materials
Details: CFRP overwrap provides most of the structural strength. Carbon fibers give high tensile strength-to-weight ratio; epoxy resin binds the fibers and bonds to the liner. Some designs use alternative matrices or fabric architectures to optimize permeability and toughness.
Seals and safety components
Details: Seals and gaskets are selected for fuel compatibility and temperature range. Safety devices include pressure relief valves and rupture disks, often stainless steel, capable of venting hydrogen safely if pressure exceeds limits.
Hydrogen compatibility and design considerations
Hydrogen permeation through polymers is a critical design consideration; materials are selected to minimize leak risk while remaining lightweight. Temperature effects, embrittlement of metals under hydrogen exposure, and the need for leak detection all shape material choices and testing protocols.
Summary
In automotive hydrogen tanks, the core combination is a polymer inner liner (commonly HDPE or PA12) surrounded by a carbon‑fiber reinforced polymer overwrap, bonded with epoxy resins and protected by an outer jacket. End fittings and safety components—often aluminum or stainless steel—along with seals and valves, complete the system. This blend provides the necessary strength, impermeability, and weight efficiency to store hydrogen at 350 bar (and often at 700 bar) while meeting stringent safety standards. Ongoing materials research seeks to further reduce weight, lower cost, and improve durability and permeation resistance.
