Amidst the global acceleration towards carbon neutrality, hydrogen energy is considered a key pillar of future energy systems. From hydrogen production via water electrolysis, high-pressure storage and transportation, to fuel cell vehicles, the entire industrial chain poses unprecedented challenges to materials: they must withstand high-pressure hydrogen (35–70 MPa), cryogenic liquid hydrogen (-253°C), and resist long-term erosion from strong alkaline electrolytes or proton exchange membrane environments. Under such harsh conditions, traditional rubbers like Nitrile Butadiene Rubber (NBR) and Ethylene Propylene Diene Monomer (EPDM) are prone to "hydrogen embrittlement," swelling, or aging failure. However, specialty silicone rubbers, thanks to their molecular stability, broad temperature elasticity, and designable chemical inertness, are gradually becoming indispensable "flexible barriers" in hydrogen energy equipment.

I. Core Sealing Challenges in Hydrogen Systems

Hydrogen is the smallest molecule in nature (kinetic diameter about 2.89 Å), making it extremely easy to diffuse through micropores; it also has high permeability and strong reductivity, which can lead to metal "hydrogen embrittlement" and polymer "bubbling." Sealing materials must meet:

Extremely low hydrogen permeability;

Resistance to aging under high-pressure hydrogen environments;

Ability to withstand -40°C to +120°C temperature cycles (for automotive applications);

Hydrogen compatibility without catalytic decomposition risks.

While ordinary silicone rubber has good temperature resistance, its hydrogen permeability is relatively high (about 10⁻⁹ cm²/s·Pa) and requires modification to improve barrier properties.

II. Key Application Scenarios and Material Solutions

Fuel Cell Stack Sealing

Proton Exchange Membrane Fuel Cells (PEMFC) operate at temperatures between 60–80°C in humid, weakly acidic environments (pH≈2–4). Silicone rubber used for sealing gaskets between bipolar plates must provide electrical insulation, have a compression set less than 25%, and exhibit low ion leaching. High-purity addition-cured Liquid Silicone Rubber (LSR) is the preferred choice due to no byproducts and low outgassing.

High-Pressure Hydrogen Pipelines and Connectors

Vehicle-mounted hydrogen storage tank outlets and hydrogen refueling gun interfaces need to withstand pressures up to 70 MPa. Ordinary silicone rubber can be "forced into" microscopic defects under high pressure, leading to microcracks. Solutions include nano-composite silicone rubber with layered silicates or graphene additives, fluorosilicone rubber (FVMQ) with trifluoropropyl groups for improved density, and multi-layer structure seals combining silicone rubber with PTFE liners.

Electrolyzer Seals (Alkaline/PEM)

Alkaline electrolyzers use 30% KOH solution at temperatures between 70–90°C. Silicone rubber offers superior alkali resistance compared to most rubbers but may still hydrolyze after prolonged immersion. Using highly cross-linked formulations with antioxidants can extend service life beyond 60,000 hours. PEM electrolyzers require even higher purity to avoid metal ion contamination of the proton membrane.

Liquefied Hydrogen Storage and Transportation Equipment (-253°C)

With a boiling point of -252.8°C, liquefied hydrogen demands materials that remain flexible at ultra-low temperatures. Ordinary silicone rubber's glass transition temperature (Tg) is around -120°C, turning brittle at -253°C. Phenyl silicone rubber lowers segmental motion energy barriers by incorporating phenyl groups, reducing Tg below -140°C, maintaining elasticity down to -200°C, suitable for liquefied hydrogen valve seals and sensor encapsulation.

III. International Standards and Testing Methods

Materials for hydrogen energy must pass rigorous certification:

ISO 11114-4: Compatibility testing of gas cylinder valve materials with hydrogen;

SAE J2579: Safety specifications for hydrogen systems in fuel cell vehicles;

CGA G-5.6: Guidelines for material selection in hydrogen environments;

Permeability testing according to ASTM D1434 measures hydrogen permeation rates;

High-pressure hydrogen aging tests assess mechanical property retention after 1,000 hours at 70 MPa and 85°C.

Currently, companies like Dow Corning, Wacker Chemie, and Shin-Etsu Chemical have launched "hydrogen-specific silicone rubber" series, claiming ISO 11114-4 Class A certification.

IV. Challenges and Frontier Directions

Balancing permeability and elasticity: High barrier fillers reduce flexibility, requiring optimization of interfacial compatibility; cost control as specialty silicones are 3–5 times more expensive than regular ones; developing embedded strain sensors in silicone seals for real-time leakage risk warnings; addressing recycling difficulties given the 15-year lifespan of hydrogen equipment, promoting recyclable designs.

Conclusion

On the road to zero-carbon futures powered by hydrogen, every cubic meter of green hydrogen's safe delivery relies on those silent silicone rubber seals. They do not participate in electrochemical reactions but protect the boundaries of these reactions; they do not generate energy but prevent energy from going out of control. From quick connectors at hydrogen stations to the core of fuel cell vehicle stacks, this flexible silicone-based material builds an invisible yet crucial safety barrier for the green energy revolution—because true clean energy lies not only in how "green" it is produced but also in how "safe" it is used.


Modified Platinum Catalyst MY 8141-8149-Mingyi Silicone