Titanium alloys, particularly Ti-6Al-4V, are increasingly recognized for their role in hydrogen-related applications due to their exceptional corrosion resistance, lightweight nature, and mechanical strength. These properties make them suitable for demanding environments such as aerospace, marine systems, and high-pressure hydrogen storage. However, challenges such as material cost and hydrogen compatibility must be carefully managed to fully leverage their potential.

One of the most significant advantages of titanium alloys in hydrogen applications is their outstanding resistance to corrosion. Unlike many metals that degrade rapidly in aggressive environments, titanium forms a passive oxide layer when exposed to oxygen or moisture. This layer, primarily composed of TiO2, is highly stable and self-repairing, providing long-term protection against corrosive media, including hydrogen-containing atmospheres. In hydrogen production and storage systems, where exposure to moisture, acids, or high-pressure hydrogen is common, this corrosion resistance is critical for maintaining structural integrity and preventing leaks.

The lightweight nature of titanium alloys further enhances their suitability for hydrogen applications, particularly in aerospace and marine propulsion. Ti-6Al-4V, for example, has a density of approximately 4.43 g/cm³, significantly lower than steel or nickel-based alloys. This weight reduction translates into improved fuel efficiency and payload capacity for hydrogen-powered aircraft and ships. In aerospace, where every kilogram matters, the use of titanium alloys in hydrogen fuel tanks, pipelines, and structural components can lead to substantial performance gains. Similarly, in marine applications, the reduced weight contributes to better buoyancy and energy efficiency.

High-pressure hydrogen storage is another area where titanium alloys excel. The ability to withstand extreme pressures without significant deformation or failure is essential for safe and efficient hydrogen containment. Ti-6Al-4V exhibits high tensile strength, often exceeding 900 MPa, and maintains its mechanical properties even at elevated temperatures. This makes it an ideal candidate for hydrogen storage vessels designed to operate at pressures of 350 bar or higher. The alloy's fatigue resistance also ensures durability under cyclic loading conditions, a common occurrence in hydrogen storage and transportation systems.

Despite these advantages, titanium alloys face limitations that must be addressed. Cost is a primary concern, as titanium extraction and processing are energy-intensive and expensive. The price of Ti-6Al-4V can be several times higher than that of stainless steel or aluminum alloys, posing a barrier to widespread adoption. However, in applications where performance and longevity outweigh initial costs, such as aerospace or high-value industrial systems, the investment in titanium alloys can be justified.

Hydrogen compatibility is another critical consideration. While titanium alloys generally resist hydrogen-induced corrosion, they are not entirely immune to hydrogen embrittlement. Under certain conditions, atomic hydrogen can diffuse into the metal lattice, leading to reduced ductility and crack propagation. This phenomenon is particularly concerning in high-stress environments or when exposed to hydrogen at elevated temperatures. Mitigation strategies include alloy modifications, surface treatments, and operational controls to minimize hydrogen exposure. For instance, adding beta-stabilizing elements like molybdenum or vanadium can improve resistance to hydrogen embrittlement.

In aerospace, titanium alloys are used in hydrogen fuel systems for both commercial and experimental aircraft. The combination of lightweight and corrosion resistance ensures that fuel lines, valves, and tanks remain reliable under the demanding conditions of flight. Similarly, in marine applications, titanium components are employed in hydrogen-powered ships and submarines, where saltwater exposure and high humidity necessitate materials with superior corrosion resistance.

High-pressure hydrogen storage systems benefit from titanium alloys in both stationary and mobile applications. Stationary storage units for industrial or energy sector use often incorporate titanium liners or composite overwraps to enhance safety and longevity. Mobile applications, such as hydrogen transport trailers or vehicle fuel tanks, leverage the alloy's strength-to-weight ratio to maximize storage capacity while minimizing weight.

Research continues to explore ways to optimize titanium alloys for hydrogen applications. Advances in additive manufacturing, for example, enable the production of complex titanium components with tailored microstructures for improved hydrogen resistance. Surface engineering techniques, such as plasma electrolytic oxidation, can further enhance the protective oxide layer, reducing the risk of hydrogen uptake.

In summary, titanium alloys like Ti-6Al-4V offer a compelling combination of corrosion resistance, lightweight properties, and mechanical strength for hydrogen applications. Their use in aerospace, marine, and high-pressure storage systems demonstrates their versatility and performance advantages. However, cost and hydrogen compatibility remain challenges that require ongoing research and innovation. By addressing these limitations, titanium alloys can play a pivotal role in advancing hydrogen technologies across multiple industries.