Nickel-based alloys are widely recognized for their exceptional corrosion resistance, making them indispensable in hydrogen-related applications. These alloys maintain structural integrity in aggressive environments, including high-pressure hydrogen, acidic conditions, and elevated temperatures. Their reliability stems from carefully engineered compositions, such as those found in Inconel and Hastelloy families, which exhibit superior mechanical properties and resistance to hydrogen embrittlement.

The composition of nickel-based alloys is tailored to withstand harsh conditions. Inconel alloys, such as Inconel 625 and Inconel 718, contain significant amounts of nickel, chromium, and molybdenum, which contribute to their oxidation and corrosion resistance. Chromium forms a passive oxide layer that protects against corrosive media, while molybdenum enhances resistance to localized corrosion. Hastelloy alloys, including Hastelloy C-276 and Hastelloy X, incorporate additional elements like tungsten and cobalt to improve performance in reducing and oxidizing environments. These alloys are particularly effective in resisting hydrogen-induced cracking and stress corrosion cracking.

Mechanical properties of nickel-based alloys are critical for their performance in hydrogen applications. Inconel 718, for example, exhibits high tensile strength, often exceeding 1,200 MPa, and retains ductility even at cryogenic temperatures. Hastelloy C-276 demonstrates excellent toughness and fatigue resistance, with a yield strength of approximately 415 MPa. These properties ensure that components made from these alloys can endure cyclic loading and high-pressure hydrogen exposure without premature failure.

High-pressure hydrogen environments present unique challenges, including hydrogen embrittlement, where hydrogen atoms diffuse into the metal lattice, reducing ductility and fracture resistance. Nickel-based alloys mitigate this risk through their stable microstructure and low hydrogen diffusivity. Studies have shown that Inconel 625 maintains its mechanical properties after prolonged exposure to hydrogen at pressures up to 100 MPa. Similarly, Hastelloy C-276 exhibits minimal susceptibility to hydrogen-assisted cracking, making it suitable for hydrogen storage vessels and pipelines.

Manufacturing processes for nickel-based alloys involve precise control to maintain their desirable properties. Hot working, such as forging and extrusion, is commonly used to shape these materials while preserving their grain structure. Cold working techniques, including rolling and drawing, can further enhance strength but may require subsequent annealing to relieve stresses. Additive manufacturing has also emerged as a viable method for producing complex components, though post-processing heat treatments are often necessary to optimize mechanical performance.

Welding nickel-based alloys presents challenges due to their susceptibility to hot cracking and segregation of alloying elements. Techniques such as gas tungsten arc welding (GTAW) and electron beam welding (EBW) are preferred for their ability to produce high-quality joints with minimal defects. Filler metals with matching or overmatched compositions are used to maintain corrosion resistance in the weld zone. Post-weld heat treatment may be applied to restore mechanical properties and reduce residual stresses.

Applications of nickel-based alloys in hydrogen systems are extensive. In hydrogen storage, these alloys are used for high-pressure tanks and liners, where their resistance to hydrogen permeation and embrittlement is crucial. Pipelines transporting hydrogen benefit from the alloys' ability to withstand both internal pressure and external environmental corrosion. Electrolyzers, particularly those using proton exchange membranes (PEM), rely on nickel-based components for their durability in acidic and high-potential conditions.

In PEM electrolyzers, nickel-based alloys serve as bipolar plates and current collectors due to their electrical conductivity and corrosion resistance. Hastelloy C-276 is often selected for its stability in the highly oxidizing anode environment, where other materials would degrade rapidly. Similarly, Inconel 600 is used in solid oxide electrolyzers (SOECs) for its high-temperature strength and resistance to oxidation.

The performance of nickel-based alloys in hydrogen applications is further validated by their use in extreme environments. For instance, Inconel 718 has been employed in aerospace applications where hydrogen exposure is coupled with mechanical stress and thermal cycling. Hastelloy X is utilized in gas turbines that may operate with hydrogen-rich fuels, demonstrating its resilience under cyclic thermal loads.

Despite their advantages, nickel-based alloys are not without limitations. Their high cost compared to stainless steels or carbon steels can be a barrier for large-scale deployment. However, the long service life and reduced maintenance requirements often justify the initial investment in critical applications. Ongoing research aims to optimize alloy compositions and processing techniques to further enhance performance while reducing costs.

In summary, nickel-based alloys play a pivotal role in hydrogen technologies due to their corrosion resistance, mechanical robustness, and reliability in high-pressure environments. Their tailored compositions, advanced manufacturing methods, and proven performance in storage, transportation, and electrolysis make them indispensable for advancing hydrogen infrastructure. As the hydrogen economy grows, these alloys will continue to be a cornerstone of safe and efficient hydrogen systems.