Copper alloys, including brass and bronze, play a significant role in hydrogen systems due to their unique combination of corrosion resistance, thermal conductivity, and mechanical properties. These materials are particularly valuable in applications such as seals, heat exchangers, and electrolyzer components, where performance under hydrogen exposure is critical.

Corrosion resistance is a key consideration for materials in hydrogen environments. Copper alloys generally exhibit good resistance to hydrogen embrittlement, a common issue with many metals exposed to hydrogen. Unlike steel, which can suffer from hydrogen-induced cracking, copper alloys maintain their structural integrity due to their face-centered cubic (FCC) crystal structure, which is less susceptible to hydrogen diffusion. Brass, an alloy of copper and zinc, shows moderate resistance to hydrogen corrosion but may experience dezincification in aggressive environments, particularly in the presence of moisture or acidic conditions. Bronze, typically composed of copper and tin, offers superior corrosion resistance compared to brass, especially in high-temperature hydrogen applications. The addition of elements like aluminum or nickel further enhances bronze's durability, making it suitable for harsh hydrogen service conditions.

Thermal conductivity is another critical property of copper alloys in hydrogen systems. Copper itself has one of the highest thermal conductivities among metals, and while alloying reduces this property slightly, brass and bronze still outperform many alternatives. This makes them ideal for heat exchangers in hydrogen processing plants, where efficient heat transfer is essential. For example, in steam methane reforming (SMR) plants, brass or bronze heat exchangers facilitate heat recovery from hot process gases, improving overall energy efficiency. In electrolyzers, particularly alkaline and proton exchange membrane (PEM) types, copper alloys are used in cooling systems to manage the heat generated during water splitting. Their high thermal conductivity ensures uniform temperature distribution, preventing localized overheating that could degrade performance.

Seals and gaskets in hydrogen systems require materials that can maintain a tight seal under varying pressures and temperatures while resisting hydrogen permeation. Copper alloys are often used in these applications due to their malleability and ability to form gas-tight joints. Annealed copper gaskets are common in high-pressure hydrogen storage and transportation systems, where they provide reliable sealing at flange connections. Bronze seals, with their higher strength and wear resistance, are employed in dynamic sealing applications, such as compressors and valves, where repeated cycling could compromise softer materials.

In electrolyzer components, copper alloys are utilized for their compatibility with both alkaline and acidic environments. Brass fittings and connectors are frequently found in alkaline electrolyzers, where their resistance to potassium hydroxide (KOH) solutions is advantageous. However, care must be taken to avoid prolonged exposure to highly concentrated electrolytes, which can accelerate corrosion. In PEM electrolyzers, where acidic conditions prevail, bronze components are preferred due to their better resistance to acidic degradation. The use of copper alloys in bipolar plates or current collectors is less common due to the prevalence of coated stainless steel or titanium, but they may still be found in auxiliary systems where electrical conductivity is not the primary concern.

Heat exchangers in hydrogen liquefaction plants also benefit from copper alloys. The extreme cold temperatures involved in liquefaction demand materials with good thermal conductivity and low-temperature toughness. Bronze, with its excellent cryogenic properties, is often selected for tubing and headers in these systems. Its resistance to thermal fatigue ensures long service life despite repeated thermal cycling between ambient and cryogenic temperatures.

A notable limitation of copper alloys in hydrogen systems is their susceptibility to oxidation at elevated temperatures. While they perform well in reducing hydrogen atmospheres, exposure to oxygen or water vapor at high temperatures can lead to surface oxidation, potentially compromising sealing surfaces or heat transfer efficiency. Protective coatings or alloy modifications, such as the addition of chromium or silicon, can mitigate this issue.

In summary, copper alloys like brass and bronze are valuable materials in hydrogen systems due to their corrosion resistance, thermal conductivity, and adaptability to various components. Their use in seals ensures leak-free operation under high pressures, while their thermal properties make them ideal for heat exchangers and cooling systems in electrolyzers and hydrogen processing plants. Careful selection based on environmental conditions—such as temperature, pressure, and chemical exposure—is essential to maximize their performance and longevity. Future advancements in alloy formulations could further enhance their suitability for emerging hydrogen technologies.