The use of seawater for offshore hydrogen production presents a unique set of challenges and opportunities, particularly when paired with electrolysis. While seawater is an abundant resource, its direct use in hydrogen production requires overcoming significant technical hurdles, including corrosion, energy-intensive desalination, and the need for advanced pretreatment technologies. Innovations in materials science, process engineering, and system integration are critical to making seawater-based hydrogen production viable.
One of the foremost challenges in using seawater for electrolysis is corrosion. Seawater contains high concentrations of chloride ions, which accelerate the degradation of electrodes and other components in electrolyzers. Chloride-induced corrosion can lead to the formation of reactive species that damage catalyst layers, reduce efficiency, and shorten system lifespans. Alkaline electrolyzers, while more resistant to impurities than proton exchange membrane (PEM) systems, still suffer from corrosion when exposed to untreated seawater. PEM electrolyzers, which rely on expensive noble metal catalysts like platinum and iridium, are particularly vulnerable to chloride attack, leading to catalyst poisoning and membrane degradation.
To mitigate corrosion, researchers are developing advanced materials and coatings. Nickel-based alloys and titanium substrates with protective oxide layers have shown promise in resisting chloride-induced degradation. Additionally, non-precious metal catalysts, such as transition metal phosphides and sulfides, are being explored to reduce costs while maintaining performance in saline environments. Another approach involves the use of bipolar membranes in electrolyzers, which can separate chloride ions from the reaction sites, minimizing their corrosive impact.
Beyond corrosion, the energy penalty associated with seawater desalination is a major concern. Electrolysis requires high-purity water to prevent side reactions and maintain efficiency. Seawater desalination, typically achieved through reverse osmosis or distillation, consumes significant energy—approximately 3–10 kWh per cubic meter of freshwater produced, depending on the technology and salinity levels. This energy demand directly competes with the electrolysis process, reducing the overall system efficiency and increasing operational costs.
Innovations in integrated desalination-electrolysis systems aim to reduce this energy penalty. One approach involves using waste heat from industrial processes or renewable sources to power thermal desalination, thereby lowering electricity consumption. Another strategy is forward osmosis, which leverages osmotic pressure gradients to separate water from salts with lower energy input compared to reverse osmosis. Additionally, researchers are investigating direct seawater electrolysis, where selective membranes or advanced catalysts enable hydrogen production without prior desalination. While still in early stages, these methods could eliminate the need for separate desalination units, streamlining the process.
Pretreatment of seawater is another critical factor in offshore hydrogen production. Even if desalination is employed, residual impurities such as magnesium, calcium, and organic matter can foul membranes and degrade electrolyzer components. Pretreatment technologies must remove these contaminants efficiently to ensure long-term system reliability. Conventional methods like microfiltration and chemical dosing are effective but add complexity and cost.
Emerging pretreatment solutions include electrochemical precipitation, where applied voltages induce the removal of scale-forming ions before they reach the electrolyzer. Nanofiltration membranes, with their ability to selectively reject divalent ions, offer another promising avenue. Furthermore, bioinspired membranes mimicking natural filtration systems, such as those found in mangrove roots, are being explored for their potential to achieve high selectivity with low energy consumption.
The intermittent nature of renewable energy sources, often used to power offshore hydrogen production, adds another layer of complexity. Fluctuations in wind or solar power can disrupt both desalination and electrolysis processes, leading to inefficiencies. Hybrid systems that incorporate energy buffers, such as batteries or supercapacitors, can help stabilize power supply. Advanced control algorithms that dynamically adjust desalination and electrolysis rates in response to energy availability are also under development to optimize performance under variable conditions.
Scalability remains a key consideration for seawater-based hydrogen production. While laboratory-scale experiments have demonstrated feasibility, transitioning to industrial-scale operations requires addressing engineering challenges such as modular system design, maintenance accessibility in offshore environments, and integration with existing marine infrastructure. Pilot projects in coastal areas are providing valuable insights into real-world performance, but further testing is needed to validate long-term durability and cost-effectiveness.
Environmental impacts must also be carefully managed. The discharge of concentrated brine from desalination processes can harm marine ecosystems if not properly diluted or treated. Innovations in brine management, such as zero-liquid discharge systems or the extraction of valuable minerals from brine, are being explored to mitigate these effects. Additionally, hydrogen leakage during production or storage poses a climate risk due to its indirect global warming potential, necessitating robust containment and monitoring solutions.
In summary, the use of seawater for offshore hydrogen production is a technically demanding but promising avenue. Corrosion-resistant materials, energy-efficient desalination, and advanced pretreatment technologies are critical to overcoming current limitations. Continued research and pilot deployments will be essential to refine these innovations and pave the way for large-scale implementation. By addressing these challenges, seawater-based hydrogen production could play a significant role in the global transition to sustainable energy systems.