Hydrogen is recognized as a powerful clean energy carrier, offering a pathway to decarbonize hard-to-abate sectors like heavy industry and transportation. When produced using renewable electricity, the resulting fuel is called “green hydrogen.” The primary method for creating this fuel is water electrolysis, which uses an electric current to split water (\(\text{H}_2\text{O}\)) into hydrogen (\(\text{H}_2\)) and oxygen (\(\text{O}_2\)). For this technology to scale up globally and contribute to a sustainable energy system, the industry must transition the water source from highly purified freshwater to the planet’s most abundant resource: seawater. This shift is necessary to ensure that the rapid expansion of clean energy production does not create a new resource conflict.
The Critical Constraint: Freshwater Scarcity
The current technology for electrolysis relies on highly purified water to protect sensitive equipment and maximize efficiency. While the chemical reaction requires about nine liters of water to produce one kilogram of hydrogen, the total consumption, including purification and cooling, can rise to 20 to 30 liters per kilogram. Scaling this demand to meet global energy needs would place an unsustainable burden on freshwater supplies.
Globally, freshwater resources are finite and unevenly distributed, leading to intense competition for agriculture, drinking, and sanitation. If large-scale hydrogen production facilities are built in arid coastal regions, this new industrial demand would exacerbate existing water stress. Relying on a resource already in high demand for human survival and food production presents a significant environmental and social liability. Therefore, developing a method that bypasses the need for pure water is a prerequisite for responsible, high-volume hydrogen deployment.
Leveraging the Ocean’s Strategic Abundance
Shifting the feedstock to seawater transforms a resource constraint into a strategic advantage, leveraging the ocean’s vast supply. Over 96% of the world’s water is saline, covering approximately 71% of the Earth’s surface. This abundance removes the logistical and ethical conflicts associated with freshwater consumption.
Using seawater allows hydrogen production facilities to be located directly at the source, eliminating the energy and infrastructure costs of transporting water inland. It also enables the integration of electrolysis with offshore renewable energy projects, such as large-scale wind farms. Producing hydrogen directly at sea minimizes land use and allows for the creation of massive, centralized production hubs powered by consistent, high-capacity renewable sources. This strategic placement maximizes efficiency and minimizes the environmental footprint of the entire energy supply chain.
Overcoming Technical Barriers to Seawater Use
The ability to use seawater directly represents a technological breakthrough because saline water poses complex challenges to conventional electrolyzers. The most significant issue is the presence of high concentrations of chloride ions (\(\text{Cl}^-\)). During electrolysis, these chloride ions compete with the desired Oxygen Evolution Reaction (\(\text{OER}\)) at the anode, forming corrosive hypochlorite and toxic chlorine gas (\(\text{Cl}_2\)).
This competitive reaction accelerates the corrosion and degradation of electrode materials, compromising the system’s efficiency and lifespan. Another hurdle is mineral scaling. The alkalinity generated at the cathode reacts with magnesium (\(\text{Mg}^{2+}\)) and calcium (\(\text{Ca}^{2+}\)) ions in the seawater. This reaction forms solid precipitates, such as magnesium hydroxide and calcium carbonate, which block active sites on the electrode surface and reduce performance. Solving these electrochemical and material science problems through new catalysts and membrane designs is what makes large-scale seawater hydrogen production technologically viable.
Economic and Industrial Scalability Drivers
The economic importance of direct seawater electrolysis lies in its potential to reduce the cost of producing green hydrogen. Conventional electrolysis systems require pre-treatment steps to purify the raw water. This process typically involves desalination, often via reverse osmosis, followed by deionization to remove dissolved salts and minerals.
Eliminating these purification steps bypasses substantial operational expenses (\(\text{OPEX}\)) and capital expenditures (\(\text{CAPEX}\)) associated with complex pre-treatment infrastructure. The cost of desalination alone is a significant factor in the overall production price. By developing technology that handles raw or minimally-treated seawater, the final cost of green hydrogen can become more competitive with fossil fuels, driving widespread industrial adoption.