Researchers Develop Systems to Produce Green Hydrogen and Fresh Water Directly from Seawater

Researchers have developed new systems that can produce both green hydrogen and fresh drinking water directly from seawater, a breakthrough that could address intertwined energy and water shortages. A team from the Chinese Academy of Sciences has demonstrated a method that uses waste heat from electrolysis to power desalination, while a separate U.S. collaboration led by Cornell University has created a compact device that uses the full spectrum of sunlight to achieve the same goal.

For decades, using the ocean's vast water supply to produce hydrogen fuel has been a tantalizing prospect, but one fraught with technical and economic hurdles. The standard process for creating green hydrogen involves electrolysis, which uses electricity to split fresh water into hydrogen and oxygen. Seawater, however, is corrosive and contains ions like chloride that can damage expensive electrolyzer components and create harmful byproducts like toxic chlorine gas. The conventional solution has been to first desalinate seawater using energy-intensive methods like reverse osmosis and then feed the resulting fresh water into a separate electrolyzer, a process that incurs a "double energy penalty" and drives up costs. The new systems aim to bypass this inefficiency by integrating the two processes.

The Waste Heat Solution

A team led by researchers at the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences has developed a system that couples alkaline water electrolysis with low-temperature vacuum distillation. According to their paper published in Nature Energy on September 15, 2026, the key innovation is capturing the waste heat naturally generated during the electrolysis process and using it to desalinate seawater. This approach avoids direct contact between the corrosive saltwater and the sensitive electrodes.

The system works by channeling the heat from the electrolyzer to a distillation chamber containing seawater. Under a vacuum, the water boils at a much lower temperature than normal. The resulting water vapor, now free of salt and impurities, is then condensed into pure, fresh water. A portion of this fresh water is fed back into the electrolyzer to produce high-purity hydrogen, while the rest can be collected for drinking or other uses.

The Chinese team has tested the technology at increasing scales. A 20-kilowatt (kW) pilot unit reportedly operated stably for 100 days, producing 3.8 cubic meters of hydrogen and 1.2 kilograms of fresh water per hour. A larger 250-kW plant, which began operation in August 2024, achieved a hydrogen output of 48 cubic meters per hour with a purity of 99.9999%, along with 31.6 kilograms of fresh water per hour. The researchers claim this integrated system has an electrical efficiency 14.4% higher than conventional freshwater electrolysis. While the 250-kW system was reported to have run for 40 days under daily start-stop conditions without significant performance decline, the published research did not specify a continuous long-term stability test for the larger unit comparable to the 100-day test of the smaller pilot.

The Integrated Solar Approach

A different approach has been developed by a collaboration of U.S. universities led by Cornell University. Their compact, solar-powered device, detailed in the journal Energy and Environmental Science on April 9, 2025, integrates photovoltaics, water distillation, and electrolysis into a single unit designed to harness the full solar spectrum.

In this system, high-energy sunlight strikes a photovoltaic panel to generate electricity. The lower-energy light and waste heat from the panel are used to power a photothermal distillation process. Seawater is drawn into a wicking evaporator, where the solar heat turns it into vapor, leaving salts and impurities behind. This water vapor then condenses directly onto the membrane of an adjacent electrolyzer. The electricity generated by the solar panel is used to split this freshly condensed pure water into hydrogen and oxygen.

The design creates a synergistic loop. The evaporation process cools the solar panel, which increases its electricity-generating efficiency. Simultaneously, the condensation of warm vapor on the electrolyzer heats it, boosting its hydrogen production rate. A 10-by-10-centimeter prototype produced 200 milliliters of hydrogen per hour from seawater under natural sunlight with a reported 12.6% energy efficiency. The researchers estimate their technology could help lower the cost of green hydrogen to as little as $1 per kilogram within 15 years, a key target for making it competitive with hydrogen produced from fossil fuels.

What It Means and What's Next

These developments represent a significant step toward making green hydrogen production feasible in arid and coastal regions where fresh water is scarce but seawater and renewable energy sources like sunlight are abundant. By co-producing fresh water, these systems can help offset their own operational needs and provide a vital resource to local communities. The leftover concentrated brine could also become a source of valuable materials like salt, lithium, uranium, and bromine, though the economic viability of extracting these resources at scale has yet to be established.

Despite the promise, significant challenges remain before this technology can be widely deployed.

Technical and Economic Hurdles

Long-term durability is a major concern. Any system operating with seawater must withstand its corrosive nature for years to be economically viable. While the Chinese system isolates the electrolyzer from direct saltwater contact, the distillation components must still resist corrosion. Other researchers are pursuing direct seawater electrolysis, which would be even more efficient but requires developing new catalysts and membranes that are resistant to chloride poisoning and can prevent the formation of chlorine gas. Teams at RMIT University, Stanford University, and Johns Hopkins University have all reported progress on this front, using novel materials and membrane designs.

Cost remains the biggest barrier. The capital expenditure for building large-scale electrolysis and desalination facilities is substantial. The ultimate goal is to produce green hydrogen at a cost competitive with "grey hydrogen" derived from natural gas. Achieving the industry target of $1 per kilogram will require not only efficient technology but also mass production of components and access to cheap, abundant renewable electricity.

The Path to Scale

Moving from laboratory prototypes and pilot plants to industrial-scale facilities is a massive engineering undertaking. It requires integrating these systems with large-scale renewable energy projects, such as solar or offshore wind farms. Furthermore, a widespread hydrogen economy requires a new infrastructure for storing, transporting, and distributing the hydrogen gas to where it is needed, from industrial facilities to fueling stations. These technologies offer a pathway, but the road to a global hydrogen economy powered by the ocean is still long.