Chinese researchers have developed an integrated system that simultaneously produces hydrogen and fresh water from seawater, while also recovering valuable marine resources such as uranium and bromine. The innovation, led by scientists Deng Dehui and Liu Yanting from the Chinese Academy of Sciences’ Dalian Institute of Chemical Physics, aims to improve energy efficiency and reduce costs associated with green hydrogen production.
Published in the journal Nature Energy, the study outlines a new approach that builds on the conventional two-step method of hydrogen extraction from seawater, which involves desalinating seawater before electrolysis. Conventional direct seawater electrolysis faces technical challenges, including electrode corrosion caused by chloride ions and scaling from calcium and magnesium ions, while desalination followed by electrolysis is costly and energy intensive.
The team sought to address these limitations by linking the electrolysis process to a vacuum distillation unit that recycles waste heat. Typically, commercial hydrogen production systems lose about 30 percent of electricity as low-quality heat at 80 to 90 degrees Celsius, which conventional setups discard through cooling systems, thus increasing energy and water demands. By channeling this waste heat to boil seawater at a lower temperature of 40 to 50 degrees Celsius, the system generates fresh water for use in the electrolysis process, with additional excess water available.
The 250-kilowatt pilot plant designed by the researchers operates stably and improves electricity utilization efficiency by approximately 14.4 percent compared with traditional alkaline water electrolysis. The facility can produce around 380,000 standard cubic meters of hydrogen annually, achieving a purity level of 99.9999 percent, alongside 256 tonnes of fresh water per year. The remaining concentrated seawater serves as a source for further extraction of salt, uranium, bromine, and other minerals through multi-stage processes.
Economic analysis within the study indicates the system is more cost-competitive than current two-step desalination and electrolysis techniques. At electricity prices of US$0.033 per kilowatt-hour from onshore wind, the cost of hydrogen production is estimated at US$2.21 per kilogram, rising to US$2.90 per kilogram when using solar power at US$0.049 per kilowatt-hour. These figures are favorable compared to current hydrogen market prices, which hover around US$3.90 per kilogram.
The researchers emphasize the system’s operational stability, demonstrated through continuous 40-day tests involving daily start-stop cycles with no significant performance decline. Future work will focus on enhancing catalyst performance, improving recovery of waste heat, and applying artificial intelligence to optimize system parameters and maximize efficiency. The integrated approach presents a promising advancement for the sustainable generation of hydrogen and potable water from seawater.