The limited availability of freshwater resources, accounting for only approximately 3.5% of the total water on Earth, has emphasized the significance of utilizing abundant seawater for energy recycling. Seawater desalination presents a viable solution for addressing the scarcity of drinking water resources; however, traditional methods such as distillation and membrane treatment are often costly.
The acceleration of a hydrogen-based energy economy is crucial in achieving carbon neutrality and peak carbon emissions. In line with this, the "Carbon Peak by 2030 Action Plan" issued by The State Council emphasizes the need to focus on low-cost renewable energy hydrogen production and technological innovation. It also highlights the importance of accelerating research, development, and demonstration applications of hydrogen technology across various sectors such as industry, transportation, and construction.
Seawater differs significantly from freshwater, constituting approximately 96.5% of the Earth's water and containing a complex mixture of 92 chemicals and elements. The salinity of seawater is around 35 PSU (35‰), with sodium, magnesium, calcium, potassium, chlorine, and sulfate ions comprising over 99% of its total salt content. Hydrogen production from seawater faces challenges due to the presence of numerous ions, microorganisms, and particles, which can lead to issues such as competition in adverse reactions, catalyst deactivation, and membrane fouling.
Two distinct technological approaches have been developed for hydrogen production from seawater: direct production and indirect production. Direct production involves electrolysis or photolysis of water. Leading research institutions worldwide, including the Chinese Academy of Sciences, France's National Center for Scientific Research, Japan's Tohoku University of Technology, Beijing University of Chemical Technology, India's Council of Scientific and Industrial Research, and the University of Houston, are actively involved in direct hydrogen production research. Indirect production, on the other hand, combines seawater desalination technologies with hydrolytic processes like electrolysis, photolysis, and pyrolysis.
Currently, more than 90% of the world's hydrogen is produced from carbon-based energy sources, such as coal and natural gas. However, there is growing interest in water-based hydrogen production, considering the future implications of carbon neutrality and the scarcity of freshwater resources. The "in situ seawater direct electrolysis hydrogen production technology without desalination" holds immense theoretical, technological, and strategic significance.
In July of this year, the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, reported a groundbreaking development in producing hydrogen from seawater through high-temperature electrolysis using a flat tubular solid oxide fuel cell. The research team achieved an impressive energy conversion efficiency of 72.47% without the need for noble metal catalysts. Long-term experiments demonstrated minimal changes in the cell's structure, composition, and performance, while the electrolytic voltage remained significantly lower than that of room-temperature cells.
The researchers conducted electrolysis at 750℃ by passing hydrogen, acting as a carrier gas, through the solid oxide electrolytic cell containing seawater volatilized and carried from the coastal waters of Ningbo City. By heating and evaporating the seawater beforehand, most impurities were prevented from directly contacting the electrolyzer, minimizing the risk of damage.
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