Researchers from the University of Adelaide and Tianjin University have successfully split seawater without pre-treatment to produce green hydrogen. A paper on the work is published in Nature Energy.
The use of vast amounts of high-purity water for hydrogen production may aggravate the shortage of freshwater resources. Seawater is abundant but must be desalinated before use in typical proton exchange membrane (PEM) electrolysers. Here we report direct electrolysis of real seawater that has not been alkalised nor acidified, achieving long-term stability exceeding 100 h at 500 mA cm−2 and similar performance to a typical PEM electrolyser operating in high-purity water.
This is achieved by introducing a Lewis acid layer (for example, Cr2O3) on transition metal oxide catalysts to dynamically split water molecules and capture hydroxyl anions. Such in situ generated local alkalinity facilitates the kinetics of both electrode reactions and avoids chloride attack and precipitate formation on the electrodes.
A flow-type natural seawater electrolyser with Lewis acid-modified electrodes (Cr2O3–CoOx) exhibits the industrially required current density of 1.0 A cm−2 at 1.87 V and 60 °C.—Guo et al.
University of Adelaide’s Professor Shizhang Qiao, co-corresponding author, said that the researchers used a non-precious and cheap catalyst in a commercial electrolyzer.
Our work provides a solution to directly utilise seawater without pre-treatment systems and alkali addition, which shows similar performance as that of existing metal-based mature pure water electrolyser.—Yao Zheng, co-author
Seawater electrolysis is still in early development compared with pure water electrolysis because of electrode side reactions, and corrosion arising from the complexities of using seawater.
It is always necessary to treat impure water to a level of water purity for conventional electrolysers including desalination and deionisation, which increases the operation and maintenance cost of the processes. Our work provides a solution to directly utilise seawater without pre-treatment systems and alkali addition, which shows similar performance as that of existing metal-based mature pure water electrolyser.—Yao Zheng
The team will work on scaling up the system by using a larger electrolyzer so that it can be used in commercial processes such as hydrogen generation for fuel cells and ammonia synthesis.
Guo, J., Zheng, Y., Hu, Z. et al. (2023) “Direct seawater electrolysis by adjusting the local reaction environment of a catalyst.” Nat Energy doi: 10.1038/s41560-023-01195-x