An international team of scientists led by the University of Adelaide, Australia, has succeeded in producing environmentally friendly (green) hydrogen by electrolysis of seawater, without its prior purification from microorganisms and without the addition of chemicals, Xinhua reported.
Zheng Yao, one of the authors of the study, notes that performance comparable to that of conventional technology was achieved.
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.
Pure hydrogen is produced by splitting water into oxygen and hydrogen, a process known as electrolysis. Existing technologies, however, require a high degree of water purification as a raw material, which necessitates the use of chemical additives, for example alkali.
The new research, which also involved scientists from China and the US, shows that electrolysis can be achieved with seawater without prior purification and without the addition of chemicals.
“We used seawater as a starting material without the need to use any pre-treatment processes such as reverse osmosis desalination, purification or alkalinization,” the researchers explain.
The growing demand for hydrogen to partially or fully replace fossil fuel energy will significantly increase the scarcity of increasingly limited freshwater resources.
“Our work provides a solution for the direct use of seawater without pretreatment systems and alkali addition, which shows similar performance to that of existing technologies,” the scientists added.
Hydrogen is widely considered the ideal zero-emission fuel of the future.
Resources
- 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
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