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Saltwater in Place of Drinking Water

The use of hydrogen as a source of energy could form an important cornerstone of a new carbon-neutral energy supply system. Ideally, the electrolysis of water required for this could be conducted using renewable energy sources, such as the sun, water, geothermics or wind. Current technology, however, requires water of drinking quality, globally an expensive commodity, to perform this type of electrolysis. Together with international fellow researchers, Professor Dr. Peter Strasser, head of the Chair of Chemical Engineering at TU Berlin, has now published a study in the renowned journal Nature Energy on the possibilities and technical challenges of the electrolysis of salt water.

Hydrogen gained from solar-powered electrolysis of water provides a carbon-neutral as well as storable and transportable energy source of particular benefit for arid areas of the world with little access to water. However, the electrolysis involved requires water of drinking quality, an expensive resource throughout the world. It is precisely those arid areas, often located close to oceans, with sufficient solar energy potential that generally suffer most from a lack of fresh water. The purification of saltwater, however, is an expensive and carbon-intense process, rendering the overall process inefficient and no longer carbon neutral.

“To enable the use of solar and hydrogen technologies in these regions, researchers worldwide have developed an electrolysis technology capable of immediately dividing saltwater into hydrogen and oxygen without the use of a prior desalination procedure,” explains Strasser, whose own research team at TU Berlin is working intensively on different procedures and catalysts for hydrogen electrolysis. “The hydrogen which we can gain from these procedures can be transported around the world on ships or via pipes, either directly as liquid hydrogen, or, after a further local transformation, as synthetic liquid methane or synthetic gasoline. This will enable us to transition to a hydrogen-based energy infrastructure,” says Strasser.

Strasser and his fellow researchers at the National University of Ireland in Galway and the University of Liverpool have been analyzing a wide range of international publications reporting on the successful electrolysis of saltwater. In doing so they have succeeded in identifying the main challenges to be overcome to make this future form of electrolysis competitive. “Our analysis shows that future research will have to focus on both the use of new catalyst materials as well as suitable membranes. The membranes most commonly used in electrolysis are often not able to prevent the contamination of water with salt,” Strasser explains. One potentially interesting approach is the use of membranes resembling those found in certain plants such as mangrove roots. These plant membranes are capable of filtering seawater. Using similar membranes in technical electrolysis could reduce the concentration of salt on the surface of the catalytic electrodes, thus reducing the contamination of the membranes.

“As part of our study, we have demonstrated that the development of new selective catalysts and special membrane technology represents an important step towards achieving high-performance saltwater electrolysis and should continue to be researched more intensively in the future,” says Strasser. “The use of fresh water to create hydrogen in large quantities will, in our view, not remain a practicable option, particularly in those arid regions where most of the world’s cheap solar energy is generated,” he concludes.

Further Information:

You can read the complete article in the journal Nature Energy.

Contact:

Prof. Dr. Peter Strasser
TU Berlin
Chemical and Materials Engineering Division
Tel.: +49 (0)30 314-29542
pstrasser(at)tu-berlin.de