A battery cell has been developed that generates electricity from the difference in salinity between freshwater and seawater.
Professor Yi Cui, lead researcher and associate professor of materials science at Stanford University in the USA, says there are many potential sites around the world where the battery could be used. Anywhere freshwater enters the sea, such as estuaries, would provide the right conditions.
The battery design is simple: two electrodes, one positive and the other negative, are submerged in a solution of ions – electrically charged particles. The battery is filled with freshwater and a small current is applied to charge it.
The battery is drained and the freshwater replaced with seawater, which contains 60 to 100 times more ions than freshwater. This is due to the presence of sodium and chloride ions, the constituents of salt.
The saltwater increases the voltage, or electrical potential, between the two electrodes. The electricity generated by the battery is therefore much more than the initial amount used to charge it.
The seawater is then drained and replaced with freshwater and the process can begin again.
To calculate the battery’s power-generating potential Professor Cui’s team worked out that if all of the world’s rivers were used, the batteries could generate around two terawatts of electricity per year – approximately 13 per cent of the world’s consumption.
The only limiting factor according to Professor Cui could be the amount of freshwater available, as there is an almost infinite amount of saltwater compared to freshwater on the planet.
River mouths and estuaries, the optimal sites for the battery, are environmentally sensitive places. However as the process uses mixtures of water, at the same temperature as the estuary, released into an area where the two waters would already be mixing the environmental impact should be low.
According to Professor Cui, river water does not have to be the only source of freshwater. As the battery does not need to run on pure water, he believes that runoff from storms or even treated sewage water could be used.
Image by bidgee
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