Drawing inspiration from the conventional sodium-ion battery, engineers from the University of Illinois have confirmed that the same technology used to re-charge batteries in electronic devices can be used to convert salty sea water into fresh, drinkable water.
“We are developing a device that will use the materials in batteries to take salt out of water with the smallest amount of energy that we can,” said Illinois mechanical science and engineering professor Kyle Smith, who worked with graduate student Rylan Dmello on this project, and published their findings in the Journal of the Electrochemical Society . “One thing I'm excited about is that by publishing this paper, we're introducing a new type of device to the battery community and to the desalination community.”
There have been numerous humanitarian crises in recent years, many of which were / are focused in drought-stricken regions with limited access to drinkable water. Current water desalination technology used to convert salt water in to fresh water is not ideal for use in these areas as it requires far too much energy for large-scale implementation.
Specifically, the oft-used method of reverse osmosis, wherein water is pushed through a membrane that keeps salt out, is both energy-intensive as well as extremely costly. Smith and Demello’s solution overcomes these hurdles by using electricity to draw charged salt ions out of the water.
As mentioned at the start, the duo was inspired by sodium ion batteries, which contain salt water. As this portable power resource discharges, the sodium and chloride ions (the two elements of salt water) are drawn into one chamber of the battery, while fully desalinated water is left behind in the other chamber.
In a normal battery, the ions diffuse back when the current flows the other direction; however, Smith and Dmello found a way to keep the salt from the now salt-less water.
“In a conventional battery, the separator allows salt to diffuse from the positive electrode into the negative electrode,” Smith explains. “That limits how much salt depletion can occur. We put a membrane that blocks sodium between the two electrodes, so we could keep it out of the side that's desalinated.”
There are a number of advantages to this approach. For one, the battery can be small or large, thereby making it adaptable to a bevy of applications; reverse osmosis plants, it’s worth noting, tend to have to be larger to be efficient and cost effective. Also, the pressure required to pump the water is much less — after all, it’s just water flowing over the electrodes, as opposed to being forced through a membrane. This reduced need for energy, in turn, translates to reduced costs to run the technology. Finally, the rate of water flowing through it can easily be adjusted, counter to current desalination technology which requires more complex plumbing.
A modeling study was put together to see how this solution would perform with salt concentrations as high as seawater. Smith and Dmello found that it was capable of recovering approximately 80% of desalinated water.
“We believe there's a lot of promise,” Smith said. “There's a lot of work that's gone on in developing new materials for sodium ion batteries. We hope our work could spur researchers in that area to investigate new materials for desalination. We're excited to see what kind of doors this might open.”
Check out a demonstration of the technology in the clip below:
To learn more, download the study, entitled Na-Ion Desalination (NID) Enabled by Na-Blocking Membranes and Symmetric Na-Intercalation: Porous-Electrode Modeling.
Via the University of Illinois
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