Accroding to this http://www.iflscience.com/technology/how-drop-seawater-graphene-generates-electricity/ webpage, voltage would be generated if droplets of seawater (which contain ions) are dragged across the surface. However, there is no mentioning of what happened to the droplets. Do they still have their ions within them or would they turn into regular water?
$\begingroup$
$\endgroup$
Add a comment
|
1 Answer
$\begingroup$
$\endgroup$
4
According to the model explained in the paper (Generating electricity by moving a droplet of ionic liquid along graphene), the water droplets retain the Na+ and Cl- ions.
The mechanism is as follows:
When a NaCl droplet is put on a strip of graphene, a double layer of Na+ ions (purple) forms at the interface. These positive ions in the double layer draw electrons (yellow) to the top surface of the graphene sheet.
When the droplet is drawn to the right, the Na+ ions in the double layer at the back edge of the droplet desorb back into the droplet. The electrons in the graphene that were attracted to these Na+ ions are 'released' back into the graphene sheet behind the droplet.
Similarly, at the front of the droplet, Na+ ions form a double layer on the new territory covered by the droplet as it moves. These new Na+ ions attract electrons from the graphene ahead of the droplet.
The reduced electron density in front of the droplet is effectively an increase in potential in that region, the increased electron density behind the droplet is effectively a reduction in potential in that region. So, by moving the droplet, they generated a potential difference of a few mV between the front and back edge of the droplet!
No chemistry happened, no charge was transferred between the droplet and the graphene, and all salt ions remained in the droplet.
-
$\begingroup$ So it would have to be individual droplets one at a time? A long, continueous stream on the graphene won't work? What about droplets that have certain amounts of space between them? $\endgroup$ Commented May 10, 2017 at 1:31
-
$\begingroup$ Yes, the a potential is generated across each droplet that is moved across the surface. The action happens at the front and back edge of the droplet, so a continuous stream is just one droplet in this sense. In the paper, they demonstrate that two and three droplets increase the generated potential by a factor of two and three, respectively. $\endgroup$– wellCommented May 11, 2017 at 4:06
-
$\begingroup$ Does the spacing between the droplet affect the potential? And by "a factor of 2 and 3" do you mean squared or cubed? And could you give me a link for the equation they used to calculate the potential? or any graph or data related to these graphene generators? $\endgroup$ Commented May 12, 2017 at 1:41
-
$\begingroup$ Not sure about the spacing. I mean two droplets gives double the potential, three droplets gives triple the potential of a single one. The first link in my answer is a link to their manuscript. $\endgroup$– wellCommented May 12, 2017 at 4:37