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I am building a capacitor using nanomaterial grown on a substrate. We are trying to figure out what our test fixture configuration should be when doing Cyclic Voltammetry on the cell. Our group would ideally like to use a two-electrode configuration, but we believe the potentiostat is only capable of doing three electrode measurements. Our goal is to get reliable and comparable results.

An article about standardizing the capacitance measurements called "Best practice methods for determining an electrode material’s performance for ultracapacitors" says that the three electrode setup is flawed:

In a symmetrical two-electrode cell, the potential differences applied to each electrode are equal to each other and are one-half of the values shown on the X-axis of the CV chart. Therefore, for a given potential range on the X-axis of the CV, the working electrode of a three-electrode cell has twice the potential range applied as is applied to the electrodes in a twoelectrode cell and this results in a doubling of the calculated capacitance...

The article goes on to listing a few other reasons not to use it. Given this limitation, and our desire to use a two electrode set up, is there a way to do a two-electrode setup on our machine? The setup would like the one below:

enter image description here

We have been told that we can create a two-electrode system by attaching both our counter and reference onto one plate, and the working onto the other, that we would essentially have a two electrode setup. Our concern is that this would only apply voltage to one electrode, and not the other.

Is our concern valid? Can someone clarify the mechanics here for us or explain how to achieve our desired setup?

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  • \$\begingroup\$ Sorry, can you please clarify your question? I understand, you need to accurately measure the capacitance, is that correct? I can suggest several methods, all only require two wires. In fact, practically if your capacitor has two ports (and of course it has), there is no reason to have more for measurement. \$\endgroup\$ – Gregory Kornblum Jun 27 '15 at 9:03
  • \$\begingroup\$ We need to accurately measure capacitance and we would prefer to use a two-electrode configuration rather than a three-electrode configuration. My lab partners are under the assumption that the machine we use only does three-electrode measurements. We don't know how to configure our capacitor. \$\endgroup\$ – John Snow Jun 27 '15 at 15:54
  • \$\begingroup\$ What is the expected capacitance? \$\endgroup\$ – Gregory Kornblum Jun 27 '15 at 15:55
  • \$\begingroup\$ To be honest, I don't know. I would assume it to be in the neighborhood of other graphene and carbon nanotube capacitors. \$\endgroup\$ – John Snow Jun 27 '15 at 15:58
  • \$\begingroup\$ Yes, but you probably know the dimensions, etc. So calculate the expected capacitance, to the order of magnitude at least. Then we will talk about specific setup. \$\endgroup\$ – Gregory Kornblum Jun 27 '15 at 16:20
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In the meantime, a method i used a while ago for supercap evaluation. Really simple and effective.

A constant current source (with an ampermeter to make sure it's indeed constant) charges the supercap. In parallel the voltage is measured and a plot is built. With the equation It = CV, C may be determined out of the plot. In the end of charge, a power resistor is used to discharge the supercap.

In my case i had to prove that the supercap capacitance doesn't depend on the charge. Same method works for capacitance measurement.

For better accuracy select current such that charge time will be long enough, minutes or more.

Take as many points as you can to filter out any random inaccuracy.

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