What does GCD exactly mean? Do you measure electrochemical impedance Spectra? Please clarify it.

Dear Soliman,

1 – What is the iR drop in Galvanostatic Charging/Discharging GCD or any electrochemical measurements

Let me first explain the following: Potentiostats are instruments that are designed to control the potential of the working electrode (WE) relative to an ideal non-polarizable reference electrode (RE). While this is the apparent operating principle of a potentiostat, in reality the potentiostat controls the potential of the counter electrode (CE) relative to the WE (which is at virtual ground). The potential of the CE is set to the required voltage within the compliance voltage limits in order to keep the potential difference between the RE and the WE equal to the user-defined value.

Unfortunately, the electrochemical cell does not correspond to a real electrochemical cell. In a real electrochemical cell, the reference electrode is always located at a distance relative to the working electrode. This means that an additional resistance, the uncompensated resistance, can never be avoided completely. Such uncompensated resistance leads to voltage change across the electrochemical interface, called the iR drop. Even with a very low uncompensated resistance value, the voltage drop can become significant when the current is high.

2- How to minimize iR drop?

Although iR drop cannot be avoided completely, it is possible to minimize its value. The following strategies can be used:

1. Use a supporting electrolyte with high conductivity: this will reduce the total resistance of the solution (and therefore also the uncompensated resistance).

2. Reduce the size of the working electrode: the total current depends on the surface area of the working electrode. Smaller currents decrease the iR drop.

3. Use a Luggin capillary: this can be used to reduce the distance between the reference electrode and the working electrode, therefore reducing the uncompensated resistance.

4- An additional strategy that can be used to reduce the effects of the uncompensated resistance is to use the so-called positive feedback built into most of recent potentiostats. In that case, you need to switch the iR compensation “On” during the instrument setting.

Hope that may help

Source: http://www.ecochemie.nl/download/NovaTechNotes/NOVA_technical_note_7_-_Using_IR_compensation_xNOVA_1.10x.pdf

Dear Prof. Qijin Chi

thank you for your reply

i used GCD in my question as shortcut for Galvanostatic Charging/Discharging measurements.

thank you

Dear Prof. Farid

thank you very much for your detailed answer

- in my experiments,i used Na2So4 as electrolyte

-also, i try to make the distance between the WE and CE at 2 cm.

- what is the Luggin capillary?

- how can i detect the suitable voltage for each WE?

thank you very much

Hi Soliman,

I agree with Farid, WHO has offered some detailed and constructive suggestions. In short, both the arrangement of three-electrode system and using optimal parameters are important. Do you use GCD for supercapacitor or battery? Attached is a recent article from my Group.  

Dear Prof. Qijin Chi

i use GCD for supercapacitor.

thank you for your reply