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The impedance of the reference electrode should be low (less than 1kΩ). An impedance higher than 1 kΩ is not good and an impedance higher than 5 kΩ is unacceptable and must be corrected. A reference electrode with high impedance can negatively impact the 3-electrode DC and EIS measurements by adding ohmic drop.

The common cause for high impedance is the blockage of the junction frits. Adsorption of organic materials or precipitation of insoluble salts in the junction can cause clogging, resulting in high impedance (more than 1MΩ). It is advisable to use a salt bridge to prevent the electrode frits from clogging.

The impedance measurement of a Ag/AgCl reference electrode can be done as follows:

• Partially fill a beaker with 3M KCl electrolyte.
• Immerse the tip of the Reference Electrode till ~10mm from bottom into the solution.
• Add a platinum mesh (or any high surface area platinum or graphite) counter electrode to the solution.
• Connect the Reference Electrode to the Working (red) lead of the potentiostat.
• Connect the Platinum mesh to the Reference (Blue) and Counter (Black) electrode leads.
• A Potentiostatic EIS scan was set up starting from about 50 kHz and scanned to 1kHz, and 5 mV AC amplitude. The applied DC potential should be zero versus the open circuit potential (Eoc).
• Start the scan. Make sure that the DC current is nearly zero (less than 1 mA). If the DC current exceeds the limit, stop the experiment otherwise the Reference Electrode could be damaged.
• Check the magnitude and phase of the measured impedance. If the measured impedance at high frequency is resistive i.e. the phase angle is near zero (as shown in the Bode Phase plot given below) then the impedance value can be considered as the resistance of reference electrode. If the phase angle isn’t near zero, then run the experiment again with a different frequency range to find the region where the value of phase angle is nearly zero.

The impedance of Kanopy’s single compartment Ag/AgCl, 3M KCl electrodes with porous glass frit gives value typically between 330 to 340 Ω as shown in the Nyquist plot.

 

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