Stability in Potentiostat Mode – Improving Potentiostat Stability
70
Figure 9-1
Fast Combination Reference Electrode
SCE
Platinum
White
Cell Lead
100 pF to 10 nF
Electrolyte
Provide a high-frequency shunt around the cell. A small capacitor between the red and white cell leads allows
high-frequency feedback to bypass the cell, see Figure 9-2. The capacitor’s value is generally determined by
trial and error. Ten nF (10 000 pF) is a good starting point.
In a sense, this is another form of an AC-coupled low-impedance reference electrode. The counter electrode is
the low-impedance electrode, eliminating the need for an additional electrode in the solution.
Figure 9-2
High Frequency Shunt
Red
White
Green
100 pF to 10 nF
Counter
Reference
Working
Add resistance to the counter-electrode lead, see Figure 9-3. This change lowers the effective bandwidth of the
control amplifier. As a rule of thumb, select the resistor to give one volt of drop at the highest current expected
in the test being run. For example, if you expect your highest current to be around 1 mA, you can add a 1 k
resistor.
This resistor has little or no effect on the DC accuracy of the potentiostat. It can create problems in high-speed
experiments such as fast CV scans or EIS, which need high bandwidth.
