What is compliance voltage?

In conventional three-electrode system, potential is applied betweem WE and RE. Current flows between WE and CE. Compliance voltage is the maximum voltage that the potentiostat can apply on CE. It is the voltage between WE and CE.

As is shown in the diagram, suppose applied E between WE and RE is 10V, and the current is 10mA, then the compliance voltage of the system will be as high as 60V, exceeding our potentiostat compliance voltage specification (± 21V or ±30V). Once complaince voltage of the system is higher than our instrument can measure, the potentiostat will not continue to apply voltage as set.

How we know over compliance voltage
Phenomenon: The applied potential cannot reach to the set value, and the current is about tens of mA.

Eg:
In LSV test, we set 0 -2 V vs RE, at the begining, the applied potential increases linearly. Then suddenly it stops increasing after reaching a certain value, not to the 2V final potential as set, so as the response current in the system.

For potentiostatic test, we set 2V constant potential, but the actual applied potential always cannor reach 2V and current is also lower than expected. But when we lower the constant applied potential to be like 1.8V and both potential and current are normal. We can presume the over compliance voltage occurs under 2V.

Compliance voltage monitoring is closed in default setting. In the software, you can monitor the compliance voltage by checking “On” here.

When the compliance voltage monitoring is ON, a “Cell” data file will be created to record the compliance voltage info.
In the compliance voltage -time curve, if the compliance voltage increases continuously and then reaches to the maximum that the potentiostat can measure and doesn’t increase any more, it means “over compliance voltage” of the system occurs.