Some of the most common technical questions we hear have to do with iR compensation —
- Where does uncompensated iR come from?
- Do I need to use iR compensation with my experiment?
- How should I set up the iR compensation parameters?
- Why doesn’t iR compensation work on my system?
In this post we’ll attempt to answer these questions and to give you a basic understanding of iR compensation.
Some initial background information describes the general issue of iR errors. The later information concentrates on the specifics of “current interrupt” iR compensation as a means for measuring and correcting for iR error. Positive feedback iR compensation is mentioned but not discussed in detail.
This application note presumes you have a basic understanding of potentiostat operation. If not, please review the Primer on Potentiostats. Experienced potentiostat users should skip the primer and read on.
It would also help if you know some of the fundamentals of Electrochemical Impedance. Gamry has a Primer on Electrochemical Impedance on their website. Pay particular attention to how typical chemical processes are mapped into electrical circuit elements.
When do I need iR compensation?
We’ll give an approximate answer to this question here. A more complete answer requires the information discussed below and some information about the system that you are testing.
In general, iR compensation is needed when one or more of these is true:
- You are doing a quantitative test that yields a numerical result, such as a corrosion rate, equilibrium constant or a rate constant
- The solution in your cell is not very conductive
- Your currents are fairly high
- Your cell geometry is less than ideal
Unfortunately, these criteria are subjective. For example, aqueous 0.5 M potassium chloride may be considered to be very conductive in an electrochemical analysis application and poorly conductive in a plating application.
One simple run-of-thumb is often used:
- Record some initial data curves with and without iR compensation.
If the shape of the curve changes significantly when iR compensation is applied, compensation is required.
IR compensation often adds additional noise to the data, so increased noise on the plot is not considered to be a significant change.