Current and Voltage Conventions for EIS

AC measurements are largely free from problems caused by sign conventions. However, the Electrochemical Impedance Spectroscopy software does not only make AC measurements, but it also sets and reads DC values, such as the open-circuit potential and the applied DC potential. Therefore, you must be aware of the sign conventions used in the software.

Positive 1.2 mA can mean different things to workers in different areas of electrochemistry. To an analytical electrochemist it represents 1.2 mA of cathodic current. To a corrosion scientist it represents 1.2 mA of anodic current. In the Electrochemical Impedance Spectroscopy software's standard techniques we follow the corrosion convention for current. Positive currents are anodic, resulting in oxidation at a metal specimen.

This convention is the same as the current convention used in other Gamry software packages such as DC Corrosion.

In the software, all potentials are specified or reported as the potential of the working electrode with respect to either the reference electrode or the open-circuit potential. The former is always labeled as "vs Eref" and the later is labeled as "vs Eoc". The equations used to convert from one form of potential to the other are:

E vs Eoc = (E vs Eref) - Eoc

E vs Eref = (E vs Eoc) + Eoc

Regardless off whether potentials are versus Eref or versus Eoc, one sign convention is used. The more positive a potential, the more anodic it is. More anodic potentials tend to accelerate oxidation of a metal specimen.

AC current and potential are always expressed as rms (root mean square) values. By definition, rms values cannot be negative.