In potentiostatic measurements, the potential of the WE is constant and the current is monitored as a function of time. In potentiodynamic measurements, the potential is usually ramped up slowly and the current as a function of voltage is measured. The current-voltage curve around the corrosion potential (the potential where current is zero) can be fitted (Tafel analysis), giving the corrosion rate in equilibrium. Scans to higher voltage can be used to determine passivation and passivation breakdown. Cyclic voltammetry (CV) is a special form of potentiodynamic analysis, where the voltage is swung up and down repeatedly.
In electrochemical impedance spectroscopy (EIS), an AC voltage around zero or non-zero offset is applied over usually a large frequency range (sub-Hz up to MHz). EIS provides information on time-dependent phenomena like ion conduction in dielectric films, solid state chemical reactions, dipole relaxation, and so on.