In a rotating disk electrode, the electrolytes are made to flow past the electrode by convection. In this Demonstration, when the rotation speed increases, the flux of electroactive species to the surface of the electrode increases by convection (shown by the red arrow) and the current increases.
The Levich equation predicts the current observed at a rotating disk electrode and shows that the current is proportional to the square root of rotation speed. The equation is
is the current limited in voltammogram (A),
is the number of electrons transferred,
is the Faraday constant (C/mol),
is the electrode area (),
is the diffusion coefficient /s),
is rotation speed (radian/sec),
is the kinematic viscosity of the solution /sec), and
is the concentration of the electroactive species ).
The Levich equation can be used to calculate the diffusion coefficient as a function of the rotation speed and the current .
 J. Wang, Analytical Electrochemistry, 3rd ed., New York: John Wiley & Sons, 2006.