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Electrochemistry in laminar and turbulent flow conditions using rotating electrodes

Aug 22, 2022

Article

Electrochemical experiments are generally performed in cells with quiescent electrolytes. This means that the motion of molecules and ions is imparted by the natural convection process. However, forced convection is sometimes necessary in electrochemistry. In these situations, the use of rotating working electrodes is beneficial to generate forced convection. With forced convection, hydrodynamic conditions are created where the working electrode and electrolyte are in relative motion.

Which applications benefit from using rotating electrodes?

To answer this question, we will first take a deeper look at the difference between quiescent solutions and hydrodynamic conditions. Then, after spotting the differences between laminar and turbulent flow, three main rotating electrodes and their suggested applications are highlighted.

Quiescent solutions

The current measured at the working electrode is the result of redox reactions between electrons and reactants at the electrode–electrolyte interface. The reactants are brought to this interface by mass transport.

The mass transport is created by three processes:

  1. Diffusion from concentration differences between the bulk electrolyte and the interface.
  2. Migration due to the presence of an electrostatic potential. The migration is usually neglected by adding a supporting electrolyte to the solution which does not participate in the redox reaction but increases the conductivity of the electrolyte.
  3. Natural convection from density changes inside the solution. This process occurs in quiescent solutions.