Concentration-Time Dependence at Constant Current Galvanostatic Regime

4 CONCENTRATION-TIME DEPENDENCE AT CONSTANT CURRENT (GALVANOSTATIC REGIME) 

Using a three-electrode systan and a potentiostat, described in Chapter 6, a constant current can be set up and the potential vs. time can be measured. This organization of measurements is called the galvanostatic regime. 

Under a galvanostatic regime (the current density is constant), with a high concentrated background electrolyte, when charge transfer reaction is fast, the concentration gradient at the electrode surface is constant, and Equation 7.9 can be solved with the following boundary and initial conditions [2]  

Previously, only mass transport due to diffusion was taken into account. Another influence on electrochemical process can be due to convection. Convection is the collective movement of ensembles of molecules within a fluid or a gas. To take into account convection. Equation 7.8 should be used for multidimensional processes or Equation 7.9 for a one-dimensional case. 

In Equations 7.8 and 7.9, the first term is responsible for the Fickian diffusion and the second one for the convection. It is logical to assume that when convection in an electrochemical cell is changed, the Nemst diffusion layer is also changed, and therefore, we should find out how the cell current depends on hydrodynamics (fluid dynamics). A simple and common rule is that if stirring is more intensive, the Nemst diffusion layer is smaller. 

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