Non-steady-state electrolysis

As the electrolysis proceeds, there is a progressive depletion of the Ox species at the interface of the test electrode (cathode). The depletion extends farther and farther away into the solution as the electrolysis proceeds. Thus, during this non-steady-state electrolysis, the concentration of the reactant Ox is a function of the distance x from the electrode (cathode) and the time f, [Ox] = Concurrently, concentration of the reaction product Red increases with time. For simplicity, the concentrations will be used instead of activities. Weber (19) and Sand (20) solved the differential equation expressing Pick s diffusion law (see Chapter 18) and obtained a function expressing the variation of the concentration of reactant Ox and product Red on switching on a constant current. Figure 6.10 shows this variation for the reactant. 

Figure 6.10. Variation of concentration of reactant during non-steady-state electrolysis. The number on each curve is the time elapsed since the beginning of electrolysis, t5>t4>...tj. (From Ref 23, with permission from Elsevier.)...

Figure 6.11. Variation of concentration of reactant during non-steady-state electrolysis Cq...

Juliard,A. Non-steady state electrolysis under constant current J. Phys. Chem. 57, 701 (1953). 

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