Evidence for Transient Conditions

In electrochemical systems, a steady state during current flow implies that a time-invariant distribution of the concentrations of ions and neutral species, of potential, and of other parameters is maintained in any section of the cell. The distribution may be nonequilibrium, and it may be a function of current, but at a given current it is time invariant. 

The steady state is disturbed and the system exhibits transient behavior when at least one of its parameters is altered under an external stimulus (perturbation). Transitory processes that adjust the other parameters set in (response) and at the end produce a new steady state. The time of adjustment (transition time, relaxation time) is an important characteristic of the system. 

In electrochemical systems, transient processes are of major practical significance because they are an efficient route for studying electrode reactions and phenomena (see Chapter 12). In addition, transient measurements are useful for analytical purposes (see Chapter 23). 

Fundamentals of Electrochemistry, Second Edition, By V. S. Bagotsky Copyright 2006 John Wiley Sons, Inc. 

During the transition time, a variety of processes of adjustment take place development or change of an ohmic potential gradient, a change in EDL charge density, the development of concentration gradients in the electrolyte, and so on. Each of these processes has its own rate and its own characteristic time of adjustment. 

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