Small amplitude potential or voltage step

Although the practical utility of a small potentiostatic perturbation is not great, it is worth treating this case from a methodological point of view and as an introduction to the discussion of the a.c. methods. 

In general, we may suppose that an electrode is given a certain potential E during a certain time t0 and that at t = t0 a small potential increment AE is added to E. As explained in Sect. 1.2.2, the faradaic current flowing at time tm (tm t0) will be the sum of the current/F corresponding to the mean potential and the additional current AjF, due to the application of AE. As a first approximation, the latter current can be expressed by 

The partial derivatives [more formally to be written as (djF/dE)co CR, etc.] are, in fact, parameters to be derived from the rate equation, expressing jF as a function of E, cQ and cR. Throughout Sect. 2, the rate 

Moreover, it is convenient to introduce some short-hand notations as follows. 

Using eqns. (22), we can write down the relationship between Ac0, AcR, and Aj f.  

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