Application of cyclic reciprocal derivative chronopotentiometry with programmed currents to the study of the reversibility of electrode processes

The general equations corresponding to the dt/dE - E curves obtained in cyclic reciprocal derivative chronopotentiometry with programmed currents of the form I(t(i))=(- 1)(i+1)I(i)t(i)(u) with u greater than or equal to 0 are deduced. These expressions are valid for reversible, quasirreversible and irreversible electrode processes. Easily applicable criteria are proposed for the characterisation of reversible and irreversible processes based on the influence of the power of time of the programmed current in the apparent reversibility of the charge transfer. This technique is able to evaluate electrochemical rate constants of the order of those that can be calculate in voltammetric techniques by operating in a time scale ten times greater. These theoretical equations have been tested experimentally for the system Fe(CN)(6)(3-)/ Fe(CN)(6)(4-) in Na2SO4 which behaves as totally reversible when a current ramp is applied (u = 1) whereas it can be considered as quasirreversible when two successive programmed currents with u less than or equal to 1/2 are applied. We have also studied the system Ce4+/Ce3+ in H2SO4, which behaves as totally irreversible for any value of u. (C) 1999 Elsevier Science Ltd. All rights reserved.