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 cyc lic reciprocal derivative chronopotentiometry with programmed currents of t he 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 f or the characterisation of reversible and irreversible processes based on t he influence of the power of time of the programmed current in the apparent reversibility of the charge transfer. This technique is able to evaluate e lectrochemical rate constants of the order of those that can be calculate i n voltammetric techniques by operating in a time scale ten times greater. T hese theoretical equations have been tested experimentally for the system F e(CN)(6)(3-)/ Fe(CN)(6)(4-) in Na2SO4 which behaves as totally reversible w hen a current ramp is applied (u = 1) whereas it can be considered as quasi rreversible when two successive programmed currents with u less than or equ al 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.