As an alternative to the numerous state-of-the-art versions of voltammetry, a kinetics-sensitive double-step voltcoulometry is introduced. The transient current flowing in response to a potential step across the electrochemical cell is integrated and simultaneously processed by a deliberately selected time-domain “cascade” filter, while scanning the applied potential. In contrast to the widely used sampling scheme of sampling the transient current just before and in the end of the excitation pulse, three values of the transient charge are sampled in the interval between subsequent excitation pulses. Each measuring period is preceded by a single measurement of the steady-state current with the excitation pulse being switched off. The latter measurement makes it possible to actively compensate the parasitic charge across the feedback capacitor of the integrator, due to the steady-state current, while storing the steady-state current data. The goal of introducing the third sampling event resides in discriminating the kinetics of the transient charge via the parameter β that enters the time dependence of the transient charge Δq∝tβ. In general, our filtering scheme is capable of eliminating both any constant or linear components in the transient charge (β=0, 1). Moreover, any superlinear transient charge (β>1) is detected as a peak of the Δq versus potential plot with its sign being opposite to that one of a sublinear redox reaction (0<β<1). This enhanced performance of our double-step voltcoulometry is documented by a series of experiments on aqueous solutions of ascorbic acid using a carbon fiber microelectrode as the working electrode. Finally, how to assess the degree of reversibility of the redox reaction and deduce the time constant RC of the double-layer charging current is shown.

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