Single Pulse Voltammetry: Reversible Electrochemical Reactions

Abstract

In a single potential step voltammetric technique, several constant potentials (of increasing amplitude) are applied with a time length t 1. When stationary electrodes are used, the time interval between two consecutive potentials must be much greater than t 1, for the initial conditions to be restored (Scheme 2.1). If a Static Mercury Drop Electrode (SMDE) is used, the initial conditions are simply restored by making the drop fall. The measured current at a fixed time value \( t={t}_1 \) is plotted versus the corresponding potential steps discretely [1–3]. The resulting current–potential curve has a sigmoidal shape whose position and slope depend on the reversibility of the electrode process and the wave height is independent of the electron transfer rate. At each fixed potential value, the current–time variation (which has a typical cottrellian behavior for reversible processes at planar electrodes when considering diffusive transport only) can be registered. If the length time is in the range 2–200 ms, the electrochemical technique is called Normal Pulse Voltammetry (NPV), originally known as Normal Pulse Polarography (NPP). This technique was introduced by Barker [5–7] and it was originally designed for the Dropping Mercury Electrode (DME), in which the potential pulse is applied at the end of the life of the drop, with the current being dependent on the relation between the pulse time and the drop lifetime. The main reason for measuring the current at the end of short time intervals is to eliminate the capacitative component (see Sect. 1.9) in order to optimize the sensitivity. Today the DME electrode is scarcely used and most electrochemical techniques are used at stationary electrodes