Chronoamperometric study
In order to investigate the reason of bleaching at negative potentials during BE experiments, chronoamperometric study was subsequently applied since this method is one of the best established technique and naturally fastest method to determine the number of heterogeneous electron transfer. Since KNO3 is also reduced at negative potentials [28] and may exceed the current of MB+ adsorption/reduction therefore, the chronoampermetric experiments at variable negative potentials were carried out only in the presence of KCl supporting electrolyte. In this regard, the counter electrode was separated from the working electrode using a membrane frit in order to avoid provable dye oxidation due to formation of OCl−species. The potential was varied by −50 mV steps starting from −0.3 V. The currents were sampled in every 25 ms. The features of diffusive currents were noticed at potentials lower than −0.55 V, which is consistent with Fig. 2. As per Fig. 2, the fast electron reactions were taken place at potentials lower than −0.48 V, where the reactions were diffusion controlled. Fig. 7 shows the current transient at −0.7 V. The current transient shows the hyperbolic decay of cathodic currents. The number of electron (n) transfer was obtained by applying Cottrell's equation: