Influence of the coupling of IrO2 and PtOx on the charging / discharging process at the electrode / electrolytic solution interface

This work aimed to determine the voltammetric charges at the electrode / electrolytic solution interface of the IrO2, PtOx and IrO2-PtOx electrodes. The scanning electron microscope characterization (SEM) showed the presence of the IrO2 and PtOx coating deposited on titanium supports. Also, this characterization revealed that the surface of the prepared electrodes is porous and rough. The cyclic voltammetry measurements allowed to show that the voltammetric charge is high at low scan rates. This result is due to the accessibility of the internal and external surfaces of prepared electrodes by electrolytic solution. In contrast, for the high scan rates, only the external (geometric) surface is in touch with the electrolyte. The voltammetric charge decreases when the pH of electrolyte increases. Regardless of the electrolytic solution the voltammetric charges increases in the order: PtOx < IrO2 < PtOx-IrO2. In the absence of free protons (KClO4 and KOH medium), the electrolyte diffuses inside the pores of the deposit regardless of its composition. Thus, all our electrodes have a large number of internal active sites. This study revealed that the processes which take place at the electrode / electrolyte interface are complex. These processes depend on several factors including the composition of the deposit, the proton concentration, etc. The linear correlations between the total voltammetric charge (q*tot) and the total capacitance (Ctot) show that they can be used to represent the extension of the electrochemically active surface.