Specific features of the interaction of a mechanically renewable graphite electrode with solutions based on propylene carbonate

The electrochemical behavior of a mechanically renewable graphite electrode at its interface with LiClO4 solutions in propylene carbonate (PC) is studied by cyclic voltammetry (CVA) and impedance methods. It is shown that in the potential region from −1.0 to 0.5 V (vs. aqueous saturated calomel electrode), this electrode can be considered as ideally polarizable. This allows the dependences of the electric double layer capacitance С on the graphite-electrode potential E to be obtained. These С vs. E curves are characterized by the presence of a minimum at the potential independent of the salt concentration; moreover, the minimum itself deepens with electrolyte dilution. The analysis shows that the position of this minimum in the С vs. E curves corresponds to the potential of zero charge (PZC) of this electrode. An essential feature of these С vs. E curves is that they demonstrate the capacitance values (in the vicinity of PZC and at the potentials corresponding to positive surface charges) substantially lower as compared with the similar dependences observed on electrodes of mercury and other s,p-metals. Assuming that this peculiarity of graphite electrode is associated with its semiconductor properties, the procedure of processing experimental results is developed based on the approach known from the literature. With the use of this procedure, the components of the overall potential drop (φ) at the electrode-solution interface which correspond to the potential drops in the space charge region in graphite surface layer (φ1) and in the electric double layer at its interface with solution (φ2) are calculated. The results obtained make it possible to quantitatively assess the semiconductor characteristics of the graphite material such as the flat band potential and the concentration of charge carriers in the conduction band and also to propose and substantiate the conclusion that the chemisorption properties of graphite and mercury electrodes with respect to PC molecules are close.