Determination of A.C. Impedance Spectroscopic and Cyclic Voltammetric Behavior of Some Heterocarbonyl Compounds in Both Aprotic and Aqueous Media

The electrochemical behavior of eosin, isatin and alloxan in aqueous KNO3 and NaClO4 solutions on the Hanging Mercury Drop Electrode [HMDE] and in aprotic DMF and CH3CN on the Pt-disk electrode at 298 K was investigated using the Cyclic Voltammetry (CV) and the Electrochemical Impedance Techniques (EIS). In the CV experiment, the electroreduction of eosin in both aqueous and non-aqueous media are characterized by a single-electron reversible step, whereas the response of isatin in the same solutions is completely irreversible and a diffusion-controlled process is observed only in aprotic media. The CV results of alloxan in sodium perchlorate solution revealed limited stability of the anion radical and instability of the dianion. Generally, charge transfer processes to alloxan suffer from clearly kinetic contribution. EIS data of these compounds is mostly characterized by a semicircle similar to that expected for a purely capacitive response. In case of the presence of relaxations of the electrode-solution interface, a Warburg impedance locus at low frequencies with a partially resolved semicircle at high frequencies was obtained.