Studies of surface-modified glassy carbon electrodes obtained by electrochemical treatment. Its effect on Ru(bpy)2+ 3 adsorption and the electron transfer rates of the Fe2+/Fe3+ couple

CESAR A BARBERO; JUANA J SILBER; LEONIDES SERENO

JOURNAL OF ELECTROANALYTICAL CHEMISTRY - (Print)

ELSEVIER SCIENCE SA

Lugar: Amsterdam; Año: 1988 vol. 248 p. 321 - 340

1572-6657

Glassy carbon electrodes were treated electrochemically by cycling the electrode between - 500 and 1860 mV (vs. SCE) in 1 M H2SO4 at a sweep rate of 150 mV/s. The modified glassy carbon (MGC) electrode surfaces obtained have been characterized by cyclic and step potentiostatic techniques. The redox reactions of the surface functionalities attributed to the quinone-like structures of these MGC electrodes are slow and exhibit apparent diffusion control. Thus, when a given catalytic effect depends on the redox state of the surface, it will also depend on the time scale of the experiment. The conditions for obtaining reproducible MGC electrodes are given. Cyclic voltammetric studies show that Ru(bpy)2+3 adsorbs strongly on MGC electrodes while the adsorption is negligible on freshly polished electrodes. The adsorption fits the Temkin isotherm, giving the value of the repulsive interaction between the molecules. The value of ?G = −39.6 was calculated for the process. A specific interaction between the bipyridyl moieties and the surface functionalities is proposed. Appreciable photocurrents are observed for Ru(bpy)2+3 adsorbed on a MGC electrode which may lead to future applications. On the other hand, by measuring the formal heterogeneous rate constants (ks) for Fe2+/Fe3+ it is possible to show how the catalytic efficiency of MGC depends on the degree of modification of its surface.