Highly boron-doped diamond electrodes: surface modifications by low amounts of noble-metal oxides

In electrochemical kinetics, the activity of different electrode materials can be discussed by considering a given electrode reaction and comparing the exchange current densities (j0). Such an approach is possible because, at the equilibrium potential (overpotential equal to zero), the electrode/electrolyte potential difference depends on the electrode work function. In other words, the true electrode potential is the difference between the equilibrium potential and the electrode work function, thus the polarization is greater, the lower is the value of the latter. Assuming that the considered electron transfer reaction has an ideal outer-sphere behavior, once the different values of j0 have been obtained, a plot of –Log j0 vs. the electrode work function should give a straight line, as shown initially by Bockris, Mannan and Damjanovic, and subsequently by Galizzioli and Trasatti; in both cases, the Fe3+/Fe2+ simple electron exchange reaction was considered. Following the above exposed approach, the first topic of the present communication is the electrochemical determination of the electrode work function for different samples (as prepared, oxidized, thermal treated) of conductive, boron-doped diamond electrode (BDD). In view of the response of electrochemical parameters to changes in the nature of the electrode surface, experiments have been carried out also on the behavior of Fe3+/Fe2+ redox couple at BDD electrodes modified by ruthenium dioxide. The electron-transfer parameters have been studied at BDD surfaces with modifications from the level of sub-monolayers to a few monolayers (nominally, from 1E13 to 1E17 RuO2 “molecules”/cm2). In this context, previous works have shown the great chemical, electrochemical and thermal stabilities of both BDD and BDD/RuO2 specimens (whose characterization has already been done, by studying, in particular, the chlorine evolution reaction [3-6]). While a monotone effect has been reported in ref. [6] for modifications based on IrO2, an unexpected behavior was presently recorded, possibly due to strong metal-oxide/support interactions, particularly evident in the case of very low deposits. [1] J. O’M. Bockris, R. J. Mannan and A. Damjanovic, J. Chem. Phys., 48, 1898 (1968). [2] D. Galizzioli and S. Trasatti, J. Electroanal. Chem., 44, 367 (1973). [3] S. Ferro, A. De Battisti, I. Duo, Ch. Comninellis, W. Haenni and A. Perret, J. Electrochem. Soc., 147, 2614 (2000). [4] A. De Battisti, S. Ferro and M. Dal Colle, J. Phys. Chem. B, 105, 1679 (2001). [5] S. Ferro and A. De Battisti, J. Phys. Chem. B, 106, 2249 (2002). [6] I. Duo, S. Ferro, A. De Battisti and Ch. Comninellis, “Conductive Metal-Oxide nanoparticles on synthetic boron-doped diamond surfaces”, in “Catalysis at Nanoparticles Surfaces”; A. Wieckowski, E. R. Savinova and C. G. Vayenas Eds.; Marcel Dekker, Inc.; Projected publication date: 2002