ELECTROCHEMICAL-BEHAVIOR OF THE PASSIVE TIN ELECTRODE IN H2SO4 SOLUTIONS AT VERY POSITIVE POTENTIALS

The passive state of the tin electrode in concentrated H2SO4 solutions was studied using electrochemical and photoelectrochemical measuremen ts, photocurrent spectroscopy and impedance spectroscopy. At high anod ic overpotentials ( > 0.6 V vs. Hg/Hg2SO4/K2SO4 (sat.)) the passivatin g layer becomes photoactive. This phenomenon is believed to be due to the formation of a high valency tin oxide. Experimental impedance spec tra are compared with simulated spectra using a physical model of the interface based on the so-called surface charge approach. This model d escribes the growth of a barrier film under kinetic and high-field-ass isted migration limitations, as well as its dissolution at the film-so lution interface.