Real Condition of Oxidized Platinum Electrodes: Part 2. —Resolution of Reversible and Irreversible Processes by Optical and Impedance Studies

Abstract

The reversible component in Pt surface oxidation (demonstrated in Part 1) has been characterised by means of electric modulated reflectance measurements and related to the electrochemical oxide formation and reduction processes studied by means of cyclic voltammetry. The reversible component gives a maximum response both in modulated reflectance and a.c. measurements at ca. 0.90 V and then decreases with increasing potential.

The reversible component produced in the initial stages of oxidation is consumed at higher potentials or on holding the potential above 0.9 V. This is consistent with potentiodynamic results which show that a more stable oxide is produced at higher potentials or on holding the potential constant for some time and can be reduced only at relatively lower positive potentials. The change of properties of the surface oxide with time and/or with increasing positive potential and coverage, is consistent with a rearrangement of the initially formed ad-layer by a place-exchange mechanism. Such a process is absent at iridium.