FAST-PULSED AMPEROMETRIC DETECTION AT NOBLE-METAL ELECTRODES - A STUDY OF OXIDE FORMATION AND DISSOLUTION AT PLATINUM IN 0.1 M NAOH

Results of a potential-step chronocoulometric study of oxide formation at a Pt-rotated minidisk electrode (0.00785 cm2) indicate that the an odic charge (q(a)) grows ca. as a linear function of the log time (t) for t = ca. 2-30 ms. Furthermore. the slope of the linear q(a) - log { t/ms} plot is proportional to the applied overpotential for oxide form ation. The anodic peak current observed during linear potential-scan v oltammetric experiments is nearly a linear function of scan rate (phi) for small phi (1000 < mV s-1) but shows substantial negative deviatio n from linearity for phi > 1000 mV s-1. The peak potential for oxide f ormation shifts in a positive direction for increasing values of phi, suggesting that this process is kinetically slow relative to large phi values. Reverse potential-step chronocoulometric measurements demonst rate that the background current in so-called ''reverse-pulsed amperom etric detection (RPAD)'' can be decreased by inhibiting the conversion of the hydrous oxide (PtOH) to the inert oxide (PtO). Data also indic ate that the rate of cathodic dissolution of surface oxide is dependen t on applied potential for t < 2 to 30 ms. Oxide reduction continues e ven for t > 1000 ms.