Fast‐pulsed amperometric detection at electrodes: A study of oxide formation and dissolution at platinum in 0.1 M NaOH

Abstract

Results of a potential‐step chronocoulometric study of oxide formation at a Pt‐rotated minidisk electrode (0.00785 cm²) indicate that the anodic 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 formation. The anodic peak current observed during linear potential‐scan voltammetric experiments is nearly a linear function of scan rate (ϕ) for small ϕ (1000 < mV s⁻¹) but shows substantial negative deviation from linearity for ϕ > 1000 mV s⁻¹. The peak potential for oxide formation shifts in a positive direction for increasing values of ϕ, suggesting that this process is kinetically slow relative to large ϕ values. Reverse potential‐step chronocoulometric measurements demonstrate that the background current in so‐called “reverse‐pulsed amperometric detection (RPAD)” can be decreased by inhibiting the conversion of the hydrous oxide (PtOH) to the inert oxide (PtO). Data also indicate that the rate of cathodic dissolution of surface oxide is dependent on applied potential for t < 2 to 30 ms. Oxide reduction continues even for t > 1000 ms.