Similarity of Heterogeneous Kinetics to Delay of Double-Layer Capacitance Using Chronoamperometry

Abstract

Chronoamperometric curves for the oxidation of a ferrocenyl derivative via a potential step, calculated using the Cottrell equation, showed less diffusion-controlled currents on a platinum wire electrode. This lower deviation cannot be explained via Butler–Volmer heterogeneous kinetics, but was ascribed to the negatively capacitive current associated with a redox reaction. The deviation in fully oxidized electrical potential corresponds to the non-zero concentration at the electrode surface, which cannot be predicted using the Nernst equation. This equation expresses the relationship between the electrical potential and activity at the electrode surface rather than the concentration. The diffusion equation determines the relationship between the current and surface concentration rather than activity. Negative capacitance or a non-zero concentration may arise from structure formation on the electrode owing to dipole–dipole interactions, which are similar to the generation of double-layer capacitance, including frequency dispersion. Following this concept, we derive expressions for a lowered diffusion-controlled current and time-dependent surface concentration. The negatively capacitive current shows the time dependence of t−0.9, which is similar to the decay of double-layer capacitive currents. The surface concentration decays with t−0.4-dependence.

Electrochemistry of Neodymium in an Equimolar NaCl-KCl Melt without and with Addition of Fluoride Ions

“…60 In turn, the change in the structure of the EDL depends on the electron work function. [61][62][63][64][65] Petrii considered the relationship between zero charge potentials of platinum metals and electron work functions. 61 In the study 62 the theoretical expressions for the potential energy of surface electrons in the metal electrodes and the work function were obtained.…”