Voltammetry: Factors Affecting Measurements

Faradaic current results from oxidation or reduction of an analyte at the working and auxiliary electrodes. Cathodic current from analyte reduction carries positive charge, while anodic current from oxidation is negatively charged. Nonfaradaic charging current, produced by changes in electrode potential, must be accounted for separately before measuring the faradaic component.

The applied potential at the working electrode governs faradaic current flow and determines the magnitude of current produced. The current magnitude depends on the rate of the resulting oxidation or reduction reaction occurring at the electrode surface. Higher potentials drive faster electron transfer rates, increasing current proportionally.

Mass transport processes—diffusion, migration, and convection—facilitate movement of ions or molecules from the electrode surface to bulk solution and vice versa. Diffusion transports species from high to low concentration regions in a time-dependent manner. Migration involves charged particles attracted or repelled by electrodes, while convection uses mechanical means to move reactants toward and products away from the electrode.

The rate of electron transport kinetics determines reversibility. When electron transport kinetics are fast, the redox reaction reaches equilibrium and the system is electrochemically reversible. Conversely, slow electron transport kinetics result in an electrochemically irreversible system where the reaction cannot maintain equilibrium conditions.

Diffusion transports ions or molecules from regions of high concentration to regions of low concentration, with effects on mass transport rate being time-dependent. This concentration gradient-driven process is a primary mechanism moving analyte species toward the electrode surface, directly affecting the faradaic current magnitude and measurement accuracy.

Electron transport kinetics determine whether a system behaves as electrochemically reversible or irreversible, which fundamentally affects how voltammetric techniques like voltammetric techniques cyclic voltammetry respond to applied potentials. Fast kinetics produce predictable, equilibrium-based responses, while slow kinetics require different analytical approaches and interpretations.

Convection uses mechanical means to transport reactants toward the electrode and remove products away from it, independent of charge. Migration, by contrast, involves charged analyte particles being attracted or repelled by electrodes based on their charge. Both mechanisms complement diffusion to control overall mass transport rates and faradaic current.