A Universal Parameter Governs Peak Currents of Kinetic Systems in Square‐Wave Voltammetry

Square‐wave voltammetry (SWV) is a powerful electroanalytical technique widely explored for studying mechanistic, kinetic, and thermodynamic aspects of various redox processes. Although theoretical framework of SWV is established more than 40 years ago, a key limitation still remains unresolved. In particular, the absence of a unified formalism that accurately describes the behavior of peak currents across diverse kinetic and experimental conditions is seen as a major drawback of SWV. In linear scan voltammetry (LSV), the Randles–Sevcik equation is a relationship that links the peak current with concentration of redox species of interest, their diffusion coefficients, and other parameters of redox systems exhibiting no kinetic hindrances. In the SWV, however, due to its pulsed excitation scheme, there is a series of complex, permanent time‐dependent perturbations going on in interfacial concentration gradients. These perturbations, along with the interplay between square‐wave amplitude, potential step, temperature, diffusion coefficient, and electron transfer kinetics, hinder the derivation of a general analytical expression for peak current magnitudes in SWV. In this study, a series of theoretical simulations of a simple one‐electron redox system (Red ⇌ O x + e − ) governed by Butler–Volmer kinetics and diffusion‐controlled mass transport are performed. Through this approach, a novel dimensionless parameter “ X ” defined as X = constant ⋅ [( dE ⋅ F )/(RT)] ⋅ [(Esw/dE )]^0.5 ⋅ [K /(1 + K)] is identified, which incorporates the contributions of critical physical and experimental variables: temperature T , potential step d E , square‐wave amplitude E sw , standard rate constant of electron transfer k s , frequency f , diffusion coefficient D ( k s , f , and D are all incorporated in definition of dimensionless kinetic parameter K ). The results show that when the ratio E sw / d E is kept constant, SW peak currents remain nearly unchanged over a wide range of temperatures and kinetic regimes. This invariance indicates that the single unified parameter “ X ” governs the peak currents in SWV.