Sinusoidal Potential Scans for Unified Capacitance Measurement in Double-Layer and Redox-Active Electrolyte Systems

This study addresses challenges in capacitance measurement stemming from significant variations in results obtained through different analytical methods, which complicate the comparison of energy storage performance. It proposes sinusoidal potential scans as a unified and consistent approach for capacitance measurement across various analytical methods. The investigation begins with cyclic voltammetry (CV) measurements using triangular potential scans, highlighting discrepancies in capacitance values when analyzed with conventional methods. Numerical simulations were conducted to replicate these responses, distinguishing between Faradaic and non-Faradaic contributions, and revealing that discrepancies persist regardless of current type. Extended to CV with sinusoidal potential scans, commonly visualized as Lissajous plots in electrochemical impedance spectroscopy, the concept is validated through experimental results which demonstrate that capacitance values obtained using both differential and integral approaches are consistent across all analyses. The model was employed to investigate the effects of key parameters such as redox-active surface area, reaction rate constant, and constant phase element parameters, confirming that sinusoidal scans unify capacitance measurements, providing consistent values even when these parameters are varied. In summary, this study highlights the reliability and robustness of sinusoidal potential scans for capacitance evaluation, particularly in systems with mixed Faradaic and non-Faradaic contributions.