Electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy measures how an electrochemical system responds to small alternating electrical signals across a range of frequencies. Its frequency-dependent impedance helps distinguish processes such as charge transfer, diffusion, and capacitive storage.

Impedance: Impedance is the frequency-dependent opposition a system presents to alternating current, combining resistance and reactance. The measured quantity is the ratio of voltage to current, including their phase difference.
Electrochemical cell: An electrochemical cell converts chemical and electrical energy through reactions at electrodes and an ion-conducting electrolyte. It is the physical system whose response the technique measures.
Battery impedance: Battery impedance is the frequency-dependent opposition to current within a battery and its interfaces. Spectra help track internal resistance, interfacial change, and aging.
Cyclic voltammetry: Cyclic voltammetry measures current while an electrode potential is swept forward and backward over a defined range. It probes potential-dependent reactions, whereas impedance resolves response by frequency.
Identifiability: Identifiability is the possibility of determining unique model parameters from available observations. Different circuit parameters can produce nearly indistinguishable impedance spectra.
Nyquist plot: A Nyquist plot graphs the imaginary part of a complex response against its real part. It displays impedance spectra as arcs and diffusion-related lines.
Small-signal analysis: Small-signal analysis studies a system’s response to perturbations small enough to approximate its behavior as linear. The alternating stimulus must be small enough to avoid substantially changing the system.
Corrosion monitoring: Corrosion monitoring measures changes in materials and environments to assess metal deterioration over time. Impedance can estimate protective-coating performance and corrosion-related interfacial processes.
Chronoamperometry: Chronoamperometry records current over time after a step change in electrode potential. Its time-domain stimulus contrasts with frequency-domain impedance measurements.
Model selection: Model selection is the process of choosing among competing mathematical descriptions of observed data. A good spectral fit alone does not establish that a proposed circuit is physically correct.

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