Faradaic and non-faradaic processes are two fundamentally distinct categories of electrochemical behaviour that occur at electrode surfaces. Understanding the difference between them is essential for interpreting electrochemical data correctly, designing meaningful experiments, and drawing accurate conclusions from measurements in battery research.
The distinction between faradaic and non-faradaic processes underpins nearly every electrochemical technique used in battery materials research, from cyclic voltammetry to electrochemical impedance spectroscopy (EIS). Misidentifying contributions from each process can lead to incorrect capacity values, flawed rate capability assessments, and unreliable comparisons between materials.
What are faradaic and non-faradaic processes in electrochemistry?
A faradaic process involves the transfer of charge across an electrode–electrolyte interface through an oxidation or reduction reaction, governed by Faraday’s laws of electrolysis. A non-faradaic process, by contrast, does not involve charge transfer across the interface; instead, it results from the rearrangement of ions and solvent molecules at the electrode surface in response to changes in potential.
Both types of process occur simultaneously in any real electrochemical system. The faradaic contribution arises from reactions such as lithium-ion intercalation into a graphite anode or the reduction of a cathode active material. The non-faradaic contribution arises from the charging and discharging of the electrical double layer, the thin region of charge separation that forms at the electrode–electrolyte interface.
In battery research, distinguishing between these two contributions is not merely academic. It directly affects how specific capacity, coulombic efficiency, and rate performance are interpreted and reported.
How does a faradaic process work at the electrode surface?
A faradaic process occurs when an electroactive species undergoes a redox reaction at the electrode surface, transferring electrons to or from the electrode. This electron transfer is accompanied by a chemical transformation, such as the reduction of a metal ion or the intercalation of lithium into a host lattice. The current produced is directly proportional to the rate of the reaction, as described by Faraday’s laws.
Charge transfer kinetics and overpotential
The rate of a faradaic process depends on both the thermodynamics and kinetics of the reaction. When current flows, the electrode potential deviates from its equilibrium value by an amount known as the overpotential. This deviation drives the reaction forward and is influenced by factors including the exchange current density, temperature, and the activation energy of the charge-transfer step.
In battery materials research, faradaic reactions include lithium-ion intercalation and deintercalation, conversion reactions, alloying reactions, and electrolyte decomposition reactions that form the solid electrolyte interphase (SEI) layer on the anode surface during the first cycles. Each of these processes consumes charge in a way that is, in principle, measurable and attributable to a specific chemical event.
How does a non-faradaic process work at the electrode surface?
A non-faradaic process occurs when the electrode potential changes and ions in the electrolyte redistribute at the electrode surface to form or modify the electrical double layer. No electrons cross the interface, and no chemical reaction takes place. In this regime, the electrode behaves like a capacitor, storing charge electrostatically rather than through chemistry.
The double-layer capacitance arises because the electrode surface carries a charge, which attracts a layer of oppositely charged ions from the electrolyte. This arrangement stores energy without any faradaic reaction occurring. The magnitude of the double-layer capacitance depends on the electrode surface area, the dielectric properties of the electrolyte, and the ionic concentration.
Pseudocapacitance as an intermediate case
Some materials exhibit pseudocapacitive behaviour, in which surface or near-surface faradaic reactions produce a capacitor-like current response. Although charge transfer does occur in pseudocapacitance, the process is fast and surface-confined, making it appear non-faradaic in certain measurement windows. This intermediate behaviour is particularly relevant when characterising nanostructured electrode materials, where the surface-to-volume ratio is high.
What is the difference between faradaic and non-faradaic current?
Faradaic current results from charge transfer across the electrode–electrolyte interface through redox reactions and is directly related to the amount of material reacted, as quantified by Faraday’s laws. Non-faradaic current, also called capacitive or charging current, results from the redistribution of ions at the interface without any chemical reaction and is proportional to the scan rate in voltammetric experiments.
In practical terms, faradaic current carries information about the electrochemical reactions occurring in the cell, whereas non-faradaic current represents a background contribution that must be accounted for. In cyclic voltammetry, for example, the non-faradaic baseline current scales linearly with scan rate, whereas faradaic peak currents scale with the square root of scan rate for diffusion-controlled processes. This difference in scan-rate dependence is one of the primary tools used to separate the two contributions.
The ratio of faradaic to non-faradaic current has direct implications for the measured coulombic efficiency of a cell. Non-faradaic charge does not contribute to useful energy storage but is included in the total charge passed during a cycle, which can distort efficiency calculations if not properly accounted for.
Why does the faradaic-to-non-faradaic ratio matter in battery testing?
The ratio of faradaic to non-faradaic contributions in a battery cell determines how much of the measured current and stored charge is attributable to useful electrochemical reactions versus capacitive effects. A high non-faradaic contribution relative to the faradaic signal can obscure reaction features, inflate apparent capacity at high scan rates, and complicate the interpretation of rate capability data.
This ratio becomes particularly important when testing materials with low specific capacity in mAh/g or small active masses, where the double-layer capacitance of the electrode substrate, current collector, or binder can represent a significant fraction of the total measured charge. In half-cell testing, where a small quantity of active material is evaluated against a lithium metal counter electrode, careful electrode preparation and cell design are necessary to minimise non-faradaic artefacts.
The ratio also affects EIS measurements. In an impedance spectrum, the double-layer capacitance appears as a distinct element in the equivalent-circuit model, typically represented by a constant phase element (CPE) in parallel with the charge-transfer resistance. Accurately separating these contributions requires well-designed test cells with low and reproducible geometric parameters.
How do you identify faradaic and non-faradaic contributions in your data?
Faradaic and non-faradaic contributions can be separated by analysing the scan-rate dependence of current in cyclic voltammetry, by fitting equivalent-circuit models to EIS data, or by applying galvanostatic intermittent titration technique (GITT) protocols. Each method exploits the different time-scale behaviour of charge-transfer reactions versus double-layer charging.
Cyclic voltammetry scan-rate analysis
In cyclic voltammetry, the total current at a given potential can be expressed as the sum of a capacitive term, proportional to scan rate, and a diffusion-controlled faradaic term, proportional to the square root of scan rate. By measuring voltammograms at multiple scan rates and plotting current against both scan rate and its square root, it is possible to deconvolute the two contributions quantitatively at each potential.
Electrochemical impedance spectroscopy
EIS separates faradaic and non-faradaic processes by their frequency response. At high frequencies, the impedance is dominated by ohmic resistance and the double-layer capacitance. At intermediate frequencies, the charge-transfer resistance associated with faradaic reactions becomes visible as a semicircle in the Nyquist plot. At low frequencies, diffusion-limited faradaic processes appear as a Warburg element. Fitting an appropriate equivalent-circuit model allows each contribution to be quantified independently.
Galvanostatic methods
Under galvanostatic conditions, the non-faradaic current charges the double layer almost instantaneously at the start of a current pulse, producing a rapid potential step. The subsequent, slower potential evolution reflects the faradaic reaction. GITT exploits this behaviour by applying short current pulses separated by rest periods, allowing the double-layer response and the faradaic overpotential to be distinguished from one another.
How EL-Cell GmbH supports the study of faradaic and non-faradaic processes
Accurately resolving faradaic and non-faradaic contributions requires test cells with well-defined geometry, minimal parasitic capacitance, and stable, reproducible interfaces. EL-Cell GmbH designs its test cells and instruments specifically to meet these requirements in battery materials research.
- The PAT-Cell and PAT-Cell-Force provide standardised three-electrode configurations that isolate working-electrode behaviour from counter-electrode artefacts, enabling cleaner separation of faradaic signals.
- The PAT-Tester-i-16 integrates galvanostatic and potentiostatic control with full EIS capability across all 16 channels, allowing scan-rate studies, GITT protocols, and impedance measurements within a single instrument.
- The ECD-4-nano electrochemical dilatometer adds a mechanical dimension to electrochemical measurements, enabling correlation of faradaic intercalation reactions with electrode thickness changes at nanometre resolution.
- EL-Software provides flexible scripting and data export tools, supporting the custom protocols needed to deconvolute capacitive and faradaic contributions systematically.
If you are designing experiments that require precise separation of faradaic and non-faradaic contributions, we would be glad to discuss which cell configuration and measurement protocol best suit your research. Contact us to speak with our team directly, or visit el-cell.com to explore the full PAT Series product range.
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