Electrochemistry: Frequently Asked Questions (FAQ)

The rise time of the potentiostat is defined as the interval required for the output signal to increase from 10% to 90% of its final amplitude. This parameter is relevant primarily in experiments involving very fast or transient electrochemical events. It should be noted that reliable measurement of such rapid processes is only possible when the time constant of the electrochemical cell is shorter than the time intervals of interest. For further guidance, please contact your local Metrohm Autolab support office.

No, the lowest current range on an instrument refers to the setting optimized for high-sensitivity current measurement, but the actual lowest measurable current can be several orders of magnitude lower, limited by factors such as noise interference, cell characteristics, measurement conditions and cabling etc. In contrast, current resolution is defined by the analog-to-digital converter’s bit depth and the selected range, reflecting the smallest change in current the instrument can distinguish, not the smallest detectable current itself. For best measurement quality, users should choose the smallest appropriate current range to maximize resolution while being mindful that noise and system limits often determine the true detection threshold, not just the hardware’s nominal range or resolution.

The three-electrode cell setup is the most used electrochemical cell. In this case, the electrochemical sell uses 3 electrodes: the working electrode (WE), the reference electrode (RE) and the counter (or auxiliary) electrode (CE). During an electrochemical measurement, the current flows between the CE and the WE. The potential difference is controlled between the WE and the CE and accurately measured between the RE and S. In the 3-electrode setup, S is connected to WE and therefore, the potential of WE vs RE is accurately measured and/or controlled. The potential between the WE and CE usually is not measured but, when the application requires, it is possible to monitor it.

A four-electrode cell setup is used in applications where the potential difference (measured between the reference electrode, RE, and the sensing electrode, S) that arises from the passage of current across a well-defined interface (between the working electrode, WE, and the counter electrode, CE) needs to be measured. This type of experimental setup is not very common in electrochemistry. It is typically used for measuring junction potentials between two immiscible phases or across a membrane, allowing the resistance of the interface or the membrane conductivity to be determined.

Open-circuit potential (OCP) in electrochemistry is the potential of the working electrode (WE) relative to the reference electrode (RE) when no external current is flowing through the system (i.e., the circuit is open). It represents the equilibrium potential of the electrode–electrolyte interface, where the rates of oxidation and reduction reactions at the electrode surface are balanced, resulting in zero net current flow.

OCP is important in electrochemical research because it provides a baseline or resting potential of the system without perturbing it by applying current or voltage. It is a good indicator of the equilibrium state in the electrochemical cell. It is a crucial parameter to understand the thermodynamic stability and corrosion behavior of materials, monitor surface changes, and serve as a reference point for other electrochemical experiments like impedance spectroscopy or polarization resistance measurements.

Cyclic voltammetry (CV) is one of the most widely used electrochemical techniques. In a potentiostatic CV experiment, the potential applied to the working electrode (WE) is swept linearly back and forth between two defined limits while the resulting current from redox processes at the electrode surface is recorded. CV provides information on oxidation and reduction potentials, the number of electrons transferred, reaction kinetics, and the reversibility or irreversibility of electrochemical processes.

A CV plot shows current versus potential with characteristic peaks for oxidation (anodic peak) and reduction (cathodic peak). The peak positions relate to the redox potentials, while peak currents relate to concentration and kinetics. Additional details on the interpretation of the CV measurements can be found in dedicated electrochemistry textbooks. Please contact Metrohm Autolab if additional help is needed.

A reference electrode provides stable and well-known electrode potential against which the potential of the working electrode is measured. Its main purpose is to act as a known and reliable voltage reference in the cell which allows accurate and reproducible measurement of the working electrode's potential in an electrochemical cell. In this application note, we listed the most used reference electrodes, together with their range of use.

A counter electrode is used as current collector in the electrochemical cell. To keep the RE potential stable, it is not desired that the current will flow through the RE. Therefore, due to the high impedance of the electrometer (i.e., RE input resistance), the current is always flowing between the WE and the CE. It is important that the CE is made of an inert material so that it will not generate any by-products which can interfere with the investigated electrochemical system. Also, it is important that the surface area of the CE is larger than the area of the WE.

An Autolab potentiostat can be tested at any time by following the procedures described in the user manuals, by running the dedicated test measurements and diagnostic tools. It is important to perform these tests using the original Autolab test (or dummy) cell and the standard cell cables delivered with the Autolab potentiostat. In case of any doubts, please contact your local Metrohm Autolab support office for help and advice.

For all Metrohm Autolab potentiostats, the standard length of the cell cables is 1.5m. We test and guarantee our instrument specifications only when using the standard length cables. It is possible to order and use longer cables for all our instruments. Please inquire at your local Metrohm Autolab support office for further details.

Compliance Voltage: This refers to the maximum voltage that the potentiostat's internal circuitry can supply to the counter electrode to achieve and maintain the desired applied voltage at the working electrode versus the reference. Think of it as the instrument's power limit. If the electrochemical cell's resistance or the demands of the experiment require a voltage greater than the potentiostat's compliance limit, the instrument will indicate an "overload” meaning it cannot maintain the desired applied potential. A higher compliance voltage offers more flexibility so, advanced models — such as VIONIC, which offers a compliance voltage of ±50 V—are better suited for high-resistance or demanding electrochemical systems.

Applied Voltage (or Potential): This is the electrical potential (voltage) that the potentiostat is set to maintain or sweep at the working electrode relative to the reference electrode in your electrochemical cell. It's the desired experimental condition you are imposing on your system to drive a reaction or make a measurement.

A potentiostat is an analytical instrument used in electrochemistry to apply a controlled voltage between a working and reference electrode, while measuring the resulting current between the working and counter electrode. Potentiostats—often called electrochemical workstations—are essential for studying a wide range of electrochemical processes.They are widely used in applications such as:

• Energy

• Corrosion analysis

• Electrocatalysis

• Electrosynthesis

• Biosensor development

It can run electrochemical techniques like cyclic and linear sweep voltammetry, amperometry, coulometry, and electrochemical impedance spectroscopy (EIS).

Read our application notes and blog post to learn more.

Understanding linear sweep voltammetry and cyclic voltammetry

Electrochemical Impedance Spectroscopy

The key difference between a potentiostat and a galvanostat lies in what they control:

A potentiostat controls voltage and measures current while a galvanostat controls current and measures voltage. Both are commonly used in electrochemical experiments, and the choice depends on whether maintaining a constant potential (potentiostat) or a constant current (galvanostat) is required. All Metrohm Autolab instruments offer both potentiostatic and galvanostatic modes, providing flexibility for various electrochemical testing needs.

Potentiostatic mode is typically used when:

• The system impedance is high.

• The experiment requires sweeping the potential across a defined range, such as in cyclic voltammetry.

• The goal is to study reaction mechanisms, redox potentials, or electrochemical kinetics.

• The interest is in observing the current response to a controlled potential (e.g., for diffusion studies or Tafel analysis).

WP: How to characterize a catalyst? Cyclic voltammetry in action

Galvanostatic mode is typically used when:

• The system impedance is low such as battery research and testing.

• The experiment requires maintaining a constant current, as in electrolysis or electrodeposition.

Application note: Galvanostatic charge-discharge of a Li-ion battery with Autolab

Yes, it is possible to have longer cell cables with the Metrohm Autolab Potentiostats and galvanostats. Please contact your local Metrohm Autolab support office for more details.

Any K-type thermocouple is compatible with VIONIC while the Metrohm Pt1000 sensor is compatible with the pX1000 module which can be installed optionally in the Autolab AUT302N, AUT204 and Multichannel M101/M204 potentiostats. Please contact your local Metrohm Autolab support office for more details.

When the cell is switched off, there is no current flowing between the CE and the WE but the potential is still being measured between the RE and S.

In the case of cell isolation, there is no electronic connection between the cell and the electronics of VIONIC. This can occur when the cell protection is triggered or VIONIC is in error state. In this case, no power from an active cell can be delivered to VIONIC. Please see the INTELLO and VIONIC user manual for more details.

When any part of the electrochemical cell (including the cell vessel or the electrolyte) is connected to ground, the electrochemical measurements can be performed only with a potentiostat and galvanostat having a floating electronics. Otherwise, in other cases, the user of the non-floating mode is recommends for achieving optimal performance. VIONIC is equipped with a selectable floating operation mode.

Yes, it is possible to monitor the measured potential and/or current with an external device. Please contact your local Metrohm Autolab support office for more details.

Yes, the Metrohm Autolab rotators and motor controller used in the RDE, RRDE, RCE experiments are controlled from both INTELLO and NOVA software and are fully integrated in the software. Hydrodynamic data analysis is available in NOVA and can be used for measurements done in INTELLO and NOVA.

All Metrohm Autolab instruments are covered by 3 years warranty (some restrictions apply, please contact your local Metrohm Autolab support office). The instruments and software are supported for at least 10 years after the instrument stopped being manufactured.

Analyzing Electrochemical Impedance Spectroscopy (EIS) data is essential for understanding key electrochemical processes such as charge transfer, ion diffusion, and electrode surface behaviour. The measured EIS data are usually represented in Nyquist plots and Bode plots. The most common approach to EIS data analysis involves a combination of visual interpretation of these plots and equivalent circuit modelling. In this way, the experimental EIS data are fitted to a theoretical electrical equivalent circuit that best describes the electrochemical system under study.

The typical equivalent electrical components (equivalent elements) include: resistors (R), capacitors (C), inductors (L), constant phase elements (CPE or Q), Warburg impedance (W), among others.

Together with validation techniques like Kramers-Kronig transforms, EIS data can be effectively analyzed to gain valuable insights into the behavior of electrochemical systems. Having a robust but user friendly, flexible fitting tool is important for a accurate and efficient EIS data analysis.

A potentiostat/galvanostat is a high-precision instrument used to control and measure electrical parameters—specifically the potential and current—in an electrochemical cell. It is the core tool for performing electrochemical experiments such as cyclic voltammetry, chronoamperometry, and chronopotentiometry, ensuring accurate control over the applied potential or current.

In contrast, an electrochemical impedance analyzer is a specialized module or functionality often integrated into or added to a potentiostat/galvanostat. It enables the application of AC signals over a wide range of frequencies to measure the electrochemical impedance of the system. This technique—known as Electrochemical Impedance Spectroscopy (EIS)—provides detailed, frequency-dependent insights into electrochemical processes.

EIS data provide a detailed and mechanistic view of electrochemical systems, offering insights into the various sequential or overlapping processes occurring at the electrode–electrolyte interface, such as charge transfer, diffusion, double-layer charging, adsorption, and many others.

Choosing the right frequency range in an Electrochemical Impedance Spectroscopy (EIS) experiment is critical to ensure the accuracy and completeness of the data. The optimal frequency range depends on the electrochemical system and the specific processes being investigated, each of which is characterized by its own time constant.

High frequencies (typically 100 kHz to 1 MHz or higher) are used to probe fast processes with low time constants, such as:

• Solution resistance (Rs)

• Double-layer capacitance (Cdl)

• Ion conduction within solid electrolytes (e.g., bulk ion mobility in solid-state batteries)
  

Mid-range frequencies (e.g., 1 Hz to 10 kHz) will give an indication of :

• Charge transfer kinetics (Rct)

• Adsorption/desorption phenomena
  

Low frequencies (below 1 Hz, down to mHz range) are essential for analyzing slow processes with large time constants, including:

• Diffusion-limited transport (represented by Warburg impedance)

• Film formation

• Corrosion processes

• Battery degradation mechanisms

For an Electrochemical Impedance Spectroscopy (EIS) measurement to be valid and interpretable using impedance theory, several fundamental conditions must be met:

Linearity: The electrochemical system must respond linearly to the applied AC signal. This means that if the amplitude of the input signal is doubled, the output response should also double, without generating harmonics. Only the fundamental frequency should be present in the response signal.

Stability (Stationarity / Time-Invariance): The electrochemical system must be in a steady state throughout the entire measurement. This means its fundamental properties (e.g., surface state, concentration profiles, film thickness, temperature) should remain constant.

Causality: The measured response of the system must be solely and directly caused by the applied AC perturbation, i.e., there should be no external influences that distort the relationship between the input and output signals.

Finiteness: The real and imaginary components of the measured impedance must have finite values across the entire theoretical frequency range. This implies that at very high and very low frequencies, the impedance tends towards a constant value or a predictable behaviour.

• Choose an AC amplitude that is small enough to keep the system’s response linearly, but large enough to get a clean and measurable signal.
• Stabilize the system: Allow the system to reach equilibrium before starting the measurement and ensure it remains unchanged during the scan.
• Perform measurements in a well-shielded and controlled environment.
• Validate your data, ideally using Kramers-Kronig transforms, and inspect Nyquist and Bode plots for smoothness and consistency.

Yes. EIS measurements above 1 MHz require the use of the special hardware (VIONIC or ECI10M module) together with specially designed cell cables. The EIS measurements above 1 MHz can be done in potentiostatic mode.

Spectroelectrochemistry is a powerful technique that combines electrochemical and spectroscopic measurements. It is used to study chemical processes—particularly redox reactions—in real time and in situ, providing a more comprehensive understanding of a system than either electrochemistry or spectroscopy alone. Electrochemical measurements offer insights into electron transfer, kinetics, and thermodynamics, while the spectroscopic measurements can bring complementary information on the molecular and structural details of the reactants, intermediates and interfaces.

By simultaneously combining the strengths of electrochemistry and spectroscopy, spectroelectrochemistry offers the following benefits:

• Combines complementary Information from 2 different techniques: Electrochemistry provides information about electron transfer, kinetics, and thermodynamics, while spectroscopy gives molecular and structural insights.
• Real-Time, In Situ Monitoring: direct observation of changes in chemical species without needing to remove samples for separate analysis. This is important for studying transient or unstable species.
• Molecular Identification and Characterization: spectroscopic "fingerprints" of electrochemically generated species allow the identification of short-lived intermediates.
• Mechanism Elucidation: By tracking the evolution of different species under defined electrochemical conditions, it is possible to elucidate the mechanisms of electron transfer reactions.
• Improved Selectivity and Sensitivity: The combination of electrochemical and optical signals enhances both selectivity and sensitivity—depending on the spectroscopic method used—enabling the detection of low concentrations of target species.
• Study of Surface Phenomena: Many spectroelectrochemical techniques are particularly sensitive to adsorbed species at the electrode surface, providing insights into adsorption/desorption processes, molecular orientation, and the formation of surface films.
• Versatility in Applications: Spectroelectrochemistry can be used in many applications such as fundamental, materials science, electrocatalysis, energy storage (e.g., batteries, fuel cells), and (bio)sensors.

Spectroelectrochemistry is used across diverse fields, offering simultaneous electrochemical and spectroscopic insights for a wide range of applications.

• Fundamental chemical research, for the elucidation of reaction mechaininisms

• Material research, for studying conducting polymers, electrochromic materials, namomaterials, organometallic compounds

• Electrocatalysis, for identifying reaction pathways, intermediates and active catalytic sites

• Energy storage and conversion, for material characterization, electrolyte studies and research on photovoltaics

• Biological and biochemical systems and sensors, for biomolecule characterization and biochemical processes

• Environmental studies on pollutant detection and quantification and water treatment

The main benefits of having an open hyphenated spectroelectrochemical system are:

• Flexibility in instrument selection: Choose the potentiostat and spectrometer that best match your specific application requirements.

• Independent instrument use: Use the potentiostat or spectrometer as stand-alone equipment when needed—ideal for maximizing lab efficiency.

• Simultaneous, synchronized measurements: Electrochemical and spectroscopic data are captured in real time and synchronized via a hardware trigger cable for precise correlation.

• Powerful electrochemical software: (i.e., NOVA or INTELLO) with user friendly synchronization setup and intuitive workflow

• Reliable local support: Benefit from professional, responsive support through Metrohm’s global network and local teams.

No, VIONIC does not have any optional modules and all functionality is included. VIONIC is an all-in-one potentiostat.

Yes, it is possible to connect VIONIC to a network. The number of connected VIONICs depends on the capacity and performance specifications of your network. Measurements can be performed simultaneously on multiple VIONIC instruments by using the same computer running the INTELLO software. We recommend to contact your IT support for preparing the network settings for connecting VIONIC to the network.

The number of connected VIONICs depends on the capacity and performance specifications of your network. Measurements can be performed simultaneously on multiple VIONIC instruments by using the same computer running the INTELLO software.

The on-board memory of VIONIC can save up to 10 million datapoints, depending on the type of the measurement. When disconnecting the computer from VIONIC during a run, INTELLO will notify the user how long the experiment can run without the computer being connected to VIONIC.

Yes, the IP address can be changed and fixed. We recommend to contact your IT administrator for more information and help.

When a VIONIC is connected to the network, the DHCP server will create a unique IP address for each VIONIC connected to the same network.

No, there is no licensing necessary to install and run INTELLO. For a free download, the user must register to access to download page. All updates are also free of charge.

INTELLO is the new control and data acquisition software which works with the VIONIC potentiostats. NOVA is the control and data acquisition software which works with the AUT302N, AUT204, AUT101, Autolab IMP as well as with the M101/M204 multichanned potentiostats. The 2 software packages are not compatible with each other but data measured with INTELLO can be exported directly to NOVA, whenever needed.

Yes, a backup of the INTELLO database can be created ant anytime from the homepage of the INTELLO software. The database can be restored from any backup file saved on the computer by using the restore button.

Yes, it is possible to copy and paste commands, group of commands and entire procedure sequences in both NOVA and INTELLO. Nevertheless, it is not possible to copy and paste commands from NOVA into INTELLO nor the other way around.

Yes, INTELLO includes a complete library of default procedures covering all electrochemical techniques. These default procedures are ready to use and editable.

INTELLO allows both routine and exploratory way of working: use of the main parameters to change only the value of the parameters which should be changed but also editing a sequence, using advance commants such as repetition loops, automatic export commands and others.

Yes, it is possible to copy and paste commands, group of commands and entire procedure sequences in both NOVA and INTELLO. Nevertheless, it is not possible to copy and paste commands from NOVA into INTELLO nor the other way around.

No, there is no licensing necessary to install and run NOVA. All potentiostats sold in the last 15 years already have the NOVA license installed in the embedded processor. For very old Autolab instruments, a license might be required which can be obtained free of charge from your Metrohm Autolab support office. NOVA can be downloaded and installed free of charge from the NOVA | Metrohm page.

Yes, NOVA includes a complete library of default procedures covering all electrochemical techniques. These default procedures are ready to use and editable. For convenience, there is also group of EC Fundamentals procedures including the most used standard procedures for every technique in electrochemistry education.