How to Choose a Potentiostat
A potentiostat is a device that controls the potential between a pair of electrodes whilst measuring the resulting current flow.
Contents
Operating Requirements
When choosing a potentiostat you need to have some idea of the voltage and current limits within which you wish to operate.
Most potentiostats offer applied potentials (voltages) of up to ±10 V. Sensitive potentiostats designed for accurate measuring of small currents (nanoamperes or less) typically offer maximum currents of up to 10 mA. Large current potentiostats (1 A or more) often do not provide small current ranges (less than microamperes), or else they are very expensive, or require 'headstage' current amplifiers. Analytical chemists usually require a mid-range potentiostat (nanoamperes to 100 mA or so). Electrosynthesis experiments usually require currents in excess of 10 mA, and a maximum current of 1 A, or more, is often useful if you need to generate a few grams of material in a reasonable timeframe.
Number of Electrodes
Two-Electrode Potentiostats
A two-electrode potentiostat uses a working and counter electrode. A disadvantage of this arrangement is that if the electrodes are further apart than the resistance between them increases and the current decreases. Thus reproducible results can be hard to achieve if electrode surface area, or separation distance, varies. Polarographic oxygen, peroxide, and nitric oxide electrode meters are all examples of two-electrode potentiostats. Note that in each of these cases the electrodes (anode and cathode) are usually built into a single probe body so that the orientation and distance between the electrodes is held constant from one experiment to the next.
eDAQ two-electrode potentiostats are:
- EP352 Biosensor isoPod for use with e-corder systems
- EP354 USB dO2 isoPod for use with e-corder systems
- EP355 USB Nitric Oxide isoPod for use with e-corder systems
Three- and four-electrode potentiostats can often be used as two-electrode potentiostats by connecting the voltage sensing (reference electrode) inputs to the appropriate current passing (auxiliary or working electrode) inputs, see below.
Three-Electrode Potentiostats
This is typically what people mean when they say a 'potentiostat'. With a 'three-electrode' potentiostat the potential is monitored between reference and working electrodes that are in close proximity, while the potential of a relatively distant auxiliary electrode is adjusted. The current flow is measured between the working and auxiliary electrodes. This has the advantage that no current actually passes through the reference electrode, so there is no electrolytic reaction occurring there, and thus the reference electrode potential can remain constant throughout the experiment. A consequence of this arrangement is that the potential between the working and auxiliary electrodes (the 'compliance' potential, which is usually not reported) can be many times the applied potential (depending on electrolyte resistance and distance between the electrodes). By attaching the potentiostat reference and auxiliary inputs to the same 'counter' electrode, a three-electrode potentiostat can be used as a two-electrode potentiostat. The following eDAQ Potentiostats below can be operated as three-electrode potentiostats.
Bipotentiostats and Multiple Working Electrodes
A bipotentiostat system features a reference and auxiliary electrode, and two working electrodes, whose potentials can be independently adjusted while the current flowing through them is monitored. This principle can be extended to any number of working electrodes, for example the
- EA164 QuadStat controls up to four working electrodes, while the
- EA362 Dual Picostat is a bipotentiostat (ie can control up to two working electrodes).
Typically the potential between the reference and first working electrode is controlled and the potentials of subsequent working electrodes are offset relative to the first electrode to achieve the desired effect. These potentiostats are often used in 'electrochemical nose' systems.
Four-Electrode Potentiostats
The term 'four-electrode potentiostat' is usually reserved for a device with two reference ('voltage sensing') electrodes and two working ('current passing') electrodes. The potential difference between the two reference electrodes is controlled while the current flow between the two working electrodes is monitored. These potentiostats are commonly used to measure the current flow across a membrane separating two compartments, or across the interface of two immiscible solvents (an ITIES experiment). The
- EA362 Dual Picostat can be used in four-electrode mode, while the
- EA167 Dual Reference Adaptor can convert most three electrode potentiostats into a four-electrode system.
Galvanostats
Some potentiostats can be operated as galvanostats. In this case the current flow is controlled while the potential is monitored. Note that you cannot control both the current and the potential simultaneously unless you have a variable load! eDAQ potentiostats that work as galvanostats are:
- ER466 Integrated Potentiostat
- EA163 Potentiostat (as well as its EA161 and EA160 predecessors)
Software
Stand-alone potentiostats can be operated without a computer, and while there are a few models on the market, most modern potentiostats are operated via software from a computer.
Check that the software offers the electrochemistry techniques you require, or whether you need extra, optional software. Often overlooked is the ease of operation of the software, and especially how the software saves experiments to the computer hard disk. For example, if each separate experiment is saved as a separate file then you will soon have hundreds of files on the computer hard disk to sort through every time you need to review a result. Some software offers library functions to do this while other software can multiple experiment into a single disk file for ease of access.
eDAQ Potentiostat Systems
eDAQ offer a variety of potentiostat systems for a variety of experimental requirements. The table below gives an indication of these.
| Name | EChem Startup System | EChem Startup System with High Bandwidth Potentiostat | Dual Picostat Bundle | QuadStat Bundle | Advanced Electrochemistry System |
|---|---|---|---|---|---|
| Product Code | ER461 | ER7163 | ER7162 | ER7005 | ERZ101 |
| Products Included | |||||
| Number of Channels | 1 | 1 | 2 (bipotentiostat) | 4 (quadpotentiostat) | 1 |
| Modes |
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| Current Ranges |
±100, 50, 20, 10, 5, 2, 1 mA ±500, 200, 100, 50, 20, 10, 5, 2, 1 µA ±500, 200, 100, 50, 20 nA |
±100, 50, 20, 10, 5, 2, 1 mA ±500, 200, 100, 50, 20, 10, 5, 2, 1 µA ±500, 200, 100, 50, 20 nA |
±10, 5, 2, 1 µA ±500, 200, 100, 50, 20, 10, 5, 2, 1 nA ±500, 200, 100, 50, 20, 10, 5, 2, 1 pA |
±10, 5, 2, 1 mA ±500, 200, 100, 50, 20, 10, 5, 2, 1 µA ±500, 200, 100, 50, 20, 10, 5, 2, 1 nA ±500, 200 pA
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±100, 50, 20, 10, 5, 2, 1 mA ±500, 200, 100, 50, 20, 10, 5, 2, 1 µA ±500, 200, 100, 50, 20 nA |
| Electrochemistry Techniques |
CV, LSV, DPV, SWV, NPV, RPV, LSSV, DPSV, SWSV, NPSV, MPV, DPA, CPE, DNPV, DBPV, CNA, CNC, CNP, PSA, CTPE, CCE, electrosynthesis, RDE*, QCM* |
CV, LSV, DPV, SWV, NPV, RPV, LSSV, DPSV, SWSV, NPSV, MPV, DPA, CPE, DNPV, DBPV, CNA, CNC, CNP, CTPE, CCE, electrosynthesis, RDE*, QCM* |
CV, LSV, DPV, SWV, NPV, RPV, LSSV, DPSV, SWSV, NPSV, MPV, DPA, CPE, DNPV, DBPV, CNA, CNC, CNP, CTPE, CCE, electrosynthesis, RDE*, QCM* |
CNA, CNC, CNP, CTPE, CCE, electrosynthesis, RDE*, QCM* CV and LSV with Chart software |
EIS Electrochemical Impedance Spectroscopy CV, LSV, DPV, SWV, NPV, RPV, LSSV, DPSV, SWSV, NPSV, MPV, DPA, CPE, DNPV, DBPV, CNA, CNC, CNP, CTPE, CCE, electrosynthesis, RDE*, QCM* |
| Typical Applications |
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Acronyms for Electrochemistry Techniques
CV cyclic voltammetry; LSV linear sweep voltammetry; DPV differential pulse voltammetry; SWV square wave voltammetry; NPV normal pulse voltammetry; RPV reverse pulse voltammetry; LSSV linear sweep stripping voltammetry; DPSV differential pulse stripping voltammetry; SWSV square wave stripping voltammetry; NPSV normal pulse stripping voltammetry; MPV multipulse voltammetry; DPA differential pulse amperometry and double pulse amperometry; CPE constant potential electrolysis, DNPV differential normal pulse amperometry; DBPV double pulse voltammetry;
CNA chronoamperometry; CNC chronocoulometry; CNP chronopotentiometry; PSA potentiometric stripping analysis; CTPE controlled potential electrolysis; CCE controlled current electrolysis; RDE rotating disk electrode*; QCM quartz crystal microbalance*
RDE and QCM require additional third party equipment*
