Working electrodeThe electrode where the reaction under study takes place. Its potential is controlled and the current through it is measured.
Reference electrodeIt keeps a constant potential to measure against. Almost no current flows through it.
Counter electrode (auxiliary)It completes the circuit so that current can flow. It is also called the auxiliary electrode.
SolutionThe conducting liquid that the three electrodes dip into.
Electrochemical cellThe vessel with its solution and its three electrodes.
PotentiostatThe instrument that controls the cell through three leads. It holds the working electrode at a set potential against the reference electrode.
Block diagram 4
Control amplifierIt drives current into the cell through the counter electrode. It adjusts its output until the measured voltage matches the signal.
ElectrometerIt measures the voltage of the reference electrode. It draws almost no current, and its output is fed back to the control amplifier.
Current-measuring resistorThe cell current flows through this resistor. The voltage drop across it measures the current.
Signal sourceIt supplies the voltage that the cell is made to follow.
How this list was compiled: Every name checked on 2026-10-03 in at least two texts. (1) Wikipedia, text only: Potentiostat (the potentiostat holds the working electrode at a constant potential against the reference electrode by tuning the current at the auxiliary electrode; the control amplifier keeps the voltage between reference and working electrode as close as it can to the input source's voltage; the current is measured as a voltage drop over a series resistor, which lies in series with the counter electrode; the reference electrode feeds a high-impedance electrometer; the solution resistance), Auxiliary electrode, Working electrode and Reference electrode. (2) An instrument maker's application note on potentiostat fundamentals (working, reference and counter or auxiliary electrode; the electrodes immersed in a conductive solution; electrodes, solution and container together as the electrochemical cell; four blocks: the electrometer, the current-to-voltage converter with its current-measurement resistor, the control amplifier, the signal; its schematic puts that resistor between the working electrode and ground). (3) DePauw University, D. Harvey, Analytical Chemistry 2.1, section 11.1 Overview of Electrochemistry (working electrode; a reference electrode whose potential remains constant; an auxiliary electrode to complete the circuit; the potentiostat; the electrochemical cell). (4) D. D. Macdonald, Transient Techniques in Electrochemistry (1977), read through full-text search (the schematic of a potentiostat with its control amplifier, current follower and voltage follower, and the counter, working and reference electrodes). A block only one of them names is left out. The drawing is wired as source 1 describes it. Licence: own work
The drawing: Drawn for this site on 2026-10-03 by script from plain geometry. Own work, nothing traced. Licence: own work
How it works
This block diagram of a potentiostat and a 3-electrode cell comes in two views: the cell with its three electrodes, and the circuit that controls it. Study the ten names, then quiz yourself.
Read the full guide
The cell
Three electrodes dip into one solution. The reaction under study happens at the working electrode. The reference electrode keeps a constant potential to measure against. The counter electrode completes the circuit, so the current flows between it and the working electrode.
The block diagram
A signal source sets the voltage wanted. The control amplifier drives current into the cell through the counter electrode. A measuring resistor in series with the cell turns that current into a voltage. The electrometer reads the reference electrode and feeds its voltage back to the amplifier, which adjusts until the two voltages match.
Questions and answers
What are the three electrodes in a three-electrode cell?
The working electrode, where the reaction under study takes place; the reference electrode, which keeps a constant potential; and the counter electrode, also called the auxiliary electrode, which completes the circuit.
What does a potentiostat do?
It holds the working electrode's potential at a set level against the reference electrode by tuning the current at the counter electrode, and it measures that current.
Why does the cell need a reference electrode?
Almost no current flows through the reference electrode, so its potential stays constant. The working electrode's potential is measured against it while the current passes through the counter electrode.
How does a potentiostat measure current?
The cell current passes through a resistor inside the instrument, and the voltage drop across that resistor measures the current. This drawing puts the resistor in the counter electrode's lead; other instruments measure on the working electrode's side.