Cell Connection Scheme

All Zahner potentiostats and power potentiostats follow the same cell connection scheme (4-electrodes connection scheme). The 4-electrode connection scheme includes connections for working electrode (WE), working electrode sense (WEs), reference electrode (RE), and counter electrode (CE). These connections are specified by their color code, WE: black, WES: blue, RE: green, and CE: red. To minimize interference, stray- and mutual inductance, the red and black power cables (current carrying cables) must be twisted together, and the green and blue sense cables must be twisted together before the measurement. Twisting is not shown in the schematic below.

4-electrode connection scheme. The current is carried through the black (WE) and red (CE) wires. The voltage is measured between the green (RE) and blue (WEs) wires.

For large current flow the object must be connected with a four-electrode connection scheme in order to minimize the error margin in the measurement.

Contact Resistance

This figure shows a typical electrical wire used to connect the potentiostat with the test object. The resistance of the wire can be divided in to two parts (wire resistance and contact resistance).

Typical electrical wire used to contact potentiostat with the test object. Resistance of the electrical wire is divided in to two different parts. 1) contact resistance and 2) wire resistance.

Two Electrode Cell Connection Scheme

Here a 2-electrode cell connection scheme is used for measurements on a cell. The WE and WEs cables are joined together to make one electrode connection and RE and CE cables are joined together to make the second electrode connection.

The measured impedance (between RE and WEs electrodes) is the sum of the cell impedance and both contact impedances.

This means that the measured voltage is the sum of the object voltage and the two voltage drops across the contact resistances.

Four Electrode Cell Connection Scheme

The advantage of a 4-electrode connection scheme is illustrated here. With the WEs and RE being directly connected to the cell, the contact resistance for the WE and CE can be ignored as they don’t affect the voltage value (not possible with 2-electrode connection scheme).

Four-electrode connection scheme and equivalent circuit diagram for a 2-electrode pouch cell.

For optimum measurement results, the WE and CE as well as the RE and WEs cables must be twisted together (not shown in the image).

Due to the high input impedance of the potentiostat the input current to the sense inputs is negligible. This means that there are no voltage drops across the contact resistances of the Sense connections. With the 4-electrode connection scheme, the contact resistances are in most cases not significant in the measured cell impedance. This is only true if the cell resistance of the test object is much smaller than the input resistance of the potentiostat. The input impedance of the potentiostat is provided in the specifications.