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# Potentiostat

A potentiostat is a control and measuring device that, in an electrolytic cell, keeps the potential of the working electrode at a constant level respect to the reference electrode. It consists of an electric circuit which controls the potential across the cell by sensing changes in its resistance, varying accordingly the current supplied to the system: a higher resistance will result in a decreased current, while a lower resistance will result in an increased current, in order to keep the voltage constant. It is a simple application of Ohm's law

${R} = {U \over I}$

As a result, the variable system resistance and the controlled current are inversely proportional

$I_o={U_c \over R_v}$
• Io is the output electrical current of the potentiostat
• Uc is the voltage that is kept constant
• Rv is the electrical resistance that varies

In a potentiostatic coulometry experiment, the cathode is usually a platinum electrode with a large surface area or a mercury pool, although other particularly reactive electrodes can be used in rare circumstances.

The functionality of a potentiostat can be extended by virtual instrumentation: in virtual instruments the potentiostat is used as an actuator.