Potentiostat:

A potentiostat is an electronic device that manages the potential of the working electrode at a constant level associative to a reference electrode. Figure is a schematic diagram of a potentiostatic coulometry.

Let consider the circuit of the diagram: The two resistances within the diagram correspond to resistances in two categories of the electrochemical cell.  Here R_s is the cell resistance among the counter electrode and the tip P of the reference electrode and R_u is the so-called uncompensated cell resistance that is the cell resistance among P and the working electrode. Since of the extremely high resistance of the inputs to the operational amplifier, there is no current in the feedback loop to the inverting input.  An operational amplifier works to keep E₁ and E₂ equivalent in the non- inverting configuration and the cell current IC is supplied through the operational amplifier to manage this condition. If we assume the path among the inverting input and the circuit general at the outcome, we see that

E₂   = E₁   = E_SCE   + I_CR_u     = E_SCE + E_C

Here in the equation E_C is the cathode potential and is equivalent to the potential difference among P and the working electrode. Because E₁ and E_SCE are constant, I_CRU must also be constant. In during of electrolysis, if R_U and R_S modifies, the operational amplifier output voltage changes within such a way so as to manage E_C = I_CR_u at a constant level.  If R_u reduces, the operational amplifier output voltage increases to manage E_C constant. If R_u increases as a result of an increase within the cell resistance or because of concentration polarisation, the outcome voltage of the operational amplifier decreases, that leads to a decrease in I_C.