Principles of Cell Operation

When an electric field is applied to two electrodes in an electrolytic solution, anions in the solution move toward the anode electrode and cations toward the cathode electrode. The number and the velocities of the ions in the bulk electrolyte determine the resistance of the solution. The ionic mobilities, or the velocity of the ion per unit electric field, depend on the charge and size of the ion, the temperature and type of solution medium, and the ionic concentration. 

As the potential that is applied across the electrodes is increased, the ionic velocities increase. Thus, the detector signal is proportional to the applied potential. This potential can be held to a constant value or it can oscillate to a sinusoidal or pulsed (square) wave. Cell current is easily measured however, the cell conductance (or reciprocal resistance) is determined by knowing the potential to which the ions are reacting. This is not a trivial task. Ionic behavior can cause the effective potential that is applied to a cell to decrease as the potential is applied. Besides electrolytic resistance that is to be measured, Faradaic electrolysis impedance may occur at the cell electrodes resulting in a double layer capacitance. Formation of the double layer capacitance lowers the effective potential applied to the bulk electrolyte. 

As the potential that is applied across the electrodes is increased, the ionic velocities increase. Thus, the detector signal is proportional to the applied potential. 

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