Interpretation of measured polarization resistance at a solid electrode/electrolyte interface

Nonuniform current distribution at an electrode surface can complicate the measurement of ohmic and polarization resistances. The problem is investigated theoretically for a rectangular cell with electrodes of different size placed symmetrically at the opposite surfaces of the electrolyte, typical for solid state electrochemical cells. The results show that the error in the measured polarization resistance is generally not expected to be large unless the electrode reaction is very fast, or the electrolyte conductivity very low. However, kinetic limitations at the counter electrode may cause distortion of the measured overpotential in cells with thin electrolytes, leading to significant errors in the measured polarization resistance. The overpotentials at the two electrodes become experimentally indistinguishable. In such cases, the use of sufficiently thick electrolytes and/or sufficiently small working electrodes in relation to the counter electrode may alleviate the problem.