A new method for measuring the Faradic resistance of a single electrode-electrolyte interface.

A new method is described for measuring the Faradic resistance of a single electrode-electrolyte interface. The method employs a test (monopolar) electrode, a potential-sensing electrode and a large reference (indifferent) electrode, along with a constant-current source capable of providing a step function of current. The method was used to measure the Faradic resistance of a 0.1 cm2 platinum electrode in contact with saline (p = 150 ohm-cm) at room temperature. It was found that for both a positive and negative current pulse, the Faradic resistance decreased almost hyperbolically with increasing current density. When the reciprocal of the Faradic resistance (Gf) was plotted versus current density and the data were fit to a polynomial curve, the results showed that for the positive pulse Gf = 0.009 + 0.05J - 0.0001J2; (SEE = 0.117); for the negative pulse, Gf = 0.007 + 0.067J - 0.0001J2; (SEE = 0.028); where Gf is in millisiemens and J is in mA/cm2 for this 0.1 cm2 electrode. These relationships permit estimating the Faradic resistance (Rf) for zero current density. For the positive pulse, Rf = 111 kilohms and for the negative pulse Rf = 143 kilohms. The method is applicable to the measurement of the Faradic resistance of a wide variety of metal electrodes.