The Capacity of Polarized Platinum Electrodes in Hydrochloric Acid

Electrode capacity of platinum electrodes was measured in hydrochloric acid by an impedance bridge. Capacity was determined as a function of polarizing voltage, concentration, and frequency. It appears that electrode capacity cannot be interpreted exactly in terms of a simple equivalent circuit. Capacity, calculated as a series circuit, goes through a minimum at 20 μf/cm 2 and +0.75 volt on the N calomel scale. Comparison of platinum with mercury at the minima indicates that the difference in potential, 1.85 volts, corresponds to the contact potential difference.