The passive films that form on Alloy C22 and on unalloyed chromium and nickel have been investigated by a combination of anodic and cathodic polarization tests, electrochemical impedance spectroscopy (EIS), and Mott-Schottky measurements. The tests were conducted at room temperature in aqueous borate buffer (pH 8.4). The films on chromium and Alloy C22 exhibit n-type behavior and the film on nickel exhibits p-type behavior. The flatband potentials of chromium, Alloy C22 and nickel are -1.0Vą 0.1, -0.48 Vą0.1 and ? +0.85V, respectively (all are reported with respect to SHE). The flatband potentials predict that the rates of the electrochemical reduction of H+ should increase significantly at potentials less than -1.15V for chromium and -0.58V for Alloy C22. Both results are in very good agreement with the cathodic polarization curves of chromium and Alloy C22. The cathodic polarization curve of nickel exhibits an abrupt increase in current density at potentials below -0.65V. The Mott-Schottky measurements indicate the most likely explanation for the high current density is that the thickness of the passive film of nickel at cathodic potentials is below the limiting thickness for tunneling.