The electrochemical oxidation of carbon black catalyst supports is recognized as a durability challenge to the commercialization of low-temperature fuel cells in the transportation sector. An investigation of the effect of the transient potentials experienced in this environment is presented. The exposure of carbon black to square wave potential cycling results in an oxidation process different than the constant potential hold historically used to characterize this corrosion process. The differences are characterized using the liquid half-cell and single fuel cell testing, coupled with electrochemical techniques and online gas analysis. Although cyclic voltammetry and X-ray photoelectron spectroscopy are unable to quantify significant differences in the surface oxide chemistry, online gas analysis measurements demonstrate different corrosion activities. (c) 2008 The Electrochemical Society.