Deleterious effects of interim cyclic voltammetry on Pt/carbon black catalyst degradation during start-up/shutdown cycling evaluation

Abstract

We investigated the deleterious effects of the common practice of measuring cyclic voltammetry (CV) on Pt/CB catalysts during long-term start-up/shutdown cycling longevity evaluation of the type used in standard protocols used in the fuel cell automotive industry. These “interim” CV measurements, which are generally conducted after a certain number of potential cycles to evaluate the electrochemically active surface area (ECSA) of Pt catalysts, result in depassivation of the passive layer formed on Pt particles during the cycling tests; this allows the platinum to again catalyze the carbon corrosion effectively during the potential cycling. This phenomenon causes additional corrosion of the CB support. The measured ECSA loss, cycle half-life N1/2 (N value at which the ECSA value was estimated to reach 1/2 of the initial value) and IR-free polarization curves show that the potential cycling, followed by intermittent CV measurements on the same electrode, termed consecutive cycling, brings about severe lifetime reduction and cell performance degradation of the Pt/CB catalyst. The quinone-hydroquinone (Q-HQ) oxidation current supports the idea that this degradation can be ascribed to severe corrosion of the CB support by the consecutive cycling. In addition, SEM and TEM images confirm that the interim CV measurements lead to severe degradation of the Pt/CB catalyst due to dissolution of platinum and carbon support corrosion. Thus, from the viewpoint of practical operation, the catalyst degradation is overestimated with this testing protocol.