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was injected into the cathode air stream, and Co 2+ contamination became more severe with decreasing temperature. To investigate in detail the mechanism of Co 2+ poisoning, AC impedance was monitored before and during Co 2+ injection, revealing that both charge transfer and mass transport related processes deteriorated significantly in the presence of Co 2+ , whereas membrane conductivity decreased to a lesser extent. Surface cyclic voltammetry and contact angle measurements further revealed changes in physical properties, such as active Pt surface area and hydrophilicity, furthering our understanding of the contamination process.Crown

A new model is proposed to describe the non-Arrhenius conductivity observed in a series of optimized fast ion-conducting silver thioborosilicate glasses. Its essential feature is that the mobile cations are thought to conduct from one open site to the next open available site and, in this process, naturally by-pass filled or unavailable sites. The thermal excitation of cations out of their equilibrium sites is taken to be the mechanism for generating the open and available anion sites. Hence, the mean free path for a drifting cation between open available sites is directly proportional to the activated carrier concentration and is therefore a strong function of temperature. There is also a weak temperature dependence for the mean free path that arises because the capture cross section for a drifting cation by a stationary anion trap varies with drift velocity, e.g. the momentum of a fast cation allows it to closely approach an anion trap while avoiding capture or back scattering. The capture cross section of a cation by an anion trap is large because the interaction is electrostatic rather than geometric in origin. The model is shown to be in good agreement with all of our experimental data for silver thioborosilicate glasses and all model parameters are physically defined and reasonable in value. The model predicts a simple high-temperature conductivity dependence that is not exponential in nature. The model is also proposed to be valid for other materials such as crystalline conductors.

The oxygen reduction reaction (ORR) catalyzed by Pt was studied in the presence of Co 2+ using cyclic voltammetry (CV), rotating disk electrode (RDE), and rotating ring-disk electrode (RRDE) techniques in an effort to understand fuel cell cathode contamination caused by Co 2+ . Findings indicated that Co 2+ could weakly adsorb on the Pt surface, resulting in a slight change in ORR exchange current densities. However, this weak adsorption had no significant effect on the nature of the ORR rate determining steps. The results from both RDE and RRDE indicated that the overall electron transfer number of the ORR in the presence production. The fuel cell performance drop observed in the presence of Co 2+ could be attributed to the reduction in overall electron transfer number and the increase in H 2 O 2 production. Higher production could intensify the attack by H 2 O 2 and its radicals on membrane electrode assembly components, including the ionomer, carbon support, Pt particles, and membrane, leading to fuel cell degradation.Crown

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