In this presentation, we will summarize the results of a kinetic study of two possible degradation mechanisms of PGM-free ORR catalysts at a high fuel cell voltage, greater than 0.8 V. The models accounting for different plausible degradation paths, fitted to the experimental data, will be presented and discussed. The models yield different relationships between the kinetic current density and reaction time giving rise to either exponential or logistic decay plots. The experimental results are better represented by the logistic decay, suggesting an autocatalytic degradation mechanism. This in turn implies that, in parallel to the four-electron ORR, the intermediates formed in the side reactions are likely responsible for the degradation of PGM-free catalysts. The measurements of the CO2 and fluoride amounts in the cathode effluent, as well as the active-site quantification by molecular probes will be also presented to verify the proposed catalyst degradation mechanism.
Acknowledgements
Financial support for this research by DOE-EERE through Fuel Cell Technologies Office is gratefully acknowledged.
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