Cathode contamination electrochemical polarization

Figure 13.10. DMFC performance losses caused by average (left) and extreme (right) contamination of the cathode by ruthenium crossover. The polarization plot for a DMFC with a Pt-Ru cathode, instead of a Pt cathode, is shown for reference in the left-hand graph. Cell temperature 75 °C [64]. (Reproduced by permission of ECS—The Electrochemical Society, from Zelenay P. Performance durability of direct methanol fuel cells.)...

High electrochemical activity and contamination tolerance. An eleetroeatalyst should be of high intrinsic activity, to diminish electrochemical reaction polarization and enhance energy conversion effieiency. More specifieally, the anode catalyst should have the ability to resist detrimental by-products such as CO and other intermediates that poison the active reaction surface the cathode catalyst should have the ability to restrain crossover methanol oxidation when liquid methanol is seleeted as the fuel. 

Figure 23.14. Impact of ruthenium on oxygen reduction performance (a) CO stripping scans for the cathode and anode, (b) steady-state anode polarization plots before and alter contamination of the eathode, (c) H2-air steady-state polarization curves, and (d) DMFC steady-state polarization curves. Methanol concentration 0.3 M, anode potential during contamination 1.3 V vs. hydrogen counter/quasi-reference electrode, cell temperature 75 °C [65]. (Reprinted by permission of ECS— The Electrochemical Society, from Piela P, Eickes C, Brosha E, Garzon F, Zelenaya P. Ruthenium crossover in direct methanol fuel cell with Pt-Ru black anode.)...

Figure 9-3. The schematic shows electrochemical corrosion processes associated with ionic contamination on circuit boards and other devices with copper conductors. In the presence of atmospheric moisture, contaminant residues like sodium chloride form sodium ions (positive) and chloride ions (negative). Current flows between metal lines due to migration of ions to electrodes of opposite polarity. For many metals, the anode corrodes when the potential becomes sufficiently positive. The anode metal dissolves and metal ions migrate towards the cathode where they may be redeposited.

---