Probing the dealloying critical potential morphological characterization and steady-state current behavior

One of the important characteristics of dealloying systems is roe location of the critical potential which marks the transition from a " passivated" alloy surface to the sustained formation of a bicontinuous porous structure. A steady-stale method for accurately determining the dealloying critical potential is compared with the more traditional approach of extrapolation from anodic polarization data. Misinterpretation in the literature of short-term potential hold data is discussed in light of these results. The dealloying critical potentials for Ag0.80Au0.20, Ag 0.75Au0.25, and Ag0.70Au0.30 were 0.80, 0.94, and 1.01 V (normal hydrogen electrode), respectively. Ute polarization data is shown to overestimate these values by 100 mV. Morphological investigations confirm the presence of porosity for a potential hold only 10 mV above the critical potential. For alloys with compositions between 70-80 atom % Ag, the critical potential increased by 20 mV per atom % decrease in the Ag composition. Long-term current fluctuations were observed during me potential hold experiments that suggest the presence of a surface corrosion instability occurring over 1-5% of the total surface area. © 2005 The Electrochemical Society. All rights reserved