Factors Controlling the Less Noble Metal Retention in Nanoporous Structures Processed by Electrochemical Dealloying

A study of the dealloying behavior of Au0.25Ag0.75 alloy in solutions with different pH values (0, 1, and 5.2) demonstrates that the retention of Ag during the parting process is a result of either oxide formation or kinetic trapping in the form of an alloy. Current-voltage data show that while the dealloying critical potential is generally independent of pH, the dissolution rate is strongly affected by the solution acidity. pH substantially affects Ag retention in both the oxide and alloy forms. To discriminate between the retention forms, two different approaches employed for removing the Ag oxide from freshly dealloyed samples comprise (i) oxide dissolution in 1 M HClO4 and (ii) oxide reduction to elemental Ag followed by a subsequent electrochemical oxidation to Ag+ ions. A critical analysis of the experimental results suggests that the pH and dissolution rate affect more significantly the amount of Ag retained in the form of oxide, while the dealloying potential has a stronger impact on Ag trapping. In addition, the Ag retained as oxide is determined to be predominantly AgO. Overall, the findings of this work could enable the development of strategies for structural and compositional control in electrochemically processed metallic nanoporous materials. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3454753] All rights reserved.