Dealloying of Ag-Au alloys in halide-containing electrolytes - Affect on critical potential and pore size

We present the results of dealloying studies of Ag0.7Au0.3 and Ag0.65Au0.35 alloys in 0.1 M HClO4 with the addition of either 0.1 M KCl, 0.1 M KBr, or 0.1 M KI. The critical overpotential decreases with the addition of halides with KI having the largest potential reduction of almost 50%. This decrease is discussed with respect to a competition between the rates of increase of Au surface diffusivity and Ag exchange current density with halide additions. The size scale of porosity produced during the dealloying of Ag0.65Au0.35 in the above electrolytes was found to increase with the addition of halides. Without the addition of halides, a pore size of approximately 8 nm is produced while 17, 16, and 67 nm is measured in the KCl-, KBr-, and KI- containing electrolytes. The value of surface diffusivity required to coarsen the dealloyed structure to these size scales has been calculated to be 2 x 10(-16) cm(2) s(-1) (0.1 M HClO4), 3 x 10(-15) cm(2) s(-1) (KBr or KCl), and 8 x 10(-13) cm(2) s(-1) (KI). (C) 2003 The Electrochemical Society.