Impact of Structure and Composition on the Dealloying of CuxAu(1-x) Bulk and Nanoscale Alloys

In this work, the impact of structure and composition on the dealloying of bulk and nanoscale alloys CuxAu(1-x) have been discussed. In comparison with the dealloying of Ag-Au alloys, the Cu-Au system exhibits dealloying curves with more features associated generally with multistage dealloying. It has been shown for the first time that three stages exist during dealloying process of bulk CuxAu(1-x) (x = 0.7 and 0.8) alloys. The dealloying critical potential, E-c, has been associated with the starting point of stage II in which the anodic current slowly increases. Analysis of data from this work along with results of others suggests a monotonic potential dependence of E-c upon the composition of bulk CuxAu(1-x) alloys in the range of x from 0.70 to 0.95. The dealloying behavior of Cu0.75Au0.25 (Cu3Au) intermetallic (length similar to 19 nm, width similar to 10 nm) and random alloy (length similar to 23 nm, width similar to 9 nm) nanorods have also been discussed. Very close values of Ec have been determined for both types of nanorods with the random alloy dealloying at slightly more negative potentials (c.a. 15-20 mV) than the intermetallic. In addition, both Cu3Au nanorods feature close to 200 mV lower E-c, than bulk alloys with identical composition. Formic acid oxidation tests reveal that the catalysts generated by platinization of as synthesized and dealloyed nanorods exhibit very good activity with peak current densities in the range of 3.5 to 5.5 mA.cm(-2). Both catalysts withstand testing of more than 1500 cycles. Overall, the results of this study demonstrate unique aspects of CuxAu(1-x) dealloying and ascertain the feasibility of nanosized frameworks (dealloyed structures or nanoparticles) as catalyst supports in fuel cell applications.