Electrochemical and Morphological Characterization of Pt–Cu Dealloying

Abstract

The results of morphological and electrochemical characterizations of Cu 0.8 Pt 0.2 , Cu 0.75 Pt 0.25 , and Cu 0.71 Pt 0.29 dealloying in 1 M H 2 SO 4 are presented. The critical potential values for these systems were measured and compared to previously reported results for the Ag-Au system. The differences between the systems are discussed in terms of their relative surface diffusivity values. Based on potential hold data, the dealloying critical potentials for Cu 0.8 Pt 0.2 , Cu 0.75 Pt 0.25 , and Cu 0.71 Pt 0.29 are 0.565, 0.730, and 0.800 V, respectively, vs a normal hydrogen reference electrode. The critical overpotentials for dealloying in the Cu-Pt system were found to be approximately 100 mV greater than that for similar compositions in the Ag-Au system.Dealloying is a corrosion process that results in the selective dissolution of one or more elements from an alloy. This process typically results in the production of a nanoporous material of the more noble element͑s͒ 1 with a completely interconnected metalvoid structure containing pores as small as 3.5 nm diam. 2 The structure can be coarsened to larger length scales; at room temperature pore sizes up to 200 nm can be easily produced 3 and at elevated temperatures structures as large as several micrometers can be achieved. 4 Various applications have been found for these structures. [5][6][7][8][9][10][11][12] One of the most important characteristics of a dealloying system is the value of the critical potential. 13 The critical potential marks the transition from alloy passivity ͑planar stability͒ to rapid dealloying ͑porosity formation͒. The dealloying process has most recently been treated as a kinetically controlled morphological transition, 14 a phase separation process, 15,16 and as a nucleation and clustering process. 17 The measurement of the critical potential is typically determined through analysis of electrochemical polarization data, although recently we have shown that this technique may overestimate the critical potential by as much as 115 mV. 18 In the same publication, an alternative method was introduced which utilizes a series of potential hold measurements. This method was later refined in a subsequent manuscript. 19 In this paper we compare the potential hold method for the measurement of critical potentials in the Cu-Pt system to that of polarization data. Not only is this system interesting due to potential applications in the area of biomedical sensors, but this system represents a contrast to the previous investigated Ag-Au system. Specifically, Pt has a value of surface diffusivity that is at least 3-4 orders of magnitude lower than that of Au under their respective electrochemical environments. c This difference in surface diffusivity allows us to make a comparison of the two systems and specifically adds to the body of knowledge aimed at understanding the role of surface diffusivity on the dealloying process. ExperimentalThe alloy samples were prepared at the Materials Preparation Center, Ames Laboratory ͑Ames, Iowa͒, by arc ...

Influence of composition on corrosion behavior of as-cast Cu–Zr alloys in HCl solution

“…Moreover, the entire alloy surface in Cu-30Zr alloy becomes unstable and shows extensive transgranular and intergranular cracking. Pugh et al have observed this phenomenon of the crack after the dealloying behavior in Pt-Cu alloy [8]. When applying −0.1 V anodic potential, some phases are removed from the electrode surface resulting in the formation of holes.…”

“…Dealloying is a corrosion process whereby one or several electronegative constituents of an alloy are preferentially removed from the alloy due to their high reactivity, leading to an altered residual structure [1][2][3][4][5][6][7][8]. Today, it is widely recognized that dealloying phenomena play an important role in many alloys, for example, in the corrosion of brass [9], stainless steel [10,11], the aluminum alloy 2024 [12], and the high-Pd dental alloys [13].…”

Formation of copper porous structures under near-equilibrium chemical vapor deposition

“…One of the most widespread method of nanoporous metal structures formation is dealloying process, which consist in selective chemical or electrochemical etching of a desired component from its alloy [29][30][31][32][33][34]. Also porous metal nanosystems can be synthesized using a template with desired pore structure.…”

Abnormal Hydrogen Absorption/Desorption Properties of Nanoporous Pt with Large Lattice Strains

“…8,9) Figure 1(a) shows the microstructure of the dealloyed nanoporous Pt. The ligament size of the nanoporous Pt was $3 nm.…”