Asynchronous Evolution of Nanoporous Silver on Dual-Phase Ag⁻Sn Alloys by Potentiostatic Dealloying in Hydrochloric Acid Solution.

Yulin Yang,Zhenhua Dan,Hui Chang,Yongfeng Liang,Fengxiang Qin,Ying Wang

doi:10.3390/nano9050743

Abstract

Evolution behavior of the nanoporous architectures has been investigated via potentiostatic electrochemical dealloying of dual-phase AgxSn100−x (x = 20, 30, 40 at.%) alloys, which consist of β-Sn and ε-Ag3Sn phases with different volume fractions in 1.2 M HCl solution. The results show that the open-circuit potentials and corrosion potentials of dual-phase Ag–Sn alloys are determined by the less noble β-Sn phases rather than chemical compositions of the Ag–Sn precursor alloys. The potentiodynamic polarization curves show that the anodic dissolution of Ag–Sn alloys is divided into two stages including the first preferential dissolution of β-Sn phases and secondary dealloying of ε-Ag3Sn phases, which is associated with the order of the nanoporous evolution. Nanoporous silver (NPS) can be fabricated by potentiostatic dealloying of dual-phase Ag–Sn alloys in HCl solution. The dealloying of two phases is asynchronous: The less noble β-Sn phases are preferentially etched to generate the larger pores, and then the more noble ε-Ag3Sn phases are dealloyed to form the finer nanoporous structure. The significant surface diffusion of Ag adatoms at the applied potential higher than the pitting potential of ε-Ag3Sn phases during the dealloying results in the coarsening of nanoporous ligaments with a time dependence of d(t) t0.1. The fractions and the difference in electrochemical stabilities of the β-Sn and ε-Ag3Sn phases in dual-phase AgxSn100−x (x = 20, 30, 40 at.%) precursor alloys determines the final nanoporous structure.

Highlights

Nanoporous metals (NPMs) with high specific surface areas have attracted great attention in a wide variety of applications including catalysis, sensors, actuators, and surface-enhanced Raman scattering (SERS) [1,2,3,4,5,6,7,8]
It is generally accepted that the formation of NPMs during dealloying involves selective dissolution of the less noble metal atoms or phases and simultaneous arrangements of the more noble metal atoms to form the ligaments under the driving force of surface diffusion [9,11,18]
The nanoporous structures obtained from the aforementioned precursors are usually affected by the disparities in chemical compositions and structure between coexistent phases, especially intermetallics, and this leads to the complexity in dealloying process

Summary

Introduction

Nanoporous metals (NPMs) with high specific surface areas have attracted great attention in a wide variety of applications including catalysis, sensors, actuators, and surface-enhanced Raman scattering (SERS) [1,2,3,4,5,6,7,8]. Studies on dealloying behavior and mechanism mainly focused on the binary precursor alloys with a single-phase solid state, such as Ag–Au [14,15,16,17,18,22,23,24], Mn–Cu [25], and Cu–Pt [26]. Those precursors are generally considered to be advantageous for obtaining ideal and isotropic bi-continuous nanoporous structures. It is necessary to determine the dealloying behavior of each coexistent phase in these dual-phase or multi-phase precursor alloys

Methods

Results

Discussion

Conclusion