ABSTRACT
Historically, dealloying is well known in corrosion science and refers to selective dissolution of one or more components out of an alloy, leaving residual nanoporous structure.2 It received signicant attention in the context of corrosion but has recently been receiving renewed attention because porous metals with excellent chemical and physical properties can be fabricated by this method. Dealloying has a long history and was as an ancient technique, called depletion gilding, used by the Incas for the illusion of shining bulk gold by surface-dealloyed gold-copper alloys.3,4 In the period of civil war, the study of dezincication of brass was an example of selective dissolution.5 However, owing to the limitation of observation in the past, few people speculated that nanoporous structure was formed during alloy corrosion. Although nanoporous metals have been prepared by dealloying since the last century, such as Raney nickel from aluminum-nickel alloys in 1927,6 their microstructure and performance still lack adequate investigation. Until 1960s, Pickering and Swann rst studied gold alloy corrosion by transmission electron microscopy (TEM) and revealed that the dealloyed alloy has a nanoporous structure with feature size of ~10 nm.7 In 1979, Forty exhibited the TEM image of monolithic nanoporous gold (np-Au) by dealloying AuAg alloy in nitric acid and proposed the mechanism of nanoporous evolution during dealloying.8 In the 1980s, AuAg alloy precursors were widely studied for dealloying by Sieradzki and Newman.4 They indicated two key parameters for dealloying, concentration of noble metal in precursor and the minimum etching potential.9,10 In 1997, Corcoran et al. studied the nanopore evolution with applied potentials during dealloying by using in situ neutron scattering.11 Recently, TEM tomography has been used for further disclosing the 3D bicontinuous nanostructure of nanoporous metals.12,13 In 2001, Erlebacher et al. demonstrated a much more sophisticated atomistic model for simulating the nanoporosity evolution and studying the kinetics and potential dependence during the dealloying process.14 With the development of dealloying techniques and theories, many novel nanoporous metals have been realized in the last 10 years. Nanoporous Pt, Pd, Cu, and Au were fabricated by dealloying PtCu,15,16 PdCu,17 CuMn,18 and multicomponent metallic glasses.19,20 Ultrane nanoporous gold has been made by low-temperature dealloying.21 At present, the dealloying technique has become a robust method to fabricate new types of nanoporous metals, alloys, and composites.
