• PDF / 2,013,134 Bytes
• 6 Pages / 585 x 783 pts Page_size
• 90 Downloads / 293 Views

DOWNLOAD

REPORT

---

tion Dealloying has emerged as a convenient and versatile method for making nanoporous metal with high structural definition. Dealloying is the selective dissolution of less noble elements from an alloy, leaving behind a porous structure. The current interest in interface-controlled phenomena displayed by dealloyed nanoporous metals and their potential applications reflects the relative ease of manufacturing nanoporous materials using a simple ambient-temperature corrosion process, as well as the general interest of the materials community in nanomaterials. The interest in nanomaterials, one of the current trends in materials science, started out from the thought that pushing the characteristic scale of the microstructure down to the 2–5 nm range might maximize the number of defects in a material. New material behaviors were expected through mixing local properties of matter in the core of the defects into the more conventional behavior of crystalline matter.1,2 Owing to their modified atomic short-range order, grain boundaries were the defects of choice in early studies of “nanocrystalline” materials, and this class of solids remains the subject of active research. Subsequently, it was recognized that a materials design strategy based on maximizing the number of operando tunable interfaces by manipulating electronic structure could yield additional new behavior.3 This requires control of

the space-charge region at interfaces by external stimuli. Nanoporous metals afford an implementation of this strategy— their pore space can be filled with electrolyte, and the capacitive coupling between the ionic and electronic conduction paths in the electrolyte and the metal, respectively, provide for control of interfacial electric charge (Figure 1).4 Importantly, dealloying can be used to tune the characteristic structure size down to few nanometers, so that the suggested interface-controlled behavior of the nanomaterial can indeed be achieved. Various schemes for exploiting this behavior have emerged in the past decade, specifically, in such instances where the nanoporous metal is converted into a hybrid material by adding aqueous solutions in the pore space as a second phase, which is intermixed with the metal at the nanoscale. The interface between the fluid and the metal can store energy, provide functionality for sensing or actuation, or contribute strongly to the material’s mechanical behavior. In several instances, suggested operando tunable properties have been demonstrated based on this scheme. Various aspects of dealloying as a preparation scheme for nanoporous metals have been the subject of an earlier issue of MRS Bulletin.5 Since then, the preparation approaches have seen drastic progress due to liquid-metal dealloying strategies that enable dealloying of more application-relevant materials. Cutting-edge characterization techniques such as

Jörg Weissmüller, Institute of Materials Physics and Technology, Hamburg University of Technology; and Hybrid Materials Systems Group, Helmholtz-Zentrum Geesthacht, Germany; wei