Dealloying, the selective dissolution of less noble elements from an alloy, enables the preparation of monolithic macroscale bodies, which at the nanostructure level exhibit a network of “ligaments” with a well-defined characteristic size that can be tuned to between a few nanometers and several microns. These porous solids can be made with macroscale dimensions, and, prior to dealloying, can be shaped to form engineered components. Their surface-to-volume ratio is extremely large and their bicontinuous structure provides transport pathways to tune the surface state under control of an electric or chemical potential. These materials present new opportunities for exploring the impact of surfaces on material behaviors and for exploiting surface effects in novel materials design strategies. New experimental approaches unraveling surface effects involving small-scale plasticity and elasticity have been demonstrated. Approaches to new functional materials include electrochemical potential switching of strength, stiffness, fracture resistance, fluid sorption, actuation, and quasi-piezoelectric strain sensing.

The structural characterization of dealloyed nanoporous metals is a fundamental and active area of research, needed for the optimization of these structures for catalytic, electrosensing, biomedical, and mechanical functions. The prediction of properties requires identifying and quantifying salient structural characteristics, while insights into the relevant mechanisms of dealloying and coarsening can be achieved through in situ observations of structural evolution. Three-dimensional structural characterization techniques have advanced such that nanoscale quantification of topology, morphology, and crystallographic parameters are achievable, yet the field is new enough that the assessment and comparison of such parameters of different nanoporous metals are just beginning. Here, we explore the state of the art in structural characterization, focusing on nanoporous gold to exemplify the challenges, the achievements, and the potential associated with establishing an appropriate set of structural parameters for this unique class of materials.

Dealloying has evolved from a problematic corrosion process to a versatile tool for scalable fabrication of nanostructured metals. While the original, and majority of, work in the area has focused on electrochemical dealloying, a powerful variation of dealloying—liquid metal dealloying—has recently gained popularity. This process relies on a melt to carry out selective dissolution, replacing the traditional electrolyte solution. While electrolytes and molten metals are both suitable dealloying media, they can lead to very different morphologies. In this article, we compare and contrast what is known about the microscale physics and chemistry controlling microstructural evolution in electrochemical and liquid metal dealloying. We conclude that the core phenomenology of porosity evolution—a competition between dissolution and interface diffusion—is similar in both dealloying processes, but that the relative magnitudes of these two processes control interfacial pattern formation.

Nanoporous metals made by dealloying are macroscopic network architectures that can contain ∼1015 nanoscale struts or ligaments per sample. Their mechanical performance is critical to their applications as functional or lightweight high-strength materials. Testing nanoporous metals at the macroscopic scale offers opportunities for unraveling the properties of nanoscale solids in general. The central questions in this area include whether the macroscopic strength and elastic modulus of nanoporous metals can be correlated with the properties of nanoscale ligaments by the classical Gibson–Ashby equations, whether the dealloying-made network structure differs from the conventional foam metals, how network connectivity influences mechanical response, and how ligament size and surface properties affect the elastic and plastic response of nanoscale solids and that of nanoporous metals, particularly the tension–compression asymmetry in strength. This article reviews the fundamental observations of the mechanical response of nanoporous metals with a focus on gold and the emerging understanding of the aforementioned issues.

Metallic materials are key for electrochemical energy conversion and storage when they are tailored into electrodes designed for rapid reaction kinetics, high electrical conductivities, and high stability. Nanoporous metals formed by dealloying could meet all of these requirements, as the dealloyed products beckon energy researchers with their fascinating structures and outstanding performance. In this article, we discuss the characteristics of dealloyed materials related to their functions in energy devices. We then review nanoporous metal electrodes for applications in fuel cells, supercapacitors, and batteries to provide insights into selection and design criteria for meeting the diverse needs of energy conversion and storage.

Nanoporous metals obtained by dealloying have attracted significant attention for their unusual catalytic properties, and as model materials for fundamental studies of structure–property relationships in a variety of research areas. There has been a recent surge in the use of these metals for biomedical and bioanalytical applications, where many exciting opportunities exist. The goal of this article is to provide a review of recent progress in using nanoporous metals for biological applications, including as biosensors for detecting biomarkers of disease and multifunctional neural interfaces for monitoring and modulating the activity of neural tissue. The article emphasizes the unique properties of nanoporous gold and concludes by discussing its utility in addressing important challenges in biomedical devices.