Dealloyed Air- and Water-Sensitive Nanoporous Metals and Metalloids for Emerging Energy Applications

Abstract

Nanoporous metals and metalloids are a broad class of materials whose fabrication involves the selective removal of one or more sacrificial elements from a parent alloy, also known as dealloying, which produces a bulk, monolithic framework with interconnected nanoscale ligaments and pores. The first reports within this field tended to focus on precious nanoporous metals (e.g., nanoporous gold) to provide an explanation of the fundamental mechanisms that underpin conventional, aqueous solution dealloying. As the community has grown, researchers have begun to explore various nonprecious metal and metalloid elements to expand the application space and versatility of nanoporous metals and metalloids. Air- and water-sensitive elements represent a particularly promising exploration for emerging energy applications; combining their chemical reactivity with the high specific surface area and unique morphology of nanoporous metals could enable significant advances in metal fuels for on-board hydrogen generation, next-generation battery electrodes, (electro)­catalysts, and more. However, sensitivity to air and water imposes a significant fabrication barrier: The conventional aqueous solution dealloying approach either cannot create these materials at all or cannot create these materials without simultaneously forming a surface oxide film, which prevents them from being used in the applications mentioned above. To mitigate this issue, the community has developed several unique dealloying strategies involving various electrochemical, liquid metal, and thermal methods. In this review, we present those dealloying strategies and their reaction mechanisms, provide concrete examples of their fabrication and application in energy applications, and analyze their advantages and drawbacks with a focus on recyclability, complexity, and scalability.

Designing Nanoarchitecture of NiCu Dealloyed Nanoparticles on Hierarchical Co Nanosheets for Alkaline Overall Water Splitting at Low Cell Voltage

“…However, if we have to consider such a nanoporous material as electrocatalyst in an electrolyzer, percolation may not be a sufficient condition as per Weissmüller et al since the open space created by dissolution must allow for electrolyte penetration and the formation of an electrochemical double layer (C dl ) . Thus, a 2D-hierarchical nanosheets support further may provide enhanced surface catalytic sites to the dealloyed nanoporous catalysts toward water splitting reactions with additional exposed active sites, better electrical conductivity, as well as ionic transportation during electrocatalysis. , Therefore, we considered high energy (100) surface exposed Co nanosheets as the support to the dealloyed NiCu alloy and as a catalyst for the half reaction, as it is an effective OER catalyst. The chemisorption (OH – ) and subsequent oxygen-containing intermediate formation (*OH, *O, and *OOH) are found to be significantly enhanced on Co active sites. , …”

“…6 Thus, a 2D-hierarchical nanosheets support further may provide enhanced surface catalytic sites to the dealloyed nanoporous catalysts toward water splitting reactions with additional exposed active sites, better electrical conductivity, as well as ionic transportation during electrocatalysis. 11,19 Therefore, we considered high energy (100) surface exposed Co nanosheets as the support to the dealloyed NiCu alloy and as a catalyst for the half reaction, as it is an effective OER catalyst. The chemisorption (OH − ) and subsequent oxygen-containing intermediate formation (*OH, *O, and *OOH) are found to be significantly enhanced on Co active sites.…”

“…Erlebacher et al proposed that the Au–Ag alloy membranes transformed into a unique 3D solid/void bicontinuous nanoporous structure consisting of a Au-rich surface through the percolation interfacial dissolution of Ag atoms . Other metals or more-noble metal rich nanoporous alloys also have been explored through selective leaching; for example, fabrication of nanoporous Pt by dealloying of Pt–Cu alloy, , or preparation of nanoporous Pd by dealloying of Pd–Co and Pd–Ni–P alloys. , These dealloyed nanoporous materials were found to be efficient support as compared to the original alloy, for instance, nanoporous gold can support cracking at high velocity . In the present study, we considered a low-cost NiCu alloy, and as per the selective leaching theory, we expect a Ni-deficient and Cu-rich final alloy after dealloying.…”

Electrochemistry of Thin Films and Nanostructured Materials

“…Depending on the dimensionality (in which the materials are not nanoscaled) they are divided into nanoparticles (0D), filamentary structures (nanotubes, nanowires, nanorods, nanofibers) (1D), layered or lamellar structures (nanosheets, thin films) (2D), and bulk nanostructured materials (3D) [ 53 , 54 , 55 ]. In recent decades, many interesting nanostructured materials with unique properties have been obtained, and it is worth mentioning a few particular examples: colloidal nanocrystals [ 56 , 57 ], buckminsterfullerene C 60 [ 58 ], covalent organic frameworks (COFs) [ 59 , 60 ], carbon nanotubes (CNTs) [ 61 , 62 ], metal, semiconductor, and polymer nanowires and nanotubes [ 63 , 64 , 65 ], and nanoporous materials such as anodic aluminum oxide (AAO) [ 66 , 67 , 68 ], anodic titanium oxide [ 69 , 70 , 71 ], metals [ 72 , 73 ], zeolites [ 74 ], and others [ 75 ].…”

Dealloying fabrication of hierarchical porous Nickel–Iron foams for efficient oxygen evolution reaction

“…Additionally, when the specific surface area of the substrate increases, a large number of active sites exposed by the substrate itself can play a significant role in OER, achieving an effect of dual advantages ( Wu et al, 2019 ). Dealloying is an easily achievable strategy in many nanoporous fabrication techniques, and it has been widely used in the production of electrocatalysts ( Chen et al, 2018 ; Fu et al, 2022 ). However, there are no reports on the modification of metal foam substrates.…”