Why is diffusion in metals and on metal surfaces universal?

Homologous Temperature Regulated Hierarchical Nanoporous Structures by Dealloying

Nanoporous metals, fabricated via dealloying, offer versatile applications but are typically limited to unimodal porous structures, which hinders the integration of conflicting pore-size-dependent properties. A strategy is presented that exploits the homologous temperature (TH)-dependent scaling of feature sizes to generate hierarchical porous structures through multistep dealloying at varied TH levels, adjusted by altering dealloying temperatures or the material melting points. This technique facilitates the creation of monolithic architectures of bimodal porous nickel and trimodal porous carbon, each characterized by well-defined, self-similar bicontinuous porosities across distinct length scales. These materials merge extensive surface area with efficient mass transport, showing improved current delivery and rate capabilities as electrodes in electrocatalytic hydrogen production and electrochemical supercapacitors. These results highlight TH as a unifying parameter for precisely tailoring feature sizes of dealloyed nanoporous materials, opening avenues for developing materials with hierarchical structures that enable novel functionalities.

Ultrafine nanoporous intermetallic catalysts by high-temperature liquid metal dealloying for electrochemical hydrogen production

Intermetallic compounds formed from non-precious transition metals are promising cost-effective and robust catalysts for electrochemical hydrogen production. However, the development of monolithic nanoporous intermetallics, with ample active sites and sufficient electrocatalytic activity, remains a challenge. Here we report the fabrication of nanoporous Co₇Mo₆ and Fe₇Mo₆ intermetallic compounds via liquid metal dealloying. Along with the development of three-dimensional bicontinuous open porosity, high-temperature dealloying overcomes the kinetic energy barrier, enabling the direct formation of chemically ordered intermetallic phases. Unprecedented small characteristic lengths are observed for the nanoporous intermetallic compounds, resulting from an intermetallic effect whereby the chemical ordering during nanopore formation lowers surface diffusivity and significantly suppresses the thermal coarsening of dealloyed nanostructure. The resulting ultrafine nanoporous Co₇Mo₆ exhibits high catalytic activity and durability in electrochemical hydrogen evolution reactions. This study sheds light on the previously unexplored intermetallic effect in dealloying and facilitates the development of advanced intermetallic catalysts for energy applications.

Nanoscale intermetallic compounds are promising catalysts but the synthesis remains a challenge. The authors develop a dealloying technique to fabricate nanoporous intermetallic electrocatalysts with fine structures for efficient hydrogen production.

Spontaneous evolution of bicontinuous nanostructures in dealloyed Li-based systems

Dealloying, the selective dissolution of one or more of the elemental components of an alloy, is an important corrosion mechanism and a technologically relevant process used to fabricate nanoporous metals for a variety of applications including catalysis, sensing, actuation, supercapacitors and radiation-damage-resistant materials. In noble-metal alloy systems for which the ambient-temperature solid-state diffusivity is minuscule, dealloying occurs at a composition-dependent critical potential above which bicontinuous nanoporous structures evolve and below which a full-coverage layer of the more-noble component forms causing the alloy surface to become passive. In contrast, for alloy systems exhibiting significant solid-state diffusive transport, our understanding of dealloying-induced morphologies and the electrochemical parameters controlling this are largely unexplored. Here, we examine dealloying of Li from Li-Sn alloys and show that depending on alloy composition, particle size and dealloying rate, all known dealloyed morphologies evolve including bicontinuous nanoporous structures and hollow core-shell particles. Furthermore, we elucidate the role of bulk diffusion in morphology evolution using chronopotentiometry and linear sweep voltammetry. Our results may have implications for lithium-ion battery development while significantly broadening the spectrum of strategies for obtaining new nanoporous materials through dealloying.