Emerging Metal Single-Atom Materials: From Fundamentals to Energy Applications

Abstract

Conspectus With the development of nanotechnology and characterization techniques, it has been realized that the reactivity of metal nanoparticles mainly depends on some unsaturated coordination atoms on the surface. However, only a small fraction of the surface exposed atoms can access the reactants and act as reactive sites, resulting in low utilization of metal atoms. Moreover, due to the complex structure of metal nanoparticles, the metal atoms exposed on the surface are likely to be in different chemical environments and may act as multiple active centers to catalyze the reactants, which brings great difficulties in the establishment of the structure–activity relationship of metal nanoparticles. Reducing the size of metal nanoparticles to increase the fraction of atoms on the surface is usually regarded as a straightforward and effective approach to enhancing their activity. When the metal nanoparticles are transformed into metal subnanoclusters or even metal single atoms (MSAs), discrete energy-level distribution and distinctive lowest unoccupied molecular orbital-highest occupied molecular orbital (LUMO–HOMO) gap are generated due to the unique quantum size effect. Because of the uniform active sites, maximum metal utilization, unsaturated coordination environment, and strong metal–support interaction, MSA materials often show distinct reactivity, selectivity, and stability from traditional metal nanomaterials. In the past decade, MSA materials have rapidly become the research frontier in catalysis, battery, sensing, and other fields. MSA materials not only provide a new solution for understanding the mechanism of reaction from atomic and molecular scales and studying the structure–activity relationship but also are expected to become a new family of functional materials with large-scale application potential. This Account highlights the recent advancements in the preparation and applications of MSAs in our group. The Account begins with a brief introduction to the structural properties of MSAs. After understanding the basic structural characteristics of MSAs, we summarize three common stabilization strategies for MSAs, including spatial confinement, coordination, and defect/vacancy design strategies. The controllable fabrication of stable and efficient MSAs is important for the investigation of the structure-performance relationship and a prerequisite for various applications. Some typical bottom-up and top-down strategies for the synthesis of MSAs are also briefly introduced. Furthermore, we review our recent advancements in the design and synthesis of MSAs and their applications, including the oxygen reduction reaction (ORR), the hydrogen evolution reaction (HER), the oxygen evolution reaction (OER), photocatalytic H2 production, lithium–sulfur (Li–S) batteries, and the electrocatalytic carbon dioxide reduction reaction (CO2RR). Finally, the current challenges and our perspectives on the preparation and applications of advanced MSAs have been provided.

On the Road from Single-Atom Materials to Highly Sensitive Electrochemical Sensing and Biosensing

“…SAMs are isolated metal atoms anchored by surrounding coordination species of solid supports . The active sites in SAMs are the metal single atoms and surrounding supports, including the short-range coordination atoms and long-range uncoordination atoms . The rapid development of SAMs affords maximum atom utilization efficiency, providing the perfect approach for synthesizing cost-effective catalysts and promoting atom economy.…”

“…Specifically, advanced nanocatalysts with different sizes have attracted a great deal of attention in different catalytic reactions. − The downsizing of nanoparticles is considered to be an efficient strategy for enhancing their catalytic activity . At the limits of nanomaterial synthesis in terms of size and composition, SAMs have recently been developed rapidly in multidisciplinary research fields . Due to well-defined active sites and strong metal–support interactions, SAMs have superior activity and selectivity .…”

“…19 At the limits of nanomaterial synthesis in terms of size and composition, SAMs have recently been developed rapidly in multidisciplinary research fields. 20 Due to well-defined active sites and strong metal−support interactions, SAMs have superior activity and selectivity. 21 Compared with nanocatalysts, SAMs exhibit remarkable improvements in catalytic performance, triggering extensive research interest in energy storage and conversion, 22 environmental management, 23 biosensing, 24 and biomedicine.…”

Single-atom catalysts: promotors of highly sensitive and selective sensors

“…9,10 Reducing the size of metal nanoparticles is considered to be an effective way to increase the number of catalytically exposed atoms, and this naturally changes the surface atomic structure, electronic configuration and surface defects. 11 These changes may have advantageous geometric and electronic effects on the coordination environments, enhancing the catalysts' activity. The most typical example is single-atom catalysts (SACs), in which the active metal sites are isolated on the support or stabilized by coordinated non-metallic atoms, resulting in maximized atom utilization efficiency and catalytic activity.…”

Electronic and Structural Engineering of Atomically Dispersed Isolated Single‐Atom and Alloy Architectures

“…These could result in maximum metal utilization, an electron-deficient coordination environment, and strong metal-support interactions. [22,23] At the atomic scale, all the isolated metal species are in direct contact with surface sites, thereby maximizing the number of interfacial atoms. This is less likely to occur in nanoparticles with unexposed interior atoms and a lack of sites to form interfaces.…”