Race on High‐loading Metal Single Atoms and Successful Preparation Strategies

Abstract

Although single-atom catalysts (SACs) show significantly higher catalytic performance compared to conventional and nanoparticle-based catalysts (NPs) at the same amount of metal loading, their overall catalytic performance may still be unable to compete with the NPs in many applications due to the limited active sites. Generally, trace amounts of metal (less than 1 wt%) can be successfully loaded onto supports in an atomically-dispersed feature, and higher metal loading usually results in aggregation of the metal atoms. Hence, it is very important to further increase the density of isolated metal atoms in these rising-star SACs to pave the ways for widespread applications or even to replace the NPs. On the other hand, it is well known that this is one of the most challenging topics on SACs research. In this review, the advanced strategies to overcome this challenge and achieve high loading of isolated metal atoms on various supports will be extensively discussed together with the examples showing the research efforts to enrich the metal active sites from the pioneer works with metal loading below 0.2 wt% to the recently-reported SACs with metal loading over 20 wt%. Besides, there are still plenty of rooms to further improve the quantity and quality of metal loading on different supports, and outlooks of this scope is provided. We hope that this comprehensive review aids in the development of synthesis techniques for the new-generation SACs with richer active sites.

Highly Efficient Electrocatalytic Oxygen Evolution Over Atomically Dispersed Synergistic Ni/Co Dual Sites

“…As one popular material system in SACs, metal‐nitrogen‐carbon (M−N−C) materials have made great strides in terms of synthetic methods, structural characterizations, and catalytic applications [18, 19] . However, the metal sites in most reported M−N−C materials are homonuclear with relatively low loading, resulting in unsatisfactory catalytic activity [20, 21] . On the other hand, the matrixes (including carbon materials and inorganic compounds) supporting these atomic metal sites typically have a low specific surface area, which is not conducive to the uniform dispersion of metal sites, as well as the charge and mass transfer during the electrocatalytic process [22] .…”

“…[18,19] However, the metal sites in most reported MÀ NÀ C materials are homonuclear with relatively low loading, resulting in unsatisfactory catalytic activity. [20,21] On the other hand, the matrixes (including carbon materials and inorganic compounds) supporting these atomic metal sites typically have a low specific surface area, which is not conducive to the uniform dispersion of metal sites, as well as the charge and mass transfer during the electrocatalytic process. [22] A recent study shows that the introduction of additional metal sites can induce strong synergistic interactions to boost the electrocatalytic performance.…”

Controlling Activity of Heterogeneous Cu Single‐Atom Catalysts by Fine‐Tuning the Redox Properties of CeO2‐TiO2 Supports

“…This observation is important for potential applications in exhaust gas catalysis. This is related to the need to run combustion engines at lower temperature which stipulates the design of catalysts able to achieve full CO conversion in the temperature range around 150 °C or less, referred to as “150 °C‐challenge” [7b] …”

New Folding 2D‐Layered Nitro‐Oxygenated Carbon Containing Ultra High‐Loading Copper Single Atoms

“…The highest loading of Cu atoms on the 2D nanosheets determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES) was ≈15.9 ± 1.2 wt.%, which are among the highest metal loading SACs, especially on 2D supports that have been reported. [36,[42][43][44][45][46] Example comparison on high metal-loading SACs especially on 2D nanomaterial supports can also be found in Section S7 (Supporting Information). The exfoliated F2DS-Cu nanosheets have a specific surface area between 140-170 m 2 g −1 , depending on the metal loading contents (Section S8, Supporting Information).…”