Anchoring Sites Engineering in Single‐Atom Catalysts for Highly Efficient Electrochemical Energy Conversion Reactions

Abstract

Single‐atom catalysts (SACs) have been at the frontier of research field in catalysis owing to the maximized atomic utilization, unique structures and properties. The atomically dispersed and catalytically active metal atoms are necessarily anchored by surrounding atoms. As such, the structure and composition of anchoring sites significantly influence the catalytic performance of SACs even with the same metal element. Significant progress has been made to understand structure–activity relationships at an atomic level, but in‐depth understanding in precisely designing highly efficient SACs for the targeted reactions is still required. In this review, various anchoring sites in SACs are summarized and classified into five different types (doped heteroatoms, defect sites, surface atoms, metal sites, and cavity sites). Then, their impacts on catalytic performance are elucidated for electrochemical reactions based on their distance from the metal center (first coordination shell and beyond). Further, SACs anchored on two typical types of hosts, carbon‐ and metal‐based materials, are highlighted, and the effects of anchoring points on achieving the desirable atomic structure, catalytic performance, and reaction pathways are elaborated. At last, insights and outlook to the SAC field based on current achievements and challenges are presented.

Emerging Ultrahigh‐Density Single‐Atom Catalysts for Versatile Heterogeneous Catalysis Applications: Redefinition, Recent Progress, and Challenges

“…At present, the hotspot research directions of SACs include the following: coordination environment (including the first coordination and adjacent environment), [17,18] molecular engineering (involving precursor molecular design and molecular catalyst grafting), [19,20] support engineering (for example, nanostructure design and defect structure regulation), [21,22] thermodynamic stability (such as thermal atomization in preparation and stability in application), [23,24] dynamic catalytic structures (dynamic change and plasticity of metal atoms in catalytic reaction process), [25,26] batch preparation (such as gram-level and kilogram-level preparation), [27,28] and ultrahigh content (limit loading on differentiated supports and site density/distance effect of metal atoms) [29,30] (see Figure 2 left for details). It is obvious that the SACs can be considered for mass production (batch preparation in industrial conditions) and practical applications when the foregoing five points are fully studied and optimized.…”

Au single atom-anchored WO3/TiO2nanotubes for the photocatalytic degradation of volatile organic compounds

“…One major concern for SAC is a substantial tendency for single atoms to aggregate due to their high surface energy, resulting in thermodynamic instability. 10,13,14 As shown in Fig. 6c, on directly loading the Au species on W/T without OVs, the degradation performance of toluene by Au-W/T obviously deteriorated after one recycle experiment.…”

“…10–12 However, originating from the high surface energy of isolated single metal atoms on supports, the metal atom would tend to aggregate, forming clusters or nanoparticles. 13,14 Therefore, appropriate synthetic strategies are essential for the preparation of SACs with these desirable properties. In order to synthesize high-quality SACs, several strategies have been invoked, including (i) designing coordination sites to adsorb and bind metal precursors or metal atoms; (ii) spatially confining single metal atoms into molecular cages; (iii) exploiting defect vacancies in supporting materials to anchor single atom.…”

Macro/Micro‐Environment Regulating Carbon‐Supported Single‐Atom Catalysts for Hydrogen/Oxygen Conversion Reactions

“…[12,13] The formation of strong chemical bonds between the single metal atoms and the supports plays crucial role in preventing metal aggregations. [3,14] Especially, carbon nanomaterials featuring large specific surface areas, excellent electronic conductivity, flexible surface physical/chemical properties, and superior stability, have been extensively explored as ideal supports to stabilize single metal atoms. [15] The catalytic performance of carbon-supported single-atom catalysts (SACs) mainly correlates to the specific surface area, coordination configuration, the atomic dispersion state, and the physical/chemical properties of carbon substrates and metal centers.…”