Catalysis with Two-Dimensional Materials Confining Single Atoms: Concept, Design, and Applications

Abstract

Two-dimensional materials and single-atom catalysts are two frontier research fields in catalysis. A new category of catalysts with the integration of both aspects has been rapidly developed in recent years, and significant advantages were established to make it an independent research field. In this Review, we will focus on the concept of two-dimensional materials confining single atoms for catalysis. The new electronic states via the integration lead to their mutual benefits in activity, that is, two-dimensional materials with unique geometric and electronic structures can modulate the catalytic performance of the confined single atoms, and in other cases the confined single atoms can in turn affect the intrinsic activity of two-dimensional materials. Three typical two-dimensional materials are mainly involved here, i.e., graphene, g-C3N4, and MoS2, and the confined single atoms include both metal and nonmetal atoms. First, we systematically introduce and discuss the classic synthesis methods, advanced characterization techniques, and various catalytic applications toward two-dimensional materials confining single-atom catalysts. Finally, the opportunities and challenges in this emerging field are featured on the basis of its current development.

Atomically Dispersed Semimetallic Selenium on Porous Carbon Membrane as an Electrode for Hydrazine Fuel Cells

“…[8,9] Recently,s ingle-atom catalysts,e specially atomically dispersed metals anchored on conductive nitrogen (N)-doped carbons (AMCs), have been intensively studied for numerous applications [10][11][12][13][14][15] because of their maximized atom utilization, unusual electronic structure and intriguing properties that differ from their nanoparticles (NPs) counterpart in terms of that is,improved activity and/or selectivity. [16,17] Although there has been progress in the design of AMCs by pyrolysis of carefully engineered metal/carbon precursors (i.e.m etal-organic frameworks (MOFs), [18] in which metal atoms were coordinated with Na toms and in the form of typical MN n atomic configuration (n represents coordination number), controlling the aggregation of single atoms in carbons during synthesis and in the later utilization remains challenging,b ecause the high surface energy makes them easily aggregate into NPs at high pyrolysis temperature and in complex catalytic reactions,w hich decrease their activity. [19] Though avery low concentration of the metal in the precursor could logically prevent the aggregation of single atoms during pyrolysis,t he low content of single atoms in AMC is not conducive to meeting the requirements of practical applications (> 1wt%metal content [18] ).…”

“…[17] In this regard, av ery important family of semi-metal elements, that is,selenium (Se), has rarely been discussed. [17] In this regard, av ery important family of semi-metal elements, that is,selenium (Se), has rarely been discussed.…”

Single‐Atom Catalysts in Catalytic Biomedicine

“…To uncover the relationship between structure and performance and to further exploit high‐performance SACs for biomedical applications, the most intuitive and convincing strategy is to directly visualize the single metal atoms on the support materials and monitor the electronic states and actual configurations of the dispersed metal atoms through multiple advanced characterization techniques . Aberration‐corrected high‐resolution transmission electron microscopy (ac‐HRTEM) or aberration‐corrected high‐angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) has been acknowledged as an indispensable tool that allows visualizing at the atomic level and distinguishing the coordination environment of dispersed metal atoms on the supports . The isolated metal atoms have been generally identified as the active catalytic sites for catalytic reactions.…”

Boosting the Loading of Metal Single Atoms via a Bioconcentration Strategy

“…In electrochemistry, atomically dispersed transition metal atom coordinated with nitrogen in carbon‐based (M‐N‐C) materials are particularly appealing, because the isolated M‐N‐C centers have been proven to be the highly active sites in various electrochemical reactions, especially in oxygen reduction reaction (ORR) . Despite the outstanding activity and selectivity of M‐N‐C single atoms, the high surface energy of single atoms brings about the challenges in the chemical synthesis . The traditional synthesis of M‐N‐C materials involves in the pyrolysis process of metal‐containing porphyrin or phthalocyanine complexes .…”