ReviewThe assembling principle and strategies of high-density atomically dispersed catalysts
Graphical abstract
Atomically dispersed catalysts have the ultra-high atom utilization, extremely high catalytic capacity, excellent selectivity. Studying the general preparation technology of high-loading atomically dispersed catalysts will help to further promote its industrial application. It is of great significance to explore simple and general synthesis strategies to obtain atomically dispersed catalysts with high metal loadings.
Introduction
Under the current background of energy shortages and environmental pollution, the development of continuous green energy and various energy storage devices has been a research hotspot [1], [2], [3], [4], [5], [6], [7], [8], [9]. At present, one of the most important problems in converting harmful gases into renewable energy sources such as hydrocarbons, nitrogen and hydrogen and improving the performance of energy storage devices is the selection and synthesis of efficient catalysts. Theoretically, atomically dispersed catalysts (ADCs) have been regarded as the emerging catalysts by virtue of their ultra-high atom utilization, extremely high catalytic capacity and excellent selectivity [10], [11], [12], [13], [14]. As early as in 2011, Zhang et al. firstly reported and constructed the decentralized single Pt atoms anchored on FeOx surface, which displayed excellent activity and stability for both oxidation and preemptive oxidation of CO in H2 [15]. With the development of nanocatalysis and the advancement of characterization technology, researchers have found that surface unsaturated coordination atoms are often the active sites of catalysis, so the distribution of atoms on the catalyst surface can be controlled by controlling the size, morphology, and crystal face of nanocrystals to improve catalytic performance. When the size of nanocrystals is reduced to atomic clusters and single atoms, its energy level structure and electronic structure will undergo fundamental changes. Because of this unique structural characteristics, single-atom catalysts often show different activity, selectivity and stability from traditional nanocatalysts[16], [17], [18], [19], [20], [21], [22], [23], [24]. At present, ADCs have proved their advantages in the fields as follows: carbon monoxide oxidation [25], oxygen reduction (ORR) [13], [26], [27], [28], [29], [30], [31], [32], [33], hydrogen evolution (HER) [34], [35], [36], [37], [38], [39], [40], [41], oxygen evolution (OER) [42], [43], carbon dioxide reduction (CO2RR) [44], [45], [46], [47], methane reforming to produce H2 [48], and organic synthesis [49], [50].
Since the concept of single-atom catalyst was proposed, this type of material has experienced rapid development for the first 10 years. However, the single-atom catalyst itself did not appear in the last decade. It has always existed in traditional catalysts. The attention of researchers to it can be traced back to 1925. In that year, Taylor boldly concluded that there must be an isolated catalytic reaction center in heterogeneous catalysts [51]. However, limited by the development of catalytic characterization technology, it was not possible to present a convincing evidence at that time. In the 1990 s, the rapid advancement of transmission electron microscopy (TEM) technology allowed everyone to “personally” see the catalyst dispersed in the form of single atoms for the first time [52]. However, the widespread application of single-atom catalysts has experienced a long wait. Therefore, characterization has always been a major challenge for the development of single-atom catalysts. Since 2011, the wide application of scanning transmission electron microscopy (STEM), scanning tunneling electron microscopy (STM), X-ray absorption spectroscopy (XAS) and various in situ characterization techniques (e.g. in situ fourier-transform infrared spectroscopy) have allowed researchers to have a more comprehensive method to confirm the state and coordination of single atoms surroundings [53], [54], [55]. In addition, many auxiliary characterization methods are also widely used in the structure characterization of single atoms, such as the use of synchrotron radiation technology to explore the coordination configuration of isolated catalytic reaction centers. With the development of advanced characterization techniques and synthesis strategies, the ADCs have entered a period of accelerated development [56]. The rapidly accelerated surface free energy, quantum size effect, unsaturated coordination environment and the interaction of metal-carrier can efficiently control the selectivity, activity, and stability of single atoms in the catalytic process [57], [58]. However, metal atoms also have high surface energy and thermodynamic instability, and tend to aggregate into metal clusters and even nanoparticles, especially under high temperature conditions. In order to avoid agglomeration, the traditional solution is to sacrifice the metal loading to prepare the atomic level dispersion catalysts, but the metal loading content of the obtained ADCs is often less than 2 wt%, which greatly limits the performances for the diverse applications. Recently, numrous efforts have devoted to achieving the HADCs with high metal loading ≥ 3 wt%, as listed in Table 1, which demonstrate the exellent performances for the applications such as ORR [1], [59], [60], OER [59], [61], [62], CO2RR [1], [63], [64], photocatalytic H2 evolution [65] and so on. While the controllable preparation of the high-density atomically dispersed catalysts (HADCs) with high loading content (>3 wt%) still presents great challenges [66]. Consequently, the development of high-efficent strategy to achieve HADCs via stablizing the high density single atom active sites and low-cost macroscale preparation is highly demanded [67].
Herein, the present review gives prominence to the assembling principle and strategies for the preparation of HADCs and discuss how to accomplish the atomically dispersion of metal precursors and stabilize the as-formed single atoms to avoid migration and agglomeration (Fig. 1). At the same time, the key to the synthesis of atomic-level dispersed catalysts is discussed from theoretical perspective. Finally, the major problems and prospects for the synthesis strategy and application of HADCs are presented, and the challenges and opportunities for further research on HADCs are presented.
Section snippets
Theoretical guidance
During the process of preparing HADCs, for purpose of avoiding the tendency of single atoms to agglomerate, a crucial issue is to form a strong chemical bond between the single atom and the supports, while the bond force is greater than the interaction force between the single atoms, which follows the fundamental assembling principle for preparation of HADCs. For different supports, solving this problem can be roughly divided into the following three types [68]:
Form metal (M)-oxygen (O) M−On
Preparation strategies for HADCs
At present, the existing preparation methods for ADCs roughly contain the following two categories: one type requires more advanced cutting-edge instruments, such as atomic layer deposition (ALD) [79] and mass-selected soft-landing method [67]; the other type belongs to traditional catalyst preparation methods, such as wet-chemistry method (co-precipitation, impregnation method, etc.) [15], [70], [80]. Among them, 1) ALD is an advanced thin film deposition technology, which is usually supported
Summary and outlook
In the present review, the the assembling principle and comment strategies for the preparation of high-density activity sites ADCs are classified and summarized. As the active center of catalytic materials, atomically dispersed metal has outstanding activity, high selectivity, and maximized atomic efficiency. Therefore, the study of atomically dispersed metal in catalysis helps us design more efficient and low-cost catalysts. These ADCs with high-density active site show great potential in
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
J.Z. acknowledge the financial support from the National Natural Science Foundation of China (Nos. 21875221, 21571157, and U1604123), the Youth Talent Support Program of High Level Talents Special Support Plan in Henan Province (ZYQR201810148), Creative talents in the Education Department of Henan Province (19HASTIT039), and the project supported by State Key Laboratory of Advanced Technology for Materials Synthesis and Processing (Wuhan University of Technology) (2019-KF-13).
References (145)
- et al.
Biocomposite of sodium-alginate with acidified clay for wastewater treatment: Kinetic, equilibrium and thermodynamic studies
Int. J. Biol. Macromol.
(2020) - et al.
Enhancing hydrogen production from steam electrolysis in molten hydroxides via selection of non-precious metal electrodes
Int. J. Hydrogen Energy
(2020) - et al.
Design and optimization of electrochemical cell potential for hydrogen gas production
J. Energy Chem.
(2021) - et al.
Thermodynamic and kinetic study of synthesised graphene oxide-CuO nanocomposites: A way forward to fuel additive and photocatalytic potentials
J. Mol. Liq.
(2020) - et al.
Formulation of zeolite supported nano-metallic catalyst and applications in textile effluent treatment
J. Environ. Chem. Eng.
(2020) - et al.
1D Cu(OH)2 nanorod/2D SnO2 nanosheets core/shell structured array: Covering with graphene layer leads to excellent performances on lithium-ion battery
Appl. Surf. Sci.
(2018) - et al.
Design of single-atom metal catalysts on various supports for the low-temperature water-gas shift reaction
Catal. Today
(2017) - et al.
Relating catalysis between fuel cell and metal-air batteries
Matter
(2020) - et al.
Materials design for rechargeable metal-air batteries
Matter
(2019) - et al.
Strategies for design of electrocatalysts for hydrogen evolution under alkaline conditions
Mater. Today
(2020)
Progress toward commercial application of electrochemical carbon dioxide reduction
Chem
Green synthesis and biological evaluation of novel 5-fluorouracil derivatives as potent anticancer agents
Saudi Pharm. J.
Single-atom platinum confined by the interlayer nanospace of carbon nitride for efficient photocatalytic hydrogen evolution
Nano Energy
Highly-dispersed iron oxide nanoparticles anchored on crumpled nitrogen-doped MXene nanosheets as anode for Li-ion batteries with enhanced cyclic and rate performance
J. Power Sources
Soft landing of ions as a means of surface modification
Int. J. Mass Spectrom
Cascade anchoring strategy for general mass production of high-loading single-atomic metal-nitrogen catalysts
Nat. Commun.
Weakening hydrogen adsorption on nickel via interstitial nitrogen doping promotes bifunctional hydrogen electrocatalysis in alkaline solution
Energy Environ. Sci.
The multifaceted reactivity of single-atom heterogeneous catalysts
Angew. Chem. Int. Ed.
Electrochemical production of sustainable hydrocarbon fuels from CO2 co-electrolysis in eutectic molten melts
ACS Sustainable Chem. Eng.
Single-atom electrocatalysts
Angew. Chem. Int. Ed.
Single-atom catalysts: A new frontier in heterogeneous catalysis
Acc. Chem. Res.
Carbon nanosheets containing discrete Co-Nx-By-C active sites for efficient oxygen electrocatalysis and rechargeable Zn–air batteries
ACS Nano
Insights into single-atom metal–support interactions in electrocatalytic water splitting
Small Methods
Single-atom catalysis of CO oxidation using Pt1/FeOx
Nat. Chem.
The golden crown: A single Au atom that boosts the CO oxidation catalyzed by a palladium cluster on titania surfaces
J. Phys. Chem. Lett.
Thermally stable single atom Pt/m-Al2O3 for selective hydrogenation and CO oxidation
Nat. Commun.
Defective N/S-codoped 3D cheese-like porous carbon nanomaterial toward efficient oxygen reduction and Zn-Air batteries
Small
Atomically dispersed Pt1-Polyoxometalate catalysts: How does metal-support interaction affect stability and hydrogenation activity?
J. Am. Chem. Soc.
Critical factors dictating reversibility of the zinc metal anode
Energy Environ. Mater.
Atomically dispersed metal active centers as a chemically tunable platform for energy storage devices
J. Mater. Chem. A
Atomic level dispersed metal–nitrogen–carbon catalyst toward oxygen reduction reaction: synthesis strategies and chemical Energy Environ
Mater.
Advanced electrocatalysts with single-metal-atom active sites
Chem. Rev.
Catalytically active interfaces in titania nanorod-supported copper catalysts for CO oxidation
Nano Research
Atomic interface effect of a single atom copper catalyst for enhanced oxygen reduction reactions
Energy Environ. Sci.
Earth-abundant nanomaterials for oxygen reduction
Angew. Chem. Int. Ed.
Sulfuration of an Fe-N-C catalyst containing FexC/Fe species to enhance the catalysis of oxygen reduction in acidic media and for use in flexible Zn-Air batteries
Adv. Mater.
Co2P-CoN double active centers confined in N-doped carbon nanotube: Heterostructural engineering for trifunctional catalysis toward HER, ORR, OER, and Zn-Air batteries driven water splitting
Adv. Funct. Mater.
Boosting defective carbon by anchoring well-defined atomically dispersed metal-N4 sites for ORR, OER, and Zn-air batteries
Appl. Catal. B-Environ.
2D single-atom catalyst with optimized iron sites produced by thermal melting of metal–organic frameworks for oxygen reduction reaction
Small Methods
2 D MXene-based energy storage materials: Interfacial structure design and functionalization
ChemSusChem
Ruthenium anchored on carbon nanotube electrocatalyst for hydrogen production with enhanced Faradaic efficiency
Nat. Commun.
Tailoring the d-band centers enables Co4N nanosheets to be highly active for hydrogen evolution catalysis
Angew. Chem. Int. Ed.
Ruthenium-cobalt nanoalloys encapsulated in nitrogen-doped graphene as active electrocatalysts for producing hydrogen in alkaline media
Nat. Commun.
2D thin nanoflakes assembled on mesoporous carbon nanorods for enhancing electrocatalysis and for improving asymmetric supercapacitors
Adv. Funct. Mater.
Rational inert-basal-plane activating design of ultrathin 1T' phase MoS2 with a MoO3 heterostructure for enhancing hydrogen evolution performances
Nanoscale
Confining Pd nanoparticles and atomically dispersed pd into defective MoO3 nanosheet for enhancing electro- and photocatalytic hydrogen evolution performances
ACS Appl. Mater. Interfaces
A metal–organic framework-derived bifunctional oxygen electrocatalyst
Nat. Energy
Carbon dioxide electroreduction on single-atom nickel decorated carbon membranes with industry compatible current densities
Nat. Commun.
Elucidating the electrocatalytic CO2 reduction reaction over a model single-atom nickel catalyst
Angew. Chem. Int. Ed.
Cited by (16)
Constructing fully exposed Pt atomically dispersed catalysts for enhanced multifunctional selective hydrogenation reactions
2024, Chemical Engineering JournalRational design of carbon-supported single and dual atom catalysts for bifunctional oxygen electrocatalysis
2023, Current Opinion in ElectrochemistryCitation Excerpt :Traditional catalysts are based on noble metals, such as Pt/C for ORR, and RuO2 or IrO2 for OER; yet the wide-spread application of MABs has been impeded by the high costs, poor durability and unsatisfactory bifunctional activity of these precious metal-based catalysts [2]. Therefore, it is of fundamental and technological significance to develop high-performance, low-cost bifunctional electrocatalysts for MABs, and nanocomposites based on transition metals atomically dispersed within a nitrogen-doped carbon scaffold have been recognized as viable alternatives, due largely to the formation of unique MNx coordination moieties [3–5]. Typically, a rechargeable MAB consists of four major components, a metal plate (anode), an aqueous (alkaline) solution or conducting polymer electrolyte, a bifunctional air cathode catalyst, and a membrane separator [6].
Enzyme-like nanomaterials-integrated microfluidic technology for bioanalysis
2023, TrAC - Trends in Analytical ChemistryCitation Excerpt :In recent years, some platinum group metals, such as palladium- and iridium-based nanomaterials, also have been demonstrated enzyme-like activities [50,51]. With the advancement of characterization techniques, researchers have discovered that when the size of nanocrystals is reduced to single atoms, their electronic structure and energy level structure will change fundamentally, thereby enhancing the catalytic ability obviously [52]. Single-atom catalysts often show better activity, selectivity and stability than traditional catalysts [53–55].
Coordinating single-atom catalysts on two-dimensional nanomaterials: A paradigm towards bolstered photocatalytic energy conversion
2022, Coordination Chemistry ReviewsCitation Excerpt :Their unique and splendid properties play a large part in elevating photocatalytic performance, and more versatile applications are waiting to be exploited in the arena of 2D material-based SACs. Thanks to the ingenious synthesis routes of SACs and the evolution of advanced characterization techniques, the blossom of SACs has brought about a comprehensive study, especially in nano-synthesis [124]. In fact, different synthetic approaches and characterization techniques related to SACs have been presented in previous reviews [46,57,85,87,90,125–127].
- 1
These authors have contributed equally.