Synthesis Of Single-atom Catalysts Research Articles

Single-Atom Underpotential Deposition at Specific Sites of N-Doped Graphene for Hydrogen Evolution Reaction Electrocatalysis

Single-atom catalysts (SACs) have the advantages of good active site uniformity, high atom utilization, and high catalytic activity. However, the study of its controllable synthesis still needs to be thoroughly investigated. In this paper, we deposited Cu SAs on nanoporous N-doped graphene by underpotential deposition and further obtained a Pt SAC by a galvanic process. Electrochemical and spectroscopic analyses showed that the pyridine-like N defect sites are the specific sites for the underpotential-deposited SAs. The obtained Pt SAC exhibits a good activity in a hydrogen evolution reaction with a turnover frequency of 25.1 s−1. This work reveals the specific sites of UPD of SAs on N-doped graphene and their potential applications in HERs, which provides a new idea for the design and synthesis of SACs.

Metal–Organic Framework (MOF)‐based Single Atom Catalysts (SACs) for Photocatalytic Energy Conversion

AbstractRecently metal–organic frameworks (MOFs) have been demonstrated as potential precursors for obtaining single atom catalysts (SACs). Although SACs are attracting significant scientific attention due to their exceptional catalytic properties, the synthesis of SACs is still challenging due to their high surface free energy and this limits the growth of SACs. However, recent scientific research indicates that MOFs, due to their interesting structural feature, tunable pore size, high porosity, and exceptional thermal and chemical stability, can be an ideal candidate for the development of SACs. Current environmental crisis highly demands development of efficient photocatalysts for sustainable energy conversions such as photocatalytic hydrogen evolution, photocatalytic carbon dioxide, oxygen reduction, and so forth. MOF‐based SACs are emerging as most potent photocatalyst for such energy conversion. This review summarizes the advances in the field of MOF‐based SAC systems for photocatalytic energy conversions referred to above, along with mechanistic aspects. The complementarity of MOFs and SACs in the principle of photocatalysis have been elucidated. This review also seeks to offer an insight into the challenges involved and the future prospects of MOF‐based SAsystems.

Microwave‐Assisted Rapid Synthesis of MOF‐Based Single‐Atom Ni Catalyst for CO2 Electroreduction at Ampere‐Level Current

AbstractCarbon‐based single‐atom catalysts (SACs) have attracted tremendous interest in heterogeneous catalysis. However, the common electric heating techniques to produce carbon‐based SACs usually suffer from prolonged heating time and tedious operations. Herein, a general and facile microwave‐assisted rapid pyrolysis method is developed to afford carbon‐based SACs within 3 min without inert gas protection. The obtained carbon‐based SACs present high porosity and comparable carbonization degree to those obtained by electric heating techniques. Specifically, the single‐atom Ni implanted N‐doped carbon (Ni1−N−C) derived from a Ni‐doped metal–organic framework (Ni‐ZIF‐8) exhibits remarkable CO Faradaic efficiency (96 %) with a substantial CO partial current density (jCO) up to 1.06 A/cm2 in CO2 electroreduction, far superior to the counterpart obtained by traditional pyrolysis with electric heating. Mechanism investigations reveal that the resulting Ni1−N−C presents abundant defective sites and mesoporous structure, greatly facilitating CO2 adsorption and mass transfer. This work establishes a versatile approach to rapid and large‐scale synthesis of SACs as well as other carbon‐based materials for efficient catalysis.

Chemical Kinetics of Metal Single Atom and Nanocluster Formation on Surfaces: An Example of Pt on Hexagonal Boron Nitride.

The production of atomically dispersed metal catalysts remains a significant challenge in the field of heterogeneous catalysis due to coexistence with continuously packed sites such as nanoclusters and nanoparticles. This work presents a comprehensive guidance on how to increase the degree of atomization through a selection of appropriate experimental conditions and supports. It is based on a rigorous macro-kinetic theory that captures relevant competing processes of nucleation and formation of single atoms stabilized by point defects. The effects of metal-support interactions and deposition parameters on the resulting single atom to nanocluster ratio as well as the role of metal centers formed on point defects in the kinetics of nucleation have been established, thus paving the way to guided synthesis of single atom catalysts. The predictions are supported by experimental results on sputter deposition of Pt on exfoliated hexagonal boron nitride, as imaged by aberration-corrected scanning transmission electron microscopy.

Microwave and template assisted synthesis of atomically dispersed Co–N2 sites on carbon spheres for Fenton-like reaction

Recently, single atomic metals supported on carbon materials have attracted great interests because of their high catalytic activity and stability in peroxymonosulfate (PMS)-based Fenton-like process. Herein, we propose a convenient strategy to synthesize Co single atoms supported on nitrogen-doped carbon spheres (Co@MNC) via microwave treatment. The microwave irradiation can simultaneously induce the formation of carbon defects and immobilize the Co single atoms in N doped carbon support in a few minutes. The obtained Co@MNC can activate PMS for efficient catalytic oxidation of organic pollutants. The radical quenching tests and electron paramagnetic resonance (EPR) verify that Co (IV)-oxo species, 1O2, and O2•− are responsible for the remediation of organic pollutants. Density functional theory (DFT) calculations confirm that unique and low coordinated Co–N2 on void or edge defects are favorable for PMS adsorption. The electrons will then transfer from Co atoms to adsorbed PMS via the bonded N. Co (IV)-oxo species and other ROSs are therefore generated for pollutants degradation. This work provides a fast method for the synthesis of single atom catalysts for efficient Fenton-like reactions.

Single-atom Anchored Curved Carbon Surface for Efficient CO2 Electro-reduction with Nearly 100% Co Selectivity And Industrially-relevant Current Density.

Although single metal atoms on porous carbons (PCs) have been widely used in electrochemical CO2 reduction reaction, these systems have long relied on flat graphene-based models, which are far beyond reality because of abundant curved structures in PCs, the effect of curved surface has long been ignored. In addition, the selectivity generally decreases under high current density, which severely limits practical application. Herein, the theoretical calculations reveal that the single-Ni-atom on curved surface can simultaneously enhance the total density of states around Fermi level and decrease the energy barrier for *COOH formation, thereby enhancing catalytic activity. We report a rational molten salt approach for preparing PCs with ultra-high specific surface area of up to 2635 m2 g-1 . As determined by cutting-edge techniques, single-Ni-atom on curved carbon surface is obtained and used as catalysts for electrochemical CO2 reduction. The CO selectivity reaches up to 99.8% under industrial-level current density of 400mA cm-2 , outperforming state-of-the-art PC-based catalysts. Not only this work offers a new method for the rational synthesis of single atom catalysts with strained geometry to host rich active sites, but also provides in-depth insights for the origin of catalytic activity of curved structure-enriched PC-based catalysts. This article is protected by copyright. All rights reserved.

Molten salt assisted synthesis of Single-Atom nickel catalysts for electroreduction of CO2 with nearly 100% CO selectivity

The synthesis of single-atom catalysts (SACs) with target architecture owning ultrathin layered morphology, high surface area and exposed metal active sites is still a great challenge. Herein, we chose 2D bimetallic ZIF-L as precursor combined with molten salt assisted method realizing the aimed synthesis of single-atom Ni imbedded in porous and ultrathin N-doped carbon nanosheets for efficient electrocatalytic CO2 reduction. Molten salt assisted method avoids the collapse, agglomeration, and shrinkage of precursor nanosheets in synthetic process, and benefits the formation of porous structure of nitrogen-doped carbon nanosheets with exposed single-atom Ni active sites. The as-synthesized MS-L-Ni-NC exhibits remarkable electrocatalytic CO2-to-CO performance with the faradaic efficiency over 95.9% in a wide potential range from −0.7 to −1.0 V vs. RHE in H-type cell. An optimal FECO of 98.7% at −0.8 V vs. RHE and a large current density of 20.6 mA·cm−2 at −1.0 V are observed for the MS-L-Ni-NC, which are much higher than those of D-L-Ni-NC without molten-salt assistance and MS-Ni-NC with 3D bimetallic ZIF as precursor. DFT calculations reveal that the coordinated unsaturated pyridine Ni-N sites are the active centers for ECO2RR.

Recent Advances on Single‐Atom Catalysts for CO2 Reduction

Continuous consumption of fossil energy and excessive CO2 emission severely restrict human society. Sustainable carbon cycle is a promising technology to simultaneously relieve greenhouse effect and energy crisis based on electrocatalysis and photocatalysis. However, the energy conversion efficiency is confined by the poor carriers utilization and insufficient reactive sites. Single‐atom catalysts (SACs) display outstanding performance in effectively overcoming the aforementioned problems. Herein, recent advances of SACs for enhancing the efficiency, selectivity, and long‐range stability of CO2 reduction are provided. First, the characteristics of SACs have been introduced in detail to provide rational design for SACs based on the relationship between structure and performance, including type, structure, and synthesis of SACs. Then, the high performance of SACs in electrocatalytic, photocatalytic, and thermocatalytic CO2 reduction has been discussed for disclosing reaction mechanism, such as charge transfer, activation barriers, and reaction pathway. In particular, the strategies of enhancing CO2 reduction performance have been summarized to provide deep insight into designing and developing more efficient SACs. Finally, an outlook on the current challenges and perspectives of SACs for electrocatalytic, photocatalytic, and thermocatalytic CO2 reduction is proposed. This review aims to provide a systematic reference for developing SACs in advanced CO2 catalytic conversion.

Construction of a single-atom palladium catalyst by electronic metal-support interaction and interface confinement effect with remarkable performance in Suzuki coupling reaction

Atomically distributed metal catalysts with maximal atom utilization and distinctive catalytic properties have drawn attention in a variety of reactions. However, accessing excellent catalytic efficiency while preserving high stability is critical but challenging. Here we report a straightforward strategy by synergizing electronic metal-support interaction and interface confinement effect, which enables the precise construction of atomic palladium atoms supported over UiO-66-NH2. For the Suzuki coupling of bromobenzene with phenylboronic acid, this palladium catalyst demonstrates extraordinary catalytic performance in terms of activity (turnover frequency of 13043 h−1), selectivity (>99 %), and yield (>99 %). Additionally, it shows excellent recyclability, storage stability, and wide substrate scope. The experimental characterizations and DFT calculations demonstrate the high catalytic activity is attributed to the optimized electronic metal-support interactions and positive valence state of palladium atoms over the support. This study provides fundamental insights into the precise synthesis of single atom catalysts and their application in organic transformations.

A general synthesis of single atom catalysts with controllable atomic and mesoporous structures

A general synthesis of single atom catalysts with controllable atomic and mesoporous structures

Hollow mesoporous atomically dispersed metal-nitrogen-carbon catalysts with enhanced diffusion for catalysis involving larger molecules

Single-atom catalysts (SACs) show great promise in various applications due to their maximal atom utilization efficiency. However, the controlled synthesis of SACs with appropriate porous structures remains a challenge that must be overcome to address the diffusion issues in catalysis. Resolving these diffusion issues has become increasingly important because the intrinsic activity of the catalysts is dramatically improved by spatially isolated single-atom sites. Herein, we develop a facile topo-conversion strategy for fabricating hollow mesoporous metal-nitrogen-carbon SACs with enhanced diffusion for catalysis. Several hollow mesoporous metal-nitrogen-carbon SACs, including Co, Ni, Mn and Cu, are successfully fabricated by this strategy. Taking hollow mesoporous cobalt-nitrogen-carbon SACs as a proof-of-concept, diffusion and kinetic experiments demonstrate the enhanced diffusion of hollow mesoporous structures compared to the solid ones, which alleviates the bottleneck of poor mass transport in catalysis, especially involving larger molecules. Impressively, the combination of superior intrinsic activity from Co-N4 sites and the enhanced diffusion from the hollow mesoporous nanoarchitecture significantly improves the catalytic performance of the oxidative coupling of aniline and its derivatives.

Strong electronic interaction of indium oxide with palladium single atoms induced by quenching toward enhanced hydrogenation of nitrobenzene

The realization of efficient and fully controllable synthesis of single atom catalysts is an exciting frontier, yet still challenging in the modern catalysis field. Here we describe a straightforward high-temperature quenching approach to precisely construct isolated palladium atoms supported over cubic indium oxide, with individual palladium atoms coordinated with four neighboring oxygen atoms. This palladium catalyst achieves exceptional catalytic efficiency in the selective hydrogenation of nitrobenzene to aniline, with more than 99% chemoselectivity under almost 100% conversion. Moreover, it delivers excellent recyclability, anti-CO poisoning ability, storage stability, and substrate tolerance. DFT calculations further reveal that the high catalytic activity stems from the optimized electronic structure and the charge states of palladium atoms in the defect-containing indium oxide. Our findings provide an effective approach to engineering single atom catalysts at the atomic level and open the door to a wide variety of catalytic reactions.

Rare earth praseodymium-based single atom catalyst for high performance CO2 reduction reaction

Rare earth single-atom catalysts (SACs) can be used to obtain atomically dispersed species on supports to provide the maximum number of well-defined active sites, which would subsequently maximize the utilizationof rare earth metals. However, the design and synthesis of SACs are mostly based on transition metals, and rare earth SACs have been rarely explored. Herein, we report a rare earth praseodymium SAC dispersed on a porous carbon substrate by utilizing the cascade anchoring strategy, with a metal loading of up to 5.07 wt%. This praseodymium SAC exhibits excellent catalytic performance for the electrochemical CO2 reduction reaction (CO2RR) and achieves high selectivity for CO, with a faradaic efficiency (FECO) of up to 93% at a low potential of −0.43 V vs RHE. Experiments and theoretical calculations confirm that the isolated praseodymium atoms on the substrate are critical for improving the CO2RR performance of the material.

A minireview on the synthesis of single atom catalysts.

Single atom catalysis is a prosperous and rapidly growing research field, owing to the remarkable advantages of single atom catalysts (SACs), such as maximized atom utilization efficiency, tailorable catalytic activities as well as supremely high catalytic selectivity. Synthesis approaches play crucial roles in determining the properties and performance of SACs. Over the past few years, versatile methods have been adopted to synthesize SACs. Herein, we give a thorough and up-to-date review on the progress of approaches for the synthesis of SACs, outline the general principles and list the advantages and disadvantages of each synthesis approach, with the aim to give the readers a clear picture and inspire more studies to exploit novel approaches to synthesize SACs effectively.

MXenes as Superexcellent Support for Confining Single Atom: Properties, Synthesis, and Electrocatalytic Applications.

Single atom catalysts (SACs) have shown their noticeable potential and gradually become a new favorite in catalytic field due to the particular selectivity, high catalytic performance, and strong durability. The most important factor in the synthesis of SACs is the selection of appropriate support and formation of metal-support interaction. Among a large number of nanomaterials, MXenes can be utilized as benign supports for fixing SACs because of their expansive specific surface area, regulable bandgap, superior electronic conductivity, and strong mechanical stability. The structure and property of MXenes can be manipulated by changing transition metal elements and surface termination. Here, the uniqueness and superiority of MXenes as superexcellent supports for confining SACs are analyzed from structure and property. The synthetic strategy of MXene-supported SACs is also summarized, especially emphasizing the immobilization of isolated atom against aggregation by utilizing the formidable metal-support covalent coordination interaction. In addition, the applications of MXene-supported SACs in electrocatalytic field are highlighted, including hydrogen evolution reaction, oxygen evolution reaction, overall water splitting, oxygen reduction reaction, and nitrogen reduction reaction. Finally, the challenges and prospects are pointed out for the further understanding and practical application of MXene-supported SACs in electrocatalysis.

Interaction of First Row Transition Metals with M2C (M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W) MXenes: A Quest for Single-Atom Catalysts

The synthesis of single-atom catalysts (SACs) is one of the main challenges in heterogeneous catalysis and electrocatalysis since it requires substrates with high thermal/chemical stability on whic...

Rational design of ultrahigh loading metal single-atoms (Co, Ni, Mo) anchored on in-situ pre-crosslinked guar gum derived N-doped carbon aerogel for efficient overall water splitting

Rationally designing single-atom catalysts (SACs) is a potential strategy to reach efficient energy conversion as they combine the merits of both maximizing atomic utilization and minimizing the cost of the heterogeneous catalysts. However, when increasing the loading capacity of single-atoms, how to effectively prevent the aggregation of metal single atoms to achieve higher atom utilization efficiency is an urgent issue. Herein, we develop an in-situ pre-crosslinking method to prepare a series of metal single-atoms anchored on nitrogen-doped carbon aerogel (M-SA@NCA, M = Co, Ni, Mo) as high-efficiency bifunctional catalysts for hydrogen/oxygen evolution reactions (HER/OER). Thanks to theintrinsic chemical crosslinking ability between the metal ions and the substrate functional groups, these metal single-atoms can be effectively and stably anchored in the three-dimensional network as crosslinked point of the substrate, thus endowing M-SA@NCA with ultrahigh single-atom loading (Co, ~27.30 wt%; Ni, ~18.35 wt%; Mo, ~18.16 wt%), and therefore display more active sites, and excellent stability (up to 100 h for water-splitting in 1.0 M KOH). Furthermore, the systematic X-ray absorption fine structure (XAFS), in-situ attenuated total internal reflection (in-situ ATR spectra) and density functional theory (DFT) calculation are used to acquire deep insight on the bonding modes between metal single-atoms and substrates, and the influence of different configuration on the catalytic performance. The combined results reveal that Co atoms facilitate the formation of pyrr-N, and the optimal configuration is CoN4 in HER process with smallest onset potential of 12.5 mV, closing to the Pt/C (20 wt%); while the best OER catalyst is Ni-SA@NCA with NiC2N2-o-5 moieties, outperforming the benchmarked IrO2. This work provides a solution for investigating the interaction between single-atom-substrate configuration and catalytic performance, and represents a critical step towards the rational design and synthesis of SACs with extremely high single-atom loading, maximum atomic utilization efficiency and thus superior catalytic activity.

Silver Single Atom in Carbon Nitride Catalyst for Highly Efficient Photocatalytic Hydrogen Evolution.

Single atom catalysts (SACs) with the maximized metal atom efficiency have sparked great attention. However, it is challenging to obtain SACs with high metal loading, high catalytic activity, and good stability. Herein, we demonstrate a new strategy to develop a highly active and stable Ag single atom in carbon nitride (Ag-N2 C2 /CN) catalyst with a unique coordination. The Ag atomic dispersion and Ag-N2 C2 configuration have been identified by aberration-correction high-angle-annular-dark-field scanning transmission electron microscopy (AC-HAADF-STEM) and extended X-ray absorption. Experiments and DFT calculations further verify that Ag-N2 C2 can reduce the H2 evolution barrier, expand the light absorption range, and improve the charge transfer of CN. As a result, the Ag-N2 C2 /CN catalyst exhibits much better H2 evolution activity than the N-coordinated Ag single atom in CN (Ag-N4 /CN), and is even superior to the Pt nanoparticle-loaded CN (PtNP /CN). This work provides a new idea for the design and synthesis of SACs with novel configurations and excellent catalytic activity and durability.

Single Atoms for Energy Applications

Single Atoms for Energy Applications

Insights into Single‐Atom Metal–Support Interactions in Electrocatalytic Water Splitting

AbstractElectrochemical water splitting is a promising approach for energy conversion and storage. The exploration of low‐cost, efficient, and durable electrocatalysts is of great significance for realizing a large‐scale application and forming a sustainable chemistry. Recently single‐atom catalysts (SACs), with isolated metal atoms anchored on supports, exhibit distinctive performances for electrocatalytic water splitting. Single‐atom catalysis is emerging as a new frontier for bridging the homogeneous and heterogeneous catalyses. Therefore, the synthesis of SACs with excellent durability is highly desirable but challenging. Here, recent progress of SACs in supports and synthetic strategies, characterization techniques, and the electrochemical application toward water splitting is summarized. Fully understanding the interactions between the single‐atom metal and the support is extremely important for the design and preparation of highly stable SACs as well as the improvement of electrocatalytic activity, which are particularly discussed in this context. Finally, the current challenges and future opportunities for the development of this field are discussed.