Activity Of Single-atom Catalysts Research Articles

Oxidized single nickel atoms embedded in Ru matrix for highly efficient hydrogen evolution reaction

It is desirable but challenging to fine adjust the electronic structure of single atom to enhance the activity of single atom catalysts (SACs). Herein, we embedded an oxidized single nickel atom into pure ruthenium (Ru) metal (NiRu SAC), thereby constructing an atomic-level interface with high catalytic activity. NiRu SAC exhibits a long-term durability and an extremely low overpotential for hydrogen evolution reaction (optimal value reaches 17 mV) at 10 mA cm−2 which is superior to that of the commercial Pt/C catalyst and most reported Ru-based catalysts. NiRu-0.2 SAC also shows a remarkable oxygen evolution reaction (OER) performance of 210 mV at 10 mA cm−2, and a resulted excellent water splitting property (1.5 V vs. RHE @ 10 mA cm−2). Density functional theory (DFT) calculations demonstrate the fabricated oxidized single-nickel-atomic interface (between single nickel atom and neighboring Ru/O atom) not only lowers the energy barrier for water dissociation but also optimizes the H adsorption through the interaction between the interfacial Ru and O atoms. The single-atomic tailoring provides a new idea to further enhance the performance of single atom catalysts to satisfy the industrial applications.

Machine-learning-accelerated discovery of single-atom catalysts based on bidirectional activation mechanism

Single-atom catalysts (SACs) have provided new impetus to the field of catalysis because of their high activity, high selectivity, and theoretically full utilization of active atoms. However, the ambiguous activation mechanism prevents a clear understanding of the structure-activity relationship and results in a great challenge of rational design of SACs. Herein, by combining density functional theory (DFT) calculations with machine learning (ML), we explore 126 SACs to analyze and develop the structure-activity relationship for the electrocatalytic nitrogen reduction reaction (NRR). We first propose a bidirectional activation mechanism with a new descriptor for catalytic activity, which provides new insights for the rational design of SACs. More importantly, we establish a ML model for predicting the catalytic performance of NRR, validated by both DFT calculations and experimental works. The successful ML prediction in this work helps with the accelerated design and discovery of new catalysts by computational screening with high practical significance. • A bidirectional activation mechanism is proposed for building catalytic theory • A new descriptor of N ie-d is applied for evalulating the catalytic activity for NRR • The developed ML model could predict the catalytic performance of SACs accurately Single-atom catalysts (SACs) have provided a new impetus to the field of catalysis. The key challenges in the development of SACs are to explore the structure-activity relationship and predict the catalytic performance of SACs. Our work addresses these challenges by examining a series of SACs supported on 2D materials via the combination of density functional theory (DFT) calculations and machine learning (ML). The proposed “bidirectional activation mechanism” not only explains some experimental results but also can be extended to other catalytic reactions, laying the foundations for constructing catalytic theory. Moreover, the developed ML model could predict the catalytic activity of SACs for the nitrogen reduction reaction with reliable accuracy, as validated by previous DFT and experimental work. This work provides new insights into catalysis theory and will accelerate the discovery of SACs, hugely influencing the real-world energy field. Singh and co-workers propose a bidirectional activation mechanism with a new descriptor of N ie-d for providing insights into catalysis on the basis of DFT calculations. Their developed ML model with high accuracy could accelerate the design of SACs for NRR.

Designing efficient single-atomic catalysts for bifunctional oxygen electrocatalysis via a general two-step strategy

The rational design of efficient electrocatalysts based on comprehensive mechanistic insights is crucial to widespread penetration of future sustainable and eco-friendly energy technologies. Herein, via systematic first-principles calculations, we propose a general two-step strategy for developing highly active single-atom catalyst (SACs) supported on a prototypical substrate (g-C3N4) for bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Our results show that the intrinsic activity can be properly evaluated by a robust screening rule, and, particularly, the descriptor can be readily calculated by a few handy and basic properties. According to the knowledge, we propose an effective approach (i.e., creating an N vacancy in the cavity of g-C3N4) that enables further activity improvement. Specifically, the predicted ORR/OER activity on Ag and Rh based SACs are comparable or even outperforms that of respective benchmark catalysts. This study not only provides several promising candidates for bifunctional ORR/OER, but also directs a new avenue for rational design of high-performance catalysts.

Low temperature surface oxygen activation in crystalline MnO2 triggered by lattice confined Pd single atoms

Tuning the coordination environment is the research axis of single atom catalysts (SACs). SACs are commonly stabilized by various defects from support. Here, we report a lattice confined Pd SAC using MnO2 as support. Compared with the Pd clusters anchored on the surface, the lattice confined Pd single atoms allows spontaneous exaction of surrounding lattice oxygen at room temperature when employed in CO oxidation. The MnO2 supported Pd SAC exhibited a high turnover frequency of 0.203 s−1 at low reaction temperature, which is higher than that of recently reported Pd SACs. Theoretical calculations also confirmed the confined monatomic Pd activate lattice oxygen with an ultralow energy barrier. Our results illustrate that the unique coordination environment of single atom provided by lattice confinement is promising to boost the activity of SACs.

High-Throughput Screening of Synergistic Transition Metal Dual-Atom Catalysts for Efficient Nitrogen Fixation.

Great enthusiasm in single-atom catalysts (SACs) for the nitrogen reduction reaction (NRR) has been aroused by the discovery of metal-Nx as a promising catalytic center. However, the poor activity and low selectivity of available SACs are far away from the industrial requirement. Through the first-principles high-throughput screening, we find that Fe-Fe distributed on graphite carbon nitride (Fe2/g-CN) can manipulate the binding strength of the target reaction species (compromises the ability to adsorb N2H and NH2), therefore achieving the best NRR performance among 23 transition metal (TM) centers. Our results show that Fe2/g-CN achieves a high theoretical Faradaic efficiency of 100% and, impressively, the lowest limiting potential of -0.13 V. Particularly, multiple-level descriptors shed light on the origin of NRR activity, achieving a fast prescreening among various candidates. Our predictions not only accelerate discovery of catalysts for ammonia synthesis but also contribute to further elucidate the structure-performance correlations.

Theoretical screening of VSe2 as support for enhanced electrocatalytic performance of transition-metal single atoms

Single-atom catalysts (SACs) have attracted enormous attentions in heterogeneous catalysts due to the maximized atomic utilization and extraordinary catalytic performance. Similar to homogeneous catalytic ligands, the support in SACs plays a vital role in the catalytic properties. Herein, we present a series of transition-metal atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Os, Ir and Pt) anchored on a vanadium diselenide (VSe2) monolayer as electrocatalysts through density functional theory calculations. Pd@VSe2 stands out among the considered SACs with a low overpotential of 0.38 V, exhibiting the excellent performance of oxygen reduction reaction (ORR). Meanwhile, a liner trend between the adsorption Gibbs free energy of the OH (ΔGOH*) and the predicted ηORR is revealed, which may serve as a simple descriptor for the inherent ORR catalytic activity of SACs. Particularly, Pt@VSe2 shows extraordinarily low theoretical overpotential of −0.04/0.47 V for hydrogen/oxygen evolution reaction, which transcends the state-of-the-art Pt and IrO2 and thereby can be exploited as highly-efficient bifunctional electrocatalyst for overall water splitting. This work broadens the perception of designing multifunctional electrocatalysts based on two-dimensional VSe2 material and offers a new paradigm for investigating advanced SACs.

Reconstructing 1D Fe Single-atom Catalytic Structure on 2D Graphene Film for High-Efficiency Oxygen Reduction Reaction.

The ordinary intrinsic activity and disordered distribution of metal sites in zero/one-dimensional (0D/1D) single-atom catalysts (SACs) lead to inferior catalytic efficiency and short-term endurance in the oxygen reduction reaction (ORR), which restricts the large-scale application of hydrogen-oxygen fuel cells and metal-air batteries. To improve the activity of SACs, a mild synthesis method was chosen to conjugate 1D Fe SACs with 2D graphene film (Fe SAC@G) that realized a composite structure with well-ordered atomic-Fe coordination configuration. The product exhibits outstanding ORR electrocatalytic efficiency and stability in 0.1 M KOH aqueous solution. DFT-D computational results manifest the intrinsic ORR activity of Fe SAC@G originated from the newly-formed FeN4 -O-FeN4 bridge structure with moderate adsorption ability towards ORR intermediates. These findings provide new ways for designing SACs with high activity and long-term stability.

Selective Hydrogenation on a Highly Active Single-Atom Catalyst of Palladium Dispersed on Ceria Nanorods by Defect Engineering.

Single-atom catalysis represents a new frontier that integrates the merits of homogeneous and heterogeneous catalysis to afford exceptional atom efficiency, activity, and selectivity for a range of catalytic systems. Herein we describe a simple defect engineering strategy to construct an atomically dispersed palladium catalyst (Pdδ+, 0 < δ < 2) by anchoring the palladium atoms on oxygen vacancies created in CeO2 nanorods. This was confirmed by spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurement. The as-prepared catalyst showed exceptional catalytic performance in the hydrogenation of styrene (99% conversion, TOF of 2410 h-1), cinnamaldehyde (99% conversion, 99% selectivity, TOF of 968 h-1), as well as oxidation of triethoxysilane (99% conversion, 79 selectivity, TOF of 10 000 h-1). This single-atom palladium catalyst can be reused at least five times with negligible activity decay. The palladium atoms retained their dispersion on the support at the atomic level after thermal stability testing in Ar at 773 K. Most importantly, this synthetic method can be scaled up while maintaining catalytic performance. We anticipate that this method will expedite access to single-atom catalysts with high activity and excellent resistance to sintering, significantly impacting the performance of this class of catalysts.

Engineering the Low Coordinated Pt Single Atom to Achieve the Superior Electrocatalytic Performance toward Oxygen Reduction.

Configuring metal single-atom catalysts (SACs) with high electrocatalytic activity and stability is one efficient strategy in achieving the cost-competitive catalyst for fuel cells' applications. Herein, the atomic layer deposition (ALD) strategy for synthesis of Pt SACs on the metal-organic framework (MOF)-derived N-doped carbon (NC) is proposed. Through adjusting the ALD exposure time of the Pt precursor, the size-controlled Pt catalysts, from Pt single atoms to subclusters and nanoparticles, are prepared on MOF-NC support. X-ray absorption fine structure spectra determine the increased electron vacancy in Pt SACs and indicate the Pt-N coordination in the as-prepared Pt SACs. Benefiting from the low-coordination environment and anchoring interaction between Pt atoms and nitrogen-doping sites from MOF-NC support, the Pt SACs deliver an enhanced activity and stability with 6.5 times higher mass activity than that of Pt nanoparticle catalysts in boosting the oxygen reduction reaction (ORR). Density functional theory calculations indicate that Pt single atoms prefer to be anchored by the pyridinic N-doped carbon sites. Importantly, it is revealed that the electronic structure of Pt SAs can be adjusted by adsorption of hydroxyl and oxygen, which greatly lowers free energy change for the rate-determining step and enhances the activity of Pt SACs toward the ORR.

Recent advances in single-atom catalysts for CO oxidation

ABSTRACT Single-atom catalysts (SACs) have received boosting attention due to their high atom utilization and incredible activities in a wide range of catalytic processes. Numerous SACs have been investigated for CO oxidation both experimentally and theoretically, including noble-metal catalysts (Pt, Au, Pd, etc.) and non-noble-metal catalysts (Fe, Co, Ni, etc.), in which the atomically dispersed metal atoms are anchored on supports via strong metal-support interactions. This unique structure of SACs contributes to activating the adsorbed CO and O2 and stabilizing the intermediates. Electron transfer between the metal atom and the support plays an important role in tuning the electronic structure, which can greatly influence the activity, selectivity, and stability of SACs. In this review, the design principles and synthesis methods of SACs for CO oxidation are discussed with emphasis on single-atom active sites and metal-support interactions. Four CO oxidation mechanisms over SACs are evaluated. Moreover, the challenges and future research directions for SAC-catalyzed CO oxidation are outlined.

Hydrodechlorination and deep hydrogenation on single-palladium-atom-based heterogeneous catalysts

Halophenols are widely present in wastewater and groundwater, which threaten global water safety and human health. Importantly, hydrodechlorination (HDC) via heterogeneous catalysis is efficient and environmentally friendly. To further improve the catalytic performance and atomic economy, Pd-based single atom catalysts (SACs) were prepared through electrostatic attraction and used in the catalytic HDC for the first time. By substituting different defect-rich supports, the coordination environments of atomically dispersed Pd-atoms were mediated with different catalytic performance. The results demonstrate that the Pd/CeO2 SACs have the highest HDC activity and remain stable during cycle tests. The moderately intensive metal-support interactions (MIMSI) effect was identified as a critical factor for the higher activity of SACs, unlike the traditional strong metal-support interaction effect. The HDC process on Pd SACs was further investigated by combining kinetic experiments with density functional theory calculations, which facilitated the recognition of HDC intermediates and an understanding of the reaction mechanism.

Recent Developments on the Single Atom Supported at 2D Materials Beyond Graphene as Catalysts

Two dimensional (2D) layered materials have proven to be crucial platforms for anchored individual and isolated metal atoms acting as active single atom catalysts (SACs). Therefore, an accurate loc...

Cover Feature: Controlled One‐pot Synthesis of Nickel Single Atoms Embedded in Carbon Nanotube and Graphene Supports with High Loading (ChemNanoMat 7/2020)

The cover feature shows the controllable synthesis of nickel single atoms embedded in nitrogen-doped carbon nanotubes (NiSA−N-CNT) and graphene (NiSA−N-G). Addition of citric acid introduces amorphous carbon on the layered g-C3N4-Ni and, after annealing under the same conditions, NiSA−N-G was obtained instead of NiSA−N-CNT. NiSA−N-G with Ni atomic loading of ∼6 wt% catalysts shows better activity and stability for the CO2 reduction reaction than NiSA−N-CNT with Ni loading of ∼15 wt% due to the more open and exposed active sites in NiSA−N-G. The exposed active sites are most important for the electrocatalytic activity of single atom catalysts. More information can be found in the Full Paper by Chang Liu, Qianfan Zhang, San Ping Jiang et al.

Metal-Organic Framework-Based Catalysts with Single Metal Sites.

Metal-organic frameworks (MOFs) are a class of distinctive porous crystalline materials constructed by metal ions/clusters and organic linkers. Owing to their structural diversity, functional adjustability, and high surface area, different types of MOF-based single metal sites are well exploited, including coordinately unsaturated metal sites from metal nodes and metallolinkers, as well as active metal species immobilized to MOFs. Furthermore, controllable thermal transformation of MOFs can upgrade them to nanomaterials functionalized with active single-atom catalysts (SACs). These unique features of MOFs and their derivatives enable them to serve as a highly versatile platform for catalysis, which has actually been becoming a rapidly developing interdisciplinary research area. In this review, we overview the recent developments of catalysis at single metal sites in MOF-based materials with emphasis on their structures and applications for thermocatalysis, electrocatalysis, and photocatalysis. We also compare the results and summarize the major insights gained from the works in this review, providing the challenges and prospects in this emerging field.

Descriptor-Based Design Principle for Two-Dimensional Single-Atom Catalysts: Carbon Dioxide Electroreduction.

Single-atom catalysis has recently emerged as a promising approach for catalyzing the carbon dioxide reduction reaction (CO2RR). In this study, we present a principle for designing active single-atom catalysts (SACs) for CO2RR. We systematically examine totally 24 transition metals supported by a graphitic carbon nitride (g-CN) monolayer and find that their catalytic activities are highly correlated with the adsorption free energies of two intermediate species (OH and OCH). We then identify two important intrinsic descriptors, namely, the number of electrons in the outmost d-shell and the enthalpy of vaporization of the transition metal. Test calculations on transition metals supported by a C2N monolayer indicate that both descriptors are quite universal for SACs of CO2RR. Based on these results, we show that Ni@g-CN, Cu@g-CN, and Co@C2N are promising SACs for CO2RR. This study offers an effective principle for designing highly active SACs for CO2RR on the basis of intrinsic properties of transition metals.

Molecular Design of Single‐Atom Catalysts for Oxygen Reduction Reaction

AbstractFuel cells are highly attractive for direct chemical‐to‐electrical energy conversion and represent the ultimate mobile power supply solution. However, presently, fuel cells are limited by the sluggish kinetics of the cathodic oxygen reduction reaction (ORR), which requires the use of Pt as a catalyst, thus significantly increasing the overall cost of the cells. Recently, nonprecious metal single‐atom catalysts (SACs) with high ORR activity under both acidic and alkaline conditions have been recognized as promising cost‐effective alternatives to replace Pt in fuel cells. Considerable efforts have been devoted to further improving the ORR activity of SACs, including tailoring the coordination structure of the metal centers, enriching the concentration of the metal centers, and engineering the electronic structure and porosity of the substrate. Herein, a brief introduction to fuel cells and fundamentals of the ORR parameters of SACs and the origin of their high activity is provided, followed by a detailed review of the recently developed strategies used to optimize the ORR activity of SACs in both rotating disk electrode and membrane electrode assembly tests. Remarks and perspectives on the remaining challenges and future directions of SACs for the development of commercial fuel cells are also presented.

A perspective on oxide-supported single-atom catalysts.

Single-atom catalysts (SACs) can not only maximize the metal atom utilization efficiency, but also show drastically improved catalytic performance for various important catalytic processes. Insights into the working principles of SACs provide rational guidance to design and prepare advanced catalysts. Many factors have been claimed to affect the performance of SACs, which makes it very challenging to clarify the correlation between the catalytic performance and physicochemical characteristics of SACs. Oxide-supported SACs are one of the most extensively explored systems. In this minireview, some latest developments on the determining factors of the stability, activity and selectivity of SACs on oxide supports are overviewed. Discussed also are the reaction mechanisms for different systems and methods that are employed to correlate the properties with the catalyst structures at the atomic level. In particular, a recently proposed surface free energy approach is introduced to fabricate well-defined modelled SACs that may help address some key issues in the development of SACs in the future.

Geometric structures, electronic characteristics, stabilities, catalytic activities, and descriptors of graphene-based single-atom catalysts

Abstract Single-atom catalysts (SACs) have been a research hotspot due to their high catalytic activity, selectivity, and atomic utilization rates. However, the theoretical research of SACs is relatively fragmented, which restricts further understanding of SAC stability and activity. To address this issue, we report our analysis of the geometric structures, electronic characteristics, stabilities, catalytic activities, and descriptors of 132 graphene-based single-atom catalysts (M/GS) obtained from density functional theory calculations. Based on the calculated formation and binding energies, a stability map of M/GS was established to guide catalyst synthesis. The effects of metal atoms and support on the charge of metal atoms are discussed. The catalytic activities of M/GS in both nitrogen and oxygen reduction reactions are predicted based on the calculated magnetic moment and the adsorption energy. Combined with the electronegativity and d-band center, a two-dimensional descriptor is proposed to predict the O adsorption energy on M/GS. More importantly, this theoretical study provides predictive guidance for the preparation and rational design of highly stable and active single-atom catalysts using nitrogen doping on graphene.

Enhanced Activity of C2N-Supported Single Co Atom Catalyst by Single Atom Promoter.

The remarkable chemical activity of metal single-atom catalysts (SACs) lies in their unique electronic states associated with the low-coordination nature of single-atom sites. Yet, electronic state manipulation normally requires direct contact with other atoms, which inevitably changes the low-coordination environment. Herein, we found by first-principle calculations that the activity of a Co SAC for HCOOH dehydrogenation is appreciably enhanced via electronic state manipulation by a noncontact single atom promoter. A Co atom and a Sn/Ge/Pb atom are anchored in the same cavity of a graphitic C2N monolayer. Surprisingly, the nonbonded promoter makes two far splitting spin states of Co almost degenerate via charge redistribution of C2N support. Further, the high-spin Co gives a remarkably low reaction barrier comparable to Pt or Pd catalysts. Our results demonstrate that the activity of a SAC can be tuned via a noncontact promoter, casting new insights into electronic state modulation of SACs on graphene-like support.

Coordination tailoring towards efficient single-atom catalysts for N2 fixation: A case study of iron-nitrogen-carbon (Fe@N-C) systems

Abstract N2 fixation using electrochemical methods offers a promising strategy for NH3 production. However, it remains a grand challenge to efficiently produce NH3 in a large scale due to the low activity and poor selectivity of the current electrocatalysts. Herein, by means of density functional theory (DFT) computations, we systematically explored the great potential of two-dimensional (2D) single-atom catalysts (SACs), namely carbon-based iron-nitrogen systems (Fe@Nx, x = 0–4), for N2 electroreduction. Significantly, the catalytic activity and selectivity of Fe@Nx systems are influenced by the coordination environment of single Fe atom. Among all the proposed configurations, Fe@N2-opp, in which two N atoms are located at the opposite coordination sites of single Fe atom, exhibits the highest activity and selectivity for N2 electroreduction, with a limiting potential of −0.63 V. By examining the scaling relations for the single vacancy and double vacancy-based SACs, we constructed a volcano plot to describe the catalytic activity of carbon-based SACs and proposed an optimal nitrogen adsorption energy for N2 electroreduction. This work calls for more attention to the coordination effect to the single-atom active site, and helps provide guidance for further developing more effective carbon-based SACs for N2 fixation.