Carbon-supported Single-atom Catalysts Research Articles

In Situ Modulated Nickel Single Atoms on Bicontinuous Porous Carbon Fibers and Sheets Networks for Acidic CO2 Reduction.

Carbon-supported single-atom catalysts exhibit exceptional properties in acidic CO2 reduction. However, traditional carbon supports fall short in building high-site-utilization and CO2-rich interfacial environments, and the structural evolution of single-atom metals and catalytic mechanisms under realistic conditions remain ambiguous. Herein, an interconnected mesoporous carbon nanofiber and carbon nanosheet network (IPCF@CS) is reported, derived from microphase-separated block copolymer, to improve catalytic efficiency of isolated Ni. In IPCF@CS nanostructure, highly mesoporous IPCF hinders stacking of CS that provides additional fully exposed sites and abundant bicontinuous mesochannels of IPCF facilitate smooth CO2 transport. Such unique features enable enhanced Ni utilization and local CO2 enrichment, which cannot be achieved over conventional pore-deficient and discontinuous porous carbon fibers-based supports. In situ X-ray and Infrared spectroscopy coupling constant-potential calculations reveal the dynamic distortion of the planar Ni-N4 to an out-of-plane configuration with expanded Ni-N bond during operating CO2 electroreduction. The potential-driven low-valance-state Ni-N4 possesses enhanced intrinsic electrokinetics for CO2 activation and CO desorption yet inhibiting hydrogen evolution. The favorable electronic and interfacial reaction environments, resulted from the in situ tailored Ni site and IPCF@CS support, achieve an FE of near 100% at 540mAcm-2, a TOF of 55.5 s-1, and a SPCE of 89.2% in acidic CO2-to-CO electrolysis.

Optimizing s‐p Orbital Overlap between Sodium Polysulfides and Single‐Atom Indium Catalyst for Efficient Sulfur Redox Reaction

P‐block metal carbon‐supported single‐atom catalysts (C‐SACs) have emerged as a promising candidate for high‐performance room‐temperature sodium‐sulfur (RT Na‐S) batteries, due to their high atom utilization and unique electronic structure. However, the ambiguous electronic‐level understanding of Na‐dominant s‐p hybridization between sodium polysulfides (NaPSs) and p‐block C‐SACs limits the precise control of coordination environment tuning and electro‐catalytic activity manipulation. Here, s‐p orbital overlap degree (OOD) between the s orbitals of Na in NaPSs and the p orbitals of p‐block C‐SACs is proposed as a descriptor for sulfur reduction reaction (SRR) and sulfur oxidation reaction (SOR). Compared to NG and NG‐supported InN4 (NG‐InN4) SACs, the nitrogen‐doped graphene‐supported InN5 (NG‐InN5) SACs show the largest s‐p OOD, demonstrating the weakest shuttle effect and the lowest reaction energy barriers in both SRR and SOR. Accordingly, the designed catalysts allow the Na‐S pouch batteries to retain a high capacity of 490.7 mAh g‐1 at 2 A g‐1 with a Coulombic efficiency of 96% at a low electrolyte/sulfur (E/S) ratio of 4.5 μl. This work offers an s‐p orbital overlap descriptor describing the interaction between NaPSs and p‐orbital‐dominated catalysts for high‐performance RT Na‐S batteries.

Optimizing s-p Orbital Overlap Between Sodium Polysulfides and Single-Atom Indium Catalyst for Efficient Sulfur Redox Reaction.

P-block metal carbon-supported single-atom catalysts (C-SACs) have emerged as a promising candidate for high-performance room-temperature sodium-sulfur (RT Na-S) batteries, due to their high atom utilization and unique electronic structure. However, the ambiguous electronic-level understanding of Na-dominant s-p hybridization between sodium polysulfides (NaPSs) and p-block C-SACs limits the precise control of coordination environment tuning and electro-catalytic activity manipulation. Here, s-p orbital overlap degree (OOD) between the s orbitals of Na in NaPSs and the p orbitals of p-block C-SACs is proposed as a descriptor for sulfur reduction reaction (SRR) and sulfur oxidation reaction (SOR). Compared to NG and NG-supported InN4 (NG-InN4) SACs, the nitrogen-doped graphene-supported InN5 (NG-InN5) SACs show the largest s-p OOD, demonstrating the weakest shuttle effect and the lowest reaction energy barriers in both SRR and SOR. Accordingly, the designed catalysts allow the Na-S pouch batteries to retain a high capacity of 490.7 mAh g-1 at 2 A g-1 with a Coulombic efficiency of 96 % at a low electrolyte/sulfur (E/S) ratio of 4.5 μl mg-1. This work offers an s-p orbital overlap descriptor describing the interaction between NaPSs and p-orbital-dominated catalysts for high-performance RT Na-S batteries.

Controllable Microwave Heating for Energy-Efficient and Universal Synthesis of Atomically Dispersed Metals on Nitrogen-Doped Carbon Nanofibers.

Carbon-supported single-atom catalysts (SACs) have shown great potential in electrocatalysis, whereas traditional synthesis methods typically involve energy-intensive carbonization processes and unfavorable atomic migration and aggregation. Herein, an energy-efficient and universal strategy is developed to rapidly fabricate various SACs on nitrogen-doped hierarchically porous carbon nanofibers (M-TM/NPCNFs, TM = Fe, Co, Ni, FeCo, and FeNi) by electrospinning and controllable microwave heating technique. Such microwave heating technique enables an ultrafast heating rate (ramping to 900°C in 5 min) to greatly suppress the random migration and aggregation of metal species. Meanwhile, the energy consumption and time can be reduced to 2.5% and less than half an hour, respectively, compared to traditional pyrolysis methods. As a proof of concept, the synthesized M-Fe/NPCNFs with abundant Fe-N4 sites exhibit remarkable oxygen reduction reaction (ORR) activity with a high half-wave potential (E1/2 = 0.88 V) in alkaline media, excellent performance in Zn-air battery with a large discharge specific capacity (801 mAh g-1) and long-term cycle durability (over 1000 h), demonstrating the great potential of the microwave heating technique in efficient fabrication of SACs for energy related applications.

Two-Dimensional Topological Platinum Telluride Superstructures with Periodic Tellurium Vacancies for Efficient and Robust Catalysis.

Defect engineering in the inherently inert basal planes of transition metal dichalcogenides (TMDs), involving the introduction of chalcogen vacancies, represents a pivotal approach to enhance catalytic activity by exposing high-density catalytic metal single-atom sites. However, achieving a single-atom limit spacing between chalcogen vacancies to form ordered superstructures remains challenging for creating uniformly distributed high-density metal single-atom sites on TMDs comparable to carbon-supported single-atom catalysts (SACs). Here we unveil an efficient TMD-based topological catalyst for hydrogen evolution reaction (HER), featuring high-density single-atom reactive centers on a few-layer (7 × 7)-PtTe2-x superstructure. Compared with pristine Pt(111), PtTe2, and (2 × 2)-PtTe2-x, (7 × 7)-PtTe2-x exhibits superior HER performance owing to its substantially increased density of undercoordinated Pt sites, alongside exceptional catalytic stability when operating at high current densities. First-principles calculations confirm that multiple types of undercoordinated Pt sites on (7 × 7)-PtTe2-x exhibit favorable hydrogen adsorption Gibbs free energies, and remain active upon increasing hydrogen coverage. Furthermore, (7 × 7)-PtTe2-x possesses nontrivial band topologies with robust edge states, suggesting potential enhancements for HER. Our findings are expected to advance TMD-based catalysts and exploration of topological materials in catalysis.

Open-cage metallo-azafullerenes as efficient single-atom catalysts toward oxygen reduction reaction.

Very recently, open-cage metallo-azafullerenes PbC100N4H4 and Pb2C100N4H4 containing one Pb-N4-C moiety have been synthesized via the electron beam. Herein, we utilized density functional theory calculations in combination with abinitio molecular dynamics (AIMD) simulations to study the geometric and electronic structures, bonding properties, thermodynamic stability, and catalytic performance of MC100N4H4 and M2C100N4H4 (M = Ge, Sn, Pb). Metal-nitrogen distances and metal-metal distances increase along with the metal radius while the metal atom is positively charged. Energy decomposition analysis revealed that the bonding interactions between M and the C100N4H4 fragment could be described as the donor-acceptor interaction between M(ns0(n-1)d10np4) and C100N4H4 fragment, in which the orbital interactions terms contribute more than the electrostatic interactions. AIMD simulations demonstrate that those metallo-azafullerenes exhibit thermodynamic stability at room temperature. These metallo-azafullerenes, which could serve as typical carbon-supported single-atom catalysts, possess enhanced catalytic performance toward the oxygen reduction reaction (ORR) compared to the planar catalysts, which is attributed to the curvature of metallo-azafullerenes. GeC100N4H4 and SnC100N4H4 exhibit high catalytic performance in the 4e-ORR pathway to H2O, whereas only PbC100N4H4 is suitable for the 2e-ORR reaction pathway because of the difficulty in obtaining electrons. All M2C100N4H4 favors the 4e-reaction pathway due to the presence of the axial metal atom. Our finding of open-cage metallo-azafullerenes as efficient single-atom catalysts holds profound implications for both fundamental research in catalysis and practical applications in fuel cells and other electrochemical devices.

Design Principle of Carbon-Supported Single-Atom Catalysts – Interplay between d-Orbital Periodicity and Local Hybridization

Design Principle of Carbon-Supported Single-Atom Catalysts – Interplay between d-Orbital Periodicity and Local Hybridization

Shedding light on the reversible deactivation of carbon-supported single-atom catalysts in hydrogenation reaction

Shedding light on the reversible deactivation of carbon-supported single-atom catalysts in hydrogenation reaction

Carbon-coordinated atomic cobalt directly embedded on carbon cloth for alkaline hydrogen evolution at high current density

Electrocatalysts for high current density hydrogen evolution reaction (HER) under alkaline conditions is critical for the widespread application of water electrolysis. Carbon-supported single-atom catalysts (SACs) stabilized by N atoms have been demonstrated as efficient electrocatalysts, but mostly for acidic HER. For alkaline HER, although defective-, edge-, and dual-sites have been found to improve the adsorption pathways of the intermediates, there is still a great challenge to precisely synthesize those complex configurations in experiments to maximize the synergistic effects. Since C atom has relatively weak electronegativity than N atom, it can induce different charge redistribution of the metal atom center. However, the reported C-coordinated SACs were derived from the N-containing precursors, which could not exclude the influence of heteroatoms on the activity completely. Herein, we reported the synthesis of carbon-coordinated CoC4 sites and ultra-small Co cluster directly embedded on pure carbon cloth (Co-SA/CC) via the high temperature shockwave (HTS) method. The C atoms on the first coordination shell can tune the local electronic structure and up-shift the d-band center of the Co atom, thus strengthening H2O molecule adsorption and promoting water dissociation. The self-supporting electrode with CoC4 can lower the interfacial contact resistance, leading to higher HER performance compared with that of Pt/C at high current density (e.g. 1000 mA/cm2). These results provide a new insight into the fundamental understanding of design and synthesis of C-coordinated atomically dispersed catalytic sites.

Rapid Melt-Quenching Enables General Synthesis of High-Loading Single-Atom Catalysts with Bicontinuous Nanoporous Structure.

Single-atom catalysts have attracted extensive attention due to their unique atomic structures and extraordinary activities in catalyzing chemical reactions. However, the lack of general and efficient approaches for producing high-density single atoms on suitably tailored supporting matrixes hinders their industrial applications. Here, a rapid melt-quenching strategy with high throughput to synthesize single atoms with high metal-atom loadings of up to 9.7 wt% or 2.6 at% on nanoporous metal compounds is reported, representing several-fold improvements compared to benchmarks in the literature. Mechanism characterizations reveal that the high-temperature melting provides the essential liquid environment and activation energy to achieve the atomization of metals, while the following rapid-quenching pins the isolated metal atoms and stabilizes the coordination environment. In comparison with carbon-supported single-atom catalysts, various collaboration combinations of single atoms and nanoporous metal compounds can be synthesized using the strategy, thus achieving efficient hydrazine oxidation-assisted H2 production. This synthesis protocol is highly compatible with automatic operation, which provides a feasible and general route to design and manufacture specific single-atom catalysts with tunable atomic metal components and supporting matrixes, thus promoting the deployment of single-atom catalysts for various energy technology applications.

Implanting single-atom N2-Fe-B2 catalytic sites in carbon hosts to stabilize high-loading and lean-electrolyte lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries suffer from soluble lithium polysulfide (LiPS) shuttling and sluggish redox kinetics. The rational design of carbon-supported single-atom catalysts (SACs) as both LiPS immobilizers and sulfur redox promoters is of great significance for high-loading and lean-electrolyte Li-S batteries. However, the most popular nonpolar porphyrin-like transition metal-nitrogen (M-N4) SACs cannot maximize the catalytic activity of the metal center. Herein, a B, N co-coordinated N2-Fe-B2 SAC embedded in a B, N-rich carbon matrix (denoted as Fe SAs@BCN) is disclosed for the first time to construct state-of-the-art Li-S batteries. We reveal experimentally and theoretically that the asymmetric N2-Fe-B2 configuration not only rapidly captures LiPSs through strong Lewis acid-base interactions, but also greatly catalyzes the bidirectional sulfur redox chemistry by lowering the Li2S deposition/decomposition energy barriers. As such, the well-designed SACs enable Li-S batteries to promise extraordinary durability (82% retention over 1000 cycles at 5 C) and high areal capacities even under harsh sulfur mass loadings. More encouragingly, a 359 Wh kg−1 pouch cell with an ultrahigh loading of 11.6 mg·S cm−2 and a lean electrolyte to sulfur (E/S) ratio of 3 µL mg·S−1 is further demonstrated. This work shows that N2-Fe-B2 SACs hold great promise in realizing high-energy-density Li-S batteries.

Edge-hosted Atomic Co-N4 Sites on Hierarchical Porous Carbon for Highly Selective Two-electron Oxygen Reduction Reaction.

Not only high efficiency but also high selectivity of the electrocatalysts is crucial for high-performance, low-cost, and sustainable energy storage applications. Herein, we systematically investigate the edge effect of carbon-supported single-atom catalysts (SACs) on oxygen reduction reaction (ORR) pathways (two-electron (2 e- ) or four-electron (4 e- )) and conclude that the 2 e- -ORR proceeding over the edge-hosted atomic Co-N4 sites is more favorable than the basal-plane-hosted ones. As such, we have successfully synthesized and tuned Co-SACs with different edge-to-bulk ratios. The as-prepared edge-rich Co-N/HPC catalyst exhibits excellent 2 e- -ORR performance with a remarkable selectivity of ≈95 % in a wide potential range. Furthermore, we also find that oxygen functional groups could saturate the graphitic carbon edges under the ORR operation and further promote electrocatalytic performance. These findings on the structure-property relationship in SACs offer a promising direction for large-scale and low-cost electrochemical H2 O2 production via the 2 e- -ORR.

Microenvironment Modulation in Carbon‐Supported Single‐Atom Catalysts for Efficient Electrocatalytic CO2 Reduction

The electrocatalytic CO2 reduction reaction (ECRR) becomes an effective way to reduce excess CO2 in the air and a promising strategy to maintain carbon balance. Carbon-supported single-atom catalysts (C-SACs) is a kind of cost savings and most promising catalysts for ECRR. For C-SACs, the key to achieving efficient ECRR performance is to adjusting the electronic structure of the central metal atoms by modulating their microenvironment of the catalysts. Not only the coordination numbers and hetero-atom coordination, but also the regulation of diatomic sites have a great influence on the performance of C-SACs. This review mainly focuses on recent studies for the microenvironment modulation in C-SACs for efficient ECRR. We hope that this review can contribute readers a comprehensive insight in the current research status of C-SACs for ECRR, as well as provide help for the rational design of C-SACs with better ECRR performance.

Unsymmetrically N, S-coordinated single-atom cobalt with electron redistribution for catalytic hydrogenation of quinolines

Engineering unsymmetrical coordination is an efficient strategy for improving the performance of carbon supported single-atom catalysts for diverse applications. However, the exploration of this strategy to prepare carbon supported single-atom catalysts for hydrogenation reaction is still in infancy, especially for hydrogenation of quinolines. Herein, we report a protein-metal-ion-network strategy for preparation of single-atom cobalt supported on hierarchically porous carbon (SA-Co/NSPC). SA-Co/NSPC features unsymmetrically N/S-coordinated metal center, i.e., Co1–N3S1. Moreover, the carbon matrices possess an ultra-thin two-dimensional morphology and hierarchically porous structures. SA-Co/NSPC catalyst with Co1–N3S1 active site exhibits excellent catalytic performance for hydrogenation of N-heterocycles. The DFT calculation results show that the site of Co1–N3S1 reveals a significant electron redistribution in comparison to the Co1–N4, leading to a lower H* diffusion barrier and quinoline hydrogenation reaction barrier. SA-Co/NSPC catalyst combined with the unique hierarchically porous structure and high active Co1–N3S1 owns extraordinary catalytic performance for hydrogenation of quinolines.

Sp-Hybridized Nitrogen as New Anchoring Sites of Iron Single Atoms to Boost the Oxygen Reduction Reaction.

Carbon supported single-atom catalysts with metal-Nx configuration are considered as one of the most efficient catalysts for the oxygen reduction reaction (ORR). However, most of the metal-Nx active sites are composed by pyridinic N at the defect locations of graphene-like supports. Here, we employ graphdiyne (GDY) as a new carbon substrate to synthesize an iron (Fe) single atom catalyst (Fe-N-GDY), showing excellent catalytic performance. Benefitting from the abundant acetylenic bonds in GDY, sp-N anchored metal atoms are created without forming defects. The sp-N and OH ligands regulate the electronic structure of Fe atoms and optimize the adsorption energy of ORR intermediates on the active sites by reducing the electron local density of Fe atoms, which accelerates the reaction kinetics and promotes the ORR activity of Fe-N-GDY. Furthermore, the practical application of Fe-N-GDY is corroborated by its high power density and long-term performance via assembling a zinc-air battery.

A Site Distance Effect Induced by Reactant Molecule Matchup in Single-Atom Catalysts for Fenton-Like Reactions.

Understanding the site interaction nature of single-atom catalysts (SACs), especially densely populated SACs, is vital for their application to various catalytic reactions. Herein, we report a site distance effect, which emphasizes how well the distance of the adjacent copper atoms (denoted as dCu1-Cu1 ) matches with the reactant peroxydisulfate (PDS) molecular size to determine the Fenton-like reaction reactivity on the carbon-supported SACs. The optimized dCu1-Cu1 in the range of 5-6 Å, which matches the molecular size of PDS, endows the catalyst with a nearly two times higher turnover frequency than that of dCu1-Cu1 beyond this range, accordingly achieving record-breaking kinetics for the oxidation of emerging organic contaminants. Further studies suggest that this site distance effect originates from the alteration of PDS adsorption to a dual-site structure on Cu1 -Cu1 sites when dCu1-Cu1 falls within 5-6 Å, significantly enhancing the interfacial charge transfer and consequently resulting in the most efficient catalyst for PDS activation so far.

Carbon-supported single-atom catalysts for advanced rechargeable metal-air batteries

To address the fossil energy crisis and environmental problems, the urgent demand for clean energy has promoted the rapid development of advanced rechargeable metal-air batteries based on the redox reaction couples of gases, such as the oxygen reduction, oxygen evolution, carbon dioxide reduction and carbon dioxide evolution reactions. High-efficiency electrocatalysts are highly desirable to enhance the conversion efficiency of these reactions for enhancing battery performance. Significant advances in single-atom catalysts (SACs) on carbon matrices have been witnessed in recent years as attractive and unique systems to improve the electrocatalytic activities for high-performance rechargeable Zn- and Li-air batteries. This review summarizes the latest achievements in the applications of carbon-supported SACs in metal-air batteries, with a particular focus on the rational design of SACs and their fundamental electrocatalytic mechanism at the atomic level. The future development and perspectives of SACs in the field of metal-air batteries are also discussed.

Limiting the Uncoordinated N Species in M-Nx Single-Atom Catalysts toward Electrocatalytic CO2 Reduction in Broad Voltage Range.

Carbon-supported single-atom catalysts (SACs) are extensively studied because of their outstanding activity and selectivity toward a wide range of catalytic reactions. Amidst its development, excess dopants (e.g., nitrogen) are always required to ensure the high loading content of SACs on the carbon support. However, the use of excess dopants is accompanied by formation of miscellaneous structures (particularly the uncoordinated N species) on catalysts, leading to adverse effects on their performance. Herein, the synthesis of carbon-supported Ni SACs with precisely controlled single-atom structure via joule heating strategy, showing the coordination of 80% of N dopants with metal elements, is reported. The preclusion of the unfavorable N species is confirmed to be the main reason for the superior performance of optimized Ni SACs in electrocatalytic carbon dioxide reduction reaction, which demonstrates unprecedented activity, selectivity, and stability under an exceptionally broad voltage range (>92% CO selectivity in the range of -0.7 to -1.9V reversible hydrogen electrode). Such a synthetic strategy is further applicable for the design of SACs with various metals. This work demonstrates a facile method for preclusion of unfavorable dopants in the SACs and its importance in catalytic application.

Hydrogen Passivation of M–N–C (M = Fe, Co) Catalysts for Storage Stability and ORR Activity Improvements (Adv. Mater. 38/2021)

Single-Atom Catalysts Carbon-supported single-atom catalysts are subjected to surface oxidation and hydroxylation upon long-term exposure to ambient environment, causing severe performance degradation. The hydrogen passivation strategy developed by Jianglan Shui and co-workers in article number 2103600 can protect the catalytic active sites and ultimately improve the storage stability of single-atom catalysts.

Heteroatom-doped porous carbon-supported single-atom catalysts for electrocatalytic energy conversion

Electrocatalysts play a crucial role in the development of renewable energy conversion and storage nanotechnologies. The unique advantages of heteroatom-doped porous carbon-supported single-atom electrocatalysts (SAC-HDPCs) are clear. These SAC-HDPCs exhibit outstanding activity, selectivity and stability due to their distinct electronic structure, satisfactory conductivity, controllable porosity and heteroatom-doping effect. Rapid and significant developments involving the synthesis, characterization, and structure-property-function relationship of SAC-HDPCs have been made in recent years. In this review, we describe recent research efforts involving advanced (in situ) characterization techniques, innovative synthetic strategies, and electrochemical energy conversion examples of SAC-HDPCs. The electrocatalytic performance of SAC-HDPCs is further considered at an atomic level, and the mechanisms underlying this performance are also discussed in detail. We expect that these analyses and deductions will be useful for the design of new materials and may help to establish a foundation for the design of future SAC-HDPCs.