Single-atom Sites Research Articles

Modulating Electronic Density of Single-Atom Ni Center by Heteroatoms for Efficient CO2 Electroreduction.

Single-atom catalysts (SACs) with unique geometric and electronic configurations have triggered great interest in many important reactions. However, controllably modulating the electronic structure of metal centers to enhance catalytic performance remains a challenge. Here, the electronic structure of Ni centers over Ni1-NC SACs by introducing electron-rich phosphorus or electron-deficient boron for electrochemical CO2 reduction (CO2RR) is systematically tailored. It is found that the Ni1-PNC with Ni1-N3P site exhibits superior performance with a current density of 14.6mA cm-2 and a Faradaic efficiency of 90.6% at -0.8V versus RHE for CO production, far exceeding Ni1-NC and Ni1-BNC SACs. Detailed characterizations and theoretical calculations reveal a linear relationship between the valence state of Ni species and the CO2RR performance. The incorporation of P species facilitates the electronic localization around the Ni1 center, significantly promoting the adsorption of CO2 and the formation of key *COOH intermediate to enhance CO2RR. This work provides a feasible approach to quantitatively manipulate the electronic structure of single-atom metal sites and to rationally design highly efficient catalysts for boosted performance.

Refining the Distinct Cu-N4 Coordination in Mesoporous N-Doped Carbon to Boost Selective Deuteration under Mild Conditions.

Deuterated compounds have broad applications across various fields, with dehalogenative deuteration serving as an efficient method to obtain these molecules. However, the diverse electronic structures of active sites in the heterogeneous system and the limited recyclability in the homogeneous system significantly hinder the advancement of dehalogenative deuteration. In this study, we present a catalyst composed of copper single-atom sites anchored within an ordered mesoporous nitrogen-doped carbon matrix, synthesized via a mesopore confinement method. The Cu1/OMNC-1100 catalyst, characterized by Cu-N4 sites, demonstrates exceptional performance, high functional group tolerance, and remarkable durability in the deuteration of 2-bromo-6-methoxynaphthalene under relatively mild conditions (80 °C, 2 MPa of CO). Experimental results combined with X-ray absorption fine structure analysis reveal that Cu-N3 sites can be converted into more stable Cu-N4 counterparts at higher pyrolysis temperatures, resulting in enhanced catalytic activity. This work demonstrates a strategy for designing single-atom site catalysts with tunable coordination environments, providing a promising approach to improving catalytic performance in selective dehalogenative reactions under relatively mild conditions.

Phase-Engineered Bi-RuO2 Single-Atom Alloy Oxide Boosting Oxygen Evolution Electrocatalysis in Proton Exchange Membrane Water Electrolyzer.

Engineering nanomaterials at single-atomic sites can enable unprecedented catalytic properties for broad applications, yet it remains challenging to do so on RuO2-based electrocatalysts for proton exchange membrane water electrolyzer (PEMWE). Herein, the rational design and construction of Bi-RuO2 single-atom alloy oxide (SAAO) are presented to boost acidic oxygen evolution reaction (OER), via phase engineering a novel hexagonal close packed (hcp) RuBi single-atom alloy. This Bi-RuO2 SAAO electrocatalyst exhibits a low overpotential of 192mV and superb stability over 650h at 10mA cm-2, enabling a practical PEMWE that needs only 1.59V to reach 1.0 A cm-2 under industrial conditions. Operando differential electrochemical mass spectroscopy analysis, coupled with density functional theory studies, confirmed the adsorbate-evolving mechanism on Bi-RuO2 SAAO and that the incorporation of Bi1 improves the activity by electronic density optimization and the stability by hindering surface Ru demetallation. This work not only introduces a new strategy to fabricate high-performance electrocatalysts at atomic-level, but also demonstrates their potential use in industrial electrolyzers.

Revealing the Potential-Dependent Rate-Determining Step of Oxygen Reduction Reaction on Single-Atom Catalysts.

Single-atom catalysts (SACs) have attracted widespread attention due to their potential to replace platinum-based catalysts in achieving efficient oxygen reduction reaction (ORR), yet the rational optimization of SACs remains challenging due to their elusive reaction mechanisms. Herein, by employing ab initio molecular dynamics simulations and a thermodynamic integration method, we have constructed the potential-dependent free energetics of ORR on a single iron atom catalyst dispersed on nitrogen-doped graphene (Fe-N4/C) and further integrated these parameters into a microkinetic model. We demonstrate that the rate-determining step (RDS) of the ORR on SACs is potential-dependent rather than invariant within the operative potential range. Specifically, under the charge-neutral condition, the RDS is calculated to be water desorption with the highest barrier, while as the potential increases, it gradually transitions to the protonation of *OH species, O2* species, and O* species, regardless of the protonation of *OH species as the potential-determining step. Moreover, we reveal the critical role of the dynamic adsorption of axially adsorbed water in facilitating the release of the single-atom site, thus enhancing the ORR rate. Our work has resolved the long-standing controversies over the RDS of ORR on SACs and implies that the step with the lowest exothermicity is not always synonymous with the RDS, highlighting the importance of examining the kinetic barriers under realistic potential conditions for understanding the electrocatalytic performance.

Targeting Synthesis of Diatomic Catalysts by Selective Etching and Sequential Adsorption of Metal Atom.

Diatomic catalysts featuring a tunable structure and synergetic effects hold great promise for various reactions. However, their precise construction with specific configurations and diverse metal combinations is still challenging. Here, a selective etching and metal ion adsorption strategy is proposed to accurately assign a second metal atom (M2) geminal to the single atom site (M1-Nx) for constructing diatomic sites (e.g., Fe-Pd, Fe-Pt, Fe-Ru, Fe-Zn, Co-Fe, Co-Ni, and Co-Cu). In this strategy, hydrogen peroxide selectively etches the positively charged carbon atoms near the M1-Nx moiety (denoted as α-C) and produces vacancy, which could trap the M2 at the subsequent adsorption step. These catalysts show optimized electronic structure and enhanced oxygen reduction activity compared to single-site counterparts, and the representative Fe-Pd-NC and Co-Fe-NC catalysts stand as the most active oxygen reduction reaction catalysts (half-wave potential of 0.92 and 0.91 V, respectively). The selective etching of α-C in single-atom catalysts reported here represents a new post-treatment strategy for the targeting synthesis of diatomic sites.

Highly selective in-situ generation of 1O2 via electronic structure regulation of single atom sites in electro-Fenton system

Highly selective in-situ generation of 1O2 via electronic structure regulation of single atom sites in electro-Fenton system

Acetylene semi-hydrogenation catalyzed by Pd single atoms sandwiched in zeolitic imidazolate frameworks via hydrogen activation and spillover.

The semi-hydrogenation of alkynes into alkenes rather than alkanes is of great importance in the chemical industry, and palladium-based metallic catalysts are currently employed. Unfortunately, a fairly high cost and uncontrollable over-hydrogenation impeded the application of Pd-based catalysts on a large scale. Herein, a sandwich structure single atom Pd catalyst, Z@Pd@Z, was prepared via impregnation exchange and epitaxial growth methods (Z stands for ZIF-8), in which Pd single atoms were stabilized by pyrrolic N in a zeolitic imidazolate framework (ZIF-8). Semi-hydrogenation of acetylene was performed and Z@Pd@Z achieved 100% acetylene conversion at 120 °C with an ethylene selectivity of more than 98.3% at an extra low Pd concentration. Z@Pd@Z exhibited a specific activity of 1872.69 mLC2H4 mgPd-1 h-1, surpassing most of the reported Pd-based catalysts. The existence of Pd single atoms coordinated by nitrogen (Pd-N4) was verified by XAS (synchrotron X-ray absorption spectroscopy), which provided active sites for H2 dissociation and the dissociated hydrogen quickly spilled over the surface of the outer ZIF layer to hydrogenate alkyne to ethene; besides, the catalytic activity could be controlled by adjusting the thickness of the outer ZIF layer. The confinement of the ZIF on Pd single-atom sites and the high energy barrier of ethylene hydrogenation were found to be responsible for the superior C2H2 semi-hydrogenation activity. This work opens up valuable insights into the design of ZIF-derived single-atom catalysts for efficient acetylene selective hydrogenation.

Trinuclear copper cluster-based COF with a high content of Cu–N2 single-atom sites: A multivariate signal-amplified photoelectrochemical aptasensor for the sensitive detection of mycotoxins

Trinuclear copper cluster-based COF with a high content of Cu–N2 single-atom sites: A multivariate signal-amplified photoelectrochemical aptasensor for the sensitive detection of mycotoxins

Electronic Structure Modulation Induced by the Synergy of Cobalt Low-Nuclearity Clusters and Mononuclear Sites for Efficient Oxygen Electrocatalysis.

The development of high-performance bifunctional single-atom catalysts for use in applications, such as zinc-air batteries, is greatly impeded by mild oxygen reduction and evolution reactions (ORR and OER). Herein, we report a bifunctional oxygen electrocatalyst designed to overcome these limitations. The catalyst consists of well-dispersed low-nuclearity Co clusters and adjacent Co single atoms over a nitrogen-doped carbon matrix (CoSA+C/NC). The precisely tailored asymmetric electronic structures are achieved with strong electronic interactions between these Co species. The Co clusters optimize the adsorption/desorption strength of oxygenated intermediates on single-atomic Co sites to endow exceptional activity under alkaline conditions with a half-wave potential (E1/2) of 0.91 V and an overpotential (η) of 340 mV at 10 mA cm-2. In addition, a zinc-air battery assembled with CoSA+C/NC achieves a high power density of 284.1 mW cm-2 and a long operational lifespan of 400 h, superior to those of the benchmark Pt/C + RuO2. Experimental findings and theoretical analysis reveal that the enhanced bifunctional activity stems from the synergistic interactions between Co clusters and single-atomic Co sites. Consequently, the overbinding of *OH is suppressed with accelerated *OH removal. This work establishes the design principle of advanced electrocatalysts with multiphase metal species bearing strong electronic interactions.

Constructing Heterojunction Photocatalyst Systems with Spatial Distribution of Au Single Atoms for CO2 Reduction.

In single-atomic photocatalyst systems, the spatial distribution of single atoms on heterojunctions and its impact on photocatalytic processes, particularly on carrier dynamics and the CO2 reduction process involving multielectron reactions, remains underexplored. To address this gap, a WO3/TiO2 nanotube heterojunction with a spatially selective distribution of Au single atoms was developed using an oxygen vacancy anchoring strategy for CO2 photoreduction. By anchoring Au atoms onto the WO3 or TiO2 components, a substantial number of active sites are generated and the electron transfer pathways from the heterojunction toward Au sites are formed, thereby enhancing carrier separation and concentration. As a result, the total yield of CO2 reduction products increases by 6.3 times and 3.9 times, respectively. More importantly, due to significant differences in adsorption properties, energy band structures, and reaction energy barrier, as well as a 2-fold difference in carrier lifetime, the selective distribution of Au single-atom sites results in completely different CO2 photoreduction products: when Au atoms are anchored on WO3 and TiO2 components, the product selectivity is 67.6% CH4 and 82.9% CO, respectively. This study clarifies the vital role of the spatial distribution of single atoms on the selectivity of electron-demanding products.

Constructing SiO2-Supported Atomically Dispersed Platinum Catalysts with Single-Atom and Atomic Cluster Dual Sites to Tame Hydrogenation Performance

Constructing SiO₂-Supported Atomically Dispersed Platinum Catalysts with Single-Atom and Atomic Cluster Dual Sites to Tame Hydrogenation Performance

Engineering d-p Orbital Hybridization in a Single-Atom-Based Solid-State Electrolyte for Lithium-Metal Batteries.

Regulating lithium salt dissociation kinetics by enhancing the interaction between inorganic fillers and lithium salts is vital for enhancing the ionic conductivity in solid-state composite polymer electrolytes (CPEs). However, the influence of fillers' external electronic environments on lithium salt dissociation dynamics remains unclear. Here, we design single-atom sites in metal-organic framework fillers for poly(ethylene oxide) (PEO)-based CPEs, boosting lithium salt dissociation through an electrocatalytic strategy. This strategy enhances lithium-ion conductivity by tuning the coupling strength between the d and p orbitals of the fillers, as captured by a newly identified descriptor (λ) via high-throughput density functional theory (DFT) calculations and machine learning. The optimal single atom (Ti) sites are incorporated into a ZIF-8 matrix for PEO-based CPEs, achieving an ionic conductivity exceeding 10-3 S cm-1 at 30 °C. Additionally, the electrolyte forms a robust solid electrolyte interphase and is compatible with LiCoO2, LiNi0.9Co0.05Mn0.05O2, and sulfur cathodes. Consequently, the solid-state lithium metal battery with the electrolyte demonstrates excellent cycling stability, maintaining performance over 5000 cycles at 10 C with LiFePO4 cathodes and stable operation at -30 °C. These findings highlight the transformative potential of engineering d-p orbital hybridization by incorporating single-atom sites into inorganic fillers for designing highly ion-conductive CPEs.

Engineering d–p Orbital Hybridization in a Single‐Atom‐Based Solid‐State Electrolyte for Lithium‐Metal Batteries

Regulating lithium salt dissociation kinetics by enhancing the interaction between inorganic fillers and lithium salts is vital for enhancing the ionic conductivity in solid‐state composite polymer electrolytes (CPEs). However, the influence of fillers’ external electronic environments on lithium salt dissociation dynamics remains unclear. Here, we design single‐atom sites in metal‐organic framework fillers for poly(ethylene oxide) (PEO)‐based CPEs, boosting lithium salt dissociation through an electrocatalytic strategy. This strategy enhances lithium‐ion conductivity by tuning the coupling strength between the d and p orbitals of the fillers, as captured by a newly identified descriptor (λ) via high‐throughput density functional theory (DFT) calculations and machine learning. The optimal single atom (Ti) sites are incorporated into a ZIF‐8 matrix for PEO‐based CPEs, achieving an ionic conductivity exceeding 10⁻³ S cm⁻¹ at 30 °C. Additionally, the electrolyte forms a robust solid electrolyte interphase and is compatible with LiCoO₂, LiNi₀.₉Co₀.₀₅Mn₀.₀₅O₂, and sulfur cathodes. Consequently, the solid‐state lithium metal battery with the electrolyte demonstrates excellent cycling stability, maintaining performance over 5000 cycles at 10 C with LiFePO₄ cathodes and stable operation at ‐30 °C. These findings highlight the transformative potential of engineering d‐p orbital hybridization by incorporating single‐atom sites into inorganic fillers for designing highly ion‐conductive CPEs.

Non-Aqueous Electrochemical CO2 Reduction to Multivariate C2-Products Over Single Atom Catalyst at Current Density up to 100mAcm-2.

Electrochemical CO2 reduction reaction (CO2-RR) in non-aqueous electrolytes offers significant advantages over aqueous systems, as it boosts CO2 solubility and limits the formation of HCO3 - and CO3 2- anions. Metal-organic frameworks (MOFs) in non-aqueous CO2-RR makes an attractive system for CO2 capture and conversion. However, the predominantly organic composition of MOFs limits their electrical conductivity and stability in electrocatalysis, where they suffer from electrolytic decomposition. In this work, electrically conductive and stable Zirconium (Zr)-based porphyrin MOF, specifically PCN-222, metalated with a single-atom Cu has been explored, which serves as an efficient single-atom catalyst (SAC) for CO2-RR. PCN- 222(Cu) demonstrates a substantial enhancement in redox activity due to the synergistic effect of the Zr matrix and the single-atom Cu site, facilitating complete reduction of C2 species under non-aqueous electrolytic conditions. The current densities achieved (≈100mAcm- 2) are 4-5 times higher than previously reported values for MOFs, with a faradaic efficiency of up to 40% for acetate production, along with other multivariate C2 products, which have never been achieved previously in non-aqueous systems. Characterization using X-ray and various spectroscopic techniques, reveals critical insights into the role of the Zr matrix and Cu sites in CO2 reduction, benchmarking PCN-222(Cu) for MOF-based SAC electrocatalysis.

Mesoporous Atomically Dispersed Fe Catalysts with Enhanced Nonradical Pathways in Fenton-like Reactions: The Role of SiO2 Templates.

Single-atom catalysts (SACs) are extensively applied in Fenton-like catalytic processes to treat water pollutants. However, the role of the porous structures of SACs supports in catalytic reactions is often overlooked despite its significant contribution to mass diffusion during the reaction. Herein, we adopted a hard-template-assisted approach to fabricate Fe-based SACs (Fe-SACs) featuring a mesoporous architecture. The SiO2 template not only adjusts the pore architecture of the support but also facilitates the conversion of active sites from nanoscale sites to single-atom sites, thereby improving the selectivity for pollutant degradation via nonradical pathways (singlet oxygen and electron transfer mechanism). The experimental results demonstrated that using large-sized SiO2 (∼200 nm) as a template leads to metal aggregation on its surface, forming Fe nanoparticles (Fe-NPs). Fe-NPs exhibit narrow pore structures that prevent peroxymonosulfate (PMS) from being activated, resulting in a slow degradation of pollutants primarily through radical pathways. In contrast, employing small-sized SiO2 (∼10 nm) as a hard template not only produces supports with mesoporous structures but also promotes the building of single-atom active sites. The prepared Fe-SACs effectively activated PMS through nonradical pathways and removed contaminants at a rate k of 0.89 min-1, 33 times faster than Fe-NPs. This template-assisted method sheds light on the synthesis of effective Fenton-like catalysts with porous structures that enhance the efficient breakdown of contaminants in wastewater.

Industry-Level Electrocatalytic CO2 to CO Enabled by 2D Mesoporous Ni Single Atom Catalysts.

Electrocatalytic CO2 reduction reaction (eCO2RR) has captivated widespread attentions, yet achieving the requisite efficiency, selectivity and stability for industrial applications poses a persistent challenge. Here, we report the synthesis of 2D mesoporous Ni single atom catalysts in N-doped carbon framework via a bottom-up interfacial assembly strategy. The 2D mesoporous Ni-N-C catalyst showcases an ultrathin thickness (~6.7 nm) with well-distributed 5 to 40 nm-width mesopores in plane and a high surface area. As a result, the Ni single atom sites with a high density (~6.0 wt %) are almost completely exposed and can be accessible, and the mass transfer can be greatly promoted even at high current densities. Thus, a high current density of 446 mA cm-2 with >95 % CO selectivity in a flow cell can be obtained. Concurrently, the catalyst demonstrates an impressive stability, maintaining a 50-hours continuous electrolysis in the membrane electrode assembly test and achieving an energy efficiency of 42 %. Finite element analysis reveals that the 2D mesoporous design enhances CO2 diffusion, ensuring efficient adsorption and swift CO desorption at high current densities. Our study paves a way for the fabrication of 2D mesoporous single atom catalysts with nearly 100 % accessibility and expedited mass transport.

​Industry‐Level Electrocatalytic CO2 to CO Enabled by 2D Mesoporous Ni Single Atom Catalysts

Electrocatalytic CO2 reduction reaction (eCO2RR) has captivated widespread attentions, yet achieving the requisite efficiency, selectivity and stability for industrial applications poses a persistent challenge. Here, we report the synthesis of 2D mesoporous Ni single atom catalysts in N‐doped carbon framework via a bottom‐up interfacial assembly strategy. The 2D mesoporous Ni‐N‐C catalyst showcases an ultrathin thickness (~6.7 nm) with well‐distributed 5 to 40 nm‐width mesopores in plane and a high surface area. As a result, the Ni single atom sites with a high density (~6.0 wt.%) are almost completely exposed and can be accessible, and the mass transfer can be greatly promoted even at high current densities. Thus, an industry‐level current density of 446 mA cm‐2 with > 95% CO selectivity in a flow cell can be obtained. Concurrently, the catalyst demonstrates an impressive stability, maintaining a 50‐hours continuous electrolysis in the membrane electrode assembly test and achieving an energy efficiency of 42%. Finite element analysis reveals that the 2D mesoporous design enhances CO2 diffusion, ensuring efficient adsorption and swift CO desorption at high current densities. Our study paves a way for the fabrication of 2D mesoporous single atom catalysts with nearly 100% accessibility and expedited mass transport.

Salt template-assisted polymer tethering strategy to achieve high dispersed cobalt single atoms/clusters on porous carbon catalysts for effective Fenton-like reactions

The exploration of the synthesis of porous carbon-supported metal nanocatalysts with high metal loading and dispersion for the development of heterogenous catalysts is important. However, this remains a challenging subject. In this paper, a salt template-assisted polymer tethering strategy was proposed to prepare Co single atom and ultrafine cluster anchored on porous carbon (Co-NPC) with a high-loading of 16.9wt%, thereby exposing high density of reaction sites. The obtained Co-NPC catalyst exhibited excellent catalytic performance for almost 100% degradation of bisphenol A (BPA) within 20min, which is much faster than the CoSA-NPC catalyst with only single atom sites and Co-NC without salt template added. Radical quenching experiments and electron paramagnetic resonance tests verified that both the nonradical oxidation pathway by 1O2, the electron transfer and radical oxidation pathway by •OH, SO4•- appeared during the degradation process. After 3 cycles, the removal rate of BPA did not decrease significantly. The fixed bed experiment revealed that Co-NPC could realize the continuous degradation of methylene blue (MB) with almost 100% degradation efficiency. This research indicated that the strategy by pyrolyzing metal coordinated polymer is a potential method for the synthesis of high metal loading catalyst at gram scale, meeting the requirement of practical applications.

MOF-derived S, N co-doped porous carbon matrix with single Fe atoms and CoSx nanoparticles dual-sites for enhanced oxygen reduction

Metal-air batteries, as a clean energy technology, are of great significance in alleviating the increasingly serious energy and environmental problems, but the sluggish oxygen reduction reaction (ORR) kinetics of air–cathode severely restrict their development. In this work, a zeolitic imidazole frameworks (ZIFs)-derived dual-site electrocatalyst (Fe/CoSx-SNC) composed of Fe single atom and ultrafine cobalt sulfide nanoparticle sites supported on S, N co-doped porous carbon was successfully prepared. Benefited from the advantages of large specific surface area, high porosity, high-density metal centers, and synergistic effects between the dual sites, Fe/CoSx-SNC electrocatalyst presents excellent electrocatalytic ORR activity with a half-wave potential of 0.885 V, a kinetic current density of 27.00 mA cm−2 (at 0.80 V), and good stability, which are superior to the commercial 20 % Pt/C catalyst. The density functional theory (DFT) calculations reveals that the presence of cobalt sulfide nanoparticles could effectively modulate the electron density around Fe single atom, which reduces the desorption energy barrier (rate-determining step) of *OH on Fe sites. In addition, the rechargeable zinc-air battery assembled with Fe/CoSx-SNC as air cathode oxygen catalyst exhibits a high peak power density of 156.63 mW cm−2 and over 100 h of cycling stability. This study provides a straightforward and feasible approach to precisely adjusting the coordination environment and constructing high-performance metal single-atom-based oxygen electrocatalysts, which will be beneficial to promoting the development of metal-air batteries.

The synergistic effect of Co atomic clusters and single atoms facilitates the fenton-like reaction on A- and R-TiO2

The regulation of single atom (SA) sites is crucial for the promotion of advanced oxidation processes (AOPs). Here A- and R-TiO2 with Co mixed sites (clusters and single atoms, CS) were prepared to degrade sulfamethoxazole (SMX) by activating peroxymonosulfate (PMS). Co CS/A-TiO2+PMS system can completely remove SMX within 14 min under secondary effluent and dark conditions, and its rate constant (0.4926 min-1) was 4.4, 3.2 and 2.5 times higher than that of Co SA/R-TiO2, Co SA/A-TiO2 and Co CS/R-TiO2 systems, respectively. Experiments and calculations verified that the electron configuration of Co SA was optimized by Co clusters, facilitating the adsorption, conversion and desorption of PMS by Co SA, leading to the enhancement of Fenton-like activity. Co CS/A-TiO2 catalytic sponges exhibited exceptional degradation performance in microreactor treatment experiment. This work reveals the synergistic effect between SA and clusters at atomic level and provides an all-purpose strategy (catalytic sponge) for the recovery of non-magnetic catalysts in wastewater treatment.