Single Atomic Structure Research Articles

Theoretical investigation of 4d noble metal (Ru, Rh or Pd) single atom structures influencing surface oxygen behavior on SnO2(1 1 0)

Surface oxygen species play a key role in determining the chemi-resistive gas sensing performance of SnO2. Through surface modification, the type of oxygen species at different working temperatures can be modulated, leading to changes in carrier concentration and surface activity. Single atom structures (SAS) hold enormous potential in the gas sensing domain; however, the impact of different SAS on surface oxygen species on SnO2 remains unclear, resulting in inconsistent improvements in sensing properties. This study conducted a theoretical investigation of different 4d noble metal SAS (Ru, Rh, and Pd) modified SnO2(110) surface, encompassing both electronic and chemical sensitization. All three SAS, when substituting penta-coordinated Sn atom (Sn5c), can inject holes and create a thicker depletion layer to varying degrees. Ru and Rh SAS can accelerate the decomposition of adsorbed O2 and O3. More importantly, Ru and Rh can hinder the combination of adsorbed O* species with adjacent two-coordinated lattice oxygen (O2c), enhancing the chemical stability of O*, which plays a decisive role in detecting reducing gases, with Ru exhibiting a better effect. This theoretical work not only enhances methods and mechanisms for adjusting surface oxygen species and improving the sensing performance of SnO2-based gas sensors, but also provides useful guidance for screening and designing SAS in experimental procedures on different semiconductor metal oxide surfaces.

Synergistic ROS Generation via Core-Shell Nanostructures with Increased Lattice Microstrain Combined with Single-Atom Catalysis for Enhanced Tumor Suppression.

This study emphasizes the innovative application of FePt and Cu core-shell nanostructures with increased lattice microstrain, coupled with Au single-atom catalysis, in significantly enhancing •OH generation for catalytic tumor therapy. The combination of core-shell with increased lattice microstrain and single-atom structures introduces an unexpected boost in hydroxyl radical (•OH) production, representing a pivotal advancement in strategies for enhancing reactive oxygen species. The creation of a core-shell structure, FePt@Cu, showcases a synergistic effect in •OH generation that surpasses the combined effects of FePt and Cu individually. Incorporating atomic Au with FePt@Cu/Au further enhances •OH production. Both FePt@Cu and FePt@Cu/Au structures boost the O2 → H2O2 → •OH reaction pathway and catalyze Fenton-like reactions. This enhancement is underpinned by DFT theoretical calculations revealing a reduced O2 adsorption energy and energy barrier, facilitated by lattice mismatch and the unique catalytic activity of single-atom Au. Notably, the FePt@Cu/Au structure demonstrates remarkable efficacy in tumor suppression and exhibits biodegradable properties, allowing for rapid excretion from the body. This dual attribute underscores its potential as a highly effective and safe cancer therapeutic agent.

Boron Regulated Fe Single-Atom Structures for Electrocatalytic Nitrate Reduction to Ammonia

Boron Regulated Fe Single-Atom Structures for Electrocatalytic Nitrate Reduction to Ammonia

Engineering bimetallic single-atom catalysts utilizing the reducibility of HxMoO3 for high efficiency hydrogen evolution

Bimetallic single-atom catalysts have garnered substantial interest due to their extraordinary catalytic prowess, which arises from atomic-level synergistic effects that can significantly enhance hydrogen evolution reaction (HER) kinetics beyond the capabilities of monometallic single-atom catalysts. However, the fabrication of bimetallic single-atom catalysts remains a tremendous challenge. Herein, we introduce an in-situ reduction method to fabricate bimetallic single-atom catalysts anchored on hydrogenated molybdenum trioxide (HxMoO3, 0 < x ≤ 2). Intriguingly, HxMoO3 exhibits inherent reducing capabilities that facilitate the in-situ reduction of some metal ions to metallic single atoms in steps on its surface, thereby enabling the constructing of bimetallic single-atom structures. As a testament to this strategy, the prepared PtM/HxMoO3 catalysts (M = Ag, Au, Pd, Rh) with ultra-low noble metal loadings (wt% < 1%) on the nano-HxMoO3 support exhibit remarkable efficiency in HER. Outperforming both monometallic single-atom catalysts (M/HxMoO3) and commercial Pt/C, these catalysts demonstrate enhanced HER performance, and the PtPd/HxMoO3 exhibits outstanding performance with an overpotentials of 10 mV at 10 mA/cm2, Tafel slope of 36 mV/dec, and long-term durability in acidic media. The presence of Pt single-atom significantly enhances the electrochemical surface area (ECSA) and accelerates the kinetics of the HER for other metal single atoms.

Thermal Transport across Liquid–Solid Interface with a Single-Atomic Structure Based on the Radial Density Depletion Length at a Surface Solid Atom

Thermal Transport across Liquid–Solid Interface with a Single-Atomic Structure Based on the Radial Density Depletion Length at a Surface Solid Atom

Highly dispersed carbon-encapsulated FeS/Fe3C nanoparticles distributed in Fe-N-C for enhanced oxygen electrocatalysis and Zn-air batteries

Transition metal single-atom catalysts (SACs) have been widely used in oxygen reduction reactions (ORR) and oxygen evolution reaction (OER) due to its greatest atomic utilization and low costs, which catalytic performance can be further enhanced by electron distribution adjustment. Herein, we synthesized a carbon-encapsulated FeS/Fe3C nanoparticles doped carbon-based Fe single atom catalyst from fluid catalytic cracking (FCC) slurry though a one-pot pyrolysis. The synergistic effect between FeS/Fe3C nanoparticles and Fe single atom structure (FeNx) promotes the ORR/OER processes, which may due to the reduction of the adsorption free energy of intermediates. Meanwhile, the polyaromatic hydrocarbon in FCC slurry enhances the graphitization of catalyst to facilitate charge transfer in electrocatalysis process, and the carbon-encapsulated nanoparticles sites possess higher stability and dispersion. As a result, the optimized catalyst (FeS/Fe3C@Fe-N-C) presents a high nanoparticles dispersion and graphitization level, which has a higher ORR catalytic ability (E1/2 = 0.91 V vs RHE) compared with commercial Pt/C (20 wt%, E1/2 = 0.879 V vs RHE) and a similar OER catalytic ability (E10 = 0.1.506 V vs RHE) compared with RuO2 (E10 = 1.518 V vs RHE). A liquid Zn-air battery assembled with FeS/Fe3C@Fe-N-C show a peak power density of 113 mW cm−2 and an open potential of 1.432 V. This work sheds light on a new method to design transition metal active sites carbon based single-atom catalyst for enhanced ORR and OER processes.

Single-atom iridium doped ultrathin MoS2 layers as a highly efficient catalyst for the hydrodeoxygenation of 5-hydroxymethylfurfural

The catalytic transformation of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) is of great importance within the context of biomass valorization, but remains a major challenge due to the complicated reaction networks. Herein, single-atom Ir doped ultrathin MoS2 layers were synthesized and used as catalyst for the hydrodeoxygenation of HMF, yielding 96.5% of DMF. The single atomic structure of Ir was determined by X-ray diffraction (XRD), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray absorption fine structure analysis (XAFS), and X-ray photoelectron spectroscopy (XPS). Furthermore, the Ir doped MoS2 catalyst showed excellent stability and did not deactivate after five reaction cycles. This work expands the applications of single-atom catalysts and introduces a new and highly efficient catalyst for the sustainable production of DMF.

Iron-Single-Atom Nanozyme with NIR Enhanced Catalytic Activities for Facilitating MRSA-Infected Wound Therapy.

Patients with methicillin-resistant Staphylococcus aureus (MRSA) infections may have higher death rates than those with non-drug-resistant infections. Nanozymes offer a promising approach to eliminating bacteria by producing reactive oxygen species. However, most of the conventional nanozyme technologies encounter significant challenges with respect to size, composition, and a naturally low number of active sites. The present study synthesizes a iron-single-atom structure (Fe-SAC) via nitrogen doped-carbon, a Fe-N5 catalyst (Fe-SAC) with a high metal loading (4.3 wt.%). This catalyst permits the development of nanozymes consisting of single-atom structures with active sites resembling enzymes, embedded within nanomaterials. Fe-SAC displays peroxidase-like activities upon exposure to H2O2. This structure facilitates the production of hydroxyl radicals, well-known for their strong bactericidal effects. Furthermore, the photothermal properties augment the bactericidal efficacy of Fe-SAC. The findings reveal that Fe-SAC disrupts the bacterial cell membranes and the biofilms, contributing to their antibacterial effects. The bactericidal properties of Fe-SAC are harnessed, which eradicates the MRSA infections in wounds and improves wound healing. Taken together, these findings suggest that single Fe atom nanozymes offer a novel perspective on the catalytic mechanism and design, holding immense potential as next-generation nanozymes.

Advancements in Single Atom Catalysts for Electrocatalytic Nitrate Reduction Reaction

AbstractDue to the urgent demand for nitrate wastewater treatment, the quest for an efficient and environmentally friendly treatment method has emerged as a new research focus. The utilization of single‐atom catalysts (SACs) in electrocatalytic nitrate reduction reaction (NO3RR) for ammonia production is presently recognized as an effective strategy to address pollution issues and obtain high value‐added products. In this review, we summarized the recent research advancements in NO3RR based on SACs. This review includes a comprehensive analysis of the identification and structural determination techniques for SACs, as well as the mechanism of NO3RR over SACs. Furthermore, this review investigates the impact of regulating single atom structures on NO3RR, providing valuable insights for enhancing reaction efficiency. It explores the application of in‐situ technology in real‐time monitoring and control of NO3RR. Finally, perspectives and challenges regarding the application of SACs in NO3RR are presented. Overall, this extensive review offers valuable insights for researchers and industry professionals in the field of nitrate reduction and environmental catalysis.

Antioxidant activities of metal single-atom nanozymes in biomedicine.

Nanozymes are a class of nanomaterials with enzyme-like activity that can mimic the catalytic properties of natural enzymes. The small size, high catalytic activity, and strong stability of nanozymes compared to those of natural enzymes allow them to not only exist in a wide temperature and pH range but also maintain stability in complex environments. Recently developed single-atom nanozymes have metal active sites composed of a single metal atom fixed to a carrier. These metal atoms can act as independent catalytically active centers. Metal single-atom nanozymes have a homogeneous single-atom structure and a suitable coordination environment for stronger catalytic activity and specificity than traditional nanozymes. The antioxidant metal single-atom nanozymes with the ability of removing reactive oxygen species (ROS) can simulate superoxidase dismutase, catalase, and glutathione peroxidase to show different effects in vivo. Furthermore, due to the similar structure of antioxidant enzymes, a metal single-atom nanozyme often has multiple antioxidant activities, and this synergistic effect can more efficiently remove ROS related to oxidative stress. The versatility of single-atom nanozymes encompasses a broad spectrum of biomedical applications such as anti-oxidation, anti-infection, immunomodulatory, biosensing, bioimaging, and tumor therapy applications. Herein, the nervous, circulatory, digestive, motor, immune, and sensory systems are considered in order to demonstrate the role of metal single-atom nanozymes in biomedical antioxidants.

Regulation Strategy of Nanostructured Engineering on Indium-Based Materials for Electrocatalytic Conversion of CO2.

Electrochemical carbon dioxide reduction (CO2 RR), as an emerging technology, can combine with sustainable energies to convert CO2 into high value-added products, providing an effective pathway to realize carbon neutrality. However, the high activation energy of CO2 , low mass transfer, and competitive hydrogen evolution reaction (HER) leads to the unsatisfied catalytic activity. Recently, Indium (In)-based materials have attracted significant attention in CO2 RR and a series of regulation strategies of nanostructured engineering are exploited to rationally design various advanced In-based electrocatalysts, which forces the necessary of a comprehensive and fundamental summary, but there is still a scarcity. Herein, this review provides a systematic discussion of the nanostructure engineering of In-based materials for the efficient electrocatalytic conversion of CO2 to fuels. These efficient regulation strategies including morphology, size, composition, defects, surface modification, interfacial structure, alloying, and single-atom structure, are summarized for exploring the internal relationship between the CO2 RR performance and the physicochemical properties of In-based catalysts. The correlation of electronic structure and adsorption behavior of reaction intermediates are highlighted to gain in-depth understanding of catalytic reaction kinetics for CO2 RR. Moreover, the challenges and opportunities of In-based materials are proposed, which is expected to inspire the development of other effective catalysts for CO2 RR.

Noble-metal-free dual CuNi single-atom embedded in ultrathin ZnIn2S4 for efficient photocatalytic H2 evolution

Developing noble-metal-free dual-metal single-atom catalysts with rich active accessible sites and excellent catalytic activity is very meaningful and challenging, especially for photocatalytic hydrogen production reaction, which can significantly reduce the cost of photocatalytic technology application while reducing the use of noble metals. Herein, a novel noble-metal-free dual CuNi single-atom modified ZnIn2S4 (CuNiSA-ZIS) photocatalyst with high hydrogen production performance were successfully prepared by a hydrothermal method. The ZnIn2S4 with a spherical nanoflower structure is composed of ultrathin nanosheets, and ACHDDAF-STEM results shows that CuNi bimetallic particles are uniformly distributed on the surface of ZnIn2S4 nanosheets and exhibit atomic level dispersion, forming dual-metal single-atom structure. The optimized 1 wt% CuNiSA-ZIS photocatalyst with the Cu/Ni ratio of 1:1 shows the optimum H2 evolution performance with a rate of up to 7844.7 μmol·g−1·h−1 using triethanolamine as a sacrificial reagent, which is significantly improved compared to pristine ZIS, Cu-ZIS and Ni-ZIS samples under simulated sunlight. Electrochemical and spectroscopic characterization results demonstrated that the improved photocatalytic activity of CuNiSA-ZIS was mainly due to the addition of the dual CuNi single atoms with a synergistic effect served as a co-catalyst for ZnIn2S4 photocatalysts, providing efficient active sites for hydrogen evolution while preventing the fast recombination of photo-generated electrons and holes. This study provides a valuable source of ideas for the design of effective noble-metal-free dual-metal single-atom catalysts.

Atomic‐level insights into single Pt atom catalysts on CeO2 support

AbstractPrecious Pt metals deposited on reducible CeO2 oxide have been widely used in exhaust gas treatment. However, the high cost of Pt metals is the main barrier that prevents from applying the Pt metals. Therefore, a lot of efforts have been dedicated to reducing the Pt size as small as possible, aiming at maximizing Pt metal utilization efficiency. The smallest ultimate size that Pt metal can be deposited on CeO2 as single atom structures. Furthermore, the supported single Pt atom catalysts enhance catalytic performance and selectivity compared to Pt cluster or Pt particle counterparts. However, the electronic structures of single Pt atom catalysts at the atomic level are a challenge for the experimentalist, leading to a lack of important information in using these catalysts. Here, we aim to figure out the nature of the high thermal stability of single Pt atom catalysts on CeO2 support using density theory functional and compared to experimental data from previous studies. This study will provide useful information on single Pt atom catalysts on CeO2 support aiming at boosting synthesis and applications applying CeO2‐supported Pt.

Fe, N-codoped carbon derived from different ligands for oxygen reduction reaction in air-cathode microbial fuel cells: Performance comparison and the associated mechanism

In order to clarify the effect of iron ligands on properties, catalysts with different structure through four kinds of ligands are prepared and the oxygen reduction reaction (ORR) activity and the maximum power density in microbial fuel cells (MFCs) are compared. The formed Fe single atoms, the metal-organic framework compound, the Prussia blue crystal and ethylenediamine coordination compound (Phen-Fe, PA-Fe, PB-Fe and EDA-Fe) exhibit the maximum power densities of 2041 ± 23 mW m−2, 1656 ± 32 mW m−2, 1062 ± 31 mW m−2, and 1865 ± 36 mW m−2, respectively. In addition, the electrochemical performance of four catalysts with different structures is significantly different, and the higher exchange current density and 4-electron pathway of Phen-Fe explained the kinetics of ORR. The structures and surface properties are explored through a series of characterizations. The different amounts of nitrogen functionalities, Fe ion, and high graphitization degree are thought to facilitate electron transfer, lower Rct and improve ORR activity. In sum, the iron ligands have a great influence on the structure and performance of catalysts, and the single-atom structure and ethylenediamine coordination structure are proved to be promising structures for ORR in MFCs.

Transition-Metal Single Atom Anchored on MoS2 for Enhancing Photocatalytic Hydrogen Production of g-C3N4 Photocatalysts.

Single-atom catalyst technology with near-100% atomic utilization and a well-defined coordination structure has provided new ideas for designing high-performance photocatalysts, which is also beneficial for reducing the usage of noble metal cocatalysts. Herein, a series of single-atomic MoS2-based cocatalysts where monoatomic Ru, Co, or Ni modify MoS2 (SA-MoS2) for enhancing the photocatalytic hydrogen production performance of g-C3N4 nanosheets (NSs) are rationally designed and synthesized. The 2D SA-MoS2/g-C3N4 photocatalysts with Ru, Co, or Ni single atoms show similar enhanced photocatalytic activity, and the optimized Ru1-MoS2/g-C3N4 photocatalyst has the highest hydrogen production rate of 11115 μmol/h/g, which is about 37 and 5 times higher than that of pure g-C3N4 and MoS2/g-C3N4 photocatalysts, respectively. Experimental and density functional theory calculation results reveal that the enhanced photocatalytic performance is mainly attributed to the synergistic effect and intimate interface between SA-MoS2 with well-defined coordination single-atomic structures and g-C3N4 NSs, which is conducive to the rapid interfacial charge transport, and the unique single-atomic structure of SA-MoS2 with modified electronic structure and appropriate hydrogen adsorption performance offers abundant reactive sites for enhancing the photocatalytic hydrogen production performance. This work provides new insight into improving the cocatalytic hydrogen production performance of MoS2 by a single-atomic strategy.

Memory-dictated dynamics of single-atom Pt on CeO2 for CO oxidation

Single atoms of platinum group metals on CeO2 represent a potential approach to lower precious metal requirements for automobile exhaust treatment catalysts. Here we show the dynamic evolution of two types of single-atom Pt (Pt1) on CeO2, i.e., adsorbed Pt1 in Pt/CeO2 and square planar Pt1 in PtATCeO2, fabricated at 500 °C and by atom-trapping method at 800 °C, respectively. Adsorbed Pt1 in Pt/CeO2 is mobile with the in situ formation of few-atom Pt clusters during CO oxidation, contributing to high reactivity with near-zero reaction order in CO. In contrast, square planar Pt1 in PtATCeO2 is strongly anchored to the support during CO oxidation leading to relatively low reactivity with a positive reaction order in CO. Reduction of both Pt/CeO2 and PtATCeO2 in CO transforms Pt1 to Pt nanoparticles. However, both catalysts retain the memory of their initial Pt1 state after reoxidative treatments, which illustrates the importance of the initial single-atom structure in practical applications.

Revealing Atomic Configuration and Synergistic Interaction of Single-Atom-Based Zn-Co-Fe Trimetallic Sites for Enhancing Oxygen Reduction and Evolution Reactions.

Anchoring single metal atom to carbon supports represents an exceptionally effective strategy to maximize the efficiency of catalysts. Recently, dual-atom catalysts (DACs) emerge as an intriguing candidate for atomic catalysts, which perform better than single-atom catalysts (SACs). However, the clarification of the polynary single-atom structures and their beneficial effects remains a daunting challenge. Here, atomically dispersed triple Zn-Co-Fe sites anchored to nitrogen-doped carbon (ZnCoFe-N-C) prepared by one-step pyrolysis of a designed metal-organic framework precursor are reported. The atomically isolated trimetallic configuration in ZnCoFe-N-C is identified by annular dark-field scanning transmission electron microscopy and spectroscopic techniques. Benefiting from the synergistic effect of trimetallic single atoms, nitrogen, and carbon, ZnCoFe-N-C exhibits excellent catalytic performance in bifunctional oxygen reduction/evolution reactions in an alkaline medium, outperforming other SACs and DACs. The ZnCoFe-N-C-based Zn-air battery exhibits a high specific capacity (liquid state: 931.8Wh kgZn -1 ), power density (liquid state: 137.8mW cm-2 ; all-solid-state: 107.9mW cm-2 ), and good cycling stability. Furthermore, density-functional theory calculations rationalize the excellent performance by demonstrating that the ZnCoFe-N-C catalyst has upshifted d-band center that enhances the adsorption of the reaction intermediates.

Design of material regulatory mechanism for electrocatalytic converting NO/NO3−to NH3progress

AbstractNitric oxide (NO)/nitrate (NO3−) exists as the most hazardous pollutions in the air/water that severely impacts human health. Conventional disposing methods are energy‐consuming and uneconomic. Moreover, ammonia (NH3) fertilizer resources acquire urgent, eco‐friendly, and economical strategies that can remove NO/NO3−pollution and simultaneously convert nitrate species, maintaining nitrogen balance. Electrochemical nitrogen (N) reduction is attracting more attention, particularly electrocatalytic NO/NO3−reduction (ENR) to ammonia supply an approach to fixed nitrogen and generate ammonia. ENR is capable of achieving high NH3yield and Faradaic efficiency (FE), avoiding competitive hydrogen evolution reactions and easily overcoming strong N≡N triple bond (941 kJ mol−1). There are abundant research studies related to ENR for decreasing hazardous NO/NO3−and supplying profitable NH3. In this review, we discuss different electrocatalytic regulations for crystalline facet engineering, heteroatom doping, heterostructure, surface vacancy engineering, and single‐atom structure, which bring various metal/nonmetal and their combined catalysts to the preferable performance, such as reactivity, selectivity, FE, and stability. Finally, we summarize the challenges and provide the perspectives to promote the industrial application of ENR.Key PointsThis review focusing on systematically introduce the different modification strategies and regulatory mechanism to enhance the electrochemical performance for NORR/NO3RR, including crystalline facet engineering, heteroatom doping, heterostructure, surface vacancy engineering, and single atom structure.

Isolated single-atom Fe-N4O1 catalytic site from a pre-oxidation strategy for efficient oxygen reduction reaction

Single-atom catalysts have recently emerged as a promising replacement for noble metal catalysts in the oxygen reduction reaction (ORR) on the cathode side of fuel cells and metal-air batteries. However, regulating the precise coordination environment of central atoms remains challenging. In particular, constructing co-coordination active site with N and O atom is rarely investigated. Here, an unreported pre-oxidation strategy is proposed to establish the Fe-O bond for the synthesis of the Fe-N4O1 single-atom structure. The obtained SA-FeN4O1-C catalyst exhibits remarkable ORR performance, possessing a half-wave potential 30 mV higher than that of the commercial Pt/C and a kinetic current density 7.4 times that of Pt/C at 0.8 V (vs. RHE). More significantly, when employed as an air cathode, the overpotential is 340 mV lower than that of Pt/C when operating at a high current density of 350 mA cm−2 in a GDE half-cell, and a maximum power density of 205.8 mW cm−2 and a high energy density of 1024.9 w h kg−1 can be achieved in a zinc-air battery. According to the DFT, axial oxygen coordination can lower the energy barrier for ORR by driving the d-band center of the Fe atom to shift away from the Fermi level and generate a moderate oxygen adsorption energy. Importantly, the essence of the formation of the Fe-N4O1 structure and single-atomic active sites was revealed. This work opens up an innovative strategy for constructing single-atom sites with axial oxygen coordination and provides valuable insight into the synthesis of atomically dispersed materials.

Isolation of Highly Reactive Cobalt Phthalocyanine via Electrochemical Activation for Enhanced CO2 Reduction Reaction.

Electrochemical CO2 -to-CO conversion offers an attractive and efficient route to recycle CO2 greenhouse gas. Molecular catalysts, like CoPc, are proved to be possible replacement for precious metal-based catalysts. These molecules, a combination of metal center and organic ligand molecule, may evolve into single atom structure for enhanced performance; besides, the manipulation of molecules' behavior also plays an important role in mechanism research. Here, in this work, the structure evolution of CoPc molecules is investigated via electrochemical-induced activation process. After numbers of cyclic voltammetry scanning, CoPc molecular crystals become cracked and crumbled, meanwhile the released CoPc molecules migrate to the conductive substrate. Atomic-scale HAADF-STEM proves the migration of CoPc molecules, which is the main reason for the enhancement in CO2 -to-CO performance. The as-activated CoPc exhibits a maximum FECO of 99% in an H-type cell and affords a long-term durability at 100mA cm-2 for 29.3h in a membrane electrode assembly reactor. Density-functional theory (DFT) calculation also demonstrates a favorable CO2 activation energy with such an activated CoPc structure. This work provides a different perspective for understanding molecular catalysts as well as a reliable and universal method for practical utilization.