Chemical Synthesis of Single Atomic Site Catalysts

Atomic-level engineering Ni-N2O2 interfacial structure for enhanced CO2 electrocatalytic reduction efficiency

The precise atomic-scale preparation of single-atomic active sites with unique coordination structures in electrocatalysts for the carbon dioxide reduction reaction (CO2RR), coupled with the elucidation of their mechanisms at the atomic level, remains a formidable challenge. In this manuscript, a simple one-pot synthesis method was adopted to successfully synthesize an O-doped Ni single-atom catalyst (Ni-NOG), characterized by a distinct Ni-N2O2 symmetric coordination structure. The incorporation of Ni-O bonds alters the electronic configuration of the catalyst's central atoms within the catalyst, thereby boosting both the catalytic selectivity and efficiency during CO2RR. The synthesized electrocatalyst exhibited outstanding performance in the CO2RR process, achieving a Faraday efficiency (FE) of 97.4 % at a potential of -0.8315 V versus to reversible hydrogen electrode (vs. RHE). Furthermore, the selectivity remained consistently above 95 % throughout a 98-hour stability test, surpassing the performance of most advanced catalysts currently available. Theoretical simulations demonstrate that the Ni-N2O2 symmetric coordination structure shows a small activation barrier in the rate-limiting step, favoring the swift generation of intermediate species and demonstrating robust catalytic activity. This work not only offers a straightforward and approach method for the preparation of single-atom catalysts but also clarifies the pivotal role of O-element doping within the coordination environment in enhancing catalyst performance.

Highly efficient nickel-based metal atom cluster/metal oxide microsensors for the rapid and accurate screening of Helicobacter pylori infection

Helicobacter pylori (H. pylori) is a prevalent bacterium that infects the stomach, can cause numerous gastric diseases, and potentially result in stomach cancer. Current H. pylori detection methods have various limitations; thus, to streamline H. pylori detection, we developed an electrochemical microsensor featuring Ni-based atom cluster (AC)/oxide nanocomposite catalysts for direct biomarker identification. By incorporating Ni ACs and transforming Ni oxides into an ultrathin, porous structure, the resulting material exhibited excellent electrocatalytic activity. In particular, it enabled the detection of urease, a biomarker specific to H. pylori, at concentrations as low as 10 ng/mL. The fabricated Ni AC/NiO@laser-etched graphene (LEG) electrochemical microsensor demonstrated excellent sensitivity and specificity in detecting urease within the concentration range of 10-100 ng/mL. Moreover, its accuracy in analyzing clinical samples matched that of commercial enzyme-linked immunosorbent assay kits, highlighting its potential as a platform for both the personal health monitoring and clinical diagnosis of H. pylori infection. This microsensor exhibited excellent sensitivity and precision and rapid recognition with intuitive operation and ease of use. It holds considerable promise in enhancing and improving medical diagnostics by providing timely and accurate information, enabling earlier interventions, and improving patient outcomes.

Hollow mesoporous metal-nitrogen-carbon electrocatalysts with enhanced oxygen reduction activity for zinc-air batteries

While great advances have been achieved in Zn-air batteries, porous cathode catalysts remain crucial and challenging to promote diffusion and boost oxygen reduction reaction (ORR). Herein, an effective strategy has been developed for the synthesis of hollow metal-nitrogen-carbon electrocatalysts to achieve the macro-/meso-/microporous structure. The h-CuNC electrocatalyst exhibits good stability and high ORR activity with a half-wave potential of 0.91 V. Theoretical calculations reveal that CuNC sites can reduce the energy barrier of *OOH adsorption, which is the rate-determining step. Zn-air battery with h-CuNC as the cathode catalyst enables high peak power density of 201 mW cm-2 and good rate performance. Our work demonstrates the concept that hollow mesoporous MNC can significantly improve the catalytic performance by enhancing diffusion.

Well-defined Pt(0) heterogeneous hydrosilylation catalysts supported by a surface bound phosphenium ligand

Single atom, low valent transition metals are important for heterogeneous catalysis but are challenging to generate and stabilize in a well-defined manner. Herein, we explored the functionalization of silica with well-defined N-heterocyclic phosphenium (NHP) ions to heterogenize low-valent metals. The surface electrostatically bound [NHP]+ ions coordinate to Pt(0) precursors, resulting in well-defined, chemisorbed [(NHP)Pt(0)Ln]+ sites. The resulting materials catalyze the hydrosilylation of alkynes and exhibit activities and selectivities that rival the current industry standard homogeneous catalysts. The catalysts leach Pt, limiting their recyclability; however, recycling studies support that the high regioselectivities arise from heterogeneous sites and Pt particles do not form on the surface. We suspect that this phosphenium-based immobilization strategy will result in stable, tunable, low valent heterogeneous transition metal catalysts in a wider array of catalytic reactions.

Sinter- and Water-Resistant Pt Enabled by High Entropy of Porous Oxide Nanofibers

Supported ultrafine noble metal species, especially for Pt, suffer from inevitable sintering at temperatures as low as 80 °C, severely limiting their stability and thus their practical applications. In this work, a strategy is demonstrated using the high-entropy effect to prevent sub-2.6 nm Pt nanoparticles from sintering. Due to the higher mixing entropy and thus lower Gibbs free energy of porous high-entropy oxide (HEO) nanofibers in the catalytic system, the supported Pt remained thermally stable up to 1000 °C, as verified by in situ HAADF-STEM observation. Even after being hydrothermally aged with 10 vol% vapor at 850 °C, this catalytic system maintained the Pt size of 2.9 nm, demonstrating remarkable sinter-resistance and water tolerance. Particularly, after aging at 850 °C, the Pt/HEO catalytic system maintained its full CO conversion for 338 h without any decline. These results highlight the positive effect of increasing configurational entropy on the thermal stability of the entire catalytic system, providing a reliable solution for catalytic conversions involving high temperatures.

Data-Driven Accelerated Discovery Coupled with Precise Synthesis of Single-Atom Catalysts for Robust and Efficient Water Purification

The development of advanced catalysts frequently employs trial-and-error methods and is lack of highly controlled synthesis, resulting in unsatisfactory development efficiency and performance. Here we propose a data-driven prediction coupled with precise synthesis strategy to accelerate the development of single-atom catalysts (SACs) for efficient water purification. The data-driven approach enables the rapid screening and prediction of high-performance SACs from 43 metals-N4 structures comprising transition and main group metal elements, followed by validation and structural modulation for improved performance through a highly controllable hard-template method. Impressively, a well-designed Fe-SAC with a high loading of Fe-pyridine-N4 sites (~3.83 wt %) and highly mesoporous structure, exhibits ultra-high decontamination performance (rate constant of 100.97 min-1 g-2), representing the best Fenton-like activities for sulfonamide antibiotics to date. Furthermore, the optimized Fe-SAC shows excellent robust environmental resistance and cyclic stability with almost 100 % degradation efficiency of sulfonamide antibiotics for 100-h continuous operation. Density functional theory calculations reveal that Fe-pyridine-N4 sites can reduce the energy barrier of intermediate O* formation, the rate-determining step, resulting in highly selective generation of singlet oxygen. The integration of data-driven method with precise synthesis strategy provides a novel paradigm for the rapid development of high-performance catalysts for environmental field as well as other important fields including sustainable energy and catalysis.

SiOx-Rh(111) Interface: Stability and Activation of Small Molecules

SiO2 supported Rh-based catalysts have been extensively used in CO hydrogenation reactions. The incorporation of promoters into the Rh/SiO2 catalyst modulates the charge on Rh, subsequently enhancing its activity and selectivity toward C2 oxygenates. Despite this, the structural and electronic properties of the Rh-SiOx interface have not been exhaustively explored. In this study, silicon was evaporated onto the Rh(111) surface, followed by annealing in O2 to form ultrathin SiOx films. The results indicate that SiOx films grow on the Rh(111) surface in a layer-plus-island mode. The stabilities of the SiOx-Rh interface in O2 with an elevated pressure and vacuum annealing were examined. Both O2 and CO can adsorb in the interface of SiOx-Rh in elevated pressures. The binding energies of Si 2p and O 1s shift as oxygen is adsorbed in the interface. The results provide evidence for the activation of small molecules in the metal-oxide interface, and show a passivation effect of an oxide coated metal surface.

Data-driven discovery of biaxially strained single atoms array for hydrogen production

The structure-performance relationship for single atom catalysts has remained unclear due to the averaged coordination information obtained from most single-atom catalysts. Periodic array of single atoms may provide a platform to tackle this inaccuracy. Here, we develop a data-driven approach by incorporating high-throughput density functional theory computations and machine learning to screen candidates based on a library of 1248 sites from single atoms array anchored on biaxial-strained transition metal dichalcogenides. Our screening results in Au atom anchored on biaxial-strained MoSe2 surface via Au-Se3 bonds. Machine learning analysis identifies four key structural features by classifying the ΔGH* data. We show that the average band center of the adsorption sites can be a predictor for hydrogen adsorption energy. This prediction is validated by experiments which show single-atom Au array anchored on biaxial-strained MoSe2 archives 1000 hour-stability at 800 mA cm-2 towards acidic hydrogen evolution. Moreover, active hotspot consisting of Au atoms array and the neighboring Se atoms is unraveled for enhanced activity.

Atomically Dispersed Metal Interfaces for Analytical Chemistry

ConspectusEngineering sensing interfaces with functional nanomaterials have aroused great interest in constructing novel analytical platforms. The good catalytic abilities and physicochemical properties allow functional nanomaterials to perform catalytic signal transductions and synergistically amplify biorecognition events for efficient target analysis. However, further boosting their catalytic performances poses grand challenges in achieving more sensitive and selective sample assays. Besides, nanomaterials with abundant atomic compositions and complex structural characteristics bring about more difficulties in understanding the underlying mechanism of signal amplification. Atomically dispersed metal catalysts (ADMCs), as an emerging class of heterogeneous catalysts, feature support-stabilized isolated metal catalytic sites, showing maximum metal utilization and a strong metal-support interfacial interaction. These unique structural characteristics are akin to those of homogeneous catalysts, which have well-defined coordination structures between metal sites with synthetic or biological ligands. By integrating the advantages of heterogeneous and homogeneous catalysts, ADMCs present superior catalytic activity and specificity relative to the nanoparticles formed by the nonuniform aggregation of active sites. ADMC-enabled sensing platforms have been demonstrated to realize advanced applications in various fields. Notably, the easily tunable coordination structures of ADMCs bring more opportunities to improve their catalytic performance, further moving toward efficient signal transduction ability. Besides, by leveraging their inherent physicochemical properties and various detection strategies, ADMC-enabled sensing interfaces not only achieve enhanced signal transductions but also show diversified output models. Such superior functions allow ADMC-enabled sensing platforms to access the goal of high-performance detection of trace targets and making significant progress in analytical chemistry.In this Account, we provide an overview of recent progress in atomically dispersed metal-involved interfaces in analytical chemistry. The engineering strategies focused on regulating metal centers, integrating multisite synergy, and tuning charge transport pathways are discussed to boost the catalytic activity and specificity of ADMCs as well as expand their multifunctionality. Combined with various transduction models, including colorimetry, electrochemistry, chemiluminescence, electrochemiluminescence, and photoelectrochemistry, ADMC-based sensors achieve efficient detection of diverse analytes. Specifically, the underlying mechanisms of signal transduction are highlighted. Finally, the perspective and challenges of the ADMC-enabled interface for analytical chemistry are further proposed. We hope that this Account will afford significant inspiration toward the design of ADMCs and the decoding of the improved sensing interfaces.

Ultrafast Synthesis of Single-Atom Catalysts for Electrocatalytic Applications

A recent development in catalytic research, single-atom catalysts (SACs) are one of the most significant categories of catalytic materials. During preparation, individual atoms migrate and agglomerate due to the high surface free energy. The rapid thermal shock strategy addresses this challenge by employing instantaneous high-temperature pulses to synthesize SACs, while minimizing heating duration to prevent metal aggregation and substrate degradation, thereby preserving atomic-level dispersion. The resultant SACs exhibit exceptional catalytic activity, remarkable selectivity, and long-term stability, which have attracted extensive attention in electrocatalysis. In this paper, cutting-edge ultrafast synthesis techniques such as Joule heating, microwave radiation, pulsed discharge, and arc discharge are comprehensively analyzed. Their ability is emphasized to achieve uniform dispersion of separated metal atoms and optimize the catalytic activity for electrocatalytic applications. A systematic summary of SACs synthesized by these rapid methods is provided, with particular emphasis on their implementation in carbon dioxide reduction reaction (CO2RR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR) systems. The review provides an in-depth discussion on the rapid synthesis strategy for development trend, remaining challenges, and the application prospects in electrocatalysis.

Deactivation Mechanism and Mitigation Strategies of Single-Atom Site Electrocatalysts

Single-atom site electrocatalysts (SACs), with maximum atom efficiency, fine-tuned coordination structure, and exceptional reactivity toward catalysis, energy, and environmental purification, have become the emerging frontier in recent decade. Along with significant breakthroughs in activity and selectivity, the limited stability and durability of SACs are often underemphasized, posing a grand challenge in meeting the practical requirements. One pivotal obstacle to the construction of highly stable SACs is the heavy reliance on empirical rather than rational design methods. A comprehensive review is urgently needed to offer a concise overview of the recent progress in SACs stability/durability, encompassing both deactivation mechanism and mitigation strategies. Herein, this review first critically summarizes the SACs degradation mechanism and induction factors at the atomic-, meso- and nanoscale, mainly based on but not limited to oxygen reduction reaction. Subsequently, potential stability/durability improvement strategies by tuning catalyst composition, structure, morphology and surface are delineated, including construction of robust substrate and metal-support interaction, optimization of active site stability, fabrication of porosity and surface modification. Finally, the challenges and prospects for robust SACs are discussed. This review facilitates the fundamental understanding of catalyst degradation mechanism and provides efficient design principles aimed at overcoming deactivation difficulties for SACs and beyond.

Controlled Synthesis of Dy/Cu Bimetallic Atoms for Efficient Artificial Photosynthesis

The birth of metal atom catalysts marked a new historical stage in the field of catalysis, allowing scientists to better understand the science of catalysis at the atomic level. On the basis of anchoring independent metal atoms, bimetal dysprosium-copper atoms are successfully anchored on graphdiyne (DyCu/GDY). Dy and Cu metal atoms are selectively anchored in triangular holes of GDY and stabilized by non-integer charge transfer and the confined space effect between the metals and GDY. The dynamic charge-transfer equilibrium caused by the inherent non-integer charge transfer between GDY and metal atoms produces sustained high activity, inducing a redistribution of surface charge. This result shows that the non-integer charge transfer strongly promotes the adsorption activation of CO2 and the desorption of the reaction intermediates, realizing the unpredictable selectivity and activity of CO2 conversion in the process of artificial photosynthesis, where the selectivity and yield of CO are 98% and 279 µmol gcat. -1 h-1, respectively.

Revealing the structure-activity relationship of Pt1/CeO2 with 17O solid-state NMR spectroscopy and DFT calculations

Single-atom catalysts (SACs) have attracted significant interest due to their exceptional and tunable performance, enabled by diverse coordination environments achieved through innovative synthetic strategies. However, various local structures of active sites pose significant challenges for precise characterization, a prerequisite for developing structure-activity relationships. Here, we combine 17O solid-state NMR spectroscopy and DFT calculations to elucidate the detailed structural information of Pt/CeO2 SACs and their catalytic behaviors. The NMR data reveal that single Pt atoms, dispersed from clusters with water vapor, exhibit a square planar geometry embedded in CeO2 (111) surface, distinct from the original clusters and other conventionally generated Pt single atoms. The square planar Pt/CeO2 SAC demonstrates improved CO oxidation performance compared to Pt/CeO2 SAC with octahedral coordination, due to moderately strong CO adsorption and low energy barriers. This approach can be extended to other oxide-supported SACs, enabling spatially resolved characterization and offering comprehensive insights into their structure-activity relationships.

Engineering the regulation strategy of active sites to explore the intrinsic mechanism over single‑atom catalysts in electrocatalysis

The development of efficient and sustainable energy sources is a crucial strategy for addressing energy and environmental crises, with a particular focus on high-performance catalysts. Single-atom catalysts (SACs) have attracted significant attention because of their exceptionally high atom utilization efficiency and outstanding selectivity, offering broad application prospects in energy development and chemical production. This review systematically summarizes the latest research progress on SACs in five key electrochemical reactions: hydrogen evolution reaction, oxygen reduction reaction, carbon dioxide reduction reaction, nitrogen reduction reaction, and oxygen evolution reaction. Initially, a brief overview of the current understanding of electrocatalytic active sites in SACs is provided. Subsequently, the electrocatalytic mechanisms of these reactions are discussed. Emphasis is placed on various modification strategies for SAC surface-active sites, including coordination environment regulation, electronic structure modulation, support structure regulation, the introduction of structural defects, and multifunctional site design, all aimed at enhancing electrocatalytic performance. This review comprehensively examines SAC deactivation and poisoning mechanisms, highlighting the importance of stability enhancement for practical applications. It also explores the integration of density functional theory calculations and machine learning to elucidate the fundamental principles of catalyst design and performance optimization. Furthermore, various synthesis strategies for industrial-scale production are summarized, providing insights into commercialization. Finally, perspectives on future research directions for SACs are highlighted, including synthesis strategies, deeper insights into active sites, the application of artificial intelligence tools, and standardized testing and performance requirements.

Single-atom catalysts confined in shell layer achieved by a modified top-down strategy for efficient CO2 reduction

High-temperature pyrolysis is a primary method for synthesizing single-atom catalysts (SACs). However, this method accelerates the migration of metal atoms within the solid support, leading to low atom utilization. Herein, we report a novel top-down synthesis strategy wherein surface-sintered nickel sulfide (NiS2) nanoparticles (NPs) are in situ atomized into single atoms, achieving confinement of the single-atom catalyst within the shell layer and synthesizing a high-performance single-atom catalyst. Systematic investigations indicate that driven by strong interactions between metal atoms and the support, the NiS2 NPs on the surface of the support atomize into single Ni atoms, which are predominantly distributed on the support surface, thus enhancing the accessibility of the active sites. Furthermore, theoretical calculations indicate that introducing S atoms into the second coordination shell around Ni atoms significantly reduces the activation energy of the CO2 reduction reaction, thereby enhancing the catalytic performance of the single-atom catalyst. In the flow cell, the Ni single-atom catalyst achieving nearly 100% Faradaic efficiency for CO (FECO) over a wide potential range of -0.5 to -1.3 V versus reversible hydrogen electrode (vs. RHE). At -1.6 V vs. RHE, the partial current density for CO reaches a maximum of 709 mA cm-2 (turnover frequency of 28.67 s-1) with a FECO of 95.9%.

Corrosion-resistant single-atom catalysts for direct seawater electrolysis

Direct seawater electrolysis (DSE) for hydrogen production is an appealing method for renewable energy storage. However, DSE faces challenges such as slow reaction kinetics, impurities, the competing chlorine evolution reaction at the anode, and membrane fouling, making it more complex than freshwater electrolysis. Therefore, developing catalysts with excellent stability under corrosion and fulfilling activity is vital to the advancement of DSE. Single-atom catalysts (SACs) with excellent tunability, high selectivity and high active sites demonstrate considerable potential for use in the electrolysis of seawater. In this review, we present the anodic and cathodic reaction mechanisms that occur during seawater cracking. Subsequently, to meet the challenges of DSE, rational strategies for modulating SACs are explored, including axial ligand engineering, carrier effects and protective layer coverage. Then, the application of in-situ characterization techniques and theoretical calculations to SACs is discussed with the aim of elucidating the intrinsic factors responsible for their efficient electrocatalysis. Finally, the process of scaling up monoatomic catalysts for the electrolysis of seawater is described, and some prospective insights are provided.

Photoinduced Translocation-Transformation Strategy for Vacancy Re-Exposure and Synthesis of Stable Single Atoms

Single-atom catalysts have attracted considerable attention owing to their unparalleled atomic-level efficiencies and distinctive structural properties. However, traditional synthesis methods often lead to less-than-optimal catalytic performance, as single atoms may occupy and block surface vacancies beneficial for catalytic activity. Achieving single-atom dispersion while retaining or reactivating vacancies remains challenging. This paper proposes a photoinduced translocation-transformation strategy using anatase TiO2 with high concentrations of surface oxygen vacancies as a support. Following N doping, Rh nanoparticles are loaded and subsequently disperse into single atoms through a photoinduced treatment accompanied by N translocation, ultimately restoring the oxygen vacancy concentrations to levels comparable to those of the original TiO2. This approach enhances the photocatalytic performance, yielding a hydrogen production rate twofold higher for the single-atom catalyst Rh(SA)/N-TiO2 than for the nanoparticle catalyst Rh(NP)/N-TiO2. This novel method is promising in organic synthesis, CO2 reduction, and nitrogen fixation applications.

Isolated Metal Centers Activate Small Molecule Electrooxidation: Mechanisms and Applications

Electrochemical oxidation of small molecules shows great promise to substitute oxygen evolution reaction (OER) or hydrogen oxidation reaction (HOR) to enhance reaction kinetics and reduce energy consumption, as well as produce high-valued chemicals or serve as fuels. For these oxidation reactions, high-valence metal sites generated at oxidative potentials are typically considered as active sites to trigger the oxidation process of small molecules. Isolated atom site catalysts (IASCs) have been developed as an ideal system to precisely regulate the oxidation state and coordination environment of single-metal centers, and thus optimize their catalytic property. The isolated metal sites in IASCs inherently possess a positive oxidation state, and can be more readily produce homogeneous high-valence active sites under oxidative potentials than their nanoparticle counterparts. Meanwhile, IASCs merely possess the isolated metal centers but lack ensemble metal sites, which can alter the adsorption configurations of small molecules as compared with nanoparticle counterparts, and thus induce various reaction pathways and mechanisms to change product selectivity. More importantly, the construction of isolated metal centers is discovered to limit metal d-electron back donation to CO 2p* orbital and reduce the overly strong adsorption of CO on ensemble metal sites, which resolve the CO poisoning problems in most small molecules electro-oxidation reactions and thus improve catalytic stability. Based on these advantages of IASCs in the fields of electrochemical oxidation of small molecules, this review summarizes recent developments and advancements in IASCs in small molecules electro-oxidation reactions, focusing on anodic HOR in fuel cells and OER in electrolytic cells as well as their alternative reactions, such as formic acid/methanol/ethanol/glycerol/urea/5-hydroxymethylfurfural (HMF) oxidation reactions as key reactions. The catalytic merits of different oxidation reactions and the decoding of structure-activity relationships are specifically discussed to guide the precise design and structural regulation of IASCs from the perspective of a comprehensive reaction mechanism. Finally, future prospects and challenges are put forward, aiming to motivate more application possibilities for diverse functional IASCs.

Advancements and Future Prospectives of Single-Atom Catalysts in CO2 Cycloaddition to Carbonates

The conversion of CO2 and epoxides into cyclic carbonates represents a promising strategy for CO2 utilization and valorization, with applications spanning pharmaceuticals, agrochemicals, polymer manufacturing, and energy storage. This concept article provides a concise perspective on the advancements in CO2 cycloaddition reactions catalyzed by single-atom catalysts (SACs), encompassing photocatalysis, thermocatalysis, and photothermal catalysis. Despite significant progress in the field, challenges such as limited catalytic activity and low stability of SACs under reaction conditions remain significant obstacles to industrial implementation. Mechanistic insights into active species are emphasized to enable the rational design and optimization of catalytic systems. In addition, key industrial challenges, such as the elimination of co-catalysts, scalability limitations, and the development of cost-effective production methods, are critically examined. By bridging fundamental research and practical applications, this concept article seeks to guide future advancements in the sustainable production of cyclic carbonates through CO2 cycloaddition.

Pulsed laser synthesis of free-standing Pt single atoms in an ice block for enhancing photocatalytic hydrogen evolution of g-C3N4

This study reports an innovative synthesis method of a Pt/g-C3N4 single atom catalyst for enhancing photocatalytic hydrogen evolution. The method involves the synthesis of free-standing Pt single atoms within an H2PtCl6 ice block using a pulsed laser reduction process, followed by transferring them onto few-layer g-C3N4 through electrostatic adsorption at low temperature. This approach eliminates the need for high-energy lasers and porous support materials during laser solid-phase synthesis. The photocatalytic activities of Pt/g-C3N4 synthesized under various laser conditions are evaluated to optimize the synthesis parameters. The optimal Pt/g-C3N4 catalyst demonstrates a significantly higher photocatalytic hydrogen evolution capability (320 μmol h-1), 129 times that of pure g-C3N4 (2.2 μmol h-1). This work expands the laser-solid phase synthesis method, offering a promising route for the production of single atom catalysts with simple operation, clear synthetic pathways, low cost, and environmental friendliness.

Toward a Circular Economy of Heteroatom Containing Plastics: A Focus on Heterogeneous Catalysis in Recycling

Plastics play a vital role in modern society, but their accumulation in landfills and the environment presents significant risks to ecosystems and human health. In addition, the discarding of plastic waste constitutes to a loss of valuable material. While the usual mechanical recycling method often results in reduced material quality, chemical recycling offers exciting opportunities to valorize plastic waste into compounds of interest. Its versatility leans on the broad horizon of chemical reactions applicable, such as hydrogenolysis, hydrolysis, alcoholysis, or aminolysis. The development of heterogeneous and supported organocatalysts has enormous potential to enhance the economic and industrial viability of these technologies, reducing the cost of the process and mitigating its global environmental impact. This review summarizes the challenges and opportunities of chemically recycling heteroatom-containing plastics through heterogeneous catalysis, covering widely used plastics such as polyesters (notably PET and PLA), BPA-polycarbonate (BPA-PC), polyurethane (PU), polyamide (PA), and polyether. It examines the potential and limitations of various solid catalysts, including clays, zeolites, and metal-organic frameworks as well as supported organocatalysts and immobilized enzymes (heterogeneous biocatalysts), for reactions that facilitate the recovery of high-value products. By reintroducing these high-value products into the economy as precursors, this approach supports a more sustainable lifecycle for plastics, aligning with the principles of a circular economy.

Organelle-Targeted Photo-triggered Delivery of Acetylperoxyl Radicals for Redox Homeostasis Modulation

Dysfunction of subcellular organelles initiates complex pathophysiological cascades and underlies numerous diseases, underscoring the need for organelle-specific therapeutic interventions. Precise spatiotemporal control of reactive oxygen species (ROS) generation within organelles offers a promising intervention approach. Herein, we report the design and synthesis of a novel series of organelle-targeted, photoactivatable acetylperoxyl radical donors (ACR575s) based on an acetyl-caged rhodamine scaffold. Blue light irradiation triggered the release of highly oxidative acetylperoxyl radicals, concomitantly generating a rhodamine dye for real-time monitoring. In vitro studies demonstrated the organelle-specific delivery of acetylperoxyl radicals, which subsequently induced concentration-dependent oxidative stress within specific subcellular compartments. Notably, this resulted in membrane damage and the modulation of macrophage polarization, providing clear evidence of the therapeutic potential of acetylperoxyl radicals in regulating redox balance and inflammatory responses. The ACR575 series provides a novel toolset for acetylperoxyl radical biology and subcellular redox regulation, enabling precise spatiotemporal control of acetylperoxyl radical-mediated oxidative stress and showing potential for applications in precise cancer therapy.

Highly Durable Rh Single Atom Catalyst Modulated by Surface Defects on Fe-Ce Oxide Solid Solution

Forming defect sites on catalyst supports and immobilizing precious metal atoms at these sites offers an efficient approach for preparing single-atom catalysts. In this study, we employed an Fe-Ce oxide solid solution (FC), which has surface oxygen that reduces more readily than that of ceria, to anchor Rh single atoms (Rh1). When utilized in the selective catalytic reduction of NO with CO (CO-SCR), Rh1/FC reduced at 500 °C-characterized by less oxidic Rh state induced by an oxygen-deficient coordination-exhibited superior activity and durability compared to Rh1/ceria and Rh1/FC reduced at 300 °C. This Rh single-atom structure was sustained after 100 hours of CO-SCR at 400 °C. Reaction intermediates formed on the catalyst surface were analyzed using in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) under NO and CO flow conditions. Additionally, the catalyst structure and the CO-SCR reaction mechanism were investigated using density functional theory (DFT). While Rh atoms located near surface Fe sites were found to be thermodynamically most stable, both NO and CO preferentially adsorbed on Rh sites. Fe plays a role in stabilizing Rh sites and facilitating oxygen transfer. This work provides valuable insights into the design of highly active and durable single-atom catalysts.

Intelligent design and synthesis of energy catalytic materials

Efficient energy conversion and storage are crucial for the sustainable development and growth of renewable energy sources. However, the limited varieties of traditional energy catalytic materials cannot match the fast-expansion requirement of raising various clean energy for industrial applications. Thus, accelerating the design and synthesis of high-performance catalysts is necessary for the application of energy equipment. Recently, with artificial intelligence (AI) technology being advanced by leaps and bounds, it is feasible to efficiently and precisely screen materials and optimize synthesis conditions in a huge unknown space. Here, we introduce and review AI techniques used in the development of catalytic materials in detail. We describe the workflow for designing and synthesizing new materials using machine learning (ML) and robotics. We summarize the sources of data collection, the intelligent algorithms commonly used to build ML models, and the laboratory modules for the intelligent synthesis of materials. We provide the illustrations of predicting the properties of catalytic materials with ML assistance in different material types. In addition, we present the potential strategies for finding material synthesis pathways, and advances in robotics to accelerate high-performance catalytic materials synthesis in the review. Finally, the summary, challenges, and potential directions in the development of AI-assisted catalytic materials are presented and discussed.

Electrochemical Fabrication of Nanoparticles and Single-Atom Catalysts via Cathodic Corrosion

While cathodic corrosion may appear as an undesired degradation process at electrode surfaces, it has become a powerful electrochemical method for fabricating nanoparticles and single-atom catalysts. In contrast to traditional wet chemical synthesis, cathodic corrosion affords rapid, straightforward, capping-agent-free production of nanoparticles, enabling fine control over size, shape, and elemental composition. This mini-review summarizes recent advances in cathodic corrosion-based synthesis, emphasizing its unique capabilities for producing metallic, alloyed, and oxide nanoparticles, as well as single-atom catalysts. It explores the effects of varying parameters such as electrode material, electrolyte composition, voltage waveform, and frequency on the characteristics of the generated particles. Furthermore, it highlights the enhanced electrocatalytic or photoelectrocatalytic performance of the nanoparticles produced via cathodic corrosion.

Interfacial Catalysis at Atomic Level

Heterogeneous catalysts are pivotal to the chemical and energy industries, which are central to a multitude of industrial processes. Large-scale industrial catalytic processes rely on special structures at the nano- or atomic level, where reactions proceed on the so-called active sites of heterogeneous catalysts. The complexity of these catalysts and active sites often lies in the interfacial regions where different components in the catalysts come into contact. Recent advances in synthetic methods, characterization technologies, and reaction kinetics studies have provided atomic-scale insights into these critical interfaces. Achieving atomic precision in interfacial engineering allows for the manipulation of electronic profiles, adsorption patterns, and surface motifs, deepening our understanding of reaction mechanisms at the atomic or molecular level. This mechanistic understanding is indispensable not only for fundamental scientific inquiry but also for the design of the next generation of highly efficient industrial catalysts. This review examines the latest developments in atomic-scale interfacial engineering, covering fundamental concepts, catalyst design, mechanistic insights, and characterization techniques, and shares our perspective on the future trajectory of this dynamic research field.

Mechanism of Hydrogen Generation Catalyzed by a Single Atom and Its Spin Regulation

Single-atom catalysts exhibit the excellent catalytic activity and selectivity, making them widely applicable in the fields of advanced materials, environmental science, and chemical synthesis. However, understanding the mechanism of single-atom catalytic reactions, such as the hydrogen generation reaction, is still challenging, which notably hampers the optimization and precise control of the reaction. Here, we immobilize a single-metal atom model catalyst into a single-molecule electrical detection platform for in situ monitoring of the catalytic hydrogen generation process at the single-event level. In combination with theoretical and experimental studies, the catalytic mechanisms of the hydrogen generation reaction, especially the selection of the catalytic center through charge, spin, and orbital quantum control, are elucidated. In addition, a hydrogen generation process via quantum spin-induced catalysis is observed, in which the turnover frequency increases by about 65 times at a magnetic field of 50 mT. This study provides valuable insights into the intrinsic mechanism of single-metal atom catalysis and opens up unique avenues for their precise control, thus offering a useful strategy for efficiently developing clean energy.

Insights on Morphology and Thermal Stability of Hollow Pt Nanospheres by In Situ Environmental TEM

The fields of catalysis and energy storage nowadays quote the use of nanomaterials with well-defined size, morphology, chemical composition, and thermal stability in the high-temperature range and under harsh conditions of reactions. We present herein an approach based on in situ environmental scanning transmission electron microscopy (STEM), combined with analytical STEM and electron tomography (ET), for the evaluation of the thermal stability of hollow Pt nanospheres under vacuum and high-pressure hydrogen environments. Spherical Pt hollow nanospheres (HNSs) with an average diameter of 15 and 34 nm were synthesized by a galvanic replacement-based procedure using either steep or continuous addition of Pt salts during synthesis. The as-synthesized HNSs exhibit complex 3D structures with shells of a few nm constituted by small Pt nanoparticles and marked by the presence of open channels. The thermal stability of Pt-based HNSs under TEM vacuum and 1 bar of hydrogen flow is reported by considering microstructural changes, e.g., the build-up of a continuous shell and its evolution until HNSs collapse at elevated temperatures (>500 °C). Experimental findings are discussed considering fundamental phenomenological issues, i.e., NP faceting, NP diffusion, and subsequent NP sintering, with respect to the behavior of the systems investigated.

Highly Accessible Electrocatalyst with In Situ Formed Copper-Cluster Active Sites for Enhanced Nitrate-to-Ammonia Conversion

Ammonia synthesis via nitrate electroreduction is more attractive and sustainable than the energy-extensive Haber-Bosch process and intrinsically sluggish nitrogen electroreduction. Herein, we have designed a single-site Cu catalyst on hierarchical nitrogen-doped carbon nanocage support (Cu1/hNCNC) for nitrate electroreduction, which achieves an ultrahigh ammonia yield rate (YRNH3) of 99.4 mol h-1 gCu-1 (2.30 mol h-1 gcat.-1) with ammonia Faradaic efficiency (FENH3) of 99.3%, far beyond the most reported single-site catalysts on carbon-based supports. The combined operando characterization and theoretical studies indicate that the in situ formed Cu-cluster active sites are responsible for the high YRNH3 and FENH3 due to the enhanced NO3- adsorption and subsequent protonation on the unique Cu3-N4 moieties, and meanwhile, the hierarchical hNCNC support facilitates the mass/charge transfer kinetics, thus promoting the high expression of intrinsic activity. The demonstration of plasma N2 oxidization and nitrate electroreduction cascade reaction manifests the great potential of the Cu1/hNCNC electrocatalyst in sustainable NH3 synthesis. These findings offer valuable insights into the design of effective catalysts for electrosynthetic reactions.

Sub-nanometer depth resolution and single dopant visualization achieved by tilt-coupled multislice electron ptychography

Real-space, three-dimensional imaging of atomic structures in materials science is a critical yet challenging task. Although scanning transmission electron microscopy has achieved sub-angstrom lateral resolution through techniques like electron ptychography, depth resolution remains limited to only 2 to 3 nanometers using single-projection setups. Attaining better depth resolution often requires large sample tilt angles and numerous projections, as demonstrated in atomic electron tomography. Here, we introduce an extension of multislice electron ptychography, which couples only a few small-angle projections to improve depth resolution by more than threefold, reaching the sub-nanometer scale and potentially approaching the atomic level. This technique maintains high resolving power for both light and heavy atoms, significantly enhancing the detection of individual dopants. We experimentally demonstrate three-dimensional visualization of dilute praseodymium dopants in a brownmillerite oxide, Ca2Co2O5, along with the accompanying lattice distortions. This approach can be implemented on widely available transmission electron microscopes equipped with hybrid pixel detectors, with data processing achievable using high-performance computing systems.

Recent progress of density functional theory studies on carbon-supported single-atom catalysts for energy storage and conversion

Single-atom catalysts (SACs) have become the forefront and hotspot in energy storage and conversion research, inheriting the advantages of both homogeneous and heterogeneous catalysts. In particular, carbon-supported SACs (CS-SACs) are excellent candidates for many energy storage and conversion applications, due to their maximum atomic efficiency, unique electronic and coordination structures, and beneficial synergistic effects between active catalytic sites and carbon substrates. In this review, we briefly review the atomic-level regulation strategies for optimizing CS-SACs for energy storage and conversion, including coordination structure control, nonmetallic elemental doping, axial coordination design, and polymetallic active site construction. Then we summarize the recent progress of density functional theory studies on designing CS-SACs by the above strategies for electrocatalysis, such as hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, CO2 reduction reaction, nitrogen reduction reaction, and electrosynthesis of urea, and electrochemical energy storage systems such as monovalent metal-sulfur batteries (Li-S and Na-S batteries). Finally, the current challenges and future opportunities in this emerging field are highlighted. This review will provide a helpful guideline for the rational design of the structure and functionality of CS-SACs, and contribute to material optimizations in applications of energy storage and conversion.

Silver single atoms and nanoparticles on floatable monolithic photocatalysts for synergistic solar water disinfection

Photocatalytic water disinfection technology is highly promising in off-grid areas due to abundant year-round solar irradiance. However, the practical use of powdered photocatalysts is impeded by limited recovery and inefficient inactivation of stress-resistant bacteria in oligotrophic surface water. Here we prepare a floatable monolithic photocatalyst with ZIF-8-NH2 loaded Ag single atoms and nanoparticles (AgSA+NP/ZIF). Atomically dispersed Ag sites form an Ag-N charge bridge, extending the lifetime of charge carriers and thereby promoting reactive oxygen species (ROS) generation. The photothermal effect of the plasmonic Ag nanoparticles reduces the bacterial resistance to ROS and impairs DNA repair capabilities. Under sunlight irradiation, the synergistic effect of Ag single atoms and nanoparticles enables 4.0 cm2 AgSA+NP/ZIF to achieve over 6.0 log inactivation (99.9999%) for the stress-resistant Escherichia coli (E. coli) in oligotrophic surface water within 30 min. Furthermore, 36 cm2 AgSA+NP/ZIF is capable of disinfecting at least 10.0 L of surface water, which meets the World Health Organization (WHO) recommended daily per capita drinking water allocation (8.0 L). This study presents a decentralized and sustainable approach for water disinfection in off-grid areas.

Substance migration in the synthesis of single-atom catalysts

Substance migration is universal and crucial in the synthesis of catalysts, which directly affects their existing form and the micro-structure of their active sites. Realizing migration during the synthesis of single-atom catalysts (SACs) is beneficial for not only increasing their metal loading capacity but also manipulating the electronic structures (coordination structure, long-range interactions, etc.) of their metal sites. This review summarizes the thermodynamics and kinetic processes involved in the synthesis of SACs to unveil the fundamental principles involved in their synthesis. For a better understanding of the effect of migration, the migration of both metal (including ions, atoms, and molecules) and nonmetal species is outlined. Moreover, we propose the research directions to guide the rational design of SACs in the future and deepen the fundamental understanding in the formation of catalysts.

On the Tracks to "Smart" Single-Atom Catalysts

Despite their enormous impact in modern heterogeneous catalysis, single-atom catalysts (SACs) continue to puzzle the catalysis community, which often struggles to draw correct conclusions in SAC-catalyzed experiments. In many cases, the reasons for such an uncertainty originate from the lack of knowledge of the exact single-atom evolution under operative conditions and the fundamental factors controlling the fate of the single atom in relation to the catalytic mechanism. This has led to confusion also about correct definition and terminology, where the coined term single-site catalysts reflects the difficulty in defining the true active species as well as in obtaining long-range ordered homogeneous supports [Chi, S.; et al. J. Catal. 2023, 419, 49-57. DOI: 10.1016/j.jcat.2023.02.003]. Most recent studies have attempted to clarify several of the key aspects that are in play during SAC catalysis. However, one largely overlooked opportunity is to take advantage of all the dynamic phenomena occurring at the single metal site to turn the conventional catalytic sequences into a smart, stimulus-responsive, and controllable evolution of the single atom under operative conditions. Such "smartness" could potentially unleash pathways that mitigate some of the typical drawbacks of SACs, such as selectivity and stability. Here we present our vision on these yet-unexplored opportunities for exploiting the dynamicity of SACs, and we discuss various examples that could be the cornerstones for the advent of a next generation of SACs, that we term here "smart" single-atom catalysts (SSACs). Despite smart-behaving SACs still being far from realization, the clues provided here suggest pathways to achieve this goal.

Polyoxometalate-Based Single-Atom Catalyst with Precise Structure and Extremely Exposed Active Site for Efficient H2 Evolution

Single-atom catalysts with precise structure and extremely high catalytic efficiency remain a fervent focus in the fields of materials chemistry and catalytic science. Herein, a nickel-substituted polyoxometalate (POM) {NiSb6O4(H2O)3[β-Ni(hmta)SbW8O31]3}15- (NiPOM) with one extremely exposed nickel site [NiO3(H2O)3] was synthesized using the conventional aqueous method. The uniform dispersion of single nickel center with well-defined structure was facilely achieved by anchoring nanosized NiPOM on graphene oxide (GO). The resulting NiPOM/GO can couple with CdS photoabsorber for the construction of low-cost and ultra-efficient hydrogen evolution system. The H2 yield can reach to 2753.27 mmol gPOM -1 h-1, which represents a record value among all the POM-based photocatalytic systems. Remarkablely, an extremely high hydrogen yield of 3647.28 mmol gPOM -1 h-1 was achieved with simultaneous photooxidation of commercial waste plastic, representing the first POM-based photocatalytic system for H2 evolution and waste plastic conversion. This work highlights a straightforward strategy for constructing extremely exposed single-metal site with precise microenvironment by facilely manipulating nanosized molecular cluster to control individual atom.

Mechanism regulation over dual-atom catalyst enables high-performance oxidative alcohol esterification

The development of heterogeneous catalysts with well-defined uniform isolated or multiple active sites is of great importance for understanding catalytic performances and studying reaction mechanisms. Herein, we present a CoCu dual-atom catalyst (CoCu-DAC) where bonded Co-Cu dual-atom sites are embedded in N-doped carbon matrix with a well-defined Co(OH)CuN6 structure. The CoCu-DAC exhibits higher catalytic activity and selectivity than the Co single-atom catalyst (Co-SAC) and Cu single-atom catalyst (Cu-SAC) counterparts in the catalytic oxidative esterification of alcohols and a variety of methyl and alkyl esters have been successfully synthesized. Kinetic studies reveal that the activation energy (29.7 kJ mol-1) over CoCu-DAC is much lower than that over Co-SAC (38.4 kJ mol-1) and density functional theory (DFT) studies disclose that two different mechanisms are regulated over CoCu-DAC and Co-SAC/Cu-SAC in three-step esterification of alcohols. The bonded Co-Cu and adjacent N species efficiently catalyze the elementary reactions of alcohol dehydrogenation, O2 activation and ester formation, respectively. The stepwise alkoxy pathway (O-H and C-H scissions) is preferred for both alcohol dehydrogenation and ester formation over CoCu-DAC, while the progressive hydroxylalkyl pathway (C-H and O-H scissions) for alcohol dehydrogenation and simultaneous hemiacetal dehydrogenation are favored over Co-SAC and Cu-SAC. Characteristic peaks in the Fourier transform infrared spectroscopy analysis may confirm the formation of the metal-C intermediate and the hydroxylalkyl pathway over Co-SAC.

Coordination Equilibrium-Assisted Coprecipitation Synthesis of Atomically Dispersed 3d Metal Catalysts

As a frontier of heterogeneous catalysis, single-atom catalysts (SACs) have been extensively studied fundamentally. One obstacle that limits the industrial application of SACs is the lack of a synthetic method that can prepare the catalysts on a large scale. Wet-chemistry methods that are conventionally used to prepare nanoparticle-based industrial catalysts might be a solution. In this work, we report a coprecipitation method using ethylenediaminetetraacetic acid (EDTA) as an equilibrium regulator to synthesize a series of atomically dispersed 3d metal over the Mg(OH)2 support. Mg(OH)2 is formed from the spontaneous dissolution of MgO, which is also the alkali source for coprecipitation to occur. The dissolution-precipitation equilibria of metal hydroxides compete with the coordination equilibria of EDTA-coordinated metal cations, leading to the coprecipitation of loaded metal and Mg2+ cations. The synthetic strategy is applicable for Fe, Co, Ni, and Cu, forming four catalysts that are active for the photodegradation of methylene blue under visible light.

Innovative Heating for the Nano Age: Exploring the Potentials of Carbothermal Shock

Heating techniques have underpinned the progress of the material and manufacturing industries. However, the explosive development of nanomaterials and micro/nanodevices has raised more requirements for the heating technique, including but not limited to high efficiency, low cost, high controllability, good usability, scalability, universality, and eco-friendliness. Carbothermal shock (CTS), a heating technique derived from traditional electrical heating, meets these requirements and is advancing at a high rate. In this review, the CTS technique, including the material to support CTS, the power supply to generate CTS, and the method to monitor CTS, is introduced, followed by an overview of the progress achieved in the application of CTS, including the modification and fabrication of nanomaterials as well as many other interesting applications, e.g., soldering/welding of micro- and macroscopic carbon materials, sintering of ceramic electrolytes, recycling of Li-ion battery, thermal tips, actuators, and artificial muscle. Problems and challenges in this area are also pointed out, and future developing directions and prospects are presented.

Switching CO-to-Acetate Electroreduction on Cu Atomic Ensembles

The electrocatalytic reaction pathway is highly dependent on the intrinsic structure of the catalyst. CO2/CO electroreduction has recently emerged as a potential approach for obtaining C2+ products, but it is challenging to achieve high selectivity for a single C2+ product. Herein, we develop a Cu atomic ensemble that satisfies the appropriate site distance and coordination environment required for electrocatalytic CO-to-acetate conversion, which shows outstanding overall performance with an acetate Faradaic efficiency of 70.2% with a partial current density of 225 mA cm-2 and a formation rate of 2.1 mmol h-1 cm-2. Moreover, a single-pass CO conversion rate of 91% and remarkable stability can be also obtained. Detailed experimental and theoretical investigations confirm the significant advantages of the Cu atomic ensembles in optimizing C-C coupling, stabilizing key ketene intermediate (*CCO), and inhibiting the *HOCCOH intermediate, which can switch the CO reduction pathway from the ethanol/ethylene on the conventional metallic Cu site to the acetate on the Cu atomic ensembles.

Manufacturing Single-Atom Alloy Catalysts for Selective CO2 Hydrogenation via Refinement of Isolated-Alloy-Islands

Single-atom alloy (SAA) catalysts exhibit huge potential in heterogeneous catalysis. Manufacturing SAAs requires complex and expensive synthesis methods to precisely control the atomic scale dispersion to form diluted alloys with less active sites and easy sintering of host metal, which is still in the early stages of development. Here, we address these limitations with a straightforward strategy from a brand-new perspective involving the 'islanding effect' for manufacturing SAAs without dilution: homogeneous RuNi alloys were continuously refined to highly dispersed alloy-islands (~1 nm) with completely single-atom sites where the relative metal loading was as high as 40 %. Characterized by advanced atomic-resolution techniques, single Ru atoms were bonded with Ni as SAAs with extraordinary long-term stability and no sintering of the host metal. The SAAs exhibited 100 % CO selectivity, over 55 times reverse water-gas shift (RWGS) rate than the alloys with Ru cluster sites, and over 3-4 times higher than SAAs by the dilution strategy. This study reports a one-step manufacturing strategy for SAA's using the wetness impregnation method with durable high atomic efficiency and holds promise for large-scale industrial applications.

Unveiling the Aggregation of M-N-C Single Atoms into Highly Efficient MOOH Nanoclusters during Alkaline Water Oxidation

M-N-C-type single-atom catalysts (SACs) are highly efficient for the electrocatalytic oxygen evolution reaction (OER). And the isolated metal atoms are usually considered real active sites. However, the oxidative structural evolution of coordinated N during the OER will probably damage the structure of M-N-C, hence resulting in a completely different reaction mechanism. Here, we reveal the aggregation of M-N-C materials during the alkaline OER. Taking Ni-N-C as an example, multiple characterizations show that the coordinated N on the surface of Ni-N-C is almost completely dissolved in the form of NO3 -, accompanied by the generation of abundant O functional groups on the surface of the carbon support. Accordingly, the Ni-N bonds are broken. Through a dissolution-redeposition mechanism and further oxidation, the isolated Ni atoms are finally converted to NiOOH nanoclusters supported by carbon as the real active sites for the enhanced OER. Fe-N-C and Co-N-C also have similar aggregation mechanism. Our findings provide unique insight into the structural evolution and activity origin of M-N-C-based catalysts under electrooxidative conditions.

Tailoring Single-Atom Coordination Environments in Carbon Nanofibers via Flash Heating for Highly Efficient Bifunctional Oxygen Electrocatalysis

The rational design of carbon-supported transition metal single-atom catalysts necessitates precise atomic positioning within the precursor. However, structural collapse during pyrolysis can occlude single atoms, posing significant challenges in controlling both their utilization and coordination environment. Herein, we present a surface atom adsorption-flash heating (FH) strategy, which ensures that the pre-designed carbon nanofiber structure remains intact during heating, preventing unforeseen collapse effects and enabling the formation of metal atoms in nano-environments with either tetra-nitrogen or penta-nitrogen coordination at different flash heating temperatures. Theoretical calculations and in situ Raman spectroscopy reveal that penta-nitrogen coordinated cobalt atoms (Co-N5) promote a lower energy pathway for oxygen reduction and oxygen evolution reactions compared to the commonly formed Co-N4 sites. This strategy ensures that Co-N5 sites are fully exposed on the surface, achieving exceptionally high atomic utilization. The turnover frequency (65.33 s-1) is 47.4 times higher than that of 20 % Pt/C under alkaline conditions. The porous, flexible carbon nanofibers significantly enhance zinc-air battery performance, with a high peak power density (273.8 mW cm-2), large specific capacity (784.2 mAh g-1), and long-term cycling stability over 600 h. Additionally, the flexible fiber-shaped zinc-air battery can power wearable devices, demonstrating significant potential in flexible electronics applications.

Renaissance of Chlorine Evolution Reaction: Emerging Theory and Catalytic Materials

Chlorine (Cl2) is one of the most important commodity chemicals that has found widespread utility in chemical industry. Most Cl2 is currently produced via the chlorine evolution reaction (CER) at the anode of chlor-alkali electrolyzers, for which platinum group-metal (PGM)-based mixed metal oxides (MMOs) have been used for more than half a century. However, MMOs suffer from the use of expensive and scarce PGMs and face selectivity problems due to the parasitic oxygen evolution reaction. Over the last decade, the field of CER catalysis has seen dramatic advances in both the theory and discovery of new catalysts. Theoretical approaches have enabled a fundamental understanding of CER mechanisms and provided catalyst design principles. The exploration of new materials has led to the discovery of CER catalysts other than MMOs, including non-PGM oxides, atomically dispersed single-site catalysts, and organic molecules, with some of which following novel reaction pathways. This minireview provides an overview of the recent advances in CER electrocatalyst research and suggests future directions for this revitalized field.

Constructing Nitrogen-Coordinated Single Atom Catalysts via Bond-Plucking Strategy for Oxidation of Benzene

Single-atom catalysts (SACs) with nitrogen-coordinated active centers feature unique electronic and geometric structures and thus show high catalytic activity for various industrial reactions. Searching for operable synthesis protocols to accurately devise SACs is vital but remains challenging because commonly used high-temperature pyrolysis always causes unpredictable structural changes and inhomogeneous single-atom sites. Herein, a mild bond-plucking strategy is reported to construct atomically dispersed Cu supported on graphene-liked C3N4 (g-C3N4) under lower than 100 °C, and Cu foam is used as the source of metal. When g-C3N4 closely coats the surface of Cu foam, Cu0 atoms on Cu foam transfer electrons to nitrogen on g-C3N4 due to the strong Lewis acbase interaction, simultaneously forming Cuδ+ (0 < δ < 2) and Cu─N bonds. Subsequently, g-C3N4 nanosheets are exfoliated out from the surface of Cu foam, eventually obtaining a well-defined Cu single atoms/g-C3N4 (Cu SAs/g-C3N4) catalyst with atomically dispersed Cu-N3 moieties. Cu SAs/g-C3N4 serves as a highly effective and durable catalyst toward the oxidation of benzene to phenol at 60 °C, with a conversion of 65.1% and selectivity of 97.6% after 12 h. The findings pave a new way to construct well-defined SACs at low costs, promoting large-scale production and industrial application.

Atomically Precise Metal-Metal Oxide Interface in Polyoxometalate-Noble Metal Hybrid Clusters

Metal-metal oxide hybrid materials, typically composed of metal nanoparticles anchored on metal oxides matrix, are devoted enormous attentions as famous heterogeneous catalysts. The interactions between noble metals and metal oxides as well as their interfaces have been proven to be the origin of their excellent catalytic performance. Deep understandings on the interactions between noble metals and metal oxides at atomic precision, thus to precisely assess their contributions to catalysis, can serve as basic principles for catalyst design. In recent years, polyoxometalates (POMs), which in principle can be regarded as atomically precise metal oxide clusters, have been shown to have strong affinity to noble metals, thus forming diverse kinds of POM-noble metal hybrid clusters. Their well-resolved atomically precise structures and hybrid nature promise them as ideal platforms to understand the interfaces and interactions between noble metals and metal oxides. In this review, metal-metal oxide interface is classified into different categories based on the different configurations of hybrid clusters, and aims to understand the interface structures and electronic correlations between POMs and noble metals at the atomic precision. Based on these basic understandings, the study provides the perspectives on the challenges and research efforts to be paid in the future.

High-Density Dual Atoms Pairs Coupling for Efficient Electromagnetic Wave Absorbers

Dual atoms (DAs), characterized by flexible structural tunability and high atomic utilization, hold significant promise for atom-level coordination engineering. However, the rational design with high-density heterogeneous DAs pairs to promote electromagnetic wave (EMW) absorption performance remains a challenge. In this study, high-density Ni─Cu pairs coupled DAs absorbers are precisely constructed on a nitrogen-rich carbon substrate, achieving an impressive metal loading amount of 4.74 wt.%, enabling a huge enhancement of the effective absorption bandwidth (EAB) of EMW from 0 to 7.8 GHz. Furthermore, the minimum reflection loss (RLmin) is -70.96 dB at a matching thickness of 3.60 mm, corresponding to an absorption of >99.99% of the incident energy. Both experimental results and theoretical calculations indicate that the synergistic effect of coupled Ni─Cu pairs DAs sites results in the transfer of electron-rich sites from the initial N sites to the Cu sites, which induces a strong asymmetric polarization loss by this redistribution of local charge and significantly improves the EMW absorption performance. This work not only provides a strategy for the preparation of high-density DA pairs but also demonstrates the role of coupled DA pairs in precisely tuning coordination symmetry at the atomic level.

Merger of Single-Atom Catalysis and Photothermal Catalysis for Future Chemical Production

Photothermal catalysis is an emerging field with significant potential for sustainable chemical production processes. The merger of single-atom catalysts (SACs) and photothermal catalysis has garnered widespread attention for its ability to achieve precise bond activation and superior catalytic performance. This review provides a comprehensive overview of the recent progress of SACs in photothermal catalysis, focusing on their underlying mechanisms and applications. The dynamic structural evolution of SACs during photothermal processes is highlighted, and the current advancements and future perspectives in the design, screening, and scaling up of SACs for photothermal processes are discussed. This review aims to provide insights into their continued development in this rapidly evolving field.

Enhanced Thermal Safety of Hydrophobic SiO2 Aerogels Through Introduction of Layered Double Oxides

This research enhances the thermal safety of hydrophobic silica aerogel (HSA) by integrating layered double oxides (LDOs). XRD and FTIR confirm that the introduction of LDOs does not affect the formation of SA. The LDO/SA composites demonstrate a low density (0.14-0.16 g/cm3), low thermal conductivity (23.28-28.72 mW/(m·K)), high porosity (93.4-96.1%), and a high surface area (899.2-1006.4 m2/g). The TG-DSC results reveal that LDO/SA shows enhanced thermal stability, with increases of 49 °C in the decomposition onset temperature and 47.4 °C in the peak decomposition temperature. The gross calorific value of LDO/SA-15% (with 15 wt% LDO) exhibits a 23.9% reduction in comparison to that of pure SA. The decrease in gross calorific value, along with improved thermal stability, indicates a boost in the thermal safety characteristics of the LDO/SA composites. This study demonstrates that incorporating LDOs enhances the thermal safety of HSA, while preserving its superior performance, thus broadening its potential applications in thermal insulation.

Construction of Interlayered Single-Atom Active Sites on Bipyridine-Based 2D Conjugated Covalent-Organic Frameworks for Boosting the C2 Products of Electrochemical CO2 Reduction

The electrochemical carbon dioxide reduction (eCO2RR) shows great potential in the realization of carbon neutrality, which requires a dedicated catalyst design. To develop electrocatalysts that favor C2 products, herein, the synthetic protocol for engineering interlayered single-atom metal active sites on the bipyridine-linked 2D conjugated covalent-organic framework (2D c-COF) has been developed by utilizing the interlayer π-π stacking. The resultant M@BTT-BPy-COF (where M = Cu, Ni, and Fe) provides fully exposed single-atom active sites with a suitable interdistance for catalyzing the key C-C coupling in the eCO2RR process. The Faradaic efficiency of ethanol (FEethanol) exceeds 40% with M@BTT-BPy-COF at -0.8 V vs RHE, outperforming most reported COF-based electrocatalysts. Density functional calculations suggest that the proximal active sites in the pore channel of COFs are the key active sites for promoting the C-C coupling to generate ethanol product. This investigation presents a novel way to engineer single-atom catalytic centers on 2D c-COFs, displaying the great potential of 2D c-COFs in electrocatalysis.

Anchoring Pt Single-Atom Sites on Vacancies of MgO(Al) Nanosheets as Bifunctional Catalysts to Accelerate Hydrogenation-Cyclization Cascade Reactions

The direct hydrogenation of 2-nitroacylbenzene to 2,1-benzisoxazole presents a significant challenge in the pharmaceutical and fine chemicals industries. In this study, a defect engineering strategy is employed to create bifunctional single-atom catalysts (SACs) by anchoring Pt single atoms onto metal vacancies within MgO(Al) nanosheets. The resultant Pt1/MgO(Al) SAC displays an exceptional catalytic activity and selectivity in the hydrogenation-cyclization of 2-nitroacylbenzene, achieving a 97.5 % yield at complete conversion and a record-breaking turnover frequency of 458.8 h-1 under the mild conditions. The synergistic catalysis between the fully exposed single-atom Pt sites within a unique Pt-O-Mg/Al moiety and the abundant basic sites of the MgO(Al) support is responsible for this outstanding catalytic performance. The current work, therefore, paves the way for developing bifunctional or multifunctional SACs that can enhance efficient organocatalytic conversions.