Single-Atom Nano-Islands (SANIs): A Robust Atomic-Nano System for Versatile Heterogeneous Catalysis Applications

Supra-Strong Metal-Support Interaction in Oxide-Solid-Solution-Derived Transition Metal Catalysts

Transition metal catalysts with electron-deficient active sites (Mδ+) can exhibit unique activity and selectivity in hydrogenation reactions but are prone to deactivation under high-temperature reaction conditions due to the reduction of Mδ+. Here the existence of a supra-strong metal-support-interaction in oxide-solid-solution-derived nickel catalysts are reported, which greatly enhances the stability of Niδ+ against reduction. It is found that the reduction of Ni species from solid solutions of NiO and magnesium aluminum spinel occurs at higher temperatures compare to pristine NiO, which is attributed to the strengthened binding of Ni atoms to ligand oxygen atoms for the former. The strength of the metal-support interaction in the final catalysts can be tuned by controlling the calcination temperature of the impregnation process and thus the degree of solid solution formation from separated oxide precursors. Notably, the optimized Ni catalyst with durable electron-deficient sites exhibits a sustained CO output with a 100% selectivity and ≈30% CO2 conversion at 600 °C in catalyzing the reverse water-gas shift reaction.

Breaking symmetry for better catalysis: insights into single-atom catalyst design

Breaking structural symmetry has emerged as a powerful strategy for fine-tuning the electronic structure of catalytic sites, thereby significantly enhancing the electrocatalytic performance of single-atom catalysts (SACs). The inherent symmetric electron density in conventional SACs, such as M-N4 configurations, often leads to suboptimal adsorption and activation of reaction intermediates, limiting their catalytic efficiency. By disrupting this symmetry of SACs, the electronic distribution around the active center can be modulated, thereby improving both the selectivity and adsorption strength for key intermediates. These changes directly impact the reaction pathways, lowering energy barriers, and enhancing catalytic activity. However, achieving precise modulation through SAC symmetry breaking for better catalysis remains challenging. This review focuses on the atomic-level symmetry-breaking strategies of catalysts, including charge breaking, coordination breaking, and geometric breaking, as well as their electrocatalytic applications in electronic structure tuning and active site modulation. Through modifications to the M-N4 framework, three primary configurations are achieved: unsaturated coordination M-Nx(x=1,2,3), non-metallic doping MX-Nx(x=1,2,3), and bimetallic doping M1M2-N4. Advanced characterization techniques combined with density functional theory (DFT) elucidate the impact of these strategies on oxidation, reduction, and bifunctional catalytic reactions. This review highlights the significance of symmetry-breaking structures in catalysis and underscores the need for further research to achieve precise control at the atomic-level.

Core-Shell Quantum Wires-Supported Single-Atom Fe Electrocatalysts for Efficient Overall Water Splitting

It is of great significance for the development of hydrogen energy technology by exploring the new-type and high-efficiency electrocatalysts (such as single atom catalysts (SACs)) for water splitting. In this paper, by combining interface engineering and doping engineering, a unique single atom iron (Fe)-doped carbon-coated nickel sulfide (Ni3S2) quantum wires (Ni3S2@Fe-SACs) is prepared as a high-performance bi-functional electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Theoretical calculation and experimental results show that the addition of atomic Fe species can effectively adjust the electronic structure of sulfide, the interfacial electron transfer modulates the d-band center position, optimizing the transient state of the catalytic process and adsorption energy of hydrogen/oxygen intermediates, and greatly accelerates the kinetics of HER and OER. The results show that the Ni3S2@Fe-SACs core-shell quantum wires array exhibit overpotentials of 46 and 219 mV for HER and OER at 10 mA cm-2 in 1 m KOH, respectively. In addition, the two-electrode electrolyzer assembled by the Ni3S2@Fe-SACs requires a voltage as low as 1.465 V to achieve alkaline overall water splitting of 10 mA cm-2. This work holds great promise for the development of highly active and highly stable electrocatalysts for future hydrogen energy conversion applications.

Advanced Palladium Nanosheet-Enhanced Phototherapy for Treating Wound Infection Caused by Multidrug-Resistant Bacteria

With the increasing spread of multidrug-resistant (MDR) bacteria worldwide, it is needed to develop antibiotics-alternative strategies for the treatment of bacterial infections. This work develops a multifunctional single-component palladium nanosheet (PdNS) with broad-spectrum and highly effective bactericidal activity against MDR bacteria. PdNS exerts its endogenous nanoknife (mechanical cutting) effect and peroxidase-like activity independent of light. Under near-infrared region (NIR) light irradiation, PdNS exhibits photothermal effect to produce local heat and meanwhile possesses photodynamic effect to generate 1O2; notably, PdNS has catalase-like activity-dependent extra photodynamic effect upon H2O2 addition. PdNS+H2O2+NIR employs a collectively synergistic mechanism of nanoknife effect, peroxidase/catalase-like catalytic activity, photothermal effect, and photodynamic effect for bacterial killing. PdNS+H2O2+NIR causes compensatory elevated phospholipid biosynthesis, disordered energy metabolism, increased cellular ROS levels and excessive oxidative stress, and inhibited nucleic acid synthesis in bacteria. In mice, PdNS+H2O2+NIR gives >92.7% bactericidal rates at infected wounds and almost the full recovery of infected wounds, and it leads to extensive down-regulation of proinflammatory pathways and comprehensive up-regulation of wound healing pathways, conferring elevated inflammation resolution and meanwhile accelerated wound repair. PdNS+H2O2+NIR represents a highly efficient nanoplatform for photoenhanced treatment of superficial infections.

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.

Nano-island-encapsulated cobalt single-atom catalysts for breaking activity-stability trade-off in Fenton-like reactions

Single-atom catalysts (SACs) have been increasingly acknowledged for their performance in sustainable Fenton-like catalysis. However, SACs face a trade-off between activity and stability in peroxymonosulfate (PMS)-based systems. Herein, we design a nano-island encapsulated single cobalt atom (CoSA/Zn.O-ZnO) catalyst to enhance the activity and stability of PMS activation for contaminant degradation via an "island-sea" synergistic effect. In this configuration, small carrier-based ZnO nanoparticles (the "islands") are utilized to confine and stabilize Co single atoms. The expansive ZnO substrate (the "sea") upholds a neutral microenvironment within the reaction system. The CoSA/Zn.O-ZnO/PMS system exhibits a remarkable selectivity in exclusively generating sulfate radicals (SO4•-), leading to a complete removal of various recalcitrant pollutants within a shorter period. Characterized by minimal leaching of active sites, robust catalytic performance, and low-toxicity decontamination, this system proves highly efficient in multiple treatment cycles and complex water matrices. The design effectively breaks the activity-stability trade-off typically associated with SACs.

Controllable Regulation of CO2 Adsorption Behavior via Precise Charge Donation Modulation for Highly Selective CO2 Electroreduction to Formic Acid

The synthesis of value-added products via CO2 electroreduction (CO2ER) is of great significance, but the development of efficient and versatile strategies for the controllable selectivity tuning is extremely challenging. Herein, the tuning of CO2ER selectivity through the modulation of CO2 adsorption behavior is proposed. Using the constructed zeolitic MOF (SNNU-339), CO2 adsorption behavior is controllably changed from *CO2 to CO2* via the precise ligand-to-metal charge donation (LTMCD) regulation. It is confirmed that the high electronegativity of the coordinate ligand directly restricts the LTMCD, reduces the charge density on the metal sites, lowers the Gibbs free energy for CO2* adsorption, and leads to the transformation of CO2 adsorption mode from *CO2 to CO2*. Owing to the modulated CO2 adsorption behavior and regulated kinetics, SNNU-339 exhibits superior HCOOH selectivity (≈330% promotion, 85.6% Faradaic efficiency) and high CO2ER activity. The wide applicability of the proposed approach sheds light on the efficient CO2ER. This study provides a competitive strategy for rational catalyst design and underscores the significance of adsorption behavior tuning in electrocatalysis.

Designing Robust Single Atom Catalysts by Three-in-One Strategy: Sub-1-nm Space Confining, Bimetallic Bonding and Reaction-Induced Forming Active Sites

It is imperative to design robust single atom catalysts (SACs) that maintain the stability of the active component under diverse reaction conditions and prevent aggregation or deactivation. Confining the single atom active site within sub-nanometer (sub-1-nm) spaces has proven effective in enhancing the stability and activity of the catalyst, owing to the strong constraints and regulations imposed on atomic behavior at this scale. Bimetallic bond atomic sites, comprising two distinct metal compositions, often exhibit unique electronic structures and catalytic properties. Designing SACs under reaction-induced conditions, such as varying temperatures, pressures, and atmospheres, can facilitate a deeper understanding of the formation and migration behavior of active sites in real reactions, as well as the optimization mechanisms for performance enhancement. The objective of this review is to promote a robust SAC design strategy that encapsulates bimetallic bonding active sites within sub-1-nm spaces and investigates catalyst preparation and performance under reaction-induced conditions. This design strategy is anticipated to bolster the catalytic activity and stability of the catalyst while also offering fresh perspectives and optimization avenues for the catalytic processes involved in practical chemical reactions.

Cohesive energy discrepancy drives the fabrication of multimetallic atomically dispersed materials for hydrogen evolution reaction

Atomically dispersed single atom (SA) and atomic cluster (AC) metallic materials attract tremendous attentions in various fields. Expanding monometallic SA and AC to multimetallic SA/AC composites opens vast scientific and technological potentials yet exponentially increasing the synthesis difficulty. Here, we present a general energy-selective-clustering methodology to build the largest reported library of carbon supported bi-/multi-metallic SA/AC materials. The discrepancy in cohesive energy results into selective metal clustering thereby driving the symbiosis of multimetallic SA or/and AC. The library includes 23 bimetallic SA/AC composites, and expanded compositional space of 17 trimetallic, quinary-metallic, septenary-metallic SA/AC composites. We chose bimetallic M1SAM2AC to demonstrate the electrocatalysis utility. Unique decoupled active sites and inter-site synergy lead to 8/47 mV overpotential at 10 mA cm-2 for alkaline/acidic hydrogen evolution and over 1000 h durability in water electrolyzer. Moreover, delicate modulations towards composition and configuration yield high-performance catalysts for multiple electrocatalysis systems. Our work broadens the family of atomically dispersed materials from monometallic to multimetallic and provides a platform to explore the complex composition induced unconventional effects.

Heteroatom Immobilization Engineering toward High-Performance Metal Anodes

Heteroatom immobilization engineering (HAIE) is becoming a forefront approach in materials science and engineering, focusing on the precise control and manipulation of atomic-level interactions within heterogeneous systems. HAIE has emerged as an efficient strategy to fabricate single-atom sites for enhancing the performance of metal-based batteries. Despite the significant progress achieved through HAIE in metal anodes for metal-based batteries, several critical challenges such as metal dendrites, side reactions, and sluggish reaction kinetics are still present. In this review, we delve into the fundamental principles underlying heteroatom immobilization engineering in metal anodes, aiming to elucidate its role in enhancing the electrochemical performance in batteries. We systematically investigate how HAIE facilitates uniform nucleation of metal in anodes, how HAIE inhibits side reactions at the metal anode-electrolyte interface, and the role of HAIE in promoting the desolvation of metal ions and accelerating reaction kinetics within metal-based batteries. Finally, we discuss various strategies for implementing HAIE in electrode materials, such as high-temperature pyrolysis, vacancy reduction, and molten-salt etching and anchoring. These strategies include selecting appropriate heteroatoms, optimizing immobilization methods, and constructing material architectures. They can be utilized to further refine the performance to enhance the capabilities of HAIE and facilitate its widespread application in next-generation metal-based battery technologies.

Promoted hydrogenation of CO2 to methanol over single-atom Cu sites with Na+-decorated microenvironment

Although single-atom Cu sites exhibit high efficiency in CO2 hydrogenation to methanol, they are prone to forming Cu nanoparticles due to reduction and aggregation under reaction conditions, especially at high temperatures. Herein, single-atom Cu sites stabilized by adjacent Na+ ions have been successfully constructed within a metal-organic framework (MOF)-based catalyst, namely MOF-808-NaCu. It is found that the electrostatic interaction between the Na+ and Hδ- species plays a pivotal role in upholding the atomic dispersion of Cu in MOF-808-NaCu during CO2 hydrogenation, even at temperatures of up to 275°C. This exceptional stabilization effect endows the catalyst with excellent activity (306 g·kgcat-1·h-1), high selectivity to methanol (93%) and long-term stability at elevated reaction temperatures, far surpassing the counterpart in the absence of Na+ (denoted as MOF-808-Cu). This work develops an effective strategy for the fabrication of stable single-atom sites for advanced catalysis by creating an alkali-decorated microenvironment in close proximity.

Atom-Level Tandem Catalysis in Lithium Metal Batteries

High-energy-density lithium metal batteries (LMBs) are limited by reaction or diffusion barriers with dissatisfactory electrochemical kinetics. Typical conversion-type lithium sulfur battery systems exemplify the kinetic challenges. Namely, before diffusing or reacting in the electrode surface/interior, the Li(solvent)x + dissociation at the interface to produce isolated Li+, is usually a prerequisite fundamental step either for successive Li+ "reduction" or for Li+ to participate in the sulfur conversions, contributing to the related electrochemical barriers. Thanks to the ideal atomic efficiency (100 at%), single atom catalysts (SACs) have gained attention for use in LMBs toward resolving the issues caused by the five types of barrier-restricted processes, including polysulfide/Li2S conversions, Li(solvent)x + desolvation, and Li0 nucleation/diffusion. In this perspective, the tandem reactions including desolvation and reaction or plating and corresponding catalysis behaviors are introduced and analyzed from interface to electrode interior. Meanwhile, the principal mechanisms of highly efficient SACs in overcoming specific energy barriers to reinforce the catalytic electrochemistry are discussed. Lastly, the future development of high-efficiency atomic-level catalysts in batteries is presented.

High-Volumetric Density Atomic Cobalt on Multishell ZnxCd1-xS Boosts Photocatalytic CO2 Reduction

The volumetric density of the metal atomic site is decisive to the operating efficiency of the photosynthetic nanoreactor, yet its rational design and synthesis remain a grand challenge. Herein, we report a shell-regulating approach to enhance the volumetric density of Co atomic sites onto/into multishell ZnxCd1-xS for greatly improving CO2 photoreduction activity. We first establish a quantitative relation between the number of shell layers, specific surface areas, and volumetric density of atomic sites on multishell ZnxCd1-xS and conclude a positive relation between photosynthetic performance and the number of shell layers. The triple-shell ZnxCd1-xS-Co1 achieves the highest CO yield rate of 7629.7 μmol g-1 h-1, superior to those of the double-shell ZnxCd1-xS-Co1 (5882.2 μmol g-1 h-1) and single-shell ZnxCd1-xS-Co1 (4724.2 μmol g-1 h-1). Density functional theory calculations suggest that high-density Co atomic sites can promote the mobility of photogenerated electrons and enhance the adsorption of Co(bpy)32+ to increase CO2 activation (CO2 → CO2* → COOH* → CO* → CO) via the S-Co-bpy interaction, thereby enhancing the efficiency of photocatalytic CO2 reduction.

Atomically Precise Single-Site Catalysts via Exsolution in a Polyoxometalate-Metal-Organic-Framework Architecture

Single-site catalysts (SSCs) achieve a high catalytic performance through atomically dispersed active sites. A challenge facing the development of SSCs is aggregation of active catalytic species. Reducing the loading of these sites to very low levels is a common strategy to mitigate aggregation and sintering; however, this limits the tools that can be used to characterize the SSCs. Here we report a sintering-resistant SSC with high loading that is achieved by incorporating Anderson-Evans polyoxometalate clusters (POMs, MMo6O24, M = Rh/Pt) within NU-1000, a Zr-based metal-organic framework (MOF). The dual confinement provided by isolating the active site within the POM, then isolating the POMs within the MOF, facilitates the formation of isolated noble metal sites with low coordination numbers via exsolution from the POM during activation. The high loading (up to 3.2 wt %) that can be achieved without sintering allowed the local structure transformation in the POM cluster and the surrounding MOF to be evaluated using in situ X-ray scattering with pair distribution function (PDF) analysis. Notably, the Rh/Pt···Mo distance in the active catalyst is shorter than the M···M bond lengths in the respective bulk metals. Models of the active cluster structure were identified based on the PDF data with complementary computation and X-ray absorption spectroscopy analysis.

Flash Nitrogen-Doped Carbon Nanotubes for Energy Storage and Conversion

In recent years, nitrogen-doped carbons show great application potentials in the fields of electrochemical energy storage and conversion. Here, the ultrafast and green preparation of nitrogen-doped carbon nanotubes (N-CNTs) via an efficient flash Joule heating method is reported. The precursor of 1D core-shell structure of CNT@polyaniline is first synthesized using an in situ polymerization method and then rapidly conversed into N-CNTs at ≈1300 K within 1 s. Electrochemical tests reveal the desirable capacitive property and oxygen catalytic activity of the optimized N-CNT material. It delivers an improved area capacitance of 101.7 mF cm-2 at 5 mV s-1 in 1 m KOH electrolyte, and the assembled symmetrical supercapacitor shows an energy density of 1.03 µWh cm-2 and excellent cycle stability over 10 000 cycles. In addition, the flash N-CNTs exhibit impressive catalytic performance toward oxygen reduction reaction with a half-wave potential of 0.8 V in alkaline medium, comparable to the sample prepared by the conventional long-time pyrolysis method. The Zn-air battery presents superior charge-discharge ability and long-term durability relative to commercial Pt/C catalyst. These remarkable electrochemical performances validate the superiorities of the Joule heating method in preparing the heteroatom-doped carbon materials for wide applications.