p-d Orbital Hybridization Induced by Asymmetrical FeSn Dual Atom Sites Promotes the Oxygen Reduction Reaction

Enhanced catalytic ozonation via FeBi bimetallic catalyst: Unveiling the role of zero-valent Bi as an oxygen vacancy-mediated electron reservoir

A series of bimetallic carbon catalysts (FeM@C, M = Bi, Ce, Co, Ni, Mn) were synthesized via pyrolysis of metal-organic framework (MOF) precursors, among which FeBi@C exhibits exceptional catalytic ozonation performance, achieving 90.73 % oxalic acid removal within 30 min and retaining 84 % of its initial activity over eight consecutive cycles. Advanced characterizations, including EPR, and in-situ Raman spectroscopy, revealed that oxygen vacancies (OV) serve as active sites for ozone adsorption, leading to the formation of reactive oxygen species (ROS) and ≡ Fe-O-O- peroxo intermediates. The post-reaction XPS analysis indicated significant shifts in binding energies and changes in the proportions of oxygen species, revealing the unique Fe-Bi synergy. The Fe2p spectra showed a decrease in Fe2+ content and a negative shift in binding energy, indicating an active Fe2+/Fe3+ redox cycle. The Bi4f spectra confirmed the presence of zero-valent Bi, which acts as an "electron reservoir", continuously donating electrons to enhance Fe2+/Fe3+ redox cycle and promote ozone activation. This unique mechanism, where zero-valent Bi sustains the electron transfer cycle, significantly enhances both the catalytic efficiency and long-term stability of the FeBi@C system, distinguishing it from conventional bimetallic catalysts. This work provides a novel strategy for designing high-performance catalysts for environmental remediation.

Microporous Hard Carbon Support Provokes Exceptional Performance of Single Atom Electrocatalysts for Advanced Air Cathodes

Single atom catalysts embracing metal-nitrogen (MNx) moieties show promising performance for oxygen reduction reaction (ORR). The modification on spatially confined microenvironments, which won copious attention with respect to achieving efficient catalysts, are auspicious but yet to be inspected for MNx moieties from modulating the energetics and kinetics of ORR. Here, Fe single atoms (SAs) are immobilized in microporous hard carbon (Fe-SAs/MPC), in which the microporous structure with crumpled graphene sheets serves confined microenvironment for catalysis. Fe-SAs/MPC holds a remarkable half-wave potential of 0.927 V and excellent stability for ORR. Theoretical studies unveil that hydrogen bonding between the intermediate of O* and micropore interior surfaces substantially promote its protonation and accelerate the overall ORR kinetics. Both the aqueous and quasi-solid-state zinc-air batteries driven by Fe-SAs/MPC air cathode show excellent stability with small charging/discharging voltage gaps. Importantly, when used as the air cathode for industrial chlor-alkali process, the applied voltage of Fe-SAs/MPC-based flow cell to reach 300 mA cm-2 is 1.57 V, which is 210 mV smaller than Pt/C-based one. These findings provide in-depth insights into the confined microenvironment of MNx moieties for boosted electrochemical performance, and pave the pathways for future catalyst development satisfying the requirement of industrial applications.

Leveraging the Intermetal Distance in Dual-Atom Catalysts: Revealing Optimized Synergistic Interactions for CO2 Electroreduction

Dual-atom catalysts (DACs) offer a potential to accelerate reaction kinetics and provide versatile active sites by the synergistic combination of two metal atoms. However, the effects of dual-atom configurations and interatomic distances on catalytic performance have yet to be thoroughly investigated. Herein, we report DACs composed of Cu/Ni species anchored on N-doped carbon (Cu/Ni-NC) for the electrochemical CO2 reduction reaction (CO2RR). The role of intermetal interactions as a function of atomic distance was systematically investigated through a combination of theoretical calculations and advanced experimental techniques, including aberration-corrected transmission electron microscopy (AC-HAADF-STEM) and X-ray absorption fine structure analysis (XAFS). Our findings reveal that a Cu-Ni atomic distance of ∼4.08 Å maximizes synergistic interactions between the two metals, significantly enhancing catalytic activity and CO selectivity. The resulting catalysts demonstrate a CO faradaic efficiency (FECO) of ∼100% at -0.9 V vs the reversible hydrogen electrode (RHE) in an H-type cell and 96.3% at -0.4 V vs RHE in the flow cell, outperforming other Cu/Ni configurations and single-metal counterparts.

Rational Dual-Atom Design to Boost Oxygen Reduction Reaction on Iron-Based Electrocatalysts

The oxygen reduction reaction (ORR) is critical for energy conversion technologies like fuel cells and metal-air batteries. However, advancing efficient and stable ORR catalysts remains a significant challenge. Iron-based single-atom catalysts (Fe SACs) have emerged as promising alternatives to precious metals. However, their catalytic performance and stability remain constrained. Introducing a second metal (M) to construct Fe─M dual-atom catalysts (Fe─M DACs) is an effective strategy to enhance the performance of Fe SACs. This review provides a comprehensive overview of the recent advancements in Fe-based DACs for ORR. It begins by examining the structural advantages of Fe─M DACs from the perspectives of electronic structure and reaction pathways. Next, the precise synthetic strategies for DACs are discussed, and the structure-performance relationships are explored, highlighting the role of the second metal in improving catalytic activity and stability. The review also covers in situ characterization techniques for real-time observation of catalytic dynamics and reaction intermediates. Finally, future directions for Fe─M DACs are proposed, emphasizing the integration of advanced experimental strategies with theoretical simulations as well as artificial intelligence/machine learning to design highly active and stable ORR catalysts, aiming to expand the application of Fe─M DACs in energy conversion and storage technologies.

Engineering Local Coordination and Electronic Structures of Dual-Atom Catalysts

Heterogeneous dual-atom catalysts (DACs), defined by atomically precise and isolated metal pairs on solid supports, have garnered significant interest in advancing catalytic processes and technologies aimed at achieving sustainable energy and chemical production. DACs present board opportunities for atomic-level structural and property engineering to enhance catalytic performance, which can effectively address the limitations of single-atom catalysts, including restricted active sites, spatial constraints, and the typically positive charge nature of supported single metal species. Despite the rapid progress in this field, the intricate relationship between local atomic environments and the catalytic behavior of dual-metal active sites remains insufficiently understood. This review highlights recent progress and major challenges in this field. We begin by discussing the local modulation of coordination and electronic structures in DACs and its impact on catalytic performance. Through specific case studies, we demonstrate the importance of optimizing the entire catalytic ensemble to achieve efficient, selective, and stable performance in both model and industrially relevant reactions. Additionally, we also outline future research directions, emphasizing the challenges and opportunities in synthesis, characterization, and practical applications, aiming to fully unlock the potential of these advanced catalysts.

Harnessing Synergistic Cooperation of Neighboring Active Motifs in Heterogeneous Catalysts for Enhanced Catalytic Performance

Understanding the intricate interplay between catalytically active motifs in heterogeneous catalysts has long posed a significant challenge in the design of highly active and selective reactions. Drawing inspiration from biological enzymes and homogeneous catalysts, the synergistic cooperation between neighboring active motifs has emerged as a crucial factor in achieving effective catalysis. This synergistic control is often observed in natural enzymes and homogeneous systems through ligand coordination. The synergistic interaction is especially vital in reactions involving tandem or cascade steps, where distinct active motifs provide different functionalities to enable the co-activation of the reaction substrate(s). Situated within a 3D spatial domain, these catalytically active motifs can shape favorable catalytic landscapes by modulating electronic and geometric characteristics, thereby stabilizing specific intermediate or transition state species in a specific catalytic reaction. In this review, we aim to explore a diverse array of the latest heterogeneous catalytic systems that capitalize on the synergistic cooperativity between neighboring active motifs. We will delve into how such synergistic interactions can be utilized to engineer more favorable catalytic landscapes, ultimately resulting in the modulation of catalytic reactivities.

From Single-Atom to Dual-Atom: A Universal Principle for the Rational Design of Heterogeneous Fenton-like Catalysts

Developing efficient heterogeneous Fenton-like catalysts is the key point to accelerating the removal of organic micropollutants in the advanced oxidation process. However, a general principle guiding the reasonable design of highly efficient heterogeneous Fenton-like catalysts has not been constructed up to now. In this work, a total of 16 single-atom and 272 dual-atom transition metal/nitrogen/carbon (TM/N/C) catalysts for H2O2 dissociation were explored systematically based on high-throughput density functional theory and machine learning. It was found that H2O2 dissociation on single-atom TM/N/C exhibited a distinct volcano-type relationship between catalytic activity and •OH adsorption energy. The favorable •OH adsorption energies were in the range of -3.11 ∼ -2.20 eV. Three different descriptors, namely, energetic, electronic, and structural descriptors, were found, which can correlate the intrinsic properties of catalysts and their catalytic activity. Using adsorption energy, stability, and activation energy as the evaluation criteria, two dual-atom CoCu/N/C and CoRu/N/C catalysts were screened out from 272 candidates, which exhibited higher catalytic activity than the best single-atom TM/N/C catalyst due to the synergistic effect. This work could present a conceptually novel understanding of H2O2 dissociation on TM/N/C and inspire the structure-oriented catalyst design from the viewpoint of volcano relationship.

Defect-Triggered Orbital Hybridization in FeMn Dual-Atom Catalysts Toward Sabatier-Optimized Oxygen Reduction

Dual single-atom catalysts (DSAs), leveraging synergistic dual-site interactions, represent a promising frontier in electrocatalysis. However, the precise synthesis of dual-atom pairs and fine-tuning of their electronic structures remain significant challenges. Herein, we construct a defect-engineered heteronuclear FeMn-DSA anchored on a porous nitrogen-doped carbon matrix (FeMnD SA/dNC) through a customized trinuclear-defect trapping strategy. This defect modulation strategy effectively stabilizes dual atomic pairs while optimizing electronic structures to approach Sabatier's optimality, significantly boosting oxygen reduction reaction (ORR) performance. The FeMnD SA/dNC achieves a high half-wave potential of 0.921 V in alkaline media, with assembled zinc-air batteries demonstrating 291 mW cm-2 peak power density and stable charge/discharge cycling for over 500 h. Theoretical calculations reveal that defect-mediated coordination adjacent to Fe-Mn diatomic centers triggers charge redistribution, suppressing antibonding orbital populations while strengthening Fe 3dz 2 with O 2p orbital hybridization. This modulation weakens O─O bonding through optimized *OOH adsorption configurations, thereby enhancing ORR kinetics. The present work provides valuable insights into the precise modulation and the underlying mechanisms of DSAs, advancing the design of electrocatalysts for energy storage and conversion applications.

Asymmetrical Triatomic Sites with Long-Range Electron Coupling for Ultra-Durable and Extreme-Low-Temperature Zinc-Air Batteries

Reversible zinc-air battery (ZAB) is a promising alternative for sustainable fuel cells, but the performance is impeded by the sluggish oxygen redox kinetics owing to the suboptimal adsorption and desorption of oxygen intermediates. Here, hetero-trimetallic atom catalysts (TACs) uniquely incorporate an electron regulatory role beyond primary and secondary active sites found in dual-atom catalysts. In situ X-ray absorption fine structure (XAFS) and Raman spectroscopy elucidate Fe in FeCoNi SA catalyst (FCN-TM/NC) functions as the main active site, leveraging long-range electron coupling from neighboring Co and Ni to boost catalytic efficiency. The ZAB equipped with FCN-TM/NC exhibits ultra-stable rechargeability (over 5500 h at 1  mA cm-2 under -60 °C). The in-depth theoretical and experimental investigations attribute such superior catalytic activity to the asymmetric FeN4 configuration, long-distance electron coupling, modulated local microenvironment, optimized d orbital energy levels, and lower energy barrier for bifunctional oxygen electrocatalysis. This work provides a comprehensive mechanistic understanding of the structure-reactivity relationship in TACs for energy conversion.

Constructing Stable Bifunctional Electrocatalyst of Co─Co2Nb5O14 with Reversible Interface Reconstitution Ability for Sustainable Zn-Air Batteries

Transition metal and metal oxide heterojunctions have been widely studied as bifunctional oxygen reduction/evolution reaction (ORR/OER) electrocatalysts for Zn-air batteries, but the dynamic changes of transition metal oxides and the interface during catalysis are still unclear. Here, bifunctional electrocatalyst of Co─Co2Nb5O14 is reported, containing lattice interlocked Co nanodots and Co2Nb5O14 nanorods, which construct a strong metal-support interaction (SMSI) interface. Unlike the recognition that transition metals mainly serve as ORR active sites and metal oxides as OER active sites, it is found that both ORR/OER sites originate from Co2Nb5O14, while Co acts as an electronic regulatory unit. The SMSI interface promotes dynamic electron transfer between Co/Co2Nb5O14, and the reversible active sites of Nb4+/Nb5+ realize bidirectional adsorption/migration of intermediates, thereby achieving dynamic reversible interface reconstitution. The electrocatalyst shows a high ORR half-wave potential of 0.84 V, a low OER overpotential of 296.3 mV, and great cycling stability over 30000 s. The ZAB shows a high capacity of 850.6 mA h·gZn-1 and can stably run 2050 cycles at 10 mA·cm⁻2. Moreover, the constructed solid-state ZAB also shows leading cycling stability in comparison with the previous studies.

Manipulating Interfacial Water Via Metallic Pt1Co6 Sites on Self-Adaptive Metal Phosphides to Enhance Water Electrolysis

Metallizing active sites to control the structural and kinetic dissociation of water at the catalyst-electrolyte interface, along with elucidating its mechanism under operating conditions, is a pivotal innovation for the hydrogen evolution reaction (HER). Here, a design of singly dispersed Pt-Co sites in a fully metallic state on nanoporous Co2P, tailored for HER, is introduced. An anion-exchange-membrane water electrolyzer equipped with this catalyst can achieve the industrial current densities of 1.0 and 2.0 A cm-2 at 1.71 and 1.85 V, respectively. It is revealed that the singly dispersed Pt-Co sites undergo self-adaptive distortion under operating conditions, which form a Pt1Co6 configuration with a strongly negative charge that optimizes reactant binding and reorganizes the interfacial water structure, resulting in an improved concentration of potassium (K+) ions in the closest ion plane. The K+ ions interact cooperatively with H2O (K·H2O), which strengthens the Pt-H binding interaction and facilitates the polarization of the H─OH bond, leading to improved HER activity. This study not only propels the advancement of cathodic catalysts for water electrolysis but also delineates a metallization strategy and an interface design principle, thereby enhancing electrocatalytic reaction rates.

Restricting Two-Electron Oxygen Reduction via Secondary Coordinated Sulfur Enabling Ultralong-Lifespan Zn-Air Batteries

The direct four-electron oxygen reduction reaction (4e- ORR) critically governs efficiency and lifespan in metal-air batteries and fuel cells, yet selectively suppressing competitive 2e- and stepwise 2e-pathways that generate corrosive hydrogen peroxide remains a major challenge. Herein, we demonstrate the strategic incorporation of secondary coordinated sulfur atoms into transition metal-N-C electrocatalysts to effectively promote direct 4e- ORR and simultaneously suppress undesirable 2e- pathways. Density functional theory (DFT) calculations and operando spectroscopy reveal that enhanced adsorption of key intermediate *OOH facilitates efficient O─O bond cleavage, underpinning altered catalytic selectivity. Importantly, this approach is universally applicable to various carbon-based catalysts, including Co─N@C, Ni─N@C, Mn─N@C, and N@C. Specifically, a sulfur-mediated Co─N/Co@C catalyst, comprising Co─N4 sites and Co nanoparticles, dramatically lowers the 2e- O2-to-H2O2 rate constant to merely 0.05-fold of its original value at 0.78 V. Consequently, Zn-air batteries using Co─N/Co@C-S as cathode exhibits an outstanding peak power density of 220 mW cm-2, remarkable lifespan over 2500 h, and outstanding rate performance from 5 to 50 mA cm-2. This work paves a generalizable route for designing highly active and selective electrocatalysts suitable for advanced long-life energy storage devices.

Atomically Dispersed Metal Catalysts for Oxygen Reduction Reaction: Two-Electron vs. Four-Electron Pathways

Developing eco-friendly electrochemical devices for electrosynthesis, fuel cells (FCs), and metal-air batteries (MABs) requires precisely designing the electronic pathway in the oxygen reduction reaction (ORR) process. Understanding the principle of developing low-cost, highly active, and stable catalysts helps to reduce the usage of noble metals in ORR. Atomically dispersed metal catalysts (ADMCs) emerge as promising alternatives to replace commercial noble metals due to their high utilization of active metal atoms, high intrinsic activity, and controllable coordination environments. In this review, the research tendency and reaction mechanisms in ORR are first summarized. The basic principles concerning the geometric size and chemical coordination of two-electron ORR (2e- ORR) catalysts were then discussed, aiming to outline the evolution of material design from 2e- ORR to four-electron ORR (4e- ORR). Subsequently, recent advances in ADMCs primarily investigated for the 4e- ORR are well-documented. These advances encompass studies on M-N-C coordination, light heteroatom doping, dual-metal atoms-based coordination, and interaction between nanoparticle (NPs)/nanoclusters (NCs) and atomically dispersed metals (ADMs). Finally, the setups for 2/4e- ORR applications, key challenges, and opportunities in the future design of ADMCs for the ORR are highlighted.

Local Electronic Regulation by Oxygen Coordination with Single- Atomic Iridium on Ultrathin Cobalt Hydroxide Nanosheets for Electrocatalytic Oxygen Evolution

Rationally optimizing the atomic and electronic structure of electrocatalysts is an effective strategy to improve the activity of the electrocatalytic oxygen evolution reaction (OER), yet it remains challenging. In this work, atomic heterointerface engineering is developed to accelerate OER by decorating iridium atoms on low-crystalline cobalt hydroxide nanosheets (Ir-Co(OH)x) via oxygen-coordinated bonds to modulate the local electronic structure. Leveraging detailed spectroscopic characterizations, the Ir species were proved to promote charge transfer through Ir-O-Co coordination between the Ir atom and the Co(OH)x support. As a result, the optimized Ir-Co(OH)x exhibits excellent electrocatalytic OER activity with a low overpotential of 251 mV to drive 10 mA cm-2, which is 63 mV lower than that of pristine Co(OH)x. The experimental results and density functional theory calculations reveal that the isolated Ir atoms can regulate the local coordination environment and electronic configuration of Co(OH)x, thus accelerating the catalytic OER kinetics. This work provides an atomistic strategy for the electronic modulation of metal active sites in the design of high-performance electrocatalysts.

Dynamic D-p-π Orbital Coupling of FeN4-Spπ Atomic Centers on Graphitized Carbon Toward Invigorated Sulfur Kinetic Chemistry

Precisely modulating d-p orbital coupling of single-atom electrocatalysts for sulfur reduction reactions in lithium-sulfur batteries maintains tremendous challenges. Herein, a dynamic d-p-π orbital coupling modulation is elucidated by unsaturated Fe centers on nitrogen-doped graphitized carbon (NG) coordinated with trithiocyanuric acid featuring with p-π conjugation to engineer Fe single atom architecture (FeN4-Spπ-NG). Intriguingly, this coordination microenvironment of the Fe center is dynamically reconstituted during charge/discharge processes, because of the formation of trilithium salts rooted from the departed axial ligands to engineer interfacial coating on the sulfur cathode, and then it recovers to the initial coordination configuration. Theoretical and experimental results unravel that the axial p-π conjugated ligand reinforcing d-p orbital coupling enables the interfacial charge interaction, thereby strengthening LiPSs adsorption, and reducing the Li2S decomposition barrier by formation of Fe─S and S─Li bonds. Thus, dynamic d-p-π orbital coupling modulation of FeN4-Spπ endow lithium-sulfur batteries with considerable electrochemical performances, highlighting an intriguingly dynamic orbital coupling modulation strategy for single atom electrocatalysts.

Turn the Harm into A Benefit: Axial Cl Adsorption on Curved Fe-N4 Single Sites for Boosted Oxygen Reduction Reaction in Seawater

Seawater electrocatalysis is urgently needed for various energy storage and conversion systems. However, the adsorption of chloride ions (Cl-) to the active sites can degrade the oxygen reduction reaction (ORR) activity and stability, thus reducing the catalytic performance. In this paper, a curved FeN4 single atomic structure is designed by utilizing curvature engineering, which can turns the harmful Cl adsorption into a benefit on the Fe single site that changes the rate determining step of ORR and reduces the overall energy barrier according to density functional theory (DFT) calculation. Experimental studies reveal the prepared highly-curved single-atom iron catalyst (HC-FeSA) exhibits excellent ORR activity in different electrolytes, with half-wave potentials of 0.90 V in 0.1 M KOH, 0.90 V in simulated seawater, and 0.75 V in natural seawater, respectively. This work opens up an avenue for the synthesis of high-performance seawater-based single-atom ORR catalysts through regulating the local atomic curvature.

Accelerated Design of Dual-Metal-Site Catalysts via Machine-Learning Prediction

Dual-metal site catalysts (DMSCs) supported on nitrogen-doped graphene have shown great potential in heterogeneous catalysis due to their unique properties and enhanced efficiency. However, the precise control and stabilization of metal dimers, particularly in oxygen activation reactions, present significant challenges in practical applications. In this study, we integrate high-throughput density functional theory calculations with machine learning techniques to predict and optimize the catalytic properties of DMSCs. Transfer learning is employed to enhance the model's generalization capability, successfully predicting catalytic performance across new metal combinations. Additionally, the application of the SISSO method enables the derivation of interpretable symbolic regression models, revealing critical correlations between electronic structure features and catalytic efficiency. This approach not only advances the understanding of dual-metal site catalysis but also provides a novel framework for the systematic design and optimization of highly efficient catalysts, with broad applicability in catalytic science.

Unveiling the Mystery of Precision Catalysis: Dual-Atom Catalysts Stealing the Spotlight

In the era of atomic manufacturing, the precise manipulation of atomic structures to engineer highly active catalytic sites has become a central focus in catalysis research. Dual-atom catalysts (DACs) have garnered significant attention for their superior activity, selectivity, and stability compared to single-atom catalysts (SACs). However, a comprehensive review that integrates geometric and electronic factors influencing DAC performance remains limited. This review systematically explores the structure of DAC, addressing key macroscopic parameters, such as spatial arrangements and interatomic distances, as well as microscopic factors, including local coordination environments and electronic structures. Additionally, metal-support interactions (MSI) and long-range interactions (LSI) are comprehensively analyzed, which play a pivotal yet underexplored role in governing DAC behavior. the integration of tailored functional groups is further discussed to fine-tune DAC properties, thereby optimizing intermediate adsorption, enhancing reaction kinetics, and expanding their multifunctionality in various electrochemical environments. This review offers novel insights into their rational design by elucidating the intricate mechanisms underlying DACs' exceptional performance. Ultimately, DACs are positioned as critical players in precision catalysis, highlighting their potential to drive significant breakthroughs across a broad spectrum of catalytic applications.

Precisely designing asymmetrical selenium-based dual-atom sites for efficient oxygen reduction

Owing to their synergistic interactions, dual-atom catalysts (DACs) with well-defined active sites are attracting increasing attention. However, more experimental research and theoretical investigations are needed to further construct explicit dual-atom sites and understand the synergy that facilitates multistep catalytic reactions. Herein, we precisely design a series of asymmetric selenium-based dual-atom catalysts that comprise heteronuclear SeN2-MN2 (M = Fe, Mn, Co, Ni, Cu, Mo, etc.) active sites for the efficient oxygen reduction reaction (ORR). Spectroscopic characterisation and theoretical calculations revealed that heteronuclear selenium atoms can efficiently polarise the charge distribution of other metal atoms through short-range regulation. In addition, compared with the Se or Fe single-atom sites, the SeFe dual-atom sites facilitate a reduction in the conversion energy barrier from *O to *OH via the coadsorption of *O intermediates. Among these designed selenium-based dual-atom catalysts, selenium-iron dual-atom catalysts achieves superior alkaline ORR performance, with a half-wave potential of 0.926 V vs. a reversible hydrogen electrode. In addition, the SeN2-FeN2-based Zn-air battery has a high specific capacity (764.8 mAh g-1) and a maximum power density (287.2 mW cm-2). This work may provide a good perspective for designing heteronuclear DACs to improve ORR efficiency.