Atomic layer deposited Pt-Ru dual-metal dimers and identifying their active sites for hydrogen evolution reaction

Spin Engineering of Dual-Atom Site Catalysts for Efficient Electrochemical Energy Conversion

Dual-atom site catalysts (DASCs) provide more advantages than single-atom systems in improving energy conversions, owing to their unique features. For example, the coupling effect may align the spin of two adjacent dual-atom active centers in parallel or antiparallel via electron exchange interactions, thereby altering reaction mechanisms and overall efficiency. While numerous reviews have explored spin-dependent electrocatalysis, there remains a lack of a comprehensive, spin-focused framework for understanding the catalytic behavior of DASCs. This review emphasizes the role of spin in dual-atom site centers for electrocatalysis research. First, spin fundamentals in electrocatalysts, including spin-selective orbital occupation, spin ordering, and spin coupling, are comprehensively summarized to provide a solid foundation for subsequent discussions. Then, spin engineering strategies of DASCs are reviewed, including manipulating the spin configuration of the central atoms, modulating coordination environments, and tuning metal-support interactions. Next, recent developments in spin engineering of DASCs are reviewed, with a focus on structure-performance relationships. Furthermore, high-throughput screening techniques integrated with machine learning are discussed for developing highly efficient DASCs based on spin engineering. The challenges and opportunities of DASCs and spin engineering are thoroughly discussed to promote the advancement of new energy applications.

Hydrogen Binding Energy Is Insufficient for Describing Hydrogen Evolution on Single-Atom Catalysts

The design principles for metal-nitrogen-carbon (M-N-C) single-atom catalysts (SACs) in the hydrogen evolution reaction (HER) have been extensively studied. Yet, consensus remains elusive, hindering advancements in hydrogen energy technologies. Although the hydrogen binding energy (ΔGH*) has long been used as a key HER descriptor during the past two decades, originating from the activity volcano of metallic surfaces, its applicability to HER SACs has been met with significant controversy. Herein, we investigate the effects of HO*/O* poisoning and H* coverage on SACs with varied metal centers and coordination environments using pH-dependent surface Pourbaix diagrams at the reversible hydrogen electrode (RHE) scale and microkinetic modeling. Our findings reveal that HO* poisoning, realistic H* adsorption strengths at active metal sites, and the potential HER activity at the coordinating N-sites are crucial factors that should be considered for accurate descriptor development. Experimental validation using a series of M-phthalocyanine/CNT catalysts (M = Co, Ni, Cu) confirms the theoretical predictions, with excellent agreement in exchange current densities and the role of N-sites in Ni/Cu-phthalocyanine/CNT catalysts. This work provides answers to a long-lasting debate on HER descriptors by establishing ΔGH* and ΔGHO* as a combined HER descriptor for SACs, offering new guidelines for catalyst design.

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.

Precise Synthesis of Dual-Atom Catalysts for Better Understanding the Enhanced Catalytic Performance and Synergistic Mechanism

ConspectusDual-atom catalysts (DACs), featuring two catalytic sites in close proximity, have emerged as a new frontier in energy-related catalysis. Compared with single-atom catalysts (SACs), DACs have more space to optimize the catalytic performance by changing the dual-atom catalytic sites and their coordination environments. Through adjusting the compositions and coordination environments of the metal sites in DACs, it is possible to finely tune the electronic and geometric properties of active centers, and then the synergistic effects for facilitating substrates activation and intermediates stabilization can be strengthened or optimized, consequently tailoring diverse reaction pathways and achieving various challenging catalytic reactions. The most important yet challenging task in DACs studies is the precise synthesis of DACs, which is crucial to understand the relationship between the catalytic performance and structure at the atomic level. In most cases, DACs were synthesized via the pyrolysis of a mixture of metal salts and organic ligands, in which two metals are randomly distributed in DACs, and it was difficult to control the M···M distance (M = metal ion) and uniform dispersion of DACs. Hence, developing innovative strategies for the precise synthesis of DACs with definite structures and high-efficiency catalytic performance is urgently needed.In this Account, we tentatively summarize the strategies for the precise synthesis of DACs and their applications in activation and conversion of small molecules such as H2O, CO2, and so on. Focusing on the precise synthesis of DACs, three types of synthesis strategies have been put forward and systematically introduced. Based on the precise synthesis strategies, the applications of the resulting DACs with high purity in synergistically activating and converting small molecules have concurrently been discussed, including the cleavage of C-C bonds, activation and reduction of CO2 and H2O, and so on. Attempts have been made to explain why the catalytic performance of DACs for these functions is much higher than what SACs have achieved. Efforts have been made on revealing the influences of dual-metal site types, the separations between dual metals, their geometry configurations and coordination environments, as well as the ligand structures on the catalytic performance. Emphasis has been placed on the analysis of the structure-reactivity relationship and revealing the synergistic mechanism at the molecular level. Finally, perspectives on the current challenges and future development of DACs have been put forward. We anticipate and believe that this Account will provide profound insights into the synthesis of structurally defined DACs and give new insights of synergistic catalytic effects in DACs.

The Cooperative Effects of the Rh-M Dual-Metal Atomic Pairs in Formic Acid Oxidation

The continuously increasing mass activity of precious metal in formic acid oxidation reaction (FAOR) is the key to achieving the practical application of direct formic acid fuel cells (DFAFCs). Herein, Rh-based dual-metal atomic pairs supported on nitrogen-doped carbon catalysts [DAP-(M, Rh)/CN] with adjacent interatomic Rh-M (M = V, Cr, Mn, Fe, Co, Ni, Cu) have been synthesized by a "host-guest" strategy. It is discovered that DAP-(Cr, Rh)/CN shows the highest mass activity of 64.1 A mg-1, which is 3.8 times higher than that of the single atom Rh catalyst (17.0 A mg-1) and two orders of magnitude higher than Pd/C (0.58 A mg-1). Interestingly, the mass activity of DAP-(M, Rh)/CN first increases from 11.7 A mg-1 (Rh-V) to 64.1 A mg-1 (Rh-Cr) and then decreases to 21.8 A mg-1 (Rh-Cu), forming a volcano curve of the reaction activity. Density functional theory calculations combined with in situ Fourier transform infrared spectrometer (FTIR) spectra reveal that formic acid oxidized on a series of DAP-(M, Rh)/CN catalysts through the formate route with the subsidiary M metal atoms binding the HCOO species and the Rh atom accepting the H atoms. The most suitable adsorption strength of HCOO on the Cr sites luckily contributes to two spontaneous elementary steps and thus accelerates the FAOR rates.

Polydisperse Pt Deposits Over TiO2-Nanotube-Array-Supported Ru Nanoparticles: Harnessing the Interfacial Synergy for Efficient Hydrogen Evolution Electrocatalysis

Developing cost-effective precious metal electrocatalysts for the hydrogen evolution reaction (HER) is key to realizing the economic viability of acidic water electrolysis. Herein, galvanic displacement is employed for in situ formation of bimetallic Pt/Ru deposits on H-intercalated TiO2 nanotube arrays. It is found that a two-step procedure yields polydisperse deposits with a dominant fraction of Ru nanoparticles coated with atomic and subnanometric Pt islands. These Pt|Ru nanointerfaces induce charge transfer from Pt to Ru, which modulates the electronic structure of Pt sites for accelerated HER kinetics. By varying the platinization time in the second step, a balance between the exposure of catalytically active Pt|Ru nanointerfaces and the total number of Pt surface sites is achieved. The optimized composite, termed Ru-30min@Pt-30min, requires an overpotential of 58 mV to deliver a current density of 100 mA cm-2 in 1.0 m HClO4 and maintains performance stability and structure integrity under prolonged operation. Moreover, it presents a 3.5-fold increase in precious metal mass activity over Pt/C at η = 80 mV. Theoretical calculations reveal that the electronic interactions generated by Pt-modification of Ru and hydrogenated TiO2 surfaces provide multiple active sites with improved Hads energetics compared to pure Pt and Ru.

Electrocatalytic Innovations at Atomic Scale: From Single-Atom to Periodic Ensembles for Sustainable Energy Conversion

Atomically dispersed catalysts, including single-atom, dual-atom, and periodic single-metal site catalysts, have revolutionized electrocatalysis by merging atomic precision with heterogeneous stability. This review traces their evolution from pioneering stabilization strategies to advanced microenvironment engineering, enabling breakthroughs in oxygen reduction, hydrogen evolution, and CO2 reduction. SACs maximize atom utilization but face multi-step reaction limits, addressed by DACs through synergistic dual-site mechanisms. PSMSCs further enhance activity via ordered atomic arrangements, ensuring uniform active sites and mechanistic clarity. Key breakthroughs include microenvironment engineering to tailor active sites, as well as advanced characterization techniques revealing dynamic restructuring under operando conditions. The transition from isolated atoms to ordered ensembles highlights the importance of atomic-level control in unlocking new catalytic mechanisms. This work underscores the transformative potential of ADCs in sustainable energy technologies and provides a roadmap for future research in rational catalyst design, dynamic behavior analysis, and scalable synthesis.

Metal cluster-mediated photocatalysis: synthesis, characterization and application

The escalation of global energy crises and environmental degradation has intensified the focus on photocatalytic technology, which harnesses solar energy for direct chemical reactions in a green manner. Metal clusters serve as multifunctional components in photocatalytic systems, with their unique properties (such as dimensions, composition, and surface modification) offering a plethora of regulatory mechanisms for designing innovative and efficient cluster-based photocatalysts. These improvements enhance light absorption, charge separation, and catalytic activity. This comprehensive review explores the fundamental principles and applications of photocatalytic technology, emphasizing the role of metal cluster materials in advancing this field. The synthetic methodologies, especially AI-assisted synthesis, characterization techniques, and modification strategies of metal cluster materials are introduced in detail, highlighting their significance in enhancing photocatalytic performance. The applications of metal clusters in various photocatalytic processes are also discussed, including water splitting, CO2 reduction, N2 fixation, pollutant degradation, H2O2 generation and selective organic synthesis, showcasing their potential in environmental remediation and energy transformation. Finally, the review concludes with an outlook on future research directions, emphasizing the need for innovating synthesis methods, developing advanced characterizations techniques, and optimizing catalytic performance to address existing challenges and unlock the full potential of cluster-based photocatalysts.

'Tearing Effect' of Alloy-Support Interaction for Alloy Redispersion in NiRu/TiO2 Hydrogenation Catalysts

Supported alloy catalysts have been extensively applied to many significant industrial chemical processes due to the abundant active sites with distinguishable geometry and electron states. However, a detailed in situ investigation of the interaction between support and alloy nanoparticles is still lacking. Here, a subversive 'tearing effect' on the interface of TiO2-supported NiRu alloy nanoparticles is in situ discovered by environmental transmission electron microscopy (ETEM) with a dramatic redispersion process of alloy nanoparticles from ~25 nm to 2-3 nm under the repeated hydrogen reduction. Dual-driven by the distinct alloy-support interaction involving the restructuring of alloy nanoparticles and growth of TiOx overlayer, larger NiRu alloy nanoparticles spontaneously disintegrate into atoms migrating on support. Atoms are finally captured by the defects generated on TiO2 during the repeat reduction, which also confines the further growth of the newly alloy nanoparticles. Owing to this specific alloy-support interaction, smaller alloy nanoparticles on TiO2 support are much more stable than the bigger ones, which holds promise for industrial applications as durable catalysts. This novel metal-support interaction with the 'tearing effect' revealed on supported alloy catalysts provides new knowledge on the structure-performance relationships in all the alloy catalysts for hydrogenation reactions.

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.

Exploring the properties, types, and performance of atomic site catalysts in electrochemical hydrogen evolution reactions

Atomic site catalysts (ASCs) have recently gained prominence for their potential in the electrochemical hydrogen evolution reaction (HER) due to their exceptional activity, selectivity, and stability. ASCs with individual atoms dispersed on a support material, offer expanded surface areas and increased mass efficiency. This is because each atom in these catalysts serves as an active site, which enhances their catalytic activity. This review is focused on providing a detailed analysis of ASCs in the context of the HER. It will delve into their properties, types, and performance to provide a comprehensive understanding of their role in electrochemical HER processes. The introduction part underscores HER's significance in transitioning to sustainable energy sources and emphasizes the need for innovative catalysts like ASCs. The fundamentals of the HER section emphasizes the importance of understanding the HER and highlights the key role that catalysts play in HER. The review also explores the properties of ASCs with a specific emphasis on their atomic structure and categorizes the types based on their composition and structure. Within each category of ASCs, the review discusses their potential as catalysts for the HER. The performance section focuses on a thorough evaluation of ASCs in terms of their activity, selectivity, and stability in HER. The performance section assesses ASCs in terms of activity, selectivity, and stability, delving into reaction mechanisms via experimental and theoretical approaches, including density functional theory (DFT) studies. The review concludes by addressing ASC-related challenges in HER and proposing future research directions, aiming to inspire further innovation in sustainable catalysts for electrochemical HER.

Bimetallic effects in carbon dioxide electroreduction

As a clean and sustainable technology, electrocatalytic carbon dioxide reduction reaction (ECO2RR) occupies a central position in the global energy transformation and climate change strategy. Compared with single metallic catalysts, bimetallic catalysts have many advantages, such as the synergistic effect between bimetals, enhanced CO2 adsorption capacity, and lower reaction energy barriers, which make them widely used in the CO2RR for the generation of multi-carbon products. This review systematically summarizes the latest advances in bimetallic effects for the CO2RR. In this paper, we start with a classified introduction on the CO2RR mechanisms, followed by a comprehensive discussion of the structure-activity relationships of various bimetallic catalysts, including regulation of metal centers, regulation of the distance between metal sites, regulation of the coordination environment, interface engineering, and strain engineering. Next, we showcase the advantages of bimetallic catalysts in the CO2RR. Then, the research progress of typical bimetallic catalysts for the ECO2RR is discussed, including diatomic catalysts, bimetallic alloys, bimetallic MOFs and bimetallic COFs. Finally, we summarize the challenges faced today from the five aspects of product selectivity, catalyst stability, product purification, theoretical simulations and in situ characterization techniques and put forward the research direction to promote the industrialization process of CO2RR.

Tuning Hydrogen Binding on Ru Sites by Ni Alloying on MoO2 Enables Efficient Alkaline Hydrogen Evolution for Anion Exchange Membrane Water Electrolysis

Ruthenium (Ru)-based electrocatalysts have shown promise for anion exchange membrane water electrolysis (AEMWE) due to their ability to facilitate water dissociation in the hydrogen evolution reaction (HER). However, their performance is limited by strong hydrogen binding, which hinders hydrogen desorption and water re-adsorption. This study reports the development of RuNi nanoalloys supported on MoO2, which optimize the hydrogen binding strength at Ru sites through modulation by adjacent Ni atoms. Theoretical simulations reveal that substituting Ni atoms for adjacent Ru atoms reduces the high hydrogen adsorption Gibbs free energy on Ru while maintaining a low energy barrier for water dissociation. As a result, the RuNi/MoO₂ catalyst shows excellent HER performance with a low overpotential of 51 mV at a current density of 100 mA cm⁻2, outperforming commercial Pt/C. Furthermore, RuNi/MoO₂ demonstrates high turnover frequency (7.06 s-1), mass activity (13.4 A mg-1), and price activity (1030.77 A dollar-1). In an AEMWE cell, RuNi/MoO₂ as the cathode catalyst achieves a current density of 1 A cm-2 at 60 °C with just 1.7 V using 1 m KOH. This work highlights the potential of RuNi/MoO₂ for ultra-high mass activity in efficient AEMWE applications.

Metal Dimers-Doped h-BN Structures as Novel Toxic Gases Sensors With Enhanced Sensitivity Properties: An ADFT Study

Toxic gases monitoring and detection are fundamental to lessening public health problems. Therefore, in this work, to explore emergent sensor materials, 3d-metal dimers-doped hexagonal boron nitride (h-BN) structures were investigated employing auxiliary density functional theory (ADFT) as novel CO and NO gas sensors. Firstly, the stabilities of Co2, Ni2, and Cu2 dimers deposited on defective h-BN were determined. Then, sensitivities of 3d-metal dimers-doped h-BN structures towards the NO and CO gases were investigated. It was found that the interaction energies of these 3d-metal dimers embedded on defective h-BN are higher than those deposited on pristine h-BN structure, which indicates that the 3d-metal dimers exhibit good stability on defective h-BN. Moreover, this work demonstrated that the CO and NO adsorption energies on 3d-metal dimers-doped h-BN structures are higher than those computed in the literature for pristine h-BN structure. Consequently, the here considered 3d-metal dimers-doped h-BN structures can be good candidates for toxic CO and NO gas detection.

Reconstructing the Coordination Environment of Fe/Co Dual-atom Sites towards Efficient Oxygen Electrocatalysis for Zn-Air Batteries

Dual-atom catalysts with nitrogen-coordinated metal sites embedded in carbon can drive the oxygen reduction and evolution reactions (ORR/OER) in rechargeable zinc-air batteries (ZABs), and the further improvement is limited by the linear scaling relationship of intermediate binding energies in the absorbate evolution mechanism (AEM). Triggering the lattice oxygen mechanism (LOM) is promising to overcome this challenge, but has yet been verified since the lacking of bridge oxygen (O) in the rigid coordination environment of the metal centers. Here, we demonstrate that suitably tailored dual-atom catalysts of FeCo-N-C can undergo out-plane and in-plane reconstruction to form the both axial O and bridge O at the metal centers, and thus activate the LOM pathway. The tailored FeCo-N-C with shortened Fe-N bonds also favors the ORR process, therefore is a promising dual-atom oxygen catalyst. The assembled rechargeable ZABs demonstrate a peak power density of 332 mW cm-2, and exhibit no notable decline after ~720 h of continuous cycling.

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.

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

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

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.

Enhanced Acidic Oxygen Evolution Reaction Performance by Anchoring Iridium Oxide Nanoparticles on Co3O4

The sluggish kinetics of the anodic process, known as the oxygen evolution reaction (OER), has posed a significant challenge for the practical application of proton exchange membrane water electrolyzers in industrial settings. This study introduces a high-performance OER catalyst by anchoring iridium oxide nanoparticles (IrO2) onto a cobalt oxide (Co3O4) substrate via a two-step combustion method. The resulting IrO2@Co3O4 catalyst demonstrates a significant enhancement in both catalytic activity and stability in acidic environments. Notably, the overpotential required to attain a current density of 10 mA cm-2, a commonly used benchmark for comparison, is merely 301 mV. Furthermore, stability is maintained over a duration of 80 h, as confirmed by the minimal rise in overpotential. Energy spectrum characterizations and experimental results reveal that the generation of OER-active Ir3+ species on the IrO2@Co3O4 surface is induced by the strong interaction between IrO2 and Co3O4. Theoretical calculations further indicate that IrO2 sites loaded onto Co3O4 have a lower energy barrier for *OOH deprotonation to form desorbed O2. Moreover, this interaction also stabilizes the iridium active sites by maintaining their chemical state, leading to superior long-term stability. These insights could significantly impact the strategies for designing and synthesizing more efficient OER electrocatalysts for broader industrial application.

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.

Strategies for Achieving Carbon Neutrality: Dual-Atom Catalysts in Focus

Carbon neutrality is a fundamental strategy for achieving the sustainable development of human society. Catalyzing CO2 reduction into various high-value-added fuels serves as an effective pathway to achieve this strategic objective. Atom-dispersed catalysts have received extensive attention due to their maximum atomic utilization, high catalytic selectivity, and exceptional catalytic performance. Dual-atom catalysts (DACs), as an extension of single-atom catalysts (SACs), not only retain the advantages of SACs, but also produce many new properties. This review initiates its exploration by elucidating the mechanism of CO2 reduction reaction (CO2RR) from CO2 adsorption and CO2 activation. Then, a comprehensive summary of recently developed preparation methods of DACs is presented. Importantly, the mechanisms underlying the promoted catalytic performance of DACs in comparison to SACs are subjected to a comprehensive analysis from adjustable adsorption capacity, tunable electronic structure, strong synergistic effect, and enhanced spacing effect, elucidating their respective superiorities in CO2RR. Subsequently, the application of DACs in CO2RR is discussed in detail. Conclusively, the prospective trajectories and inherent challenges of CO2RR are expounded upon concerning the continued advancement of DACs. This thorough review not only enhances the comprehension of DACs within CO2RR but also accentuates the prospective developments in the design of sophisticated catalytic materials.

Electrochemical Synthesis of Nickel Hexacyanoferrate and Nickel Sulfide on Nickel Foam as Sustainable Electrocatalysts for Hydrogen Generation via Urea Electrolysis

A promising approach to energy-efficient hydrogen production is coupling the hydrogen evolution reaction (HER) with the urea oxidation reaction (UOR), significantly reducing the energy requirements. However, achieving a low-cost yet high-performance electrocatalyst for both HER and UOR remains challenging. Here, we present a facile method for synthesizing nanoporous nickel sulfide (NiS) and nickel hexacyanoferrate (NiHCF) nanocubes directly on nickel foam (NF) without any added nickel source using a cyclic voltammetry technique. In this approach, NF serves simultaneously as the substrate and nickel source, streamlining the synthesis process. The unique nanoarchitecture of NiHCF and NiS promotes highly efficient catalytic activity for both UOR and HER. NiHCF catalyzes urea oxidation by dual active sites of Ni and Fe with its synergistic interaction, without the formation of NiOOH or FeOOH. For hydrogen production, the self-supporting NiHCF/NF||NiS/NF-coupled system achieves a notably low cell voltage of 1.8 V at 100 mA cm-2, which is approximately 487 mV lower than traditional IrO2/NF||Pt/C/NF water electrolysis. This innovative electrochemical method enables the controlled synthesis of Ni-based nanoelectrocatalysts, offering a sustainable, energy-efficient pathway for H2 production from urea-rich wastewater. This environmentally friendly strategy holds significant potential to reduce the global carbon footprint, paving the way for a greener future.

Understanding Pt Active Sites on Nitrogen-Doped Carbon Nanocages for Industrial Hydrogen Evolution with Ultralow Pt Usage

Engineering microstructures of Pt and understanding the related catalytic mechanism are critical to optimizing the performance for hydrogen evolution reaction (HER). Herein, Pt dispersion and coordination are precisely regulated on hierarchical nitrogen-doped carbon nanocages (hNCNCs) by a thermal-driven Pt migration, from edge-hosted Pt-N2Cl2 single sites in the initial Pt1/hNCNC-70 °C catalyst to Pt clusters/nanoparticles and back to in-plane Pt-NxC4-x single sites. Thereinto, Pt-N2Cl2 presents the optimal HER activity (6 mV@10 mA cm-2) while Pt-NxC4-x shows poor HER activity (321 mV@10 mA cm-2) due to their different Pt coordination. Operando characterizations demonstrate that the low-coordinated Pt-N2 intermediates derived from Pt-N2Cl2 under the working condition are the real active sites for HER, which enable the multi-H adsorption mechanism with an ideal H* adsorption energy of nearly 0 eV, thereby the high activity, as revealed by theoretical calculations. In contrast, the high-coordinated Pt-NxC4-x sites only allow the single-H adsorption with a positive adsorption energy and thereby the low HER activity. Accordingly, with an ultralow Pt loading of only 25 μgPt cm-2, the proton exchange membrane water electrolyzer assembled using Pt1/hNCNC-70 °C as the cathodic catalyst achieves an industrial-level current density of 1.0 A cm-2 at a low cell voltage of 1.66 V and high durability, showing great potential applications.

Manipulation of Oxidation States on Phase Boundary via Surface Layer Modification for Enhanced Alkaline Hydrogen Electrocatalysis

In alkaline water electrolysis and anion exchange membrane water electrolysis technologies, the hydrogen evolution reaction (HER) at the cathode is significantly constrained by a high energy barrier during the water dissociation step. This study employs a phase engineering strategy to construct heterostructures composed of crystalline Ni4W and amorphous WOx aiming to enhance catalytic performance in the HER under alkaline conditions. This work systematically modulates the oxidation states of W within the amorphous WOx of the heterostructure to adjust the electronic states of the phase boundary, the energy barriers associated with the water dissociation step, and the adsorption/desorption properties of intermediates during the alkaline HER process. The optimized catalyst, Ni4W/WOx-2, with a quasi-metallic state of W coordinated by a low oxygen content in amorphous WOx, demonstrates exceptional catalytic performance (22 mV@10 mA cm-2), outperforming commercial Pt/C (30 mV@10 mA cm-2). Furthermore, the operando X-ray absorption spectroscopy analysis and theoretical calculations reveal that the optimized W atoms in amorphous WOx serve as active sites for water dissociation and the nearby Ni atoms in crystalline Ni4W facilitated the release of H2. These findings provide valuable insights into designing efficient heterostructured materials for energy conversion.

Microenvironment Engineering of Heterogeneous Catalysts for Liquid-Phase Environmental Catalysis

Environmental catalysis has emerged as a scientific frontier in mitigating water pollution and advancing circular chemistry and reaction microenvironment significantly influences the catalytic performance and efficiency. This review delves into microenvironment engineering within liquid-phase environmental catalysis, categorizing microenvironments into four scales: atom/molecule-level modulation, nano/microscale-confined structures, interface and surface regulation, and external field effects. Each category is analyzed for its unique characteristics and merits, emphasizing its potential to significantly enhance catalytic efficiency and selectivity. Following this overview, we introduced recent advancements in advanced material and system design to promote liquid-phase environmental catalysis (e.g., water purification, transformation to value-added products, and green synthesis), leveraging state-of-the-art microenvironment engineering technologies. These discussions showcase microenvironment engineering was applied in different reactions to fine-tune catalytic regimes and improve the efficiency from both thermodynamics and kinetics perspectives. Lastly, we discussed the challenges and future directions in microenvironment engineering. This review underscores the potential of microenvironment engineering in intelligent materials and system design to drive the development of more effective and sustainable catalytic solutions to environmental decontamination.

Integrative catalytic pairs for efficient multi-intermediate catalysis

Single-atom catalysts (SACs) have attracted considerable research interest owing to their combined merits of homogeneous and heterogeneous catalysts. However, the uniform and isolated active sites of SACs fall short in catalysing complex chemical processes that simultaneously involve multiple intermediates. In this Review, we highlight an emerging class of catalysts with adjacent binary active centres, which is called integrative catalytic pairs (ICPs), showing not only atomic-scale site-to-site electronic interactions but also synergistic catalytic effects. Compared with SACs or their derivative dual-atom catalysts (DACs), multi-interactive intermediates on ICPs can overcome kinetic barriers, adjust reaction pathways and break the universal linear scaling relations as the smallest active units. Starting from this active-site design principle, each single active atom can be considered as a brick to further build integrative catalytic clusters (ICCs) with desirable configurations, towards trimer or even larger multi-atom units depending on the requirement of a given reaction.

Bimetallic Single-Atom Catalysts for Water Splitting

Green hydrogen from water splitting has emerged as a critical energy vector with the potential to spearhead the global transition to a fossil fuel-independent society. The field of catalysis has been revolutionized by single-atom catalysts (SACs), which exhibit unique and intricate interactions between atomically dispersed metal atoms and their supports. Recently, bimetallic SACs (bimSACs) have garnered significant attention for leveraging the synergistic functions of two metal ions coordinated on appropriately designed supports. BimSACs offer an avenue for rich metal-metal and metal-support cooperativity, potentially addressing current limitations of SACs in effectively furnishing transformations which involve synchronous proton-electron exchanges, substrate activation with reversible redox cycles, simultaneous multi-electron transfer, regulation of spin states, tuning of electronic properties, and cyclic transition states with low activation energies. This review aims to encapsulate the growing advancements in bimSACs, with an emphasis on their pivotal role in hydrogen generation via water splitting. We subsequently delve into advanced experimental methodologies for the elaborate characterization of SACs, elucidate their electronic properties, and discuss their local coordination environment. Overall, we present comprehensive discussion on the deployment of bimSACs in both hydrogen evolution reaction and oxygen evolution reaction, the two half-reactions of the water electrolysis process.

Constructing CO-immune water dissociation sites around Pt to achieve stable operation in high CO concentration environment

The serious problem of carbon monoxide (CO) poisoning on the surface of Pt-based catalysts has long constrained the commercialization of proton exchange membrane fuel cells (PEMFCs). Regeneration of Pt sites by maintaining CO scavenging ability through precise construction of the surface and interface structure of the catalyst is the key to obtaining high-performance CO-resistant catalysts. Here, we used molybdenum carbide (MoCx) as the support for Pt and introduced Ru single atoms (SA-Ru) at the Pt-MoCx interface to jointly decrease the CO adsorption strength on Pt. More importantly, the MoCx and SA-Ru are immune to CO poisoning, which continuously assists in the oxidation of adsorbed CO by generating oxygen species from water dissociation. These two effects combine to confer this anode catalyst (SA-Ru@Pt/MoCx) remarkable CO tolerance and the ability to operate stably in fuel cell with high CO concentration (power output 85.5 mW cm-2@20,000 ppm CO + H2 - O2), making it possible to directly use the cheap reformed hydrogen as the fuel for PEMFCs.

A General Metal Ion Recognition Strategy to Mediate Dual-Atomic-Site Catalysts

Heterogeneous dual-atomic-site catalysts (DACs) hold great potential for diverse applications. However, to date, the synthesis of DACs primarily relies on different atoms freely colliding on the support during synthesis, principally leading to low yields. Herein, we report a general metal ion recognition (MIR) strategy for constructing a series of DACs, including but not limited to Fe1Sn1, Fe1Co1, Fe1Ni1, Fe1Cu1, Fe1Mn1, Co1Ni1, Co1Cu1, Co2, and Cu2. This strategy is achieved by coupling target inorganometallic cations and anions as ion pairs, which are sequentially adsorbed onto a nitrogen-doped carbon substrate as the precursor. Taking the oxygen reduction reaction as an example, we demonstrated that the Fe1Sn1-DAC synthesized through this strategy delivers a record peak power density of 1.218 W cm-2 under 2.0 bar H2-O2 conditions and enhanced stability compared to the single-atom-site FeN4. Further study revealed that the superior performance arises from the synergistic effect of Fe1Sn1 dual vicinal sites, which effectively optimizes the adsorption of *OH and alleviates the troublesome Fenton-like reaction.

Materials Containing Single-, Di-, Tri-, and Multi-Metal Atoms Bonded to C, N, S, P, B, and O Species as Advanced Catalysts for Energy, Sensor, and Biomedical Applications

Modifying the coordination or local environments of single-, di-, tri-, and multi-metal atom (SMA/DMA/TMA/MMA)-based materials is one of the best strategies for increasing the catalytic activities, selectivity, and long-term durability of these materials. Advanced sheet materials supported by metal atom-based materials have become a critical topic in the fields of renewable energy conversion systems, storage devices, sensors, and biomedicine owing to the maximum atom utilization efficiency, precisely located metal centers, specific electron configurations, unique reactivity, and precise chemical tunability. Several sheet materials offer excellent support for metal atom-based materials and are attractive for applications in energy, sensors, and medical research, such as in oxygen reduction, oxygen production, hydrogen generation, fuel production, selective chemical detection, and enzymatic reactions. The strong metal-metal and metal-carbon with metal-heteroatom (i.e., N, S, P, B, and O) bonds stabilize and optimize the electronic structures of the metal atoms due to strong interfacial interactions, yielding excellent catalytic activities. These materials provide excellent models for understanding the fundamental problems with multistep chemical reactions. This review summarizes the substrate structure-activity relationship of metal atom-based materials with different active sites based on experimental and theoretical data. Additionally, the new synthesis procedures, physicochemical characterizations, and energy and biomedical applications are discussed. Finally, the remaining challenges in developing efficient SMA/DMA/TMA/MMA-based materials are presented.

Relationship between Structure and Performance of Atomic-Scale Electrocatalysts for Water Splitting

Atomic-scale electrocatalysts greatly improve the performance and efficiency of water splitting but require special adjustments of the supporting structures for anchoring and dispersing metal single atoms. Here, the structural evolution of atomic-scale electrocatalysts for water splitting is reviewed based on different synthetic methods and structural properties that create different environments for electrocatalytic activity. The rate-determining step or intermediate state for hydrogen or oxygen evolution reactions is energetically stabilized by the coordination environment to the single-atom active site from the supporting material. In large-scale practical use, maximizing the loading amount of metal single atoms increases the efficiency of the electrocatalyst and reduces the economic cost. Dual-atom electrocatalysts with two different single-atom active sites react with an increased number of water molecules and reduce the adsorption energy of water derived from the difference in electronegativity between the two metal atoms. In particular, single-atom dimers induce asymmetric active sites that promote the degradation of H2O to H2 or O2 evolution. Consequently, the structural properties of atomic-scale electrocatalysts clarify the atomic interrelation between the catalytic active sites and the supporting material to achieve maximum efficiency.

Iridium Single Atoms to Nanoparticles: Nurturing the Local Synergy with Cobalt-Oxide Supported Palladium Nanoparticles for Oxygen Reduction Reaction

A ternary catalyst comprising Iridium (Ir) single-atoms (SA)s decorated on the Co-oxide supported palladium (Pd) nanoparticles (denoted as CPI-SA) is developed in this work. The CPI-SA with 1 wt.% of Ir exhibits unprecedented high mass activity (MA) of 7173 and 770 mA mgIr -1, respectively, at 0.85 and 0.90 V versus RHE in alkaline ORR (0.1 m KOH), outperforming the commercial Johnson Matthey Pt catalyst (J.M.-Pt/C; 20 wt.% Pt) by 107-folds. More importantly, the high structural reliability of the Ir single-atoms endows the CPI-SA with outstanding durability, where it shows progressively increasing MA of 13 342 and 1372 mA mgIr -1, respectively, at 0.85 and 0.90 V versus RHE up to 69 000 cycles (3 months) in the accelerated degradation test (ADT). Evidence from the in situ partial fluorescence yield X-ray absorption spectroscopy (PFY-XAS) and the electrochemical analysis indicate that the Ir single-atoms and adjacent Pd domains synergistically promote the O2 splitting and subsequent desorption of hydroxide ions (OH-), respectively. Whereas the Co-atoms underneath serve as electron injectors to boost the ORR activity of the Ir single-atoms. Besides, a progressive and sharp drop in the ORR performance is observed when Ir-clusters and Ir nanoparticles are decorated on the Co-oxide-supported Pd nanoparticles.

From Synthesis to Mechanisms: In-Depth Exploration of the Dual-Atom Catalytic Mechanisms Toward Oxygen Electrocatalysis

Dual-atom catalysts (DACs) hold a higher metal atom loading and provide greater flexibility in terms of the structural characteristics of their active sites in comparison to single-atom catalysts. Consequently, DACs hold great promise for achieving improved catalytic performance. This article aims to provide a focused overview of the latest advancements in DACs, covering their synthesis and mechanisms in reversible oxygen electrocatalysis, which plays a key role in sustainable energy conversion and storage technologies. The discussion starts by highlighting the structures of DACs and the differences in diatomic coordination induced by various substrates. Subsequently, the state-of-the-art fabrication strategies of DACs for oxygen electrocatalysis are discussed from several different perspectives. It particularly highlights the challenges of increasing the diatomic loading capacity. More importantly, the main focus of this overview is to investigate the correlation between the configuration and activity in DACs in order to gain a deeper understanding of their active roles in oxygen electrocatalysis. This will be achieved through density functional theory calculations and sophisticated in situ characterization technologies. The aim is to provide guidelines for optimizing and upgrading DACs in oxygen electrocatalysis. Additionally, the overview discusses the current challenges and future prospects in this rapidly evolving area of research.

Asymmetric Atomic Dual-Sites for Photocatalytic CO2 Reduction

Atomically dispersed active sites in a photocatalyst offer unique advantages such as locally tuned electronic structures, quantum size effects, and maximum utilization of atomic species. Among these, asymmetric atomic dual-sites are of particular interest because their asymmetric charge distribution generates a local built-in electric potential to enhance charge separation and transfer. Moreover, the dual sites provide flexibility for tuning complex multielectron and multireaction pathways, such as CO2 reduction reactions. The coordination of dual sites opens new possibilities for engineering the structure-activity-selectivity relationship. This comprehensive overview discusses efficient and sustainable photocatalysis processes in photocatalytic CO2 reduction, focusing on strategic active-site design and future challenges. It serves as a timely reference for the design and development of photocatalytic conversion processes, specifically exploring the utilization of asymmetric atomic dual-sites for complex photocatalytic conversion pathways, here exemplified by the conversion of CO2 into valuable chemicals.

Creating High-entropy Single Atoms on Transition Disulfides through Substrate-induced Redox Dynamics for Efficient Electrocatalytic Hydrogen Evolution

The controllable anchoring of multiple metal single-atoms (SAs) into a single support exhibits scientific and technological opportunities, while marrying the concentration-complex multimetallic SAs and high-entropy SAs (HESAs) into one SAC system remains a substantial challenge. Here, we present a substrate-mediated SAs formation strategy to successfully fabricate a library of multimetallic SAs and HESAs on MoS2 and MoSe2 supports, which can precisely control the doping location of SAs. Specially, the contents of SAs can continuously increase until the accessible Mo atoms on TMDs carriers are completely replaced by SAs, thus allowing the of much higher metal contents. In-depth mechanistic study shows that the well-controlled synthesis of multimetallic SAs and HESAs is realized by controlling the reversible redox reaction occurred on the TMDs/TM ion interface. As a proof-of-concept application, a variety of SAs-TMDs were applied to hydrogen evolution reaction. The optimized HESAs-TMDs (Pt,Ru,Rh,Pd,Re-MoSe2) delivers a much higher activity and durability than state of-the-art Pt. Thus, our work will broaden the family of single-atom catalysts and provide a new guideline for the rational design of high-performance single-atom catalysts.

Toward Functionality and Deactivation of Metal-Single-Atom in Heterogeneous Photocatalysts

Single-atom heterogeneous catalysts (SAHCs) provide an enticing platform for understanding catalyst structure-property-performance relationships. The 100% atom utilization and adjustable local coordination configurations make it easy to probe reaction mechanisms at the atomic level. However, the progressive deactivation of metal-single-atom (MSA) with high surface energy leads to frequent limitations on their commercial viability. This review focuses on the atomistic-sensitive reactivity and atomistic-progressive deactivation of MSA to provide a unifying framework for specific functionality and potential deactivation drivers of MSA, thereby bridging function, purpose-modification structure-performance insights with the atomistic-progressive deactivation for sustainable structure-property-performance accessibility. The dominant functionalization of atomically precise MSA acting on properties and reactivity encompassing precise photocatalytic reactions is first systematically explored. Afterward, a detailed analysis of various deactivation modes of MSA and strategies to enhance their durability is presented, providing valuable insights into the design of SAHCs with deactivation-resistant stability. Finally, the remaining challenges and future perspectives of SAHCs toward industrialization, anticipating shedding some light on the next stage of atom-economic chemical/energy transformations are presented.

A catalyst family of high-entropy alloy atomic layers with square atomic arrangements comprising iron- and platinum-group metals

We report a catalyst family of high-entropy alloy (HEA) atomic layers having three elements from iron-group metals (IGMs) and two elements from platinum-group metals (PGMs). Ten distinct quinary compositions of IGM-PGM-HEA with precisely controlled square atomic arrangements are used to explore their impact on hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR). The PtRuFeCoNi atomic layers perform enhanced catalytic activity and durability toward HER and HOR when benchmarked against the other IGM-PGM-HEA and commercial Pt/C catalysts. Operando synchrotron x-ray absorption spectroscopy and density functional theory simulations confirm the cocktail effect arising from the multielement composition. This effect optimizes hydrogen-adsorption free energy and contributes to the remarkable catalytic activity observed in PtRuFeCoNi. In situ electron microscopy captures the phase transformation of metastable PtRuFeCoNi during the annealing process. They transform from random atomic mixing (25°C), to ordered L10 (300°C) and L12 (400°C) intermetallic, and finally phase-separated states (500°C).

Oxygen-bridging Fe, Co dual-metal dimers boost reversible oxygen electrocatalysis for rechargeable Zn-air batteries

Rechargeable zinc-air batteries (ZABs) are regarded as a remarkably promising alternative to current lithium-ion batteries, addressing the requirements for large-scale high-energy storage. Nevertheless, the sluggish kinetics involving oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) hamper the widespread application of ZABs, necessitating the development of high-efficiency and durable bifunctional electrocatalysts. Here, we report oxygen atom-bridged Fe, Co dual-metal dimers (FeOCo-SAD), in which the active site Fe-O-Co-N6 moiety boosts exceptional reversible activity toward ORR and OER in alkaline electrolytes. Specifically, FeOCo-SAD achieves a half-wave potential (E1/2) of 0.87 V for ORR and an overpotential of 310 mV at a current density of 10 mA cm-2 for OER, with a potential gap (ΔE) of only 0.67 V. Meanwhile, FeOCo-SAD manifests high performance with a peak power density of 241.24 mW cm-2 in realistic rechargeable ZABs. Theoretical calculations demonstrate that the introduction of an oxygen bridge in the Fe, Co dimer induced charge spatial redistribution around Fe and Co atoms. This enhances the activation of oxygen and optimizes the adsorption/desorption dynamics of reaction intermediates. Consequently, energy barriers are effectively reduced, leading to a strong promotion of intrinsic activity toward ORR and OER. This work suggests that oxygen-bridging dual-metal dimers offer promising prospects for significantly enhancing the performance of reversible oxygen electrocatalysis and for creating innovative catalysts that exhibit synergistic effects and electronic states.

Ru Regulated Electronic Structure of PdxCuy Nanosheets for Efficient Hydrogen Evolution Reaction in Wide pH Range

The development of highly effective catalysts for hydrogen evolution reaction (HER) in a wide pH range is crucial for the sustainable utilization of green energy utilization, while the slow kinetic reaction rate severely hinders the progress of HER. Herein, the reaction kinetic issue is solved by adjusting the electronic structure of the Ru/PdxCuy catalysts. The champion catalyst displays a remarkable performance for HER with the ultralow overpotential (27, 28, and 97 mV) in 1.0 m KOH, 0.5 m H2SO4, and 1.0 m PBS at 10 mA cm-2 and high the mass activity (3036 A g-1), respectively, superior to those of commercial Pt/C benchmarks and most of reported electrocatalysts, mainly due to its low reaction activation energy. Density functional theory (DFT) calculations indicate that Ru doping contributes an electron-deficient 3d band, which promotes water adsorption. Additionally, this also leads to an upward shift of the d-band center of Pd and a downward shift of the d-band center of Cu, further optimizing the adsorption/dissociation of H2O and H*. Results from this work may provide an insight into the design and synthesis of high-performance pH-universal HER electrocatalysts.

Atomic/molecular layer deposition strategies for enhanced CO2 capture, utilisation and storage materials

Elevated levels of carbon dioxide (CO2) in the atmosphere and the diminishing reserves of fossil fuels have raised profound concerns regarding the resulting consequences of global climate change and the future supply of energy. Hence, the reduction and transformation of CO2 not only mitigates environmental pollution but also generates value-added chemicals, providing a dual remedy to address both energy and environmental challenges. Despite notable advancements, the low conversion efficiency of CO2 remains a major obstacle, largely attributed to its inert chemical nature. It is imperative to engineer catalysts/materials that exhibit high conversion efficiency, selectivity, and stability for CO2 transformation. With unparalleled precision at the atomic level, atomic layer deposition (ALD) and molecular layer deposition (MLD) methods utilize various strategies, including ultrathin modification, overcoating, interlayer coating, area-selective deposition, template-assisted deposition, and sacrificial-layer-assisted deposition, to synthesize numerous novel metal-based materials with diverse structures. These materials, functioning as active materials, passive materials or modifiers, have contributed to the enhancement of catalytic activity, selectivity, and stability, effectively addressing the challenges linked to CO2 transformation. Herein, this review focuses on ALD and MLD's role in fabricating materials for electro-, photo-, photoelectro-, and thermal catalytic CO2 reduction, CO2 capture and separation, and electrochemical CO2 sensing. Significant emphasis is dedicated to the ALD and MLD designed materials, their crucial role in enhancing performance, and exploring the relationship between their structures and catalytic activities for CO2 transformation. Finally, this comprehensive review presents the summary, challenges and prospects for ALD and MLD-designed materials for CO2 transformation.

Platinum-Ruthenium Dual-Atomic Sites Dispersed in Nanoporous Ni0.85Se Enabling Ampere-Level Current Density Hydrogen Production

Alkaline anion-exchange-membrane water electrolyzers (AEMWEs) using earth-abundant catalysts is a promising approach for the generation of green H2. However, the AEMWEs with alkaline electrolytes suffer from poor performance at high current density compared to proton exchange membrane electrolyzers. Here, atomically dispersed Pt-Ru dual sites co-embedded in nanoporous nickel selenides (np/Pt1Ru1-Ni0.85Se) are developed by a rapid melt-quenching approach to achieve highly-efficient alkaline hydrogen evolution reaction. The np/Pt1Ru1-Ni0.85Se catalyst shows ampere-level current density with a low overpotential (46 mV at 10 mA cm-2 and 225 mV at 1000 mA cm-2), low Tafel slope (32.4 mV dec-1), and excellent long-term durability, significantly outperforming the benchmark Pt/C catalyst and other advanced large-current catalysts. The remarkable HER performance of nanoporous Pt1Ru1-Ni0.85Se is attributed to the strong intracrystal electronic metal-support interaction (IEMSI) between Pt-Se-Ru sites and Ni0.85Se support which can greatly enlarge the charge redistribution density, reduce the energy barrier of water dissociation, and optimize the potential determining step. Furthermore, the assembled alkaline AEMWE with an ultralow Pt and Ru loading realizes an industrial-level current density of 1 A cm-2 at 1.84 volts with high durability.

Switch Volmer-Heyrovsky to Volmer-Tafel Pathway for Efficient Acidic Electrocatalytic Hydrogen Evolution by Correlating Pt Single Atoms with Clusters

As cost-effective catalysts, platinum (Pt) single-atom catalysts (SACs) have attracted substantial attention. However, most studies indicate that Pt SACs in acidic hydrogen evolution reaction (HER) follow the slow Volmer-Heyrovsky (VH) mechanism instead of the fast kinetic Volmer-Tafel (VT) pathway. Here, this work propose that the VH mechanism in Pt SACs can be switched to the faster VT pathway for efficient HER by correlating Pt single atoms (SAs) with Pt clusters (Cs). Our calculations reveal that the correlation between Pt SAs and Cs significantly impacts the electronic structure of exposed Pt atoms, lowering the adsorption barrier for atomic hydrogen and enabling a faster VT mechanism. To validate these findings, this work purposely synthesize three catalysts: l-Pt@MoS2, m-Pt@MoS2 and h-Pt@MoS2 with low, moderate, and high Pt-loading, having different distributions of Pt SAs and Cs. The m-Pt@MoS2 catalyst with properly correlating Pt SAs and Cs exhibits outstanding performance with an overpotential of 47 mV and Tafel slope of 32 mV dec-1. Further analysis of the Tafel values confirms that the m-Pt@MoS2 sample indeed follows the VT reaction mechanism, aligning with the theoretical findings. This study offers a deep understanding of the synergistic mechanism, paving a way for designing novel-advanced catalysts.

Synergistic Ni-W Dimer Sites Induced Stable Compressive Strain for Boosting the Performance of Pt as Electrocatalyst for the Oxygen Reduction Reaction

Alloying Pt catalysts with transition metal elements is an effective pathway to enhance the performance of oxygen reduction reaction (ORR), but often accompanied with severe metal dissolution issue, resulting in poor stability of alloy catalysts. Here, instead of forming traditional alloy structure, we modify Pt surface with a novel Ni-W dimer structure by the atomic layer deposition (ALD) technique. The obtained NiW@PtC catalyst exhibits superior ORR performance both in liquid half-cell and practical fuel cell compared with initial Pt/C. It is discovered that strong synergistic Ni-W dimer structure arising from short atomic distance induced a stable compressive strain on the Pt surface, thus boosting Pt catalytic performance. This surface modification by synergistic dimer sites offers an effective strategy in tailoring Pt with excellent activity and stability, which provides a significant perspective in boosting the performance of commercial Pt catalyst modified with polymetallic atom sites.

Iron Triad-Based Bimetallic M-N-C Nanomaterials as Highly Active Bifunctional Oxygen Electrocatalysts

The use of precious metal electrocatalysts in clean electrochemical energy conversion and storage applications is widespread, but the sustainability of these materials, in terms of their availability and cost, is constrained. In this research, iron triad-based bimetallic nitrogen-doped carbon (M-N-C) materials were investigated as potential bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The synthesis of bimetallic FeCo-N-C, CoNi-N-C, and FeNi-N-C catalysts involved a precisely optimized carbonization process of their respective metal-organic precursors. Comprehensive structural analysis was undertaken to elucidate the morphology of the prepared M-N-C materials, while their electrocatalytic performance was assessed through cyclic voltammetry and rotating disk electrode measurements in a 0.1 M KOH solution. All bimetallic catalyst materials demonstrated impressive bifunctional electrocatalytic performance in both the ORR and the OER. However, the FeNi-N-C catalyst proved notably more stable, particularly in the OER conditions. Employed as a bifunctional catalyst for ORR/OER within a customized zinc-air battery, FeNi-N-C exhibited a remarkable discharge-charge voltage gap of only 0.86 V, alongside a peak power density of 60 mW cm-2. The outstanding stability of FeNi-N-C, operational for about 55 h at 2 mA cm-2, highlights its robustness for prolonged application.

Universal Platform for Robust Dual-Atom Doped 2D Catalysts with Superior Hydrogen Evolution in Wide pH Media

Layered 2D transition metal dichalcogenides (TMDs) have been suggested as efficient substitutes for Pt-group metal electrocatalysts in the hydrogen evolution reaction (HER). However, poor catalytic activities in neutral and alkaline electrolytes considerably hinder their practical applications. Furthermore, the weak adhesion between TMDs and electrodes often impedes long-term durability and thus requires a binder. Here, a universal platform is reported for robust dual-atom doped 2D electrocatalysts with superior HER performance over a wide pH range media. V:Co-ReS2 on a wafer scale is directly grown on oxidized Ti foil by a liquid-phase precursor-assisted approach and subsequently used as highly efficient electrocatalysts. The catalytic performance surpasses that of Pt group metals in a high current regime (≥ 100 mA cm-2) at pH ≥ 7, with a high durability of more than 70 h in all media at 200 mA cm-2. First-principles calculations reveal that V:Co dual doping in ReS2 significantly reduces the water dissociation barrier and simultaneously enables the material to achieve the thermoneutral Gibbs free energy for hydrogen adsorption.

Correlation between Heteroatom Coordination and Hydrogen Evolution for Single-site Pt on Carbon-based Nanocages

The electrocatalytic performance of single-site catalysts (SSCs) is closely correlated with the electronic structure of metal atoms. Herein we construct a series of Pt SSCs on heteroatom-doped hierarchical carbon nanocages, which exhibit increasing hydrogen evolution reaction (HER) activities along S-doped, P-doped, undoped and N-doped supports. Theoretical simulation indicates a multi-H-atom adsorption process on Pt SSCs due to the low coordination, and a reasonable descriptor is figured out to evaluate the HER activities. Relative to C-coordinated Pt, N-coordinated Pt has higher reactivity due to the electron transfer of N-to-Pt, which enriches the density of states of Pt 5d orbital near the Fermi level and facilitates the capturing of protons, just the opposite to the situations for P- and S-coordinated ones. The stable N-coordinated Pt originates from the kinetic stability throughout the multi-H-atom adsorption process. This finding provides a significant guidance for rational design of advanced Pt SSCs on carbon-based supports.

Precisely constructing orbital coupling-modulated iron dinuclear site for enhanced catalytic ozonation performance

The advancement of atomically precise dinuclear heterogeneous catalysts holds great potential in achieving efficient catalytic ozonation performance and contributes to the understanding of synergy mechanisms during reaction conditions. Herein, we demonstrate a "ship-in-a-bottle and pyrolysis" strategy that utilizes Fe2(CO)9 dinuclear-cluster to precisely construct Fe2 site, consisting of two Fe1-N3 units connected by Fe-Fe bonds and firmly bonded to N-doped carbon. Systematic characterizations and theoretical modeling reveal that the Fe-Fe coordination motif markedly reduced the devotion of the antibonding state in the Fe-O bond because of the strong orbital coupling interaction of dual Fe d-d orbitals. This facilitates O-O covalent bond cleavage of O3 and enhances binding strength with reaction intermediates (atomic oxygen species; *O and *OO), thus boosting catalytic ozonation performance. As a result, Fe dinuclear site catalyst exhibits 100% ozonation efficiency for CH3SH elimination, outperforming commercial MnO2 catalysts by 1,200-fold. This research provides insights into the atomic-level structure-activity relationship of ozonation catalysts and extends the use of dinuclear catalysts in catalytic ozonation and beyond.

Ultrafine PtCo alloy by pyrolysis etching-confined pyrolysis for enhanced hydrogen evolution

Zeolitic imidazolate framework-67 (ZIF-67) has been widely used as a precursor to developing efficient PtCo alloy catalysts for hydrogen evolution reaction (HER). However, traditional in-situ pyrolysis strategies involve complicated interface structure modulating processes between ZIF-67 and Pt precursors, challenging large-scale synthesis. Herein, a "pyrolysis etching-confined pyrolysis" approach is developed to design confined PtCo alloy in porous frameworks of onion carbon derived from ZIF-67. The confined PtCo alloy with Pt content of only 5.39 wt% exhibits a distinct HER activity in both acid (η10: 5 mV and Tafel: 9 mV dec-1) and basic (η10: 33 mV and Tafel: 51 mV dec-1) media and a drastic enhancement in stability. Density functional theory calculations reveal that the strong electronic interaction between Pt and Co allows favorable electron redistribution, which affords a favorable hydrogen spillover on PtCo alloy compared with that of pristine Pt(111). Operational electrochemical impedance spectroscopy demonstrates that the Faraday reaction process is facilitated under acidic conditions, while the transfer of intermediates through the electric double-layer region under alkaline conditions is accelerated. This work not only offers a universal route for high-performance Pt-based alloy catalysts with metal-organic framework (MOF) precursors but also provides experimental evidence for the role of the electric double layer in electrocatalysis reactions.