Tailoring of Active Sites from Single to Dual Atom Sites for Highly Efficient Electrocatalysis

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.

Insight into Impacts of π-π Assembly on Phthalocyanine Based Heterogeneous Molecular Electrocatalysis

Electrochemical CO2 reduction (CO2R) to feedstocks competes with the hydrogen evolution reaction (HER). Cobalt phthalocyanine (CoPc) immobilized onto carbon driven by π-π interaction represents a classical type of heterogeneous molecular catalyst for CO2R. However, the impacts of π conjugation on the electrocatalysis have not been clarified. Herein, the electrochemical properties of CoPc were investigated by comparison of its analogue to 2,3-naphthalocyanine cobalt (NapCo) having extended π conjugation. It is found that CoPc is redox-active on carbon to provide low oxidized Co sites for improving the CO2R activity and selectivity, while NapCo on carbon turned out to be redox-inert leading to lower performance. In addition, the redox-mediated mechanism for CO2R on CoPc tends to operate with increasing electrolyte alkalinity, which further enhances the reaction selectivity. We speculated that moderate π conjugation allows the redox-mediated mechanism on CoPc, which is critical to promote CO2R performance while depressing the competing HER.

Advances in Atomically Dispersed Metal and Nitrogen Co-Doped Carbon Catalysts for Advanced Oxidation Technologies and Water Remediation: From Microenvironment Modulation to Non-Radical Mechanisms

Atomically dispersed metal and nitrogen co-doped carbon catalysts (M-N-C) have been attracting tremendous attentions thanks to their unique MNx active sites and fantastic catalytic activities in advanced oxidation technologies (AOTs) for water remediation. However, precisely tailoring the microenvironment of active sites at atomic level is still an intricate challenge so far, and understanding of the non-radical mechanisms in persulfate activation exists many uncertainties. In this review, latest developments on the microenvironment modulation strategies of atomically dispersed M-N-C catalysts including regulation of central metal atoms, regulation of coordination numbers, regulation of coordination heteroatoms, and synergy between single-atom catalysts (SACs) with metal species are systematically highlighted and discussed. Afterwards, progress and underlying limitations about the typical non-radical pathways from production of singlet oxygen, electron transfer mechanism to generation of high-valent metal species are well demonstrated to inspire intrinsic insights about the mechanisms of M-N-C/persulfate systems. Lastly, perspectives for the remaining challenges and opportunities about the further development of carbon-based SACs in environment remediation are also pointed out. It is believed that this review will be much valuable for the further design of active sites in M-N-C/persulfate catalytic systems and promote the wide application of SACs in various fields.

Ferredoxin-Inspired Design of S-Synergized Fe-Fe Dual-Metal Center Catalysts for Enhanced Electrocatalytic Oxygen Reduction Reaction

Dual-metal center catalysts (DMCs) have shown the ability to enhance the oxygen reduction reaction (ORR) owing to their distinctive structural configurations. However, the precise modulation of electronic structure and the in-depth understanding of synergistic mechanisms between dual metal sites of DMCs at the atomic level remain challenging. Herein, mimicking the ferredoxin, Fe-based DMCs (Fe2N6-S) are strategically designed and fabricated, in which additional Fe and S sites are synchronously installed near the Fe sites and serve as "dual modulators" for coarse- and fine-tuning of the electronic modulation, respectively. The as-prepared Fe2N6-S catalyst exhibits enhanced ORR activity and outstanding Zinc-air (Zn-air) battery performance compared to the conventional single Fe site catalysts. The theoretical and experimental results reveal that introducing the second metal Fe creates a dual adsorption site that alters the O2 adsorption configuration and effectively activates the O─O bond, while the synergistic effect of dual Fe sites results in the downward shift of the d-band center, facilitating the release of OH*. Additionally, local electronic engineering of heteroatom S for Fe sites further facilitates the formation of the rate-determining step OOH*, thus accelerating the reaction kinetics.

Single-Atomic Co-N4 Sites with CrCo Nanoparticles for Metal-Air Battery-Driven Hydrogen Evolution

Designing highly active and robust earth abundant trifunctional electrocatalysts for energy storage and conversion applications remain an enormous challenge. Herein, we report a trifunctional electrocatalyst (CrCo/CoN4@CNT-5), synthesized at low calcination temperature (550 °C), which consists of Co-N4 single atom and CrCo alloy nanoparticles and exhibits outstanding electrocatalytic performance for the hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction. The catalyst is able to deliver a current density of 10 mA cm-2 in an alkaline electrolytic cell at a very low cell voltage of ∼1.60 V. When the catalyst is equipped in a liquid rechargeable Zn-air battery, it endowed a high open-circuit voltage with excellent cycling durability and outperformed the commercial Pt/C+IrO2 catalytic system. Furthermore, the Zn-air battery powered self-driven water splitting system is displayed using CrCo/CoN4@CNT-5 as sole trifunctional catalyst, delivering a high H2 evolution rate of 168 μmol h-1. Theoretical calculations reveal synergistic interaction between Co-N4 active sites and CrCo nanoparticles, favoring the Gibbs free energy for H2 evolution. The presence of Cr not only enhances the H2O adsorption and dissociation but also tunes the electronic property of CrCo nanoparticles to provide optimized hydrogen binding capacity to Co-N4 sites, thus giving rise to accelerated H2 evolution kinetics. This work highlights the importance of the presence of small quantity of Cr in enhancing the electrocatalytic activity as well as robustness of single-atom catalyst and suggests the design of the multifunctional robust electrocatalysts for long-term H2 evolution application.

Structural engineering of atomic catalysts for electrocatalysis

As a burgeoning category of heterogeneous catalysts, atomic catalysts have been extensively researched in the field of electrocatalysis. To satisfy different electrocatalytic reactions, single-atom catalysts (SACs), diatomic catalysts (DACs) and triatomic catalysts (TACs) have been successfully designed and synthesized, in which microenvironment structure regulation is the core to achieve high-efficiency catalytic activity and selectivity. In this review, the effect of the geometric and electronic structure of metal active centers on catalytic performance is systematically introduced, including substrates, central metal atoms, and the coordination environment. Then theoretical understanding of atomic catalysts for electrocatalysis is innovatively discussed, including synergistic effects, defect coupled spin state change and crystal field distortion spin state change. In addition, we propose the challenges to optimize atomic catalysts for electrocatalysis applications, including controlled synthesis, increasing the density of active sites, enhancing intrinsic activity, and improving the stability. Moreover, the structure-function relationships of atomic catalysts in the CO2 reduction reaction, nitrogen reduction reaction, oxygen reduction reaction, hydrogen evolution reaction, and oxygen evolution reaction are highlighted. To facilitate the development of high-performance atomic catalysts, several technical challenges and research orientations are put forward.

Engineering Symmetry-Breaking Centers and d-Orbital Modulation in Triatomic Catalysts for Zinc-Air Batteries

Unraveling the configuration-activity relationship and synergistic enhancement mechanism (such as real active center, electron spin-state, and d-orbital energy level) for triatomic catalysts, as well as their intrinsically bifunctional oxygen electrocatalysis, is a great challenge. Here we present a triatomic catalyst (TAC) with a trinuclear active structure that displays extraordinary oxygen electrocatalysis for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), greatly outperforming the counterpart of single-atom and diatomic catalysts. The aqueous Zn-air battery (ZAB) equipped with a TAC-based cathode exhibits extraordinary rechargeable stability and ultrarobust cycling performance (1970 h/3940 cycles at 2 mA cm-2, 125 h/250 cycles at 10 mA cm-2 with negligible voltage decay), and the quasi-solid-state ZAB displays outstanding rechargeability and low-temperature adaptability (300 h/1800 cycles at 2 mA cm-2 at -60 °C), outperforming other state-of-the-art ZABs. The experimental and theoretical analyses reveal the symmetry-breaking CoN4 configuration under incorporation of neighboring metal atoms (Fe and Cu), which leads to d-orbital modulation, a low-shift d band center, weakened binding strength to the oxygen intermediates, and decreased energy barrier for bifunctional oxygen electrocatalysis. This rational tricoordination design as well as an in-depth mechanism analysis indicate that hetero-TACs can be promisingly applied in various electrocatalysis applications.

Low-Potential Iodide Oxidation Enables Dual-Atom CoFe─N─C Catalysts for Ultra-Stable and High-Energy-Efficiency Zn-Air Batteries

The low energy efficiency and limited cycling life of rechargeable Zn-air batteries (ZABs) arising from the sluggish oxygen reduction/evolution reactions (ORR/OERs) severely hinder their commercial deployment. Herein, a zeolitic imidazolate framework (ZIF)-derived strategy associated with subsequent thermal fixing treatment is proposed to fabricate dual-atom CoFe─N─C nanorods (Co1 Fe1 ─N─C NRs) containing atomically dispersed bimetallic Co/Fe sites, which can promote the energy efficiency and cyclability of ZABs simultaneously by introducing the low-potential oxidation redox reactions. Compared to the mono-metallic nanorods, Co1 Fe1 ─N─C NRs exhibit remarkable ORR performance including a positive half-wave potential of 0.933 V versus reversible hydrogen electrode (RHE) in alkaline electrolyte. Surprisingly, after introducing the potassium iodide (KI) additive, the oxidation overpotential of Co1 Fe1 ─N─C NRs to reach 10 mA cm-2 can be significantly reduced by 395 mV compared to the conventional destructive OER. Theoretical calculations show that the markedly decreased overpotential of iodide oxidation can be ascribed to the synergistic effects of neighboring Co─Fe diatomic sites as the unique adsorption sites. Overall, aqueous ZABs assembled with Co1 Fe1 ─N─C NRs and KI as the air-cathode catalyst and electrolyte additive, respectively, can deliver a low charging voltage of 1.76 V and ultralong cycling stability of over 230 h with a high energy efficiency of ≈68%.

Electron Redistribution in Iridium-Iron Dual-Metal-Atom Active Sites Enables Synergistic Enhancement for H2O2 Decomposition

Developing efficient heterogeneous H2O2 decomposition catalysts under neutral conditions is of great importance in many fields such as clinical therapy, sewage treatment, and semiconductor manufacturing but still suffers from low intrinsic activity and ambiguous mechanism understanding. Herein, we constructed activated carbon supported with an Ir-Fe dual-metal-atom active sites catalyst (IrFe-AC) by using a facile method based on a pulsed laser. The electron redistribution in Ir-Fe dual-metal-atom active sites leads to the formation of double reductive metal active sites, which can strengthen the metal-H2O2 interaction and boost the H2O2 decomposition performance of Ir-Fe dual-metal-atom active sites. Ir-Fe dual-metal-atom active sites show a high second-order reaction rate constant of 3.53 × 106 M-1·min-1, which is ∼106 times higher than that of Fe3O4. IrFe-AC is effective in removing excess intracellular reactive oxygen species, protecting DNA, and reducing inflammation under oxidative stress, indicating its therapeutic potential against oxidative stress-related diseases. This study could advance the mechanism understanding of H2O2 decomposition by heterogeneous catalysts and provide guidance for the rational design of high-performance catalysts for H2O2 decomposition.

Arrayed Pt Single Atoms via Phosphotungstic Acids Intercalated in Silicate Nanochannels for Efficient Hydrogen Evolution Reactions

Single-atom catalysts, known for their high activity, have garnered significant interest. Currently, single-atom catalysts were prepared mainly on 2D substrates with random distribution. Here, we report a strategy for preparing arrayed single Pt (Pt1) atoms, which are templated through coordination with phosphotungstic acids (PTA) intercalated inside hexagonally packed silicate nanochannels for a high single Pt-atom loading of ca. 3.0 wt %. X-ray absorption spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy, in conjunction with the density-functional theory calculation, collectively indicate that the Pt single atoms are stabilized via a four-oxygen coordination on the PTA within the nanochannels' inner walls. The critical reduction in the Pt-adsorption energy to nearly the cohesive energy of Pt clustering is attributed to the interaction between PTA and the silicate substrate. Consequently, the transition from single-atom dispersion to clustering of Pt atoms can be controlled by adjusting the number density of PTA intercalated within the silicate nanochannels, specifically when the number ratio of Pt atoms to PTA changes from 3.7 to 18. The 3D organized Pt1-PTA pairs, facilitated by the arrayed silicate nanochannels, demonstrate high and stable efficiency with a hydrogen production rate of ca. 300 mmol/h/gPt─approximately twice that of the best-reported Pt efficiency in polyoxometalate-based photocatalytic systems.

The DFT and Machine Learning Method Accelerated the Discovery of DMSCs with High ORR and OER Catalytic Activities

The oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are crucial for the conversion of clean energy. Recently, dual-metal-site catalysts (DMSCs) have gained much attention due to their high atom utilization, stronger stability, and better catalytic performance. An advanced method that combines density functional theory (DFT) and machine learning (ML) has been employed in this study to investigate the adsorption free energies of adsorbates on hundreds of potential catalysts, with the aim of screening for catalysts that are highly active for the ORR and OER. The result of this study is that 30 DMSCs with ORR activity superior to Pt, 10 DMSCs with OER activity superior to RuO2, and 4 bifunctional catalysts for the OER and ORR are identified. This work provides guidance for the rational selection of metals on DMSCs to prepare catalysts with a high electrocatalytic performance for renewable energy applications.

Transition metals anchored on two-dimensional p-BN support with center-coordination scaling relationship descriptor for spontaneous visible-light-driven photocatalytic nitrogen reduction

Solar energy has the potential to revolutionize the production of ammonia, as it could provide a reliable and uninterrupted source of energy for the chemical reaction involved. However, improving the catalytic performance of catalysts often leads to a reduction in their band gaps, which results in insufficient photogenerated electron potential to realize the nitrogen reduction reaction (NRR), and thus the development of NRR efficient photocatalysts remains a great challenge. Herein, based on the density functional theory (DFT), a series of single-atom photocatalysts with transition metals (TMs) doped on porous boron nitride (p-BN) nanosheet are proposed for NRR. Among them, Re-B3@p-BN could effectively catalyze gas-phase N2 through the corresponding pathways with limiting potentials of 0.31 V. Meanwhile, it exhibits excellent light absorption efficiency under illumination and could spontaneously catalyse nitrogen fixation reactions due to the suitable forbidden band and high photogenerated electron potential. Moreover, a linear relationship descriptor based on the intrinsic properties has been established, using a machine learning approach by considering the combined effects of the central metal atom and the coordination atoms. This descriptor could help accelerate the development of rational and improved 2D NRR photocatalysts with high catalytic activity and high selectivity.

Enhancement of Pt-O Synergistic Sites through Titanium Vacancies for Low-Temperature Nitrogen Oxide Reduction

Improving the reaction rate of each step is significant for accelerating the multistep reaction of NO reduction by H2. However, simultaneously enhancing the activation of different gaseous reactants using single-atom catalysts remains a challenge to maximize the activity. Herein, we propose a strategy that utilizes titanium-vacancy-regulated electronic properties of single atoms and defective support (Pt1/d-TiO2) to facilitate electron transfer from edge-share O atoms (OTi) to adjacent Pt single atoms. This leads to the formation of low-valence Pt and unsaturated-charge OTi sites, which causes the catalytic reaction to follow a synergistic mechanism. Specifically, experimental and theoretical analyses demonstrate that low-valence Pt sites finely tune the adsorption of H2 molecules, consequently lowering the dissociation energy from 0.15 to as low as 0.01 eV. Moreover, using quasi-in situ spectroscopy, we clearly observe NO molecules being adsorbed on interfacial oxygen sites of a defective support. Then, the bond energy of the N-O bond is weakened through an electron acceptance-donation mechanism between unsaturated-charge OTi sites and NO, thereby facilitating NO activation. The designed single-atom catalysts with synergistic sites exhibit unmatched activity at low temperatures (above 90% NOx conversion at 100 °C), along with higher turnover frequency value (0.74 s-1) and superior stability, making them potentially suitable for industrial applications.

Recent advances in bifunctional dual-sites single-atom catalysts for oxygen electrocatalysis toward rechargeable zinc-air batteries

Rechargeable zinc-air batteries (ZABs) with high energy density and low pollutant emissions are regarded as the promising energy storage and conversion devices. However, the sluggish kinetics and complex four-electron processes of oxygen reduction reaction and oxygen evolution reaction occurring at air electrodes in rechargeable ZABs pose significant challenges for their large-scale application. Carbon-supported single-atom catalysts (SACs) exhibit great potential in oxygen electrocatalysis, but needs to further improve their bifunctional electrocatalytic performance, which is highly related to the coordination environment of the active sites. As an extension of SACs, dual-sites SACs with wide combination of two active sites provide limitless opportunities to tailor coordination environment at the atomic level and improve catalytic performance. The review systematically summarizes recent achievements in the fabrication of dual-site SACs as bifunctional oxygen electrocatalysts, starting by illustrating the design fundament of the electrocatalysts according to their catalytic mechanisms. Subsequently, metal-nonmetal-atom synergies and dual-metal-atom synergies to synthesize dual-sites SACs toward enhancing rechargeable ZABs performance are overviewed. Finally, the perspectives and challenges for the development of dual-sites SACs are proposed, shedding light on the rational design of efficient bifunctional oxygen electrocatalysts for practical rechargeable ZABs.

Inter-Metal Interaction of Dual-Atom Catalysts in Heterogeneous Catalysis

Dual-atom catalysts (DACs) have been a new frontier in heterogeneous catalysis due to their unique intrinsic properties. The synergy between dual atoms provides flexible active sites, promising to enhance performance and even catalyze more complex reactions. However, precisely regulating active site structure and uncovering dual-atom metal interaction remain grand challenges. In this review, we clarify the significance of the inter-metal interaction of DACs based on the understanding of active center structures. Three diatomic configurations are elaborated, including isolated dual single-atom, N/O-bridged dual-atom, and direct dual-metal bonding interaction. Subsequently, the up-to-date progress in heterogeneous oxidation reactions, hydrogenation/dehydrogenation reactions, electrocatalytic reactions, and photocatalytic reactions are summarized. The structure-activity relationship between DACs and catalytic performance is then discussed at an atomic level. Finally, the challenges and future directions to engineer the structure of DACs are discussed. This review will offer new prospects for the rational design of efficient DACs toward heterogeneous catalysis.

Dual Single-Atomic Co-Mn Sites in Metal-Organic-Framework-Derived N-Doped Nanoporous Carbon for Electrochemical Oxygen Reduction

Synthesizing dual single-atom catalysts (DSACs) with atomically isolated metal pairs is a challenging task but can be an effective way to enhance the performance for electrochemical oxygen reduction reaction (ORR). Herein, well-defined DSACs of Co-Mn, stabilized in N-doped porous carbon polyhedra (named CoMn/NC), are synthesized using high-temperature pyrolysis of a Co/Mn-doped zeolitic imidazolate framework. The atomically isolated Co-Mn site in CoMn/NC is recognized by combining microscopic as well as spectroscopic techniques. CoMn/NC exhibited excellent ORR activities in alkaline (E1/2 = 0.89 V) as well as in acidic (E1/2 = 0.82 V) electrolytes with long-term durability and enhanced methanol tolerance. Density functional theory (DFT) suggests that the Co-Mn site is efficiently activating the O-O bond via bridging adsorption, decisive for the 4e- oxygen reduction process. Though the Co-Mn sites favor O2 activation via the dissociative ORR mechanism, stronger adsorption of the intermediates in the dissociative path degrades the overall ORR activity. Our DFT studies conclude that the ORR on an Co-Mn site mainly occurs via bridging side-on O2 adsorption following thermodynamically and kinetically favorable associative mechanistic pathways with a lower overpotential and activation barrier. CoMn/NC performed excellently as a cathode in a proton exchange membrane (PEM) fuel cell and rechargeable Zn-air battery with high peak power densities of 970 and 176 mW cm-2, respectively. This work provides the guidelines for the rational design and synthesis of nonprecious DSACs for enhancing the ORR activity as well as the robustness of DSACs and suggests a design of multifunctional robust electrocatalysts for energy storage and conversion devices.

Atomically Dispersed Pd-N1C3 Sites on a Nitrogen-Doped Carbon Nanosphere for Semi-hydrogenation of Acetylene

Rationally designing efficient catalysts for semi-hydrogenation of acetylene is significant but challenging. Herein, Pd isolated single-atom sites (ISAS) on a covalent-organic-framework (COF)-derived nanosphere (Pd-ISAS/CN) are synthesized by a COF-absorption-pyrolysis strategy. This synthetic strategy is also applicable for Pt and Ru ISAS catalysts, demonstrating that it is a general method to synthesize noble-metal ISAS on COF-derived carbon materials. Pd-ISAS/CN exhibits outstanding reactivity and high selectivity for semi-hydrogenation of acetylene, with 92% conversion of acetylene, 80% selectivity toward ethylene at 100 °C, and corresponding activity is as high as 712 molacetylene molmetal-1 h-1. Extended X-ray absorption fine structure (EXAFS) measurement and density functional theory (DFT) calculation reveal the Pd-N1C3 sites from Pd-ISAS/CN efficiently boost the reactivity for semi-hydrogenation of acetylene. This work will bring inspiration to rationally design noble-metal-based ISAS catalysts derived from COF materials and boost catalytic performance by optimizing the coordination environment of catalytic sites.

Understanding the Bifunctional Trends of Fe-Based Binary Single-Atom Catalysts

Binary single-atom catalysts (BSACs) have demonstrated fascinating activities compared to single atom catalysts (SACs) for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Notably, Fe SACs is one of the most promising ORR electrocatalysts, and further revealing the synergistic effects between Fe and other 3d transition metals (M) for FeM BSACs are very important to enhance bifunctional performance. Herein, density functional theory (DFT) calculations are first adapted to demonstrate the role of various transition metals on the bifunctional activity of Fe sites, and a notable volcano relationship is established through the generally accepted adsorption free energy that ΔG* OH for ORR, and ΔG* O -ΔG* OH for OER, respectively. Further, ten of the atomically dispersed FeM anchored on nitrogen-carbon support (FeM-NC) are successfully synthesized with typical atomic dispersion by a facile movable type printing method. The experimental data confirms the bifunctional activity diversity of FeM-NC between the early- and late- transition metals, agrees very well with the DFT results. More importantly, the optimal FeCu-NC shows the expected performance with high ORR and OER activity, thereby, the assembled rechargeable zinc-air battery delivers a high power density of 231 mW cm-2 , and an impressive stability that can be stably operated over 300 h.

Diatomic catalysts for Fenton and Fenton-like reactions: a promising platform for designing/regulating reaction pathways

The optimization of the single-atom catalyst (SAC) performance has been the hot spot for years. It is widely acknowledged that the incorporation of adjacent single-atom sites (diatomic catalysts (DACs)) can enable synergistic effects, which can be used in cascade catalysis, dual-function catalysis, and performance regulation of intrinsic active sites. DACs have been widely applied in the CO₂ reduction reaction (CO₂RR), oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), etc.; however, their application is limited in Fenton or Fenton-like reactions. This perspective summarizes the most advanced achievements in this field, followed by the proposed opportunities in further research, including regulation of the magnetic moment, inter-atomic distance effect, strain engineering, atomic cluster (AC)/nanoparticle (NP) modification, etc. It is demonstrated that this perspective can contribute to the DAC application in Fenton or Fenton-like reactions with innovative design and mechanisms being put forward.

Synergy of dual-atom catalysts deviated from the scaling relationship for oxygen evolution reaction

Dual-atom catalysts, particularly those with heteronuclear active sites, have the potential to outperform the well-established single-atom catalysts for oxygen evolution reaction, but the underlying mechanistic understanding is still lacking. Herein, a large-scale density functional theory is employed to explore the feasibility of *O-*O coupling mechanism, which can circumvent the scaling relationship with improving the catalytic performance of N-doped graphene supported Fe-, Co-, Ni-, and Cu-containing heteronuclear dual-atom catalysts, namely, M'M@NC. Based on the constructed activity maps, a rationally designed descriptor can be obtained to predict homonuclear catalysts. Seven heteronuclear and four homonuclear dual-atom catalysts possess high activities that outperform the minimum theoretical overpotential. The chemical and structural origin in favor of *O-*O coupling mechanism thus leading to enhanced reaction activity have been revealed. This work not only provides additional insights into the fundamental understanding of reaction mechanisms, but also offers a guideline for the accelerated discovery of efficient catalysts.

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

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

Asymmetric Coordination Environment Engineering of Atomic Catalysts for CO2 Reduction

Single-atom catalysts (SACs) have emerged as well-known catalysts in renewable energy storage and conversion systems. Several supports have been developed for stabilizing single-atom catalytic sites, e.g., organic-, metal-, and carbonaceous matrices. Noticeably, the metal species and their local atomic coordination environments have a strong influence on the electrocatalytic capabilities of metal atom active centers. In particular, asymmetric atom electrocatalysts exhibit unique properties and an unexpected carbon dioxide reduction reaction (CO₂RR) performance different from those of traditional metal-N₄ sites. This review summarizes the recent development of asymmetric atom sites for the CO₂RR with emphasis on the coordination structure regulation strategies and their effects on CO₂RR performance. Ultimately, several scientific possibilities are proffered with the aim of further expanding and deepening the advancement of asymmetric atom electrocatalysts for the CO₂RR.