Coordination Sphere Research Articles

Harnessing of Cooperative Cu⋅⋅⋅H Interactions for Luminescent Low-Coordinate Copper(I) Complexes towards Stable OLEDs.

Although two-coordinate Cu(I) complexes are highly promising low-cost emitters for organic light-emitting diodes (OLEDs), the exposed metal center in the linear coordination geometry makes them suffer from poor stability. Herein, we describe a strategy to develop stable carbene-Cu-amide complexes through installing intramolecular noncovalent Cu⋅⋅⋅H interactions. The employment of 13H-dibenzo[a,i]carbazole (DBC) as the amide ligand leads to short Cu⋅⋅⋅H distances in addition to the Cu-N coordination bond. The resultant Cu(I) complexes exhibit yellow thermally activated delayed fluorescence with photoluminescence quantum yields of up to 86 % and radiative decay rate constants on the order of 106 s-1. Comparing with the analogues without Cu⋅⋅⋅H interactions, the pincer complexes have significantly improved stability. The vacuum-deposited OLEDs show high-performance electroluminescence with maximum external quantum efficiencies of up to 29.5 % and extremely small roll-offs of only 3.5 % at 10,000 cd m-2. Remarkably, the operational lifetimes (LT90) are up to 68 h with an initial luminance of 3000 cd m-2. This work proves a feasible design of robust low-coordinate metal complexes by leveraging secondary coordination interactions, which helps to overcome the long-standing stability problem.

Harnessing of Cooperative Cu···H Interactions for Luminescent Low‐Coordinate Copper(I) Complexes towards Stable OLEDs

Although two‐coordinate Cu(I) complexes are highly promising low‐cost emitters for organic light‐emitting diodes (OLEDs), the exposed metal center in the linear coordination geometry makes them suffer from poor stability. Herein, we described a strategy to develop stable carbene‐Cu‐amide complexes through installing intramolecular noncovalent Cu···H interactions. The employment of 13H‐dibenzo[a,i]carbazole (DBC) as the amide ligand leads to short Cu···H distances in addition to the Cu–N coordination bond. The resultant Cu(I) complexes exhibit yellow thermally activated delayed fluorescence with photoluminescence quantum yields of up to 86% and radiative decay rate constants on the order of 106 s−1. Comparing with the analogues without Cu···H interactions, the pincer complexes have significantly improved stability. The vacuum‐deposited OLEDs show high‐performance electroluminescence with maximum external quantum efficiencies up to 29.5% and extremely small roll‐offs of only 3.5% at 10,000 cd m‐2. Remarkably, the operational lifetimes (LT90) were determined to be up to 68 h with an initial luminance of 3000 cd m‐2. This work proves a feasible design of robust low‐coordinate metal complexes by leveraging secondary coordination interactions, which helps to overcome the long‐standing stability problem.

How Do Variants of Residues in the First Coordination Sphere, Second Coordination Sphere, and Remote Areas Influence the Catalytic Mechanism of Non-Heme Fe(II)/2-Oxoglutarate Dependent Ethylene-Forming Enzyme?

The ethylene-forming enzyme (EFE) is a Fe(II)/2-oxoglutarate (2OG) and l-arginine (l-Arg)-dependent oxygenase that primarily decomposes 2OG into ethylene while also catalyzing l-Arg hydroxylation. While the hydroxylation mechanism in EFE is similar to other Fe(II)/2OG-dependent oxygenases, the formation of ethylene is unique. Various redesign strategies have aimed to increase ethylene production in EFE, but success has been limited, highlighting the need for alternate approaches. It is crucial to incorporate an accurate and comprehensive description of the integrative and multidimensional effects of the protein environment to enhance the redesign strategy in metalloenzymes, particularly in EFE. This involves understanding the role of the second coordination sphere (SCS) and long-range (LR) interacting residues, correlated motions, electronic structure, intrinsic electric field (IntEF), as well as the stabilization of transition states and reaction intermediates. In this study, we employ a molecular dynamics-based quantum mechanics/molecular mechanics approach to examine the integrative effects of the protein environment on reactions catalyzed by EFE variants from the first coordination sphere (FCS, D191E), SCS (A198V and R171A) and LR (E215A). The study uncovers how substitutions at different positions in EFE similarly impact the ethylene-forming reaction while posing distinct effects on the hydroxylation reaction. Results predict the effect of the variants in controlling the 2OG coordination mode in the Fe(II) center. Specifically, the study suggests that D191E uniquely prefers transitioning from an off-line to an in-line 2OG coordination mode before dioxygen binding. However, studies on the 2OG flip in the presence of off-line approaching dioxygen and dioxygen binding in the D191E variant indicate that the 2OG flip might not be feasible in the 5C Fe(II) state. Calculations show the possibility of a hydrogen atom transfer (HAT)-assisted oxygen flip in EFE and its variants (other than D191E). MD simulations elucidate the characteristic dynamic change in the α7 region in the D191E variant that might contribute to its increased hydroxylation reaction. Results indicate the possibility of forming an in-line ferryl from the IM2 (Fe(III)-partial bond intermediate) in the D191E variant. This alternative pathway from IM2 may also exist in WT EFE and other variants, which are yet to be explored. The study also delineates the impact of substitutions on the electronic structure and IntEF. Overall, the calculations support the idea that understanding the integrative and multidimensional effects of the protein environment on the reactions catalyzed by EFE variants provides the basics for improved enzyme redesign protocols of EFE to increase ethylene production. The results of this study will also contribute to the development of alternate redesign strategies for other metalloenzymes.

Solvation Environment and Interface Dynamics of Li2B12H12 and Li2B12F12 Electrolytes Uncovered by Theory and Operando Optical and FTIR Spectroelectrochemistry.

In this work, we evaluated two closo-borate salts (Li2B12H12 and Li2B12F12) in propylene carbonate from theoretical and experimental perspectives to understand how the coordination environment influences their spectroscopic and electrochemical properties. The coordination environments of the closo-borate salts were modeled via density functional theory (DFT) and molecular dynamics (MD). Vibrational spectra calculated from the predicted coordination environments are in agreement with experimentally measured steady-state FTIR data. This theoretical investigation also suggested that Li2B12F12 would possess a higher ionic conductivity than Li2B12H12, which was corroborated experimentally. Additionally, an electrochemical cell was designed and fabricated that enabled operando optical and FTIR spectroelectrochemical (OP-IR-SEC) measurements. This allowed for the simultaneous measurement of the relative changes of species at a lithium electrode-liquid electrolyte interface and the visualization of lithium plating at the electrode surface. This technique could provide new chemical insights and potentially link optical changes at the electrode-electrolyte interface to specific chemical species in similar electrochemical systems. The Li2B12F12 electrolyte was found to have a higher thermal stability, which may find utility in applications for batteries that are subject to high-temperature conditions.

Hollow Pt‐Encrusted RuCu Nanocages Optimizing OH Adsorption for Efficient Hydrogen Oxidation Electrocatalysis

AbstractAs one of the best candidates for hydrogen oxidation reaction (HOR), ruthenium (Ru) has attracted significant attention for anion exchange membrane fuel cells (AEMFCs), although it suffers from sluggish kinetics under alkaline conditions due to its strong hydroxide affinity. In this work, we develop ternary hollow nanocages with Pt epitaxy on RuCu (Pt‐RuCu NCs) as efficient HOR catalysts for application in AEMFCs. Experimental characterizations and theoretical calculations confirm that the synergy in optimized Pt8.7‐RuCu NCs significantly modifies the electronic structure and coordination environment of Ru, thereby balancing the binding strengths of H* and OH* species, which leads to a markedly enhanced HOR performance. Specifically, the optimized Pt8.7‐RuCu NCs/C achieves a mass activity of 5.91 A mgPt+Ru−1, which is ~3.3, ~2.2, and ~15.0 times higher than that of RuCu NCs/C (1.38 A mgRu−1), PtRu/C (1.83 A mgPt+Ru−1) and Pt/C (0.37 A mgPt−1), respectively. Impressively, the specific peak power density of fuel cells reaches 15.9 W mgPt+Ru−1, significantly higher than those of most reported PtRu‐based fuel cells.

Hollow Pt-Encrusted RuCu Nanocages Optimizing OH Adsorption for Efficient Hydrogen Oxidation Electrocatalysis.

As one of the best candidates for hydrogen oxidation reaction (HOR), ruthenium (Ru) has attracted significant attention for anion exchange membrane fuel cells (AEMFCs), although it suffers from sluggish kinetics under alkaline conditions due to its strong hydroxide affinity. In this work, we develop ternary hollow nanocages with Pt epitaxy on RuCu (Pt-RuCu NCs) as efficient HOR catalysts for application in AEMFCs. Experimental characterizations and theoretical calculations confirm that the synergy in optimized Pt8.7-RuCu NCs significantly modifies the electronic structure and coordination environment of Ru, thereby balancing the binding strengths of H* and OH* species, which leads to a markedly enhanced HOR performance. Specifically, the optimized Pt8.7-RuCu NCs/C achieves a mass activity of 5.91 A mgPt+Ru -1, which is ~3.3, ~2.2, and ~15.0 times higher than that of RuCu NCs/C (1.38 A mgRu -1), PtRu/C (1.83 A mgPt+Ru -1) and Pt/C (0.37 A mgPt -1), respectively. Impressively, the specific peak power density of fuel cells reaches 15.9 W mgPt+Ru -1, significantly higher than those of most reported PtRu-based fuel cells.

Precisely Tailoring the Second Coordination Sphere of a Cobalt Single-Atom Catalyst for Selective Hydrogenation of Halogenated Nitroarenes.

The development of highly efficient and cost-effective nonprecious metal catalysts for the selective hydrogenation of halogenated nitroarenes is very appealing yet challenging. Here, we demonstrate that the hydrogenation activity and selectivity of Co single-atom catalyst (SAC) can be tuned by tailoring the structure of second coordination sphere via P doping. As revealed by synchrotron radiation-based X-ray absorption spectroscopy characterizations, such a P doping on N-coordinated Co SAC results in the unsymmetric Co-N4P1 coordination structure. With a combination of experimental characterizations and theoretical simulations, we find that tailoring the second coordination sphere can greatly improve H2 dissociation and product desorption. As a result, the Co-N4P1 SAC exhibits superior activity, selectivity and stability for the hydrogenation of halogenated nitroarenes to corresponding amines (20 examples, >99 % yields) at 80 °C under 0.5 MPa H2 pressure, significantly outperforming most heterogeneous catalysts reported in the literature. We expect that this work opens a new avenue for the design of highly efficient nonprecious metal SACs for important hydrogenation reactions.

Precisely Tailoring the Second Coordination Sphere of a Cobalt Single‐Atom Catalyst for Selective Hydrogenation of Halogenated Nitroarenes

AbstractThe development of highly efficient and cost‐effective nonprecious metal catalysts for the selective hydrogenation of halogenated nitroarenes is very appealing yet challenging. Here, we demonstrate that the hydrogenation activity and selectivity of Co single‐atom catalyst (SAC) can be tuned by tailoring the structure of second coordination sphere via P doping. As revealed by synchrotron radiation‐based X‐ray absorption spectroscopy characterizations, such a P doping on N‐coordinated Co SAC results in the unsymmetric Co‐N4P1 coordination structure. With a combination of experimental characterizations and theoretical simulations, we find that tailoring the second coordination sphere can greatly improve H2 dissociation and product desorption. As a result, the Co‐N4P1 SAC exhibits superior activity, selectivity and stability for the hydrogenation of halogenated nitroarenes to corresponding amines (20 examples, >99 % yields) at 80 °C under 0.5 MPa H2 pressure, significantly outperforming most heterogeneous catalysts reported in the literature. We expect that this work opens a new avenue for the design of highly efficient nonprecious metal SACs for important hydrogenation reactions.

Boron and Oxygen Dual-Doped Carbon Nitride Nanotubes with Frustrated Lewis Pairs for Efficient Electrocatalytic Ammonia Synthesis.

This work reports boron and oxygen dual-doped carbon nitride nanotubes (B/O-CNNTs) prepared via a copolymerization process for electrocatalytic ammonia synthesis from nitrogen gas (NRR) and nitrate (NO3RR) sources, respectively. By adjusting the dosage of boron oxide precursor, the texture and content of B/O dual dopants and the coordination environment in the resulting 1D CNNTs can be tuned. The best B/O-CNNTs can achieve maximum Faradaic efficiencies of 35% and 96% at -1.1V versus RHE with corresponding ammonia yields of 16.7 and 211.4µg h-1 mg-1, respectively. A comparatively higher selectivity is achieved in the NRR process compared to NO3RR. The B/O-induced coordinations boost electron transfer rates along the longitudinal axis. The presence of carbon vacancies and the unique 1D nanotubular structure enhance interactions among reactants. Concurrently, the formed frustrated Lewis pairs are pivotal in activating chemisorbed nitrogen gas or nitrate, resulting in notable accelerations of ammonia generation kinetics. In situ UV-vis spectroscopy reveals that the ideal potential of -1.1V versus RHE facilitates the involvement of free electrons in the reaction, as it aligns with the conduction potential of B/O-CNNTs. This study paves the way for the design of non-metal-based electrocatalysts with dual dopants for sustainable electrocatalysis toward ammonia synthesis.

Thermal Bistability of Magnetic Susceptibility, Light Absorption, Second Harmonic Generation, and Dielectric Properties in a Polar Spin-Crossover Iron-Rhenium Chain Material.

The bistability of multiple physical properties driven by external stimuli in a solid is a desired prerequisite for its application in memory devices with convenient data readout. We present a pathway for thermal bistability detectable in four physical properties: magnetic, light absorption, second-harmonic generation (SHG), and dielectric. We report a novel heterometallic (TBA){[FeII(phIN)4][ReV(CN)8]}·(phIN) (1) (TBA = tetrabutylammonium cation, phIN = phenyl isonicotinate) cyanido-bridged chain material. Owing to an appropriate {N6} coordination sphere of Fe(II) centers, 1 reveals a thermal spin crossover (SCO) effect which is complete and cooperative providing a distinct thermal hysteresis loop in magnetic measurements. Moreover, it exhibits simultaneous thermal bistability in (a) visible-light absorption due to the presence of efficient d-d electronic transitions in the low-spin (LS) state, (b) SHG activity as it crystallizes in a polar Cc space group due to the bulky substituent on phIN ligands, and (c) dielectric parameters, including dielectric constant, which can be correlated with subtle changes in polarity between LS and HS (high spin) phases. Thus, we present a remarkable thermally controlled hysteretic behavior in four physical functionalities realized by properly functionalizing an SCO-active coordination compound.

Experimental and Computational Studies of Steric Factors in the Isomerization of Internal Alkynes within the Coordination Environment of Half-Sandwich Metal Complexes.

The isomerization of internal alkynes Ar1C≡CAr2 within the coordination environment of low-valent half-sandwich [Ru(dppe)Cp]+ complexes via a 1,2-migration process affords vinylidene species [Ru{=C=C(Ar1)Ar2}(dppe)Cp]+. The rearrangement reactions of symmetrically and asymmetrically substituted substrates featuring different electron-donating and -withdrawing groups and of varying steric bulk were modelled using density functional theory (DFT), and the conclusions supported by experimental observations. Examination of the reaction pathway and associated activation barriers reveal a high solvent dependency for the generation of the key intermediate species [Ru(dppe)Cp]+ from [RuCl(dppe)Cp] by halide dissociation in the presence of Na+ salts of weakly coordinating anions, with the lattice enthalpy of the NaCl by-product playing a critical role in the overall thermochemical balance of the reaction. The activation barriers associated with the reaction of [Ru(dppe)Cp]+ with Ar1C≡CAr2, and the relative energies of the alkyne complexes [Ru(η2-Ar1C≡CAr2)(dppe)Cp]+, are sensitive to the electron density of the alkyne and conformational changes associated with the 'bend-back' of the substrate. The latter differs by up to 66.1 kJ/mol, which in turn impacts the barrier height of the subsequent 1,2-migration step involved in the rearrangement process and ultimately the overall thermochemical nature of the complete reaction. The relative importance of these factors is evinced by the successful rearrangement of the very sterically congested 1(9-anthryl)-2(9-phenanthryl) acetylene into the fully characterized diaryl vinylidene complex, which was isolated in 89 % yield.

Chelating Properties of N6O-Donors Toward Cu(II) Ions: Speciation in Aqueous Environments and Catalytic Activity of the Dinuclear Complexes.

This study focuses on the use of three isostructural N6O donor ligands, specifically known to form complexes with copper ions, to chelate Cu(II) from aqueous solutions. The corresponding Cu(II) complexes feature a dinuclear copper core mimicking the active site of natural superoxide dismutase (SOD) enzymes while also creating a coordination environment favorable for catalase (CAT) activity, being thus appealing as catalytic antioxidant systems. Given the critical role of copper dysregulation in the pathophysiology of Alzheimer's disease (AD), these complexes may help mitigate the harmful effects of free Cu(II) ions: the goal is to transform copper's reactive oxygen species (ROS)-generating properties into beneficial ROS-scavenging action. This study investigates the speciation, chelating efficiency, and metal selectivity of these ligands, as well as the antioxidant activity of the resulting complexes under aqueous and physiologically relevant conditions. Additionally, the ligands, equipped with functional groups for attaching targeting moieties, are conjugated with a small peptide that may act as an anti-aggregating agent of β-amyloid peptides, aiming to develop a multifunctional therapeutic strategy against Alzheimer's disease.

Synthesis, Characterization and X-Ray Structure of Mononuclear Cu(II) Complex of the Schiff Base 2,2’- [1,1’-(Ethane-1,2-Diyl) Bis (Nitriloethylidyne)]Diphenol

The reactions of the Schiff base 2,2’-[1,1’-(ethane-1,2-diyl)bis(nitriloethylidyne)]diphenol (H2L), which was synthesised by condensation of 2-hydroxyacetophenone and ethylenediamine in the 2:1 ratio, with acetate copper (II) Salt, afforded a new mononuclear complex formulated as [Cu(L)].(H2O)0.5. The ligand and the complex have been characterized by elemental analysis, FTIR, UV-Vis and 1H and 13C NMR spectroscopies. The characterization of the copper complex was completed by molar conductivity and room temperature magnetic measurements. The structure of the complex has been resolved by X-ray crystallography technic. The mononuclear copper (II) complex crystallises in the monoclinic space group C2/c with the following unit cell parameters a = 26.131(6) Å, b = 7.293(5) Å, c = 17.256(4) Å, β = 106.10(5)°, V = 3160(2) Å3, Z = 4, R1 = 0.077 and wR2 = 0.145. In the structure of the complex the ligand acts in tetradentate fashion and the coordination environment of the copper atom is best described as distorted square planar geometry.

Tailoring the Coordination Environment of Cu Single Atoms for Achieving Regioselective C–C Bond Activation of Amides

Tailoring the Coordination Environment of Cu Single Atoms for Achieving Regioselective C–C Bond Activation of Amides

Efficient electrochemical water oxidation catalyzed by a novel nickel complex: Critical effect of the flexibility of pyridine-amine based pentadentate ligand on catalytic property

Efficient electrochemical water oxidation can be realized by reasonable modulation of the ligand structure of metal complex-based molecular water oxidation catalysts (WOCs). Herein, the synthesis and prowess in electrocatalytic water oxidation of a mononuclear water-soluble nickel complex, [Ni(tmbptu)(OH2)](ClO4)2 (1, tmbptu = 2,6,10-trimethyl-1,11-bis(2-pyridyl)-2,6,10-triazaundecanone), is reported for the first time. Complex 1 is found to be an efficient homogeneous WOCs under near neutral condition with long-term catalytic stability by a series of characterizations, including dynamic light scattering (DLS) measurement, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX) analysis, chelation experiment, and Fe3+ test. Electrochemical tests reveal that water oxidation is accomplished via the generation of NiIV species generated by two successive e−/H+ proton coupled electron transfer (PCET) processes. Astonishingly, compared to the homologous complex [Ni(tmbptn)(OH2)](ClO4)2 (2, tmbptn = 2,5,8-trimethyl-1,9-bis(2-pyridyl)-2,5,8-triazanonane), which is a well-defined molecular WOC with high catalytic onset overpotential, 1 displays lower onset overpotential and much higher catalytic activity. This work suggesting that though the tertiary amine coordination environment have gain effect on the redox potential of metal center due to its poor sigma-donor effect, resulting in high onset overpotential of metal complex for water oxidation, this negative impact of the pyridine-amine ligand on the catalytic properties of complex can be weaken by adjusting the flexibility of backbone of those ligands.

Correlation between ligand-mediated silver species on TiO2 nanosheet with the photocatalytic hydrogen evolution activities.

Metal oxide photocatalysts loaded with metal species are extremely important in photocatalysis. The physicochemical states of metal species, as well as the interaction between metal species and support, determine the transfer of charge carriers between the heterointerface, which has a significant impact on photocatalytic activity. Here, we prepared anatase TiO2 nanosheets (TIO) modified with different Ag species, including single atoms, clusters, and nanoparticles, using a ligand-mediated method. The existence of different forms of Ag species on TIO was verified by high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) and high-resolution transmission electron microscope (HRTEM); Electron paramagnetic resonance (EPR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) confirmed the changed electronic properties in heterointerface and charge carrier transfer channels caused by the Ag species in different existence states; X-ray absorption fine structure (XAFS) in depth differentiated the valence states, coordination environments, and charge densities of Ag species. It is intriguing that the photocatalytic hydrogen evolution activity exhibits a hump shape, which can be attributed to the changes in the physicochemical properties of silver species in different states. In addition, the combination of density functional theory (DFT) calculations and experimental results demonstrated that the Ag single atom acted as an active site for water splitting, while the Ag cluster tended to attract electrons and promoted charge separation efficiency. This work delves into the relationship between the microscopic changes of metal species anchored on the surface of photocatalysts and their photocatalytic performance, providing further insights into precise surface engineering and performance optimization by adjusting the metal presence state on the photocatalyst surface.

Engineering the coordination of Cu–Ni dual-atom catalysts to enhance the electrochemical CO2 overall splitting

Designing the coordination environment of heteroatoms around metal sites and optimizing the electronic structure of diatomic metal sites remain significant challenges in achieving efficient CO2 overall splitting. Herein, we report four configurations (Cu/Ni–N4C2, Cu/Ni–N2C4, Cu/Ni–N2C3 and Cu/Ni–N2C2) constructed by precise regulation of the coordination environment around bimetallic atoms. Cu/Ni–N2C2 showed high performance in electrochemical CO2 reduction (ECR) and water oxidation evolution reaction (OER). In the electrochemical CO2 overall splitting reaction, it achieved a Faraday efficiency of CO (FECO) of 98.0% at a low cell voltage of −2.9 V, significantly higher than widely reported values. Moreover, the FECO is above 90% over −2.7 to −4.1 V of cell voltages. Cu/Ni–N2C2 achieved long-term ECR stability of 110 h at −100 mA cm−2. Mechanism studies revealed that the change of coordination environment around the diatomic pairs moves the d-band center of the Ni atom closer to the Fermi level, thereby modulating the adsorption capacity of the catalysts to the reaction intermediates *COOH and *O. This work presents valuable insights into the rational design of diatomic catalysts and elucidates the intricate structure-performance relationship in advancing electrochemical CO2 overall splitting technology and energy-conversion applications.

Improving macromolecular structure refinement with metal-coordination restraints.

Metals are essential components for the structure and function of many proteins. However, accurate modelling of their coordination environments remains a challenge due to the complexity and diversity of metal-coordination geometries. To address this, a method is presented for extracting and analysing coordination information, including bond lengths and angles, from the Crystallography Open Database. By using these data, comprehensive descriptions of metal-containing components are generated. A stereochemical information generator for a particular component within a specific macromolecule leverages an example PDB/mmCIF file containing the component to account for the actual surrounding environment. A matching process has been developed and implemented to align the derived metal structures with idealized coordinates from a coordination geometry library. Additionally, various strategies, depending on the quality of the matches, were employed to compile distance and angle statistics for the refinement of macromolecular structures. The developed methods were implemented in a new program, MetalCoord, that classifies and utilizes the metal-coordination geometry. The effectiveness of the developed algorithms was tested using metal-containing components from the PDB. As a result, metal-containing components from the CCP4 monomer library have been updated. The updated monomer dictionaries, in concert with the derived restraints, can be used in most structural biology computations, including macromolecular crystallography, single-particle cryo-EM and even molecular mechanics.

Regulating WOx coordination environment improves proton transfer for catalytic amine regeneration in CO2 capture

Regulating WOx coordination environment improves proton transfer for catalytic amine regeneration in CO2 capture

MOF-derived S, N co-doped porous carbon matrix with single Fe atoms and CoSx nanoparticles dual-sites for enhanced oxygen reduction

Metal-air batteries, as a clean energy technology, are of great significance in alleviating the increasingly serious energy and environmental problems, but the sluggish oxygen reduction reaction (ORR) kinetics of air–cathode severely restrict their development. In this work, a zeolitic imidazole frameworks (ZIFs)-derived dual-site electrocatalyst (Fe/CoSx-SNC) composed of Fe single atom and ultrafine cobalt sulfide nanoparticle sites supported on S, N co-doped porous carbon was successfully prepared. Benefited from the advantages of large specific surface area, high porosity, high-density metal centers, and synergistic effects between the dual sites, Fe/CoSx-SNC electrocatalyst presents excellent electrocatalytic ORR activity with a half-wave potential of 0.885 V, a kinetic current density of 27.00 mA cm−2 (at 0.80 V), and good stability, which are superior to the commercial 20 % Pt/C catalyst. The density functional theory (DFT) calculations reveals that the presence of cobalt sulfide nanoparticles could effectively modulate the electron density around Fe single atom, which reduces the desorption energy barrier (rate-determining step) of *OH on Fe sites. In addition, the rechargeable zinc-air battery assembled with Fe/CoSx-SNC as air cathode oxygen catalyst exhibits a high peak power density of 156.63 mW cm−2 and over 100 h of cycling stability. This study provides a straightforward and feasible approach to precisely adjusting the coordination environment and constructing high-performance metal single-atom-based oxygen electrocatalysts, which will be beneficial to promoting the development of metal-air batteries.