Reactive Sites Research Articles

Grid-Like Structured Sb@DNC Anode by Self-Sacrificial Etching for Fast and Durable Sodium Storage.

Alloying-type materials are promising anodes for sodium storage due to high specific capacities and appropriate redox potentials, but their practical application is impeded by rapid capacity decay from volume change during sodium ion insertion/extraction. Hence, a dual-type N-doped carbon-confined antimony (Sb) nanoparticle (Sb@DNC, where DNC contains an outer N-doped carbon armor and an inner N-doped grid-like carbon skeleton) anode material is fabricated via a self-sacrificial etching strategy to address this challenge. Specifically, the dual-type N-doped carbon matrix can prevent the agglomeration and precipitation of Sb particles, increase a large number of reactive active sites, alleviate severe volume expansion/contraction, and construct a highly interconnected electron/ion transport network. Benefiting from the exquisite structure, the Sb@DNC electrode exhibits excellent cycling stability (2400 cycles at 1.0 A g-1) and astonishing high-rate performance (331.0 mAh g-1 at 10.0 A g-1). Additionally, the state-of-the-art in/ex situ technologies reveals the sodium storage mechanism of the "battery-capacitance dual-mode" and the origin of the ability to withstand continuous volumetric strain for the Sb@DNC electrode. Finally, the derived sodium-ion full cell presents outstanding practical potential. This work emphasizes the great significance of rational structural engineering strategies in the field of alloy-type anode materials for high-performance sodium-ion batteries.

Covalent Folding of Fluorinated Polyphenylene by Sulfur Fluorine Annulative Substitution.

We report that fluorinated polyphenylene P50 undergoes folding-like sulfur fluorine annulative substitution (SFAS) to form a well-defined tubular helix H50. This is achieved with atomic precision in an exceptionally efficient manner, involving the simultaneous transformation of 98 C-F bonds with the yield per reaction site approaching 99.9%. The desired product H50 features a fully fused dibenzothiophene skeleton of 5.8 helical turns in total. It is truly monodisperse (Đ = 1.0) in nature, allowing for thorough spectroscopic characterizations. Unambiguous single crystal X-ray structure, distinct chiroptical properties, and intriguing through-cavity threading complexation are described. These results, in addition to those of H50's lower congeners, H34 and H18, illustrate the great potential of folding-like SFAS in shaping random-coiled polymer chains into higher-order functional structures.

Engineering ZnIn2S4 Nanosheets with Zinc Vacancies: Unleashing Enhanced Photocatalytic Degradation of Tetracycline.

Defect engineering is a highly effective strategy for accelerating charge transfer and enhancing the performance of photocatalysts. In this study, ZnIn2S4 nanosheets were designed and prepared with controlled Zn vacancies to optimize the electronic band structure and localized charge density of ZnIn2S4. EPR results confirmed the formation of Zn vacancies. This modification enabled efficient capture of photoexcited charges in defect centers, thereby prolonging the carrier's lifetime. Theoretical calculations demonstrated that these vacancies induced the formation of new defect states and highly efficient surface reaction sites. As anticipated, under visible light irradiation, the photocatalytic tetracycline removal rate of the ZnIn2S4 nanosheets with Zn vacancies reached 82.8% within 60 min, significantly higher than that observed for the pristine ZnIn2S4 sample. These findings offer valuable insights into the deliberate construction of metal-vacancy-containing photocatalytic nanomaterials for the enhanced degradation of micropollutants.

Eco-Friendly High-Performance Symmetric All-COF/Graphene Aqueous Zinc-Ion Batteries.

Developing high-performance aqueous symmetric all-organic batteries (SAOBs) by replacing metal-based batteries or batteries with organic electrolytes is highly attractive to achieve a greener rechargeable world. However, such a new energy storage system still exhibits unsatisfactory rate capability and cycling stability due to the limitations in electrode materials screening. Here, a novel covalent organic framework (COF) containing abundant CN and CO for the electrode material is designed, which is combined with graphene and assembled into all-COF/graphene batteries for the first time. Moreover, the co-storage of Zn2+ and H+ in COF can be achieved in a mild aqueous electrolyte. Impressively, benefiting from the extended porous structure of COF, plentiful active reaction sites, more extensive electron delocalization from CO modification at molecular level, as well as enhanced fast H+ storage capacity of graphene and CO in COF, this kind of SAOBs show excellent cycle life and high rate performance (over 15000 cycles with a capacity of 80 mAh g-1 at a high current density of 5 A g-1 in pouch cell). This work will open a new window for the design of high-performance aqueous organic batteries, further moving toward a more eco-friendly electrochemical world.

Covalent Folding of Fluorinated Polyphenylene by Sulfur Fluorine Annulative Substitution

We report that fluorinated polyphenylene P50 undergoes folding‐like sulfur fluorine annulative substitution (SFAS) to form a well‐defined tubular helix H50. This is achieved with atomic precision in an exceptionally efficient manner, involving the simultaneous transformation of 98 C–F bonds with the yield per reaction site approaching 99.9%. The desired product H50 features a fully fused dibenzothiophene skeleton of 5.8 helical turns in total. It is truly monodisperse (Đ = 1.0) in nature, allowing for thorough spectroscopic characterizations. Unambiguous single crystal X‐ray structure, distinct chiroptical properties, and intriguing through‐cavity threading complexation are described. These results, in addition to those of H50’s lower congeners, H34 and H18, illustrate the great potential of folding‐like SFAS in shaping random‐coiled polymer chains into higher‐order functional structures.

Gradient Distribution of Zincophilic Sites for Stable Aqueous Zinc-Based Flow Batteries with High Capacity.

Current collectors, as reaction sites, play a crucial role ininfluencing various electrochemical performances in emerging cost-effective zinc-based flow batteries (Zn-based FBs). 3D carbon felts (CF) are commonly used but lack effectiveness in improving Zn metal plating/stripping. Here, a current collector with gravity-induced gradient copper nanoparticles (CF-G-Cu NPs) is developed, integrating gradient conductivity and zincophilicity to regulate Zn deposition and suppress side reactions. The CF-G-Cu NPs electrode modulates Zn nucleation and growth via the zincophilic Cu/CuZn5 alloy has been confirmed by density functional theory (DFT) calculations. Finite element simulation demonstrates the gradient internal structure effectively optimizes the local electric/current field distribution to regulate the Zn2+ flux, improving bottom-up plating behavior for Zn metal and mitigating top-surface dendrite growth. As a result, Zn-based asymmetrical FBs with CF-G-Cu NPs electrodes achieve an areal capacity of 30 mAhcm-2 over 640h with Coulombic efficiency of 99.5% at 40mAcm-2. The integrated Zn-Iodide FBs exhibit a competitive long-term lifespan of 2910h (5800 cycles) with low energy efficiency decay of 0.062% per cycle and high cumulative capacity of 112800 mAhcm-2 at a high current density of 100mAcm-2. This gradient distribution strategy offers a simple mode for developing Zn-based FB systems.

Unlocking Photocycloaddition Reactivity of Tropolone by Cage-Confined Visible-Light Photocatalysis for Multilevel Selective Transformation.

The precise asymmetric photochemical transformation of organic compounds containing multiple reactive sites presents significant progress in synthetic chemistry. Herein, we report an unprecedented visible-light-induced cascade transformation of tropolone cyclic triene derivatives by using chiral photoactive metal-organic cages (cPMOCs) as enzyme-mimicking multipocket photocatalysts. The cage-confined photocatalysis promotes three successive elementary steps, i.e., enantioselective [2 + 2] photocycloaddition with chalcone, regio-, and diastereoselective α-ketol rearrangement, and a stereoselective 1,3-acyl shift, resulting in bicyclo[3.2.2]nonane skeleton with multichiral-centers unattainable by other methods. This study demonstrates how complex synthetic challenges of peri-, chemo-, and stereoselectivities could be subtly manipulated by cage-confined supramolecular catalysis for exploration of new reactivities.

Programmed Charge Transfer in Conjugated Polymers with Pendant Benzothiadiazole Acceptor for Simultaneous Photocatalytic H2O2 Production and Organic Synthesis.

While being important candidate for heterogeneous photocatalyst, conjugated polymer typically exhibits random charge transfers between the alternating donor and acceptor units, which severely limits its catalytic efficiency. Herein, inspired by natural photosystem, the concept of guiding the charge migration to specific reaction sites is employed to significantly boost photocatalytic performance of linear conjugated polymers (LCPs) with pendant functional groups via creating programmed charge-transfer channels from the backbone to its pendant moiety. The pendant benzothiadiazole, as revealed in both in situ X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations, can act as electron "reservoir" that aggregates electrons at the active sites. Moreover, the presence of charge-transfer channels, evidenced by transient absorption spectroscopy (TAS), accelerates the electron transfer, preventing the recombination of electrons and holes. As a result, in this elaborately-designed architecture, the photogenerated electron can move smoothly towards the reduction sites, facilitating the reduction of O2 into H2O2, while remaining holes are directed to oxidation centers, simultaneously oxidizing furfuryl alcohol to furoic acid. The optimized photocatalyst LCP-BT demonstrates a competitive catalytic performance with H2O2 productivity of 868.3 μmol L-1 h-1 (9.8 times higher than conventional random charge-transfer polymer LCP-1) and furfuryl alcohol conversion over 95% after 6 h.

Polyethylene Glycol-Protected Zinc Microwall Arrays for Stable Zinc Anodes.

Aqueous zinc-ion batteries promise good commercial application prospects due to their environmental benignity and easy assembly under atmospheric conditions, positioning them as a viable alternative to lithium-ion batteries. However, some inherent issues, such as chaotic zinc dendrite growth and inevitable side reactions, challenge the commercialization progress. In this work, we imprint highly ordered zinc microwall arrays to regulate the electric field toward uniform Zn deposition. Afterward, coating a polyethylene glycol protection layer on the zinc microwalls aims to passivate the surface defects that rise unintentionally by mechanical imprinting. Polyethylene glycol can also boost oriented Zn deposition along the (002) plane and inhibit hydrogen gas production, further enhancing the stability of such three-dimensional (3D) hybrid anodes. Compared to the messy electric field near the polyethylene glycol-protected Zn foil, the uniform electric field provided by these 3D hybrid anodes can regulate the Zn deposition behaviors, enabling a longer lifespan and thus certifying the necessity of adding 3D microstructures. Additionally, 3D microstructures can offer a larger surface area than that of the planar Zn foil, providing more reaction sites and higher specific capacity. In this case, the 3D hybrid electrode exhibits a good initial capacity of approximately 120 mA h/g at a current density of 5 A/g and a nice retention of more than 80% after 800 cycles. The proposed scheme paves the way for a long-term stable 3D zinc anode solution with promising application prospects.

Co-Carbonization of Straw and ZIF-67 to the Co/Biomass Carbon for Electrocatalytic Nitrate Reduction

Electrocatalytic nitrate reduction enables the recovery of nitrate from water under mild conditions and generates ammonia for nitrogen fertilizer feedstock in an economical and green means. In this paper, Co/biomass carbon (Co/BC) composite catalysts were prepared by co-carbonization of straw and metal–organic framework material ZIF-67 for electrocatalytic nitrate reduction using hydrothermal and annealing methods. The metal–organic framework structure disperses the catalyst components well and provides a wider specific surface area, which is conducive to the adsorption of nitrate and the provision of more reactive active sites. The introduction of biomass carbon additionally enhances the electrical conductivity of the catalyst and facilitates electron transport. After electrochemical testing, Co/BC-100 exhibited the best performance in electrocatalytic nitrate reduction to ammonia, with an ammonia yield of 3588.92 mmol gcat.−1 h−1 and faradaic efficiency of 97.01% at −0.5 V vs. RHE potential. This study provides a promising approach for the construction of other efficient cobalt-based electrocatalysts.

Construction of Naphtho[2,1-d]oxazoles and 1,4-Epoxyisoquinolines via Regioselectivity-Switchable Diels-Alder Reaction of 4-Alkenyloxazoles with Arynes.

A Regioselectivity-switchable Diels-Alder reaction of arynes and 4-alkenyloxazoles was explored. By regulating the reaction temperature and the polarity of the solvent, the reaction activity of aryne was controlled to selectively react with different favorable reaction sites of 4-alkenyloxazoles, providing naphtho[2,1-d]oxazoles and 1,4-epoxyisoquinolines. Density functional theory (DFT) calculations demonstrated that the Diels-Alder reaction on acyclic dienes site needs more energy than the reaction on cyclic dienes to overcome the potential reaction barrier.

Comprehensive Theoretical Insights on Spectroscopic Characterization, Solvent Effect (Polar and Nonpolar) in Electronic behavior, Topological Insights, and Molecular Docking Prediction of Taurolidine

In recent decades, sulfur-containing compounds have played a significant role in biological applications because of their unique biological and chemical characteristics. Taurolidine, a sulfur-containing derivative of the amino acid taurine, has been characterized theoretically utilizing Density Functional Theory (DFT) at the B3LYP approach along with a 6-311++G(d,p) basis set. The impact of solvents on electronic characteristics, Molecular electrostatic potential (MEP), and Fourier Molecular Orbital (FMO) in polar (water and ethanol) and nonpolar (toluene and chloroform) has been analyzed. The bond distances of S1-C16 and S1-C17 have been simulated at 1.817 Å and observed at 1.743 and 1.739 Å, respectively. These distances are increased compared to other bond distances due to the influence of sulfur atoms. The distinctive simulated vibrational wavenumbers of taurolidine revealed peaks for SO2, CH2, CN, and NH groups. The intramolecular interactions responsible for stabilizing the molecular structure of taurolidine have been addressed using NBO analysis shows significant stabilization energy from electron-donating lone pair oxygen O6 to antibonding S2-N10 with the stabilizing energy of 19.88 KJ/mol by the transition of LP(3)- σ*. The bonding characteristics and reactive sites (electron-rich and electron-poor) have been confirmed with Mulliken and MEP analysis. The carbons (C17 and C16) emphasize the increased negative potential due to the sulfonyl (SO2) group in the ortho position. The topological insights, ELF and LOL, were spotted using Multiwfn software, highlighting the localized and delocalized electron regions within the crystal structure. In addition, molecular docking was performed to predict the antagonist activity of taurolidine against β-catenin protein, yielding a binding energy of -6.86 KJ/mol, which confirms its antiproliferative property.

Eco-friendly and cost-effective epoxy binder for polymer mortar utilizing oregano oil-based hardener

Polymer mortar, consisting of a polymer binder and aggregates, offers superior properties such as enhanced strength, durability, and corrosion resistance compared to the traditional cement-based mortars. Within the polymer-based mortar, epoxy resin is one of the most commonly used resins owing to its high performance. However, its widespread adoption is hindered by costs and environmental concerns, particularly the dependence of bisphenol A-containing epoxide, a substance harmful to human health. In this work, a novel epoxy hardener derived from oregano oil (OEO) was developed to create a more eco-friendly and cost-effective binder for polymer mortar. The inclusion of OEO-based hardeners reduced the viscosity of the binder and accelerated the curing process. The Mannich base structure of the hardener induced more reactive sites in the epoxy system, resulting in a denser crosslinked network. Polymer mortars fabricated with this novel hardener exhibited improved mechanical properties, bonding strength, and corrosion resistance compared to conventional epoxy mortars. Scanning electron microscopy images also revealed a stronger interfacial bond between the epoxy resin and the aggregates. This study demonstrates the potential of OEO-based hardeners to enhance the performance of epoxy binders, providing a sustainable alternative for polymer-based mortar applications.

Enhancing the Energy Release Performance of Al/CuO Nanothermites through Hierarchical Structure

ABSTRACT The objective of this study is to enhance the mixing uniformity and contact efficiency between nano-Al and oxidizers through structural control, while suppressing the “pre – ignition fusion” effect of nanothermites. We employed biotemplate approach, utilizing Lycopodium japonicum Thunb. spores (LP) and Papilio maackii wings (PW) as sacrificial templates, to successfully fabricate hierarchically structured Al/PW-CuO and Al/LP-CuO nanothermites. At a stoichiometric ratio of Ф = 1.5, Al/PW-CuO exhibited the highest heat release of 2278.00 J/g, whereas Al/LP-CuO also achieved a substantial heat release of 1969.08 J/g. These outstanding performances are attributed to the unique structures of PW-CuO and LP-CuO, especially the spine-like plate structure of PW-CuO, which provides more reaction sites, thereby enhancing spatial utilization and heat release efficiency. This study provides new insights for the design and application of highly active nanoenergetic materials.

2D/2D Hydrogen-Bonded Organic Frameworks/Covalent Organic Frameworks S-scheme Heterojunctions for Photocatalytic Hydrogen Evolution.

Hydrogen-bonded organic frameworks (HOFs) demonstrate significant potential for application in photocatalysis. However, the low efficiency of electron-hole separation and limited stability inhibit their practical utilization in photocatalytic hydrogen evolution from water splitting. Herein, the novel dual-pyrene-base supramolecular HOF/COF 2D/2D S-scheme heterojunction between HOF-H4TBAPy (Py-HOF, H4TBAPy represents the 1,3,6,8-tetrakis (p-benzoic acid) pyrene) and Py-COF was successfully established using a rapid self-assembly solution dispersion method. Experimental and theoretical investigations confirm that the size-matching of two crystalline porous materials enables the integrated heterostructure material with abundant surface reaction sites, strong interaction, and an enhanced S-scheme built-in electric field, thus significantly improving the efficiency of photogenerated charge carrier separation and stability. Notably, the optimal HOF/COF heterojunction achieves a photocatalytic hydrogen evolution rate of 390.68 mmol g-1 h-1, which is 2.28 times higher than that of pure Py-HOF and 9.24 times higher than that of pure COF. These findings precisely acquire valuable atomic-scale insights into the ingenious design of dual-pyrene-based S-scheme heterojunction. This work presents an innovative perspective for forming supramolecular S-scheme heterojunctions over HOF-based semiconductors, offering a protocol for designing the powerful and strong-coupling S-scheme built-in electric fields for efficient solar energy utilization.

2D/2D Hydrogen‐Bonded Organic Frameworks/Covalent Organic Frameworks S‐scheme Heterojunctions for Photocatalytic Hydrogen Evolution

Hydrogen‐bonded organic frameworks (HOFs) demonstrate significant potential for application in photocatalysis. However, the low efficiency of electron‐hole separation and limited stability inhibit their practical utilization in photocatalytic hydrogen evolution from water splitting. Herein, the novel dual‐pyrene‐base supramolecular HOF/COF 2D/2D S‐scheme heterojunction between HOF‐H4TBAPy (Py‐HOF, H4TBAPy represents the 1,3,6,8‐tetrakis (p‐benzoic acid) pyrene) and Py‐COF was successfully established using a rapid self‐assembly solution dispersion method. Experimental and theoretical investigations confirm that the size‐matching of two crystalline porous materials enables the integrated heterostructure material with abundant surface reaction sites, strong interaction, and an enhanced S‐scheme built‐in electric field, thus significantly improving the efficiency of photogenerated charge carrier separation and stability. Notably, the optimal HOF/COF heterojunction achieves a photocatalytic hydrogen evolution rate of 390.68 mmol g−1 h−1, which is 2.28 times higher than that of pure Py‐HOF and 9.24 times higher than that of pure COF. These findings precisely acquire valuable atomic‐scale insights into the ingenious design of dual‐pyrene‐based S‐scheme heterojunction. This work presents an innovative perspective for forming supramolecular S‐scheme heterojunctions over HOF‐based semiconductors, offering a protocol for designing the powerful and strong‐coupling S‐scheme built‐in electric fields for efficient solar energy utilization.

Heterostructuring Uniform 2D CdS on Ru/Ti3C2-TiO2 via In situ Oxidized Ru-Loaded MXene for Boosting Photocatalytic H2 Production.

Building heterojunctions and exposing more catalytic active sites are effective strategies to enhance the photocatalytic hydrogen evolution activity. Herein, TiO2 nanosheets are oxidized in situ on Ru-loaded MXene as carriers and subsequently loaded with uniform 2D CdS via hydrothermal method to obtain 2D Ru/Ti3C2-TiO2/CdS composite photocatalysts that integrate heterojunctions and cocatalysts. The formation of heterojunction between CdS and TiO2 is conducive to promoting the separation and transfer of photogenerated charges, simultaneously, Ru/Ti3C2 with the fully exposed Ru and Ti3C2 can act as effective active sites of photocatalytic hydrogen production reaction. The composite photocatalyst exhibits an improved hydrogen production rate with 5479µmol g-1 h-1, which is 5, 3, and four times more than that of pristine CdS, CdS loaded Ti3C2-TiO2and CdS loaded Ru-TiO2 respectively. The results reveal that the notable enhancement in performance can primarily be ascribed to the introduction of the TiO2/CdS heterojunction and the efficient cocatalysts of Ru/Ti3C2. Moreover, the 2D Ti3C2 with high conductivity as carriers can increase charge transfer, and its 2D structure can serve as a template for growing 2D photocatalysts with higher activity. The interface engineering with multiple interfaces can offer novel insights for the advancement of efficient hydrogen evolution reaction catalysts.

Oxygen Vacancies and Lattice Distortion Synergistically Enhanced Piezocatalysis of CaZn2(BO3)2 for Nonantibiotic Pharmaceutical Degradation.

Piezocatalysis, an emerging green and advanced oxidation technology, has recently been widely researched in environmental treatment. However, the limited polarization efficiency of the piezocatalyst is a serious bottleneck for its practical application. The search for an excellent piezocatalyst with a high piezoelectric coefficient and abundant reactive sites remains an urgent task that needs to be developed. Herein, a piezocatalyst, CaZn2(BO3)2 (CZBO), obtained by quenching has an excellent piezocatalysis, which exhibited superior activity for ibuprofen (IBP) and carbamazepine (CBZ) removal with 100% and 83.8% efficiency under ultrasonic cavitation (120 W, 40 kHz) within 36 min, respectively. The outstanding piezocatalytic degradation was attributed to the strong polarization of the material under the synergistic effect of oxygen vacancies (OVs) and lattice distortion, which effectively facilitated the generation of a high concentration of reactive oxygen species (ROS). The lattice distortion induced by O-deficient [BO3] plane units can promote the e- and h+ pair separation and transportation, and the OVs with abundant electron-rich regions can significantly decrease O-O bond activation energy, thus collaboratively contributing to the high production of ROS for IBP and CBZ degradation. This work provides a simple avenue for enhancing piezoelectric polarization based on the OVs and lattice distortion and proposes insights into the reaction mechanisms for degrading nonantibiotic pharmaceuticals in wastewater.

Sonophotocatalytic degradation of rhodamine B dye using Zr doped ZnO nanoparticles: Kinetic study and toxicity assessment

This study investigates sonophotocatalysis for the oxidation of Rhodamine B (RhB) dye using Zr doped ZnO nanoparticles. The synthesized nanoparticles were characterized by scanning electron microscope, Fourier-transform infrared, X-ray diffraction, Brunauer Emmett-Teller, thermogravimetric analysis, and photoluminescence. The hybrid sonophotocatalysis system achieved 98.73 ± 1.25% degradation of RhB under the conditions: RhB dye concentration = 10 ppm, 4 wt% of Zr doped ZnO = 0.1 g, reaction temperature = 30 °C, time = 60 min, pH = 7. A kinetic model was developed to predict the efficiency of RhB degradation through intrinsic elementary chemical reactions. The high coefficient of determination (R2 = 0.96) indicates the model's prediction accuracy in describing the degradation kinetics of RhB within sonophotocatalysis system. The electrical energy per order (EEO) analysis demonstrated that US + UVC + 4 wt% of Zr doped ZnO significantly reduced EEO (1055 kWh m−3 order−1). The synergy index for this combination was approximately 1.60, demonstrating a significant synergistic effect. Density Functional Theory (DFT) studies were utilized to propose the most probable degradation pathway, identifying reactive sites and potential byproducts. The simulations revealed the central carbon atom (1C site) as highly susceptible to radical attacks, indicating potential decolorization pathways such as N-de-ethylation, chromophore cleavage, and ring opening. Toxicity assessments of both the parent dye and its intermediates were conducted using ECOSAR (Ecological Structure Activity Relationship) to evaluate their ecological impacts. The combination of experimental results and kinetic modeling and simulations offers a deep understanding of RhB degradation complexities, driving advancements in sustainable water treatment technologies.

Activating the Mn Single Atomic Center for an Efficient Actual Active Site of the Oxygen Reduction Reaction by Spin-State Regulation.

The ligand engineering for single-atom catalysts (SACs) is considered a cutting-edge strategy to tailor their electrocatalytic activity. However, the fundamental reasons underlying the reaction mechanism and the contemplation for which the actual active site for the catalytic reaction depends on the pyrrolic and pyridinic N ligand structure remain to be fully understood. Herein, we first reveal the relationship between the oxygen reduction reaction (ORR) activity and the N ligand structure for the manganese (Mn) single atomic site by the precisely regulated pyrrolic and pyridinic N4 coordination environment. Experimental and theoretical analyses reveal that the long Mn-N distance in Mn-pyrrolic N4 enables a high spin state of the Mn center, which is beneficial to reduce the adsorption strength of oxygen intermediates by the high filling state in antibond orbitals, thereby activating the Mn single atomic site to achieve a half-wave potential of 0.896 V vs RHE with outstanding stability in acidic media. This work provides a new fundamental insight into understanding the ORR catalytic origin of Mn SACs and the rational design strategy of SACs for various electrocatalytic reactions.