Four-electron Oxygen Reduction Reaction Research Articles

The terminal oxidase cytochrome bd-I confers carbon monoxide resistance to Escherichia coli cells

Carbon monoxide (CO) plays a multifaceted role in the physiology of organisms, from poison to signaling molecule. Heme proteins, including terminal oxidases, are plausible CO targets. Three quinol oxidases terminate the branched aerobic respiratory chain of Escherichia coli. These are the heme‑copper cytochrome bo3 and two copper-lacking bd-type cytochromes, bd-I and bd-II. All three enzymes generate a proton motive force during the four-electron oxygen reduction reaction that is used for ATP production. The bd-type oxidases also contribute to mechanisms of bacterial defense against various types of stresses. Here we report that in E. coli cells, at the enzyme concentrations tested, cytochrome bd-I is much more resistant to inhibition by CO than cytochrome bd-II and cytochrome bo3. The apparent half-maximal inhibitory concentration values, IC50, for inhibition of O2 consumption of the membrane-bound bd-II and bo3 oxidases by CO at ~150 μM O2 were estimated to be 187.1 ± 11.1 and 183.3 ± 13.5 μM CO, respectively. Under the same conditions, the maximum inhibition observed with the membrane-bound cytochrome bd-I was 20 ± 10% at ~200 μM CO.

Facet effect of MnCo2O4 nanocrystals for enhanced oxygen reduction reaction in alkaline medium

Understanding the mechanism of the four-electron transfer oxygen reduction reaction (ORR) and the structure–activity relationship of spinel oxide remains a challenge. Two bimetallic manganese-cobalt spinel oxide supported on carbon nanotube (MnCo2O4/CNT) composite materials with different crystal planes exposed are synthesized in this paper by adding unequal amounts of ammonia during the hydrothermal process. Physical characterization results indicate that the exposed surfaces of the two materials (MnCo2O4/CNT-100, MnCo2O4/CNT-800) are (001) and (112), respectively. Electrochemical tests demonstrate that the MnCo2O4/CNT-800 composite material exposed to the (112) crystal plane exhibit higher ORR catalytic activity in alkaline electrolyte, with a half-wave potential of 0.79 V and a limiting current density of 5.15 mA cm−2. The outstanding activity is attributed to the greater specific surface area, the exposure of high-index crystal plane and the high-valence metal sites on the surface. Density functional theory (DFT) calculations reveal that the active sites on the (112) crystal plane have improved adsorption and ORR thermodynamics. This work provides a strategy for developing the advanced bimetallic spinel electrocatalysts by adjusting the exposed plane.

Mechanistic Investigations into the Selective Reduction of Oxygen by a Multicopper Oxidase T3 Site-Inspired Dicopper Complex.

Understanding how multicopper oxidases (MCOs) reduce oxygen in the trinuclear copper cluster (TNC) is of great importance for development of catalysts for the oxygen reduction reaction (ORR). Herein, we report a mechanistic investigation into the ORR activity of the dinuclear copper complex [Cu2L(μ-OH)]3+ (L = 2,7-bis[bis(2-pyridylmethyl)aminomethyl]-1,8-naphthyridine). This complex is inspired by the dinuclear T3 site found in the MCO active site and confines the Cu centers in a rigid scaffold. We show that the electrochemical reduction of [Cu2L(μ-OH)]3+ follows a proton-coupled electron transfer pathway and requires a larger overpotential due to the presence of the Cu-OH-Cu motif. In addition, we provide evidence that metal-metal cooperativity takes place during catalysis that is facilitated by the constraints of the rigid ligand framework, by identification of key intermediates along the catalytic cycle of [Cu2L(μ-OH)]3+ . Electrochemical studies show that the mechanisms of the ORR and hydrogen peroxide reduction reaction found for [Cu2L(μ-OH)]3+ differ from the ones found for analogous mononuclear copper catalysts. In addition, the metal-metal cooperativity results in an improved selectivity for the four-electron ORR of more than 70% because reaction intermediates can be stabilized better between both copper centers. Overall, the mechanism of the [Cu2L(μ-OH)]3+ -catalyzed ORR in this work contributes to the understanding of how the cooperative function of multiple metals in close proximity can affect ORR activity and selectivity.

The oxygen reduction reaction activity and selectivity of porous-carbon supported transition metals (M-C: M Mn, Fe, Co, Ni, Cu) electrocatalysts

In general, both transition metal addition and nitrogen doping are important to the four-electron (4e−) oxygen reduction reaction (ORR) activity of carbon-based catalysts, in which nitrogen-containing species, such as M-Nx, pyridinic N and graphitic N, are believed to be the active sites. On the other hand, nitrogen-free carbon supported transition metals often show their excellent electroactivity toward two-electron (2e−) ORR. Herein, carbon supported transition metal catalysts (M-C: MMn, Fe, Co, Ni, Cu) with high specific surface areas were prepared by a simple zinc-mediated pyrolysis method and their ORR activity and selectivity were systematically studied. It is found that various transition metals result in a large difference in the content and type of oxygen-containing functional groups of the M-C catalysts. The results show that CuC and CoC exhibit promising ORR activity close to the 4e− transfer mechanism in 0.1 M KOH electrolyte. FeC and MnC show a mixture of 2e− and 4e− transfer pathways. NiC is an efficient catalyst for efficient H2O2 generation through a primary 2e− ORR. It is found that the ORR selectivity of M-C is correlated to the content and type of oxygen-containing functional groups in the catalysts, and C-O-C is likely an effective active site for 4e− ORR based on both experimental results and theoretical calculations.

Co3O4 Supported on Graphene-like Carbon by One-Step Calcination of Cobalt Phthalocyanine for Efficient Oxygen Reduction Reaction under Alkaline Medium

Exploiting cost-effective and durable non-platinum electrocatalysts for oxygen reduction reaction (ORR) is of great significance for the development of abundant renewable energy conversion and storage technologies. Herein, a series of Co3O4 supported on graphene-like carbon (Co3O4/C) samples were firstly effectively synthesized by one-step calcination of cobalt phthalocyanine and their electrocatalytic performances were measured for ORR under an alkaline medium. By systematically adjusting the calcination temperature of cobalt phthalocyanine, we found that the material pyrolyzed at 750 °C (Co3O4/C-750) shows the best ORR electrocatalytic performance (half-wave potentials of 0.77 V (vs. RHE) in 0.1 M KOH) among all the control samples. Moreover, it displays better stability and superior methanol tolerance than commercial 20% Pt/C. The further electrochemical test results reveal that the process is close in characteristics to the four-electron ORR process on Co3O4/C-750. In addition, Co3O4/C-750 applied in the zinc-air battery presents 1.34 V of open circuit potential. Based on all the characterizations, the enhanced electrocatalytic performances of Co3O4/C-750 composite should be ascribed to the synergistic effect between Co3O4 and the graphene-like carbon layer structure produced by pyrolysis of cobalt phthalocyanine, as well as its high specific surface area.

Sulfonic Acid Functionalization-Boosted Ultrafast, Durable, and Selective Four-Electron Oxygen Reduction Reaction: Evidenced by EC-SHINERS and DFT Studies

Sulfonic Acid Functionalization-Boosted Ultrafast, Durable, and Selective Four-Electron Oxygen Reduction Reaction: Evidenced by EC-SHINERS and DFT Studies

Cover Feature: Rapid Screening of Mechanistic Pathways for Oxygen‐Reduction Catalysts (ChemCatChem 3/2023)

The Cover Feature illustrates that the volcano plot for the oxygen reduction reaction (ORR) is impacted by a plethora of different mechanistic descriptions, including the mononuclear, dissociative, OOH dissociation, and oxide mechanisms. In their Research Article, K. S. Exner introduces the adsorption free energy of the *OH intermediate as an efficient descriptor for rapid screening of ORR pathways. The novelty of the presented work constitutes the possibility of screening all possible mechanisms by volcano analyses to identify the energetically preferred one. The introduced procedure may support future DFT-based studies so that the preferred pathway is not missed when modeling the four-electron ORR by a binding-energy approach. More information can be found in the Research Article by K. S. Exner.

Non-bonding interaction of dual atom catalysts for enhanced oxygen reduction reaction

We demonstrate the design of graphene-supported dual atom catalysts (DACs) for the four-electron oxygen reduction reaction (ORR), by utilizing the non-bonding interaction of counterpart metals (M) that synergistically tune the electronic properties and catalytic activity of the Fe active site in FeMN6-DAC and FeMN8-DAC systems, where M stands for Fe, Co, Ni, Cu, and Zn. More specifically, for Fe-M distances below 15 Å, the non-bonding interaction is significant, making the system act as the DAC. We predicted that FeNiN6-DAC and FeNiN8-DAC exhibit a low ORR overpotential (ηORR) of 0.28 V and 0.47 V, respectively, which are at the summits of volcano plots. This low ηORR originates from the high Bader charge transfer coupled with high spin density at the Fe site in both the FeNiN6-DAC and FeNiN8-DAC systems, which weakens the adsorption of OH* intermediate while enhancing its desorption to H2O. Guided by these density functional theory (DFT) computational results, we synthesized FeCoN8-DAC and FeNiN8-DAC along with N-doped graphene and confirmed their structures with scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and electron spin resonance (ESR). We verify experimentally the catalytic activities and find that FeNiN8-DAC has the low experimental overpotential of 0.39 V with a Tafel slope of 47 mVdec−1. Based on these results, we propose a DFT-guided strategy to tune the charge transfer and spin population of the active site toward designing DACs for electrochemical ORR.

The synergistic effect of “soft-hard template” to in situ regulate mass transfer and defective sites of doped-carbon nanostructures for catalysis of oxygen reduction

Nitrogen-doped carbon materials are intensively investigated as electrocatalysts toward oxygen reduction reaction (ORR). The activity of the catalysts can be effectively boosted by regulating the microstructure to construct defective three-phase interface. Herein, an N-doped carbon-based porous catalyst (DT-Fe-N-C) is fabricated by a dual-template strategy with SiO2 and pluronic F127 as the hard and soft templates. Benefited from the modulation, the mesopore-dominated DT-Fe-N-C exhibits remarkable specific surface area (990.19 m2 g-1), high Fe-Nx content and plenty of defects. Resultantly, DT-Fe-N-C shows outstanding catalytic activity to ORR with 0.853 V of half-wave potential, high stability and selectivity to the four-electron ORR mechanism. The Zn-air battery with DT-Fe-N-C outputs 219 mW cm-2 of maximum power density, 861 Wh kgZn−1 of specific energy density at 50 mA cm-2 and runs at a higher voltage than that of Pt/C-based battery. This work provides an avenue for the defect engineering in the design of non-precious metal ORR catalysts.

A cobalt corrole with a biologically relevant imidazolium pendant for boosted electrocatalytic oxygen reduction

Developing electrocatalysts with high activity and selectivity for the oxygen reduction reaction (ORR) has attracted increasing interest in the past decades. The many imidazole residues located at the active site of cytochrome c oxidases (CcOs) play crucial roles in facilitating the selective reduction of dioxygen to water. As inspired by nature, we herein reported on the synthesis of [Formula: see text] corrole 1 hanged with a biologically relevant imidazolium group and its electrocatalytic ORR features in both acidic and alkaline solutions. Complex 1 is more active and selective than its imidazolium-free analogue for electrocatalytic four-electron ORR. Importantly, 1 displayed ORR activities with the half-wave potentials at [Formula: see text] = 0.65 V versus RHE in 0.5 M [Formula: see text] solution and at [Formula: see text] = 0.81 V versus RHE in 0.1 M KOH solution. This work presents a strategy to simultaneously improve catalytic ORR activity and selectivity by hanging a cationic imidazolium unit over molecular catalytic sites.

Electrocatalytic oxygen reduction with cobalt corroles bearing cationic substituents.

Recent decades have seen increasing interest in developing highly active and selective electrocatalysts for the oxygen reduction reaction (ORR). The active site environment of cytochrome c oxidases (CcOs), including electrostatic and hydrogen-bonding interactions, plays an important role in promoting the selective conversion of dioxygen to water. Herein, we report the synthesis of three CoIII corroles, namely 1 (with a 10-phenyl ortho-trimethylammonium cationic group), 2 (with a 10-phenyl ortho-dimethylamine group) and 3 (with a 10-phenyl para-trimethylammonium cationic group) as well as their electrocatalytic ORR activities in both acidic and neutral solutions. We discovered that 1 is much more active and selective than 2 and 3 for the electrocatalytic four-electron ORR. Importantly, 1 showed ORR activities with half-wave potentials at E1/2 = 0.75 V versus RHE in 0.5 M H2SO4 solutions and at E1/2 = 0.70 V versus RHE in neutral 0.1 M phosphate buffer solutions. This work is significant for outlining a strategy to increase both the activity and selectivity of metal corroles for the electrocatalytic ORR by introducing cationic units.

Axial Coordination Effect on the Oxygen Reduction Reaction of FeN4 Electrocatalysts Based on Grand Canonical Density Functional Theory

The Fe–N–C materials are promising noble-free alternatives to Pt-based oxygen reduction reaction (ORR) electrocatalysts. Identifying the actual active structure of FeN4-based moieties is helpful for the regulation and design of high-performance electrocatalysts. However, the current theoretical researches were mostly based on the charge-neutral model (CNM), which cannot accurately describe the electrochemical interface. Herein, we employed the constant potential based grand canonical density functional theory (GC-DFT) computations to study the ORR mechanism of axially decorated FeN4 electrocatalysts. We studied around ten types of axial ligands, and the constant potential energetics and microkinetic modeling demonstrated that the Fe center can exhibit excellent activity for boosting the four-electron ORR via covalently linked −NH2 ligand. The lowering of the antibonding dz2–pz orbital is responsible for weakening the adsorption of oxygen in FeN4–Ls to promote ORR activity, and the −NH2 decoration led to the lowest antibonding orbital energy. In particular, the adsorption free energy (ΔG*O2) and O–O bond length (LO–O) of the adsorbed O2 reactant can be used as the effective energetic and geometric descriptors to describe the ORR activity of FeN4–Ls electrocatalysts. Our results not only elucidate the axial coordination effect on the ORR performance of FeN4 SACs but also demonstrate the importance of electrode potential in computational electrochemistry.

Electrodeposited Cobalt Nanosheets on Smooth Silver as a Bifunctional Catalyst for OER and ORR: In Situ Structural and Catalytic Characterization.

Developing earth-abundant, cost-effective, and active bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is key to boosting sustainable energy systems such as electrolyzers and lithium-air batteries. However, the performance of promising cobalt-based materials is impaired by the external effects of binders and carbon additives as well as inhomogeneous electrode fabrication. In this work, binder- and carbon-free flower-like Co-decorated Ag catalytic nanosheets were in situ-synthesized via a simple electrodeposition approach. The morphology, composition, and structure of Co/Ag before and after OER were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Co/Ag thin film electrodes with various Co contents exhibited a bifunctional activity toward ORR and OER due to a synergistic effect. XPS analysis suggested the formation of Co3O4 as the main active species for OER. In particular, Co (83%)/Ag surface revealed a 60 mV lower ORR overpotential than a pure Ag surface and even lower than drop-casted Co3O4 nanoparticles on Ag surface. Only 1.5% peroxide was generated, suggesting a four-electron transfer ORR. In addition, the OER onset potential on Co/Ag is 60 mV less than Co3O4. Tafel slopes of 71 and 75 mV dec-1 were obtained for ORR and OER, respectively. Importantly, the three-dimensional (3D) growth mechanism of a cobalt layer (∼1 nm) on a well-defined atomic smooth Ag surface is unraveled by in situ electrochemical scanning tunneling microscopy (EC-STM). EC-STM suggests that Co prefers to nucleate at the step edges of Ag and grows in a 3D, forming nanoparticles, where the deposition/dissolution process of the Co adlayer on Ag is reversible. This investigation may provide insights into design strategies of efficient oxygen electrocatalysts.

Nitrogen doped carbonaceous materials as platinum free cathode electrocatalysts for oxygen reduction reaction (ORR)

Comparison of physicochemical properties and electrocatalytic behavior of different N-doped carbonaceous materials as potential catalysts for oxygen reduction reaction (ORR) was attended. Ball-milling of graphite with melamine and solvothermal treatment of graphite oxide, graphene nanoplatelets (GNP) with ammonia were used as preparation methods. Elemental analysis and N2 physisorption measurements revealed the synthesis of N-doped materials with strongly different morphological parameters. Contact angle measurements proved that all three samples had good wettability properties. According to analysis of XRD data and Raman spectra a higher nitrogen concentration corresponded to a smaller size of crystallites of the N-doped carbonaceous material. Surface total N content determined by XPS and bulk N content assessed by elemental analysis were close, indicating homogenous inclusion of N in all samples. Rotating disc electrode tests showed that these N-doped materials weremuch less active in acidic medium than in an alkaline environment. Although the presence of in-plane N species is regarded to be advantageous for the ORR activity, no particular correlation was found in these systems with any type of N species. According to Koutecky–Levich analysis, both the N-containing carbonaceous materials and the reference Pt/C catalyst displayed a typical one-step, four-electron ORR route. Both ball-milled sample with high N-content but with low SSA and solvothermally synthesized N-GNP with high SSA but low N content showed significant ORR activity. It could be concluded that beside the total N content other parameters such as SSA, pore structure, structural defects, wettability were also essential for achieving high ORR activity.

Inner-pore reduction nucleation of palladium nanoparticles in highly conductive wurster-type covalent organic frameworks for efficient oxygen reduction electrocatalysis

Covalent organic frameworks (COFs) have emerged as a class of promising supports for electrocatalysis because of their advantages including good crystallinity, highly ordered pores, and structural diversity. However, their poor conductivity represents the main obstruction to their practical application. Here, we reported a novel synthesis strategy for synergistically endowing a triphenylamine-based COFs with improved electrical conductivity and excellent catalytic activity for oxygen reduction, via the in-situ redox deposition and confined growth of palladium nanoparticles inside the porous structure of COFs using reductive triphenylamine frameworks as reducing agent; meanwhile, the triphenylamine unit was oxidized to radical cation structure and affords radical cation COFs with conductivity as high as 3.2*10−1 S m−1. Such a uniform confine palladium nanoparticle on highly conductive COFs makes it an efficient electrocatalyst for four-electron oxygen reduction reaction (4e-ORR), showing excellent activities and fast kinetics with a remarkable half-wave potential (E1/2) of 0.865 V and an ultralow Tafel slope of 39.7 mV dec−1 in alkaline media even in the absence of extra commercial conductive fillers. The generality of this strategy was proved by preparing the different metal and metal alloy nanoparticles supported on COFs (Au@COF, Pt@COF, AuPd@COF, AgPd@COF, and PtPd@COF) using reductive triphenylamine frameworks as reducing agent. This work not only provides a facile strategy for the fabrication of highly conductive COF supported ORR electrocatalysts, but also sheds new light on the practical application of Zn-air battery.

Front Cover: Application of AgPt Nanoshells in Direct Methanol Fuel Cells: Experimental and Theoretical Insights of Design Electrocatalysts over Methanol Crossover Effect (ChemCatChem 23/2022)

The Front Cover shows that nanoengineering is a breakthrough way to look at the electrocatalysis field under a different perspective. In their Research Article, M. Aurélio Suller Garcia, T. Silva Rodrigues and co-workers provided the design of a hollow AgPt-based electrocatalyst with improved resistance to methanol for Direct Methanol Fuel Cells applications. After immobilization onto SiO2, the nanostructures presented remarkable stability, with a four-electron oxygen reduction reaction mechanism as the Pt/C commercial catalyst, with 20 times less Pt content. More information can be found in the Research Article by M. Aurélio Suller Garcia, T. Silva Rodrigues and co-workers.

Decrypting the Influence of Axial Coordination on the Electronic Microenvironment of Co-N 5 Site for Enhanced Electrocatalytic Reaction

Decrypting the Influence of Axial Coordination on the Electronic Microenvironment of Co-N ₅ Site for Enhanced Electrocatalytic Reaction

First-Principles Study on Pt-Based Sub-Nanocluster Carbon-Metal Hybrid Catalysts for the Oxygen Reduction Reaction

Recently, the polymer electrolyte membrane fuel cell (PEMFC) has been drawing huge attention as an eco-friendly energy conversion device which can replace an internal combustion engine without environmental contaminant such as CO2 and NOx. However, the use of expensive noble metal catalysts such as Pt is essential for the cathode because the oxygen reduction reaction (ORR) at cathode are kinetically much slower than the hydrogen oxidation at anode. For this reason, many of researchers have vigorously worked on the development of Pt-based alloy catalysts such as Pt-Co and Pt-Ni alloys to reduce noble metal usage, but there are still limitations in catalytic activity and durability for the commercialization. Herein, to overcome the limitations, we developed Pt-based carbon-metal hybrid catalyst showing high performance for ORR using density functional theory (DFT) calculation. The slab model of Pt-based carbon-metal hybrid catalyst was constructed by Pt sub-nanocluster supported on graphite with graphene-shaped carbon shell on top of the Pt sub-nanocluster. The most stable geometry of the hybrid catalyst was determined by the formation energy, and the ORR mechanism on surface of hybrid catalyst as well as electrochemical activity was investigated. As a result of investigation, we confirmed that the oxygen reduction occurs on active graphene-shaped carbon shell sites. On pure Pt sub-nanocluster hybrid catalyst, once the hydrogen superoxide (OOH) is adsorbed on carbon shell surface after the oxygen adsorption and protonation, the hydrogen peroxide (H2O2) is preferentially formed at higher onset potential than that of four-electron O2 reduction, which the final product is water (H2O). However, the formation of hydrogen peroxide in PEMFC should be avoided owing to creation of radical, resultant degradation of membrane and low energy conversion efficiency. Surprisingly, we identified that the hydrogen peroxide formed on pure Pt sub-nanocluster hybrid catalyst can be decomposed into OH and H2O with low energy barrier, whose value is much lower than desorption energy of produced hydrogen peroxide, so that subsequent reduction reaction can occur. When this four-electron ORR via hydrogen peroxide decomposition takes place, the ORR activity is improved compared to Pt(111) catalyst, where the onset potential of pure Pt sub-nanocluster hybrid catalyst presents is higher than that of Pt(111). Moreover, we introduced Pt-based alloy sub-nanocluster to reduce Pt usage further. The Pt-based alloy sub-nanocluster hybrid catalyst also exhibited increased ORR activity. For Pt-based alloy sub-nanocluster hybrid catalyst, we carried out analysis of density of state and figured out that the more orbital overlap between carbon shell and sub-nanocluster is generated, the higher catalytic activity is shown due to enrichment of electrons on carbon shell surface. We expect this work can help understanding the mechanism of activity improvement of carbon metal hybrid catalyst, suggesting promising way to design high-performance ORR catalyst with low Pt loadings.

Novel Metal-Free Composite Electrodes with Carbon Quantum Dots and Anion-Conducting Ionomers for the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is one of the bottlenecks in many electrochemical applications and plays an important role in commercial fuel cell systems. Platinum is highly used as a catalyzer especially in proton exchange membrane fuel cells. Given its rarity and cost, platinum, is not a viable choice as a catalyst, so there is a need to shift to alternative materials such as a metal-free catalyst possible in anion exchange membrane fuel cells. There were several theoretical and experimental studies to address this issue and a direction toward metal-free catalysts is of great interest. In this study, we focus on the oxygen reduction reaction in alkaline medium using a novel metal-free catalyst composite with carbon quantum dots and anion exchange ionomer (AEI). Doped carbon quantum dots were synthesized by a hydrothermal method and an AEI was integrated to improve the hydroxide ion transport and have a composite of desired functionality. These composites showed significant electrochemical activity with a good current response and four-electron ORR. The characterization comprised various microscopic, spectroscopic and electrochemical techniques. Figure 1

Synergistic Hybrid Electrocatalysts of Platinum Alloy and Single-Atom Platinum for an Efficient and Durable Oxygen Reduction Reaction.

Pt single-atom materials possess an ideal atom economy but suffer from limited intrinsic activity and side reaction of producing H2O2 in catalyzing the oxygen reduction reaction (ORR); platinum alloys have higher intrinsic activity but weak stability. Here, we demonstrate that anchoring platinum alloys on single-atom Pt-decorated carbon (Pt-SAC) surmounts their inherent deficiencies, thereby enabling a complete four-electron ORR pathway catalysis with high efficiency and durability. Pt3Co@Pt-SAC demonstrates an exceptional mass and specific activities 1 order of magnitude higher than those of commercial Pt/C. They are durable throughout 50000 cycles, showing only a 10 mV decay in half-wave potential. An in situ Raman analysis and theoretical calculations reveal that Pt3Co core nanocrystals modulate electron structures of the adjacent Pt single atoms to facilitate the intermediate absorption for fast kinetics. The superior durability is attributed to the shielding effect of the Pt-SAC coating, which significantly mitigates the dissolution of Pt3Co cores. The hybridizing strategy might promote the development of highly active and durable ORR catalysts.