Co-Co Distances Research Articles

Tracking the role of compressive strain in bowl-Like Co-MOFs structural evolution in water oxidation reaction

Dynamic structural evolution of catalyst active sites is crucial to for transition metal-catalyzed oxygen evolution reaction (OER). Yet, the elucidation of their mechanism behind the compressive-strain-induced reconstruction during OER process remains enigmatic. Here, we construct a bowl-like cobalt-based metal-organic frameworks (BL-Co-MOFs) catalyst with compressive strain to investigate the effect of strain on the structural evolution process and the OER mechanism. In situ techniques directly observe that compressive strain exists in the reconstruction of the potential-driven CoOOH-like active phase with contractile interatomic CoCo distance, promoting a direct OO radical coupling over the Co sites (Co−O−O−Co) during the OER process. This disrupts the constrains of the inherent linear scaling relationship and achieves the kinetic-faster oxide path mechanism (OPM) during OER process. Consequently, the BL-Co-MOFs exhibit a huge mass activity of 12516 A gmetal−1 and a large turnover frequency of 6888 h−1 at a low overpotential of 275 mV (300 mA cm−2).

Co-Co Dinuclear Active Sites Dispersed on Zirconium-doped Heterostructured Co9 S8 /Co3 O4 for High-current-density and Durable Acidic Oxygen Evolution.

Developing cost-effective and sustainable acidic water oxidation catalysts requires significant advances in material design and in-depth mechanism understanding for proton exchange membrane water electrolysis. Herein, we developed a single atom regulatory strategy to construct Co-Co dinuclear active sites (DASs) catalysts that atomically dispersed zirconium doped Co9 S8 /Co3 O4 heterostructure. The X-ray absorption fine structure elucidated the incorporation of Zr greatly facilitated the generation of Co-Co DASs layer with stretching of cobalt oxygen bond and S-Co-O heterogeneous grain boundaries interfaces, engineering attractive activity of significantly reduced overpotential of 75 mV at 10 mA cm-2 , a breakthrough of 500 mA cm-2 high current density, and water splitting stability of 500 hours in acid, making it one of the best-performing acid-stable OER non-noble metal materials. The optimized catalyst with interatomic Co-Co distance (ca. 2.80 Å) followed oxo-oxo coupling mechanism that involved obvious oxygen bridges on dinuclear Co sites (1,090 cm-1 ), confirmed by in situ SR-FTIR, XAFS and theoretical simulations. Furthermore, a major breakthrough of 120,000 mA g-1 high mass current density using the first reported noble metal-free cobalt anode catalyst of Co-Co DASs/ZCC in PEM-WE at 2.14 V was recorded.

Impersonating a Superconductor: High-Pressure BaCoO3, an Insulating Ferromagnet.

We report the high-pressure synthesis (6 GPa, 1200 °C) and ambient-pressure characterization of hexagonal HP-BaCoO3. The material (with a 2H crystal structure) has a short intrachain Co-Co distance of about 2.07 Å. Our magnetization investigation revealed robust diamagnetic behavior below approximately 130 K when the material was exposed to weak applied magnetic fields (10 Oe) and a distinct "half-levitation" phenomenon below that temperature, as is often observed for superconductors. Its field-dependent magnetization profile, however, unveils the characteristics of ferromagnetism, marked by a substantial magnetic retentivity of 0.22(1) μB/Co at a temperature of 2 K. Electrical resistivity measurements indicate that HP-BaCoO3 is a ferromagnetic insulator, not a superconductor.

Bonding mechanism and magnetic ordering in Laves phase λ1−MgCo2 intermetallic compound from theoretical and experimental studies

In the present work we have studied the bonding mechanism and magnetism in a hexagonal λ1−MgCo2 Laves phase intermetallic formed at rA/rB= 1.280. Ab initio theoretical calculations for MgCo2 using the projector-augmented wave method implemented in the VASP code showed that Mg carries a formal charge +1.7 |e| while Co atoms are also positively charged with around +0.7 |e| being donated to establish the interatomic covalent Co-Co bonding in a three-dimensional network of Co tetrahedra. MgCo2 is a metallic conductor with ferromagnetic properties and TC=303 K. Neutron Powder Diffraction study showed a collinear ordering of the Co moments, their alignment along the c-axis of the hexagonal unit cell with an average moment of 1.51(2) μB/atom Co. Ab initio computational studies indicate that the Co moments reach the experimentally observed value approx.1.5 μB when the unit cell volume exceeds 160 Å3 (average Co-Co distances 2.43 Å).

Doping Shortens the Metal/Metal Distance and Promotes OH Coverage in Non-Noble Acidic Oxygen Evolution Reaction Catalysts.

Acidic water electrolysis enables the production of hydrogen for use as a chemical and as a fuel. The acidic environment hinders water electrolysis on non-noble catalysts, a result of the sluggish kinetics associated with the adsorbate evolution mechanism, reliant as it is on four concerted proton-electron transfer steps. Enabling a faster mechanism with non-noble catalysts will help to further advance acidic water electrolysis. Here, we report evidence that doping Ba cations into a Co3O4 framework to form Co3-xBaxO4 promotes the oxide path mechanism and simultaneously improves activity in acidic electrolytes. Co3-xBaxO4 catalysts reported herein exhibit an overpotential of 278 mV at 10 mA/cm2 in 0.5 M H2SO4 electrolyte and are stable over 110 h of continuous water oxidation operation. We find that the incorporation of Ba cations shortens the Co-Co distance and promotes OH adsorption, findings we link to improved water oxidation in acidic electrolyte.

Tracking the Role of Defect Types in Co3O4 Structural Evolution and Active Motifs during Oxygen Evolution Reaction.

Dynamic reconstruction of catalyst active sites is particularly important for metal oxide-catalyzed oxygen evolution reaction (OER). However, the mechanism of how vacancy-induced reconstruction aids OER remains ambiguous. Here, we use Co3O4 with Co or O vacancies to uncover the effects of different defects in the reconstruction process and the active motifs relevant to alkaline OER. Combining in situ characterization and theoretical calculations, we found that cobalt oxides are converted to an amorphous [Co(OH)6] intermediate state, and then the mismatched rates of *OH adsorption and deprotonation lead to irreversible catalyst reconstruction. The stronger *OH adsorption but weaker deprotonation induced by O defects provides the driving force for reconstruction, while Co defects favor dehydrogenation and reduce the reconstruction rate. Importantly, both O and Co defects trigger highly OER-active bridge Co sites in reconstructed catalysts, of which Co defects induce a short Co-Co distance (3.38 Å) under compressive lattice stress and show the best OER activity (η10 of 262 mV), superior to reconstructed oxygen-defected Co3O4-VO (η10 of 300 mV) and defect-free Co3O4 (η10 of 320 mV). This work highlights that engineering defect-dependent reconstruction may provide a rational route for electrocatalyst design in energy-related applications.

Research on novel quantum phenomena of transition metal-doped ZrO2 nanosheets.

The spintronic properties of cubic ZrO2 (c-ZrO2) nanosheets with intrinsic defects and transition metal (TM) elements doping have been systematically studied by first-principle calculation. The results show that impurity Fe has the lowest formation energy in each monolayer compared to other defects. The most stable (111) nanosheet, coupled with the higher defect formation energy, tends to disintegrate. Only Zr vacancy (VZr) on the (110) surface or O vacancy (VO) on the (111) surface can generate a ferromagnetic ground state, while other intrinsic defects cannot introduce spin polarization. Ni-doped (110) monolayer cannot introduce a local magnetic moment, while Fe and Co can. The magnetic moments produced by Fe, Co, and Ni in the (111) sheet are 2, 4, and 1µB, respectively. Further investigation revealed that the magnetism was mainly contributed by the d orbitals of the TM atom and the p orbitals of the surrounding O atoms. Magnetic couplings show that only Co-Co doped monolayers can produce macroscopic magnetism. These are predicted to produce TCs Curie temperature above room temperature when Co-Co distances are 5.070 and 6.209 Å on the (110) surface and 7.170 and 9.485 Å on the (111) surface. The research is beneficial to the refinement of the development of spintronics.

Valence-modified selenospinels as ampere-current-bearing oxygen evolution catalysts

Industrial water electrolysis requires highly-active and ampere-current-bearing oxygen evolution reaction (OER) catalysts, but achieving such a large operating current density at low overpotentials in available OER catalysts still remains a grand challenge. Herein, we present a new type of high-valence metal modified selenospinels (Mn-CuCo2Se4) as large-current-density OER catalysts. The optimal Mn-CuCo2Se4 exhibits prominent OER activity with overpotentials of 293 and 345 mV to achieve 500 and 1000 mA cm−2, respectively, and displays large mass activity, high turnover frequency and robust stability in alkaline media. Using in situ X-ray absorption spectroscopies, we observe that a surface active layer of oxyhydroxide-like phase with contracted CoCo distance was evolved during the OER, which is responsible for the highly-active large-current-density activity. This work may open a new arena for the screening of large-current-density OER catalysts based on the wide variety of spinels compounds.

Non-synergistic photocatalysis of CO2-to-CO conversion by a binuclear complex of rigidly linking two cobalt catalytic centers

A novel binuclear cobalt complex C1 of rigidly linking two [Co(TPA)Cl]Cl moieties at meta positions of a benzene was synthesized and characterized as a catalyst for homogeneous photocatalytic CO2 reduction. Different from state-of-the-art binuclear catalyst catalyzing CO2 reduction with a synergistic catalysis mechanism, C1 catalyses CO2-to-CO conversion independently at each cobalt catalytic center. At an optimal condition, system of C1 produced CO with a TON of 721 (based on C1, corrsoponding to TON 360 per cobalt center) and a high selectivity of 91.5%. Electrochemistry and steady state spectroscopy studies revealed that a CoICoI species, generated via successive photoinduced electron transfer from excited photosensitizer to C1, is the active species of CO2 conversion. No synergistic effect of two cobalt centers exists for CO2 reduction because of larger Co-Co distance and rigid structure of C1.

Surface orientation dependent interaction of cobalt (II) precursors with alpha-alumina

The performances of alumina-supported cobalt catalysts strongly depend on Co/alumina interactions, that are poorly understood. In the present work, α-alumina surfaces are used as models of polycrystalline support, to unravel their orientation dependent behavior by GI-EXAFS. The CoII/α-alumina interactions in the dried state are investigated, with a resolution of the parallel versus perpendicular deposit formation. DFT calculations shed light on the existence of specific grafting modes. EXAFS shows that Co(OH)2 forms parallel to the R(11¯02), A(112¯0) and M(101¯0) surfaces, whatever the contact time (from 1 h to 6 days). However, a specific behavior of the C(0001) surface is observed. Whereas after one hour, the same parallel Co(OH)2 is observed, at longer times it disappears while species exhibiting long then short Co-Co distances appear. The latter is assigned to epitaxial grafting of CoII leading to a mixed phase, that is possible parallel to the C surface due to surface symmetry.

Depression of direct exchange couplings in metallic glasses: A comparative study of critical and electronic behavior in Gd6Co4.85 intermetallic compound and metallic glass

Gd-based metallic glasses enable a wider exploration for excellent magnetocaloric materials due to no requirement of compositional stoichiometry, but these metallic glasses generally show a lower ordering temperature compared with corresponding intermetallic compounds. In this paper, critical behaviors for magnetic transitions in both Gd6Co4.85 intermetallic compound and metallic glass were carefully studied based on isothermal magnetization to reveal the exchange interactions in these two different structural stages, together with experimental electronic density analyses on the compound. Obtained critical exponents close to the theoretical values predicted by the mean-field theory (MFT) in both structures suggest the majority of Gd–Gd long-range exchange interactions, while the Co-Co direct interaction accounts for the deviation of these exponents from the theoretical values in MFT. This is likely a common feature for rare earth – transition metal ferrimagnets. The ordered Co atoms in the intermetallic compound exhibit a high-spin state (~4.6 μB), in contrast with the low-spin state of Co (~1.2 μB) in the metallic glass. The reduced spin is associated with the liquid-like structure in the metallic glass (e.g. longer Co-Co distances) and responsible for the low ordering temperature. This work also indicates that the substitution of p-block elements like Al prefers the site to diminish Co moments, leading to the significantly reduced ordering temperature, and thus emphasizes the critical role of d-electron elements to maintain enough direct exchange interactions for proper transition temperature in the development of new metallic glasses with giant magnetocaloric effects.

Synthesis, structure, magnetic properties, and catecholase-like activity of a phenoxo bridged dinuclear cobalt(II) complex

A dinuclear cobalt complex Co2L2 (H2L = N,N'-bis(salicylidene)-2,2′-ethylenedianiline) have been synthesized and characterized. X-ray crystallography found that Co2L2 contains a planar Co2O2 core where two Co(II) ions are bridged by two phenoxo ligands with Co-Co distance of 3.221 Å and the coordination geometry of each cobalt(II) ion is a distorted trigonal bipyramid. The magnetic susceptibility measurements revealed that both Co(II) ions are in low-spin (S = 1/2) states and two Co(II) spin centers are antiferromagnetically coupled with the exchange coupling constant of J = −45 cm−1. Co2L2 showed catecholase-like activity when 3,5-di-tert-butylcatechol (3,5-H2dtbc) was treated with Co2L2 in the presence of O2 and NaOH with the turnover number of kcat = 803 h−1. Electron paramagnetic resonance (EPR) on the reaction mixture observed a key reaction intermediates, 3,5-di-tert-butyl-1,2-benzosemiquinonate anion radical (3,5-dtsq−) bound to Co(III)-center. This is the first time observation of Co(III)-3,5-dtsq− intermediate during the oxidation of 3,5-H2dtbc by a dicobalt(II/II) complex.

Interdependent Metal-Metal Bonding and Ligand Redox-Activity in a Series of Dinuclear Macrocyclic Complexes of Iron, Cobalt, and Nickel.

This report describes an isostructural series of dinuclear iron, cobalt, and nickel complexes bound by a redox-active macrocyclic ligand. The series spans five redox levels (34-38 e-/cluster core), allowing for a detailed investigation into both the degree of metal-metal interaction and the extent of ligand-based redox-activity. Magnetometry, electrochemistry, UV-vis-NIR absorption spectroscopy, and crystallography were used in conjunction with DFT computational analyses to extract the electronic structures of the six homodinuclear complexes. The isoelectronic, 34 e- species [(3PDI2)Fe2(PMe3)2(μ-Cl)](OTf) and [(3PDI2)Co2(PMe3)2(μ-Cl)](OTf)3 exhibit metal-metal single bonds, with varying amounts of electron density delocalization into the ligand as a function of the effective nuclear charge of the metal ions. One- and two-electron reductions of [(3PDI2)Co2(PMe3)2(μ-Cl)](OTf)3 lead to isolable products, which show successive increases in both the Co-Co distances and the extent of reduction of the ligand manifold. This trend results from reduction of a Co-Co σ* orbital, which was found to be heavily mixed with the redox-active manifold of the 3PDI2 ligand. A similar trend was observed in the 37 and 38 e- dinickel complexes [(3PDI2)Ni2(PMe3)2(μ-Cl)](OTf)2 and [(3PDI2)Ni2(PMe3)2(μ-Cl)](OTf); however, their higher electron counts lead to high-spin ground states that result from occupation of a high-lying δ/δ* manifold with significant Ni-NPDI σ* character. This change in ground state configuration reforms a M-M bonding interaction in the 37 e- complex, but formation of the 38 e- species again disrupts the M-M bond alongside the transfer of electron density to the ligand.

Tunable K vacancies in K1−Co2Se2 and their effects on structure and ferromagnetism

Abstract Deeply understanding the role of intermediate metal A on structure and related properties of ThCr2Si2-type transition metal compounds ATM2X2 is of great importance for designing novel layered functional materials. However, inducing A vacancies usually trends to destroy the original structure in reported systems so far, which hampers the further research. Here we report the controllable K vacancies in K1−xCo2Se2 system (0 ≤ x ≤ 0.3), where both the ThCr2Si2-type structure and intact tetrahedral [CoSe] layers can be maintained with the varying occupancies of K. By inducing K vacancies in structure, tetragonality of the lattice for K1−xCo2Se2 increases with the shortened a and elongated c. The (CoSe4) tetrahedron is also compressed perpendicular to the c direction resulted from the K deficiency. X-ray absorption near-edge structure reveals that the valence state of Co is basically unaffected by K deficient with the absorption edge of Co K-edge unchanged. Concerning the physical properties, K vacancies increase the resistivity of metallic K1−xCo2Se2 due to the decreased charge transfer from K+ to [CoSe] layers. More importantly, the ferromagnetic interaction of K1−xCo2Se2 is unexpectedly weakened by raising K vacancies with the Curie temperature shifted from 80 to 52 K, despite the shortened Co-Co distance. First-principles calculation reveals that the spin polarization is weakened resulted from the K vacancies, mainly attributed to the reduced charge transfer from K+ to [CoSe] host. Our results clearly indicate the domination of transferred electrons from intermediate metal A on the magnetic interaction of ATM2X2, and also show the feasibility to regulate the structure and related properties of ATM2X2 by controlling the A content.

Strain- and carrier-tunable magnetic properties of a two-dimensional intrinsically ferromagnetic semiconductor: CoBr2 monolayer

The ${\mathrm{CoBr}}_{2}$ monolayer is predicted to be an intrinsically ferromagnetic (FM) semiconductor based on the first-principles calculations. The results of the magnetic anisotropy energy show that the ${\mathrm{CoBr}}_{2}$ monolayer has an easy magnetization plane and belongs to the family of two-dimensional $XY$ magnets. The exchange interactions and thus the magnetic properties can be effectively tuned by external strain and carrier doping. The biaxial tensile strain can induce FM-antiferromagnetic (AFM) phase transition in the ${\mathrm{CoBr}}_{2}$ monolayer, by which the Co-Br-Co bond angle is enlarged deviating far away from ${90}^{\ensuremath{\circ}}$. While the compressive strain stabilizes the FM state by reducing the nearest Co-Co distance and enhancing the $p\text{\ensuremath{-}}d$ hybridization between Co and Br atoms. The ${\mathrm{CoBr}}_{2}$ monolayer remains semiconducting for the whole range of strain investigated. For the carrier doping, however, the ${\mathrm{CoBr}}_{2}$ monolayer tends to be a half-metal for both hole and electron doping. Doping not only introduces itinerant carriers, but also enhances the $p\text{\ensuremath{-}}d$ hybridization between the Co and Br atoms, both of which enhance the FM coupling significantly. The tunability of the electronic and magnetic properties of ${\mathrm{CoBr}}_{2}$ monolayer makes it a promising candidate for future nanospintronic applications.

Crystal and Magnetic Structures of La2CoPtO6 Double Perovskite.

We investigated the crystal structure and magnetic structure in cobaltite-platinate double perovskite of La2CoPtO6, employing various techniques of X-ray diffraction, neutron diffraction, and the extended X-ray absorption fine structure analysis. It is shown that the crystal symmetry is maintained as P21/n in the temperature range of <500 °C, whereas the lattice constants and the Co–Co distances undergo a continuous structural evolution toward the high-symmetry phases with increasing temperature. The Co–O bonds were overall longer and had a larger degree of structural and thermal disorders than the Pt–O bonds. As for the magnetism, an antiferromagnetic order is stabilized in the Co2+ sublattice at temperatures below 28 K. It is demonstrated that owing to the substantial distortions (quantified by a distortion parameter Σ > 0.03 Å) of the Co–Co networks, the system is not subject to spin frustration effect. Details in the magnetic structure are determined; at 12 K, the Co magnetic moment was (0.8, 0, 2.7) Bohr magneton, the magnetic propagation vector was (−0.5, 0, 0.5), and the magnetic symmetry was preferably Γ1(Ag).

Electronic structure and spin dynamics of ACo2As2(A=Ba,Sr,Ca)

The electronic structures, charge and spin dynamics of the cobalt pnictide compounds ACo2As2 (A=Ba, Sr, Ca) in the paramagnetic state are investigated by using density functional theory combined with dynamical mean-field theory. In contrast to their iron counterparts, these cobalt pnictide compounds have three-dimensional electronic structures and strong ferromagnetic low-energy spin excitations. The Co 3d eg orbitals dominate the electronic states around the Fermi level and have stronger electronic correlation strength than the Co 3d t2g orbitals. The overall electronic correlation strength is much weaker than that in the iron arsenides, however, the most strongly correlated Co 3d x2-y2 orbital, especially in CaCo2As2, has electronic correlation strength comparable to Fe 3d t2g orbitals in iron arsenides. ACo2As2 (A=Ba, Sr, Ca) shows similar electronic structures where a conduction band of primarily Co 3d x2-y2 orbital character is close to a Van Hove singularity around the Brillouin-zone corner, which promotes ferromagnetic low-energy spin excitations. Originated from its increased nearest-neighbor Co-Co distance and significantly reduced As height from the Co plane, the strong electronic correlation strength and close proximity to the Van Hove singularity of the Co 3d x2-y2 orbital in CaCo2As2 is responsible for its unique A-type antiferromagnetic order observed in experiments. In comparison, despite substantial ferromagnetic low-energy spin excitations, BaCo2As2 and SrCo2As2 remain paramagnetic down to very low temperature because the Co 3d x2-y2 orbital has weaker electronic correlation strength and is further away from the Van Hove singularity.

Important Role of Intermolecular Interaction in Cobalt(II) Single-Ion Magnet from Single Slow Relaxation to Double Slow Relaxation.

Two cobalt complexes with similar structures were synthesized using quinoline-2-carboxylic acid (HL) as the ligand. Both complexes are six-coordinated in antitriangular prism coordination geometries. There are one and four molecule units per cell for 1 and 2, respectively, with nearest Co-Co distances of 7.129 and 5.855 Å, respectively, which lead to their intermolecular interactions zj'. Both complexes are field-induced single-ion magnets. Complex 1 shows single slow relaxation under Hdc = 1.5 kOe attributed to the moment reversal, while complex 2 shows double slow relaxation resulting from intermolecular dipolar interaction and moment reversal, respectively.

Role of oxygen vacancy in the spin-state change and magnetic ordering in SrCoO3−δ

We present the first-principles investigation of the structural, electronic, and magnetic properties of SrCoO$_{3-\delta}$ ($\delta=0, 0.25, 0.5$) to understand the multivalent nature of Co ions in SrCoO$_{3-\delta}$ along the line of topotactic transition between perovskite SrCoO$_{3}$ and brownmillerite SrCoO$_{2.5}$. From the on-site Coulomb interaction $U$-dependent ground state of stoichiometric SrCoO$_{3}$, we show the proximity of its metallic ferromagnetic ground state to other antiferromagnetic states. The structural and magnetic properties of SrCoO$_{3-\delta}$ depending on their oxygen-content provide an interesting insight into the relationship between the Co-Co distances and the magnetic couplings so that the spin-state transition of Co spins can understood by the change of $pd$-hybridization depending on the Co-Co distances. The \emph{strong} suppression of the $dp\sigma$-hybridization between Co $d$ and O $p$ orbitals in brownmillerite SrCoO$_{2.5}$ brings on the high-spin state of Co$^{3+}$ $d^{6}$ and is responsible for the antiferromagnetically ordered insulating ground state. The increase of effective Co-Co distances driven by the presence of oxygen vacancies in SrCoO$_{3-\delta}$ is consistent with the reduction of the effective $pd$-hybridization between Co $d$ and O $p$ orbitals. We conclude that the configuration of neighboring Co spins is shown to be crucial to their local electronic structure near the metal-to-insulator transition along the line of the topotactic transition in SrCoO$_{3-\delta}$. Incidentally, we also find that the \textit{I2mb} symmetry of SrCoO$_{2.5}$ is energetically stable and exhibits ferroelectricity via the ordering of CoO$_{4}$ tetrahedra, where this polar lattice can be stabilized by the presence of a large activation barrier.

Identification of binuclear Co2N5 active sites for oxygen reduction reaction with more than one magnitude higher activity than single atom CoN4 site

Herein, a novel binuclear active site structure, Co2NxCy, is intentionally designed and successfully fabricated to efficiently catalyze the oxygen reduction reaction (ORR), which is achieved by precisely controlling the atomic scale structure of bimetal-organic frameworks before pyrolysis. Through discovering a two-atom site with Co-Co distance at 2.1–2.2 Å from aberration-corrected scanning transmission electron microscopy (STEM), as well as a novel shortened Co-Co path (2.12 Å) from the X-ray absorption spectroscopy, we for the first time identified the binuclear Co2NX site in the pyrolyzed catalyst. Combined with density functional theory (DFT) calculation, the structure is further confirmed as Co2N5. Excitingly, the Co2N5 site performs approximately 12 times higher activity than the conventional CoN4 site and the corresponding catalyst shows unprecedented catalytic activity in acidic electrolyte with half-wave potential of 0.79 V, approaching the commercial Pt/C catalyst and presenting the best one among the Co-N-C catalysts. Theoretical density functional theory calculations reveal that the novel binuclear site exhibits considerably reduced thermodynamic barrier towards ORR, thus contributing to the much higher intrinsic activity. Our finding opens up a new path to design efficient M-Nx/C catalysts, thus pushing the fuel cell industry field one step ahead.