As low-cost electrocatalysts for oxygen reduction reaction applied to fuel cells and metal-air batteries, atomic-dispersed transition metal-nitrogen-carbon materials are emerging, but the genuine mechanism thereof is still arguable. Herein, by rational design and synthesis of dual-metal atomically dispersed Fe,Mn/N-C catalyst as model object, we unravel that the O2 reduction preferentially takes place on FeIII in the FeN4 /C system with intermediate spin state which possesses one eg electron (t2g4eg1) readily penetrating the antibonding π-orbital of oxygen. Both magnetic measurements and theoretical calculation reveal that the adjacent atomically dispersed Mn-N moieties can effectively activate the FeIII sites by both spin-state transition and electronic modulation, rendering the excellent ORR performances of Fe,Mn/N-C in both alkaline and acidic media (halfwave positionals are 0.928 V in 0.1 M KOH, and 0.804 V in 0.1 M HClO4), and good durability, which outperforms and has almost the same activity of commercial Pt/C, respectively. In addition, it presents a superior power density of 160.8 mW cm−2 and long-term durability in reversible zinc–air batteries. The work brings new insight into the oxygen reduction reaction process on the metal-nitrogen-carbon active sites, undoubtedly leading the exploration towards high effective low-cost non-precious catalysts.

Precise tuning of the chemical environment of neighboring atomic FeN 4 sites is extremely important for optimizing Fe−N−C catalysts to produce the fast oxygen reduction reaction (ORR) kinetics both in acidic and alkaline media, but it is actually very challenging. Heteroatoms could affect the metal charge of the active center through long-range electron delocalization; however, there are a few studies on it. Herein, density functional theory (DFT) calculations demonstrate that the addition of long-range P into edge-type FeN 4 can drive the electron delocalization and decrease the band gap of the FeN 4 center, leading to a substantial decrease in the free energy barrier to direct four-electron ORR kinetics compared to P-free edge-type FeN 4 , indicating superior intrinsic ORR activity. Experimentally, by incorporating P in edge-rich FeN 4 supported on N,P-doped carbon (Fe−N−C−P/N,P−C), the created Fe−N−C catalyst presents the greatly increased acidic ORR activity, with a half-wave potential (E 1/2 ) of 0.80 V (vs a reversible hydrogen electrode), which approaches that of commercial Pt/C and also has a high half-wave potential of 0.87 V, beyond Pt/C for alkaline ORR. In addition, it shows higher proton exchange membrane fuel cell and Zn-air battery performances than the pristine Fe−C−N catalyst (Fe−N−C/ N−C). This work will guide the rational design of highly active metal atomic scale catalysts with optimized chemical surroundings in terms of P incorporation as a chemically tunable method.

A three dimensional (3D) porous framework-like N-doped carbon (PFNC) with a high specific surface area was successfully fabricated through ammonia doping and graphitization based on pomelo peel. The obtained PFNC exhibits an enhanced specific capacitance (260 F g(-1) at 1 A g(-1)) and superior cycling performance (capacitance retention of 84.2% after 10000 cycles at 10 A g(-1)) on account of numerous voids and pores which supply sufficient pathways for ion diffusion during cycling. Furthermore, a fabricated asymmetric PFNC//PFN device based on PFNC and porous flake-like NiO (PFN) arrays achieves a specific capacitance of 88.8 F g(-1) at 0.4 A g(-1) and an energy density of 27.75 Wh kg(-1) at a power density of 300 W kg(-1) and still retains 44 F g(-1) at 10 A g(-1) and 13.75 Wh kg(-1) at power density of 7500 W kg(-1). It is important that the device is able to supply two light-emitting diodes for 25 min, which demonstrates great application potential.

Understanding the relationship between the electronic state of active sites and N 2 reduction reaction (NRR) performance is essential to explore efficient electrocatalysts. Herein, atomically dispersed Fe and Mo sites are designed and achieved in the form of well-defined FeN 4 and MoN 4 coordination in polyphthalocyanine (PPc) organic framework to investigate the influence of the spin state of FeN 4 on NRR behavior. The neighboring MoN 4 can regulate the spin state of Fe center in FeN 4 from high-spin (d xy 2 d yz 1 d xz 1 d z 2 1 d x 2 −y 2 1 ) to medium-spin (d xy 2 d yz 2 d xz 1 d z 2 1 ), where the empty d orbitals and separate d electron favor the overlap of Fe 3d with the N 2p orbitals, more effectively activating N≡N triple bond. Theoretical modeling suggests that the NRR preferably takes place on FeN 4 instead of MoN 4 , and the transition of Fe spin state significantly lowers the energy barrier of the potential determining step, which is conducive to the first hydrogenation of N 2 . As a result, FeMoPPc with medium-spin FeN 4 exhibits 2.0 and 9.0 times higher Faradaic efficiency and 2.0 and 17.2 times higher NH 3 yields for NRR than FePPc with high-spin FeN 4 and MoPPc with MoN 4 , respectively. These new insights may open up opportunities for exploiting efficient NRR electrocatalysts by atomically regulating the spin state of metal centers.

Molybdenum trioxide (MoO 3 ) suffers from poor conductivity, a low rate capability, and unsatisfactory cycling stability in lithium-ion batteries. The aliovalent ion doping may present an effective way to improve the electrochemical performances of MoO 3 . Here, it is shown, by first-principle calculations, that doping MoO 3 with V by 12.5% can modulate significantly electronic structure and provide a small diffusion barrier for enhancing the electrochemical performance of MoO 3 . The ultralong Mo 0.88 V 0.12 O 2.94 nanostructures, which retain the h-MoO 3 structure and present an exceptionally high conductivity and fast ionic diffusion due to the substitution of V, facilitating lithiation/delithiation behavior, and induce a fine nanosized structure with a reduced volume change are prepared. As a result, the stress and strain are alleviated during the Li-ion intercalation/deintercalation processes, improving the cycling stability and rate capability. Such a large improvement in the electrochemical properties can be ascribed to the stabilizing effect of V, the small migration energy barrier, and short diffusion path, which arise from the introduction of V into MoO 3 . The unique engineering strategy and facile synthesis route open up a new avenue in modifying and developing other species of electrode materials.

The structure and chemical engineering of the solid electrolyte interphase (SEI) play a vital role in rechargeable batteries. The underlying correlation between the properties of the enhanced sodium (Na) ion...

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