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Guided by the mechanism exploration via the density functional theory (DFT) calculations, the chromium (Cr) doped CoFe 2 O 4 nanoflowers (Cr-CoFe 2 O 4) are designed and directly constructed on nickel foam as a bifunctional electrocatalyst for LOB, which can achieve low overpotential (0.48 V), high discharge capacity (22030 mA h g−1) and long-term cycling durability (over 500 cycles at 300 mA g−1). [Display omitted] Tailored electrocatalysts that can modulate their electronic structure are highly desirable to facilitate the reaction kinetics of oxygen evolution reaction (OER) and oxidation reduction reaction (ORR) in lithium-oxygen batteries (LOB). Although octahedron predominant inverse spinels (e.g., CoFe 2 O 4) have been proposed as promising candidates for catalytic reactions, their performance has remained unsatisfactory. Herein, the chromium (Cr) doped CoFe 2 O 4 nanoflowers (Cr-CoFe 2 O 4) are elaborately constructed on nickel foam as a bifunctional electrocatalyst that drastically improves the performance of LOB. The results show that the partially oxidized Cr6+ stabilizes the cobalt (Co) sites at high-valence and regulates the electronic structure of Co sites, facilitating the oxygen redox kinetics of LOB due to their strong electron-withdrawing capability. Moreover, DFT calculations and ultraviolet photoelectron spectrometer (UPS) results consistently demonstrate that Cr doping optimizes the e g electron filling state of the active octahedral Co sites, significantly improves the covalency of Co-O bonds, and enhances the degree of Co 3d-O 2p hybrids. As a result, Cr-CoFe 2 O 4 catalyzed LOB can achieve low overpotential (0.48 V), high discharge capacity (22030 mA h g−1) and long-term cycling durability (over 500 cycles at 300 mA g−1). This work promotes the oxygen redox reaction and accelerates the electron transfer between Co ions and oxygen-containing intermediates, highlighting the potential of Cr-CoFe 2 O 4 nanoflowers as bifunctional electrocatalysts for LOB. [ABSTRACT FROM AUTHOR]

Introduced orthorhombic and trigonal system into 0.5La 0.6 Sr 0.4 MnO 3 -0.5LaMn 0.6 Co 0.4 O 3 (LSMCO) by selectively incorporating Sr and Co cations into the LaMnO 3 framework during the sol-gel process, which is used to explore the relationship among crystal structure, electronic states and catalytic performance. [Display omitted] Sculpting crystal configurations can vastly affect the charge and orbital states of electrocatalysts, fundamentally determining the catalytic activity of lithium-oxygen (Li–O 2) batteries. However, the crucial role of crystal configurations in determining the electronic states has usually been neglected and needs to be further examined. Herein, we introduce orthorhombic and trigonal system into 0.5La 0.6 Sr 0.4 MnO 3 -0.5LaMn 0.6 Co 0.4 O 3 (LSMCO) by selectively incorporating Sr and Co cations into the LaMnO 3 framework during the sol-gel process, which is used to explore the relationship among crystal structure, electronic states and catalytic performance. Based on both experimental and theoretical calculations, the dual-crystal configurations induce strong lattice distortion, which promotes MnO 6 octahedra vibration and shortened Mn O bonds. Furthermore, the suppressed Jahn-Teller distortion weakens the orbital arrangement and accelerates the charge delocalization, leading to the conversion of Mn3+ to Mn4+ and optimized electronic states. Ultimately, this resulted in optimized Mn 3d and O 2p orbital hybridization and activated lattice oxygen function, leading to a significant improvement in electrocatalytic activity. The LSMCO catalyzed Li–O 2 battery achieves enhanced discharge capacity of 14498.7 mAh/g and cycling stability of 258 cycles. This work highlights the significance of inner structure and presents a feasible strategy for engineering crystal configurations to boost electrocatalysis of Li–O 2 batteries. [ABSTRACT FROM AUTHOR]

The upper shift of the d-band level of Fe active sites was realized by regulating electronic structure of NiFe 2 O 4 /MoS 2 heterostructure, fundamentally improving the electrocatalytic performance of NiFe 2 O 4 /MoS 2. [Display omitted] The electronic structure of cathode catalysts dominates the electrochemistry reaction kinetics in lithium-oxygen batteries. However, conventional catalysts perform inferior intrinsic activity due to the low d-band level of the active sites makes it difficult to bond with the reaction intermediates, which results in poor electrochemical performance of lithium-oxygen batteries. Herein, NiFe 2 O 4 /MoS 2 heterostructures are elaborately constructed to reach an electronic state balance for the active sites, which realizes the upper shift of the d-band level and enhanced adsorption of intermediates. Density functional theory calculation suggests that the d-band center of Fe active sites on the heterostructure moves toward the Fermi level, demonstrating the heterointerface engineering endows Fe active sites with high d-band level by the transfer and balance of electron. As a proof of concept, lithium-oxygen battery catalyzed by NiFe 2 O 4 /MoS 2 exhibits a large specific capacity of 21526 mA h g−1 and an extended cycle performance for 268 cycles. Moreover, NiFe 2 O 4 /MoS 2 with strong adsorption to intermediates promotes the uniform growth of discharge products, which is favor of the reversible decomposition during cycling. This work presents the energy band regulation of the active sites in heterostructure catalysts has great feasibility for enhancing catalytic activities. [ABSTRACT FROM AUTHOR]

• An amorphous lanthanum-nickel-iron based oxide/hydroxide (a-LNFO). • XAFS confirmed the edge- and face-shared octahedra in a-LNFO. • Randomly arranged terminal and bridging forms expose active sites. • Introducing Ni3+ is benefit to the favorable covalency of metal-oxygen bond. • The a-LNFO based Li-O 2 battery shows excellent electrochemical performance. Constructing well-designed catalysts by manipulating geometrical and electrical structures is regarded as effective strategies for high-performance lithium-oxygen chemistry. However, the high activity and stability of catalysts cannot be always realized simultaneously, which is apt to result in high overpotentials and poor cycling life. Herein, we elaborately construct an amorphous lanthanum-nickel-iron based oxide/hydroxide (a-LNFO) with mixed geometrical configurations of edge- and face-shared octahedra, which exhibits decent catalytic activity and excellent stability. The disordered structure endows randomly arranged terminal and bridging forms and ample oxygen vacancies, exposing massive active sites. Besides, the introduction of Ni3+ with e g orbital occupancy of 1 benefits to the favorable covalency of metal–oxygen bond, which results in the accelerated electron transport and appropriate bond strength between the catalyst and oxygen–containing intermediates, boosting the intrinsic activities toward oxygen evolution reaction and oxygen reduction reaction. Confirmed by X-ray absorption fine structure, short distance between distorted octahedra centers (Ni and Fe cations) reduces the reaction paths and induces strong electrostatic interactions, efficiently accelerating the reaction kinetics. Simultaneously, increased couples of metal-oxygen bonds in edge- and face-shared octahedra ensure the splendid stability. As a proof of concept, the a-LNFO catalyzed lithium-oxygen battery achieves a high specific discharge capacity of 13,617 mAh/g and superior cycling stability of 435 cycles. This work reveals the positive effect of geometrical configuration transformation from corner-shared octahedra to edge- and face-shared octahedra, which provides a feasible strategy for activating oxygen electrode reactions. [ABSTRACT FROM AUTHOR]