Multiple Electronic Phase Transitions of NiO via Manipulating the NiO6 Octahedron and Valence Control

While the multiple Mottronic and electronic phase transitions as recently discovered in nickelates (e.g., ReNiO₃) open up a new paradigm in correlated electronic applications, these applications are largely impeded by the intrinsic material metastability of the perovskite nickelates. Herein, the study demonstrates the analogous multiple electronic phase transition properties in the thermodynamically stable NiO, compared to ReNiO₃, from both perspectives of band gap regulation and orbital filling regulation. The adjustment in band gap of NiO with t_2g⁶e_g² orbital configuration is achieved via establishing biaxial tensile or compressive interfacial strains that increase or reduce the material resistivity, respectively. The relaxor ferroelectricity of 0.7Pb(Mg_2/3Nb_1/3)O₃-0.3PbTiO₃ (PMNPT) further enables an electric field adjustable resistance switch (ΔR/R) within NiO/PMNPT heterostructure with higher performances (e.g., ΔR/R of 82% upon a bias voltage of 20 V) than the reported oxides/PMNPT heterostructure. Furthermore, the magnitude in resistance switch of the tensile strained NiO via hydrogenation associated Mottronic process reaches ≈10¹¹ that exceeds the previously reported ones. This study highlights the higher material stability and easier growth of NiO, compared to ReNiO₃, with analogous multiple Mottronic and electronic phase transition properties that pave the way to its practical applications in correlated electronics.     

Single‐Phase Mixed Transition Metal Carbonate Encapsulated by Graphene: Facile Synthesis and Improved Lithium Storage Properties

Transition metal carbonates (TMCs) with complex composition and robust hybrid structure hold great potential as high‐performance electrode materials for lithium‐ion batteries (LIBs). However, poor ionic/electronic conductivities and large volume changes of TMCs during lithiation/delithiation processes have hindered their applications. Herein, single‐phase Mn? Co mixed carbonate composites encapsulated by reduced graphene oxide (Mn_xCo_1?xCO₃/RGO), in which Mn and Co species are distributed randomly in one crystal structure, are successfully synthesized through a facial liquid‐state method. When evaluated as LIB anodes, the Mn_xCo_1?xCO₃/RGO composites exhibit enhanced electrochemical performance compared with the reference CoCO₃/RGO and MnCO₃/RGO. Specifically, the Mn_0.7Co_0.3CO₃/RGO delivers an ultrahigh capacity of 1454 mA h g^?1 after 130 cycles at 100 mA g^?1 and exhibits an ultralong cycling stability (901 mA h g^?1 after 1500 cycles at 2000 mA g^?1). This is the best lithium storage performance among carbonate‐based anodes reported up to date. Such superb performance is attributed to the hybrid structure and enhanced electroconductivity due to the integration of Co and Mn into one crystal structure, which is complemented by electrochemical impedance spectroscopy and density functional theory calculations. The facile synthesis, promising electrochemical results, and scientific understanding of the Mn_xCo_1?xCO₃/RGO provides a design principle and encourages more research on TMCs‐based electrodes.     

Synthesis of Self‐Supported Ordered Mesoporous Cobalt and Chromium Nitrides

Herein, we demonstrate an ammonia nitridation approach to synthesize self‐supported ordered mesoporous metal nitrides (CoN and CrN) from mesostructured metal oxide replicas (Co₃O₄ and Cr₂O₃), which were nanocastly prepared by using mesoporous silica SBA‐15 as a hard template. Two synthetic routes are adopted. One route is the direct nitridation of mesoporous metal oxide nanowire replicas templated from SBA‐15 to metal nitrides. By this method, highly ordered mesoporous cobalt nitrides (CoN) can be obtained by the transformation of Co₃O₄ nanowire replica under ammonia atmosphere from 275 to 350 °C, without a distinct lose of the mesostructural regularity. Treating the samples above 375 °C leads to the formation of metallic cobalt and the collapse of the mesostructure due to large volume shrinkage. The other route is to transform mesostructured metal oxides/silica composites to nitrides/silica composites at 750–1000 °C under ammonia. Ordered mesoporous CrN nanowire arrays can be obtained after the silica template removal by NaOH erosion. A slowly temperature‐program‐decrease process can reduce the influence of silica nitridation and improve the purity of final CrN product. Small‐angle XRD patterns and TEM images showed the 2‐D ordered hexagonal structure of the obtained mesoporous CoN and CrN nanowires. Wide‐angle XRD patterns, HRTEM images, and SAED patterns revealed the formation of crystallized metal nitrides. Nitrogen sorption analyses showed that the obtained materials possessed high surface areas (70–90 m² g^?1) and large pore volumes (about 0.2 cm³ g^?1).     

Understanding the Structural Evolution and Redox Mechanism of a NaFeO2–NaCoO2 Solid Solution for Sodium‐Ion Batteries

Na‐ion batteries have become promising candidates for large‐scale energy‐storage systems because of the abundant Na resources and they have attracted considerable academic interest because of their unique behavior, such as their electrochemical activity for the Fe³⁺/Fe⁴⁺ redox couple. The high‐rate performance derived from the low Lewis‐acidity of the Na⁺ ions is another advantage of Na‐ion batteries and has been demonstrated in NaFe_1/2Co_1/2O₂ solutions. Here, a solid solution of NaFeO₂‐NaCoO₂ is synthesized and the mechanisms behind their excellent electrochemical performance are studied in comparison to those of their respective end‐members. The combined analysis of operando X‐ray diffraction, ex situ X‐ray absorption spectroscopy, and density functional theory (DFT) calculations for Na_{1– x} Fe_1/2Co_1/2O₂ reveals that the O3‐type phase transforms into a P3‐type phase coupled with Na⁺/vacancy ordering, which has not been observed in O3‐type NaFeO₂. The substitution of Co for Fe stabilizes the P3‐type phase formed by sodium extraction and could suppress the irreversible structural change that is usually observed in O3‐type NaFeO₂, resulting in a better cycle retention and higher rate performance. Although no ordering of the transition metal ions is seen in the neutron diffraction experiments, as supported by Monte‐Carlo simulations, the formation of a superlattice originating from the Na⁺/vacancy ordering is found by synchrotron X‐ray diffraction for Na_0.5Fe_1/2Co_1/2O₂, which may involve a potential step in the charge/discharge profiles.     

AC conductivity of nanoparticles CoxFe(1−x)Fe2O4 (x=0, 0.25 and 1) ferrites

Nanoparticles of Co_xFe_(1−x)Fe₂O₄ (x=0, 0.25 and 1) were prepared by the chemical co-precipitation method. X-ray diffraction and scanning electron microscopy were used to determine the average particle size and morphology of the prepared samples. AC conductivity is found to vary as ω^s in the frequency range 42–5×10⁶ Hz. The impedance analysis reveals that low conductivity and high impedance values are observed at low temperatures. The Nyquist impedance plots of the present investigation clearly depict the inherent phenomenon involved in the conduction mechanism of Co doped Fe₃O₄ ferrites. Regarding frequency dependence of Co_xFe_(1−x)Fe₂O₄ AC conductivity the observed behavior clearly indicates that the present ferrites are semiconductor-like.     

Synthesis and Thermoelectric Properties of InzCo4?xFexSb12 Skutterudites

The thermoelectric properties of In-filled and Fe-doped CoSb₃ (In _z Co_4−x - Fe _x Sb₁₂) skutterudites prepared by encapsulated induction melting were examined. A single δ-phase was obtained successfully by subsequent annealing at 823 K for 120 h. The Hall and Seebeck coefficients of the In _z Co_4−x Fe _x Sb₁₂ samples had positive signs, indicating p-type conduction. The electrical conductivity was increased by Fe doping, and the thermal conductivity was decreased by In filling due to phonon scattering. The thermoelectric properties were improved by In filling and Fe doping, and were closely related to the optimum carrier concentration and phonon scattering.     

Combined First‐Principle Calculations and Experimental Study on Multi‐Component Olivine Cathode for Lithium Rechargeable Batteries

The electrochemical properties and phase stability of the multi‐component olivine compound LiMn_1/3Fe_1/3Co_1/3PO₄ are studied experimentally and with first‐principles calculation. The formation of a solid solution between LiMnPO₄, LiFePO₄, and LiCoPO₄ at this composition is confirmed by XRD patterns and the calculated energy. The experimental and first‐principle results indicate that there are three distinct regions in the electrochemical profile at quasi‐open‐circuit potentials of ～3.5 V, ～4.1 V, and ～4.7 V, which are attributed to Fe³⁺/Fe²⁺, Mn³⁺/Mn²⁺, and Co³⁺/Co²⁺ redox couples, respectively. However, exceptionally large polarization is observed only for the region near 4.1 V of Mn³⁺/Mn²⁺ redox couples, implying an intrinsic charge transfer problem. An ex situ XRD study reveals that the reversible one‐phase reaction of Li extraction/insertion mechanism prevails, unexpectedly, for all lithium compositions of Li_xMn_1/3Fe_1/3Co_1/3PO₄ (0 ≤ x ≤ 1) at room temperature. This is the first demonstration that the well‐ordered, non‐nanocrystalline (less than 1% Li–M disorder and a few hundred nanometer size particle) olivine electrode can be operated solely in a one‐phase mode.     

Thermoelectric Properties of Heavy Rare Earth Filled Skutterudites Dy y Fe x Co4?x Sb12

Heavy rare earth element Dy-filled skutterudites (Dy _y Fe _x Co_4?x Sb₁₂) have been synthesized by a melting–quenching–annealing method and sintered by the spark plasma sintering technique. Our results suggest that single-phased Dy _y Fe _x Co_4?x Sb₁₂ compounds could be obtained when the Fe content is less than 1.5. The maximum filling fraction of Dy in skutterudites increases with increasing Fe content. We also found significant lattice expansion induced by Fe substitution at Co sites and Dy filling in the voids. The electrical conductivity, Seebeck coefficient, and thermal conductivity have been measured in the temperature range from 300?K to 800?K. The low-temperature Hall coefficient and carrier mobility are reported in the temperature range from 2.5?K to 300?K. The power factor for Dy _y Fe _x Co_4?x Sb₁₂ increases with increasing Fe content. A significant reduction in lattice thermal conductivity is observed in heavy rare earth element Dy-filled skutterudites due to the low localized vibrational frequency of Dy that effectively scatters low-frequency lattice phonons. The sample with composition Dy_0.41Fe_1.45Co_2.55Sb_12.28 has lattice thermal conductivity as low as 1.05?W?m^?1?K^?1 at room temperature. The thermoelectric figure of merit (ZT) reaches a maximum value of 0.67 at 750?K.     

Ultrathin‐Nanosheet‐Induced Synthesis of 3D Transition Metal Oxides Networks for Lithium Ion Battery Anodes

A general ultrathin‐nanosheet‐induced strategy for producing a 3D mesoporous network of Co₃O₄ is reported. The fabrication process introduces a 3D N‐doped carbon network to adsorb metal cobalt ions via dipping process. Then, this carbon matrix serves as the sacrificed template, whose N‐doping effect and ultrathin nanosheet features play critical roles for controlling the formation of Co₃O₄ networks. The obtained material exhibits a 3D interconnected architecture with large specific surface area and abundant mesopores, which is constructed by nanoparticles. Merited by the optimized structure in three length scales of nanoparticles–mesopores–networks, this Co₃O₄ nanostructure possesses superior performance as a LIB anode: high capacity (1033 mAh g^?1 at 0.1 A g^?1) and long‐life stability (700 cycles at 5 A g^?1). Moreover, this strategy is verified to be effective for producing other transition metal oxides, including Fe₂O₃, ZnO, Mn₃O₄, NiCo₂O₄, and CoFe₂O₄.     

Electrical Detection and Magnetic Imaging of Stabilized Magnetic Skyrmions in Fe1−xCoxGe (x < 0.1) Microplates

Magnetic skyrmions are topologically protected spin textures that are being investigated for their potential use in next generation magnetic storage devices. Here, magnetic skyrmions and other magnetic phases in Fe_1?xCo_xGe (x < 0.1) microplates (MPLs) newly synthesized via chemical vapor deposition are studied using both magnetic imaging and transport measurements. Lorentz transmission electron microscopy reveals a stabilized magnetic skyrmion phase near room temperature (≈280 K) and a quenched metastable skyrmion lattice via field cooling. Magnetoresistance (MR) measurements in three different configurations reveal a unique anomalous MR signal at temperatures below 200 K and two distinct field dependent magnetic transitions. The topological Hall effect (THE), known as the electronic signature of magnetic skyrmion phase, is detected for the first time in a Fe_1?xCo_xGe nanostructure, with a large and positive peak THE resistivity of ≈32 nΩ cm at 260 K. This large magnitude is attributed to both nanostructuring and decreased carrier concentrations due to Co alloying of the Fe_1?xCo_xGe MPL. A consistent magnetic phase diagram summarized from both the magnetic imaging and transport measurements shows that the magnetic skyrmions are stabilized in Fe_1?xCo_xGe MPLs compared to bulk materials. This study lays the foundation for future skyrmion‐based nanodevices in information storage technologies.     

Synthesis and Characterization of 2D Molybdenum Carbide (MXene)

Large scale synthesis and delamination of 2D Mo₂CT _x (where T is a surface termination group) has been achieved by selectively etching gallium from the recently discovered nanolaminated, ternary transition metal carbide Mo₂Ga₂C. Different synthesis and delamination routes result in different flake morphologies. The resistivity of free‐standing Mo₂CT _x films increases by an order of magnitude as the temperature is reduced from 300 to 10 K, suggesting semiconductor‐like behavior of this MXene, in contrast to Ti₃C₂T _x which exhibits metallic behavior. At 10 K, the magnetoresistance is positive. Additionally, changes in electronic transport are observed upon annealing of the films. When 2 μm thick films are tested as electrodes in supercapacitors, capacitances as high as 700 F cm^?3 in a 1 m sulfuric acid electrolyte and high capacity retention for at least 10,000 cycles at 10 A g^?1 are obtained. Free‐standing Mo₂CT _x films, with ≈8 wt% carbon nanotubes, perform well when tested as an electrode material for Li‐ions, especially at high rates. At 20 and 131 C cycling rates, stable reversible capacities of 250 and 76 mAh g^?1, respectively, are achieved for over 1000 cycles.     

Novel Multi‐functional Mixed‐oxide Catalysts for Effective NOx Capture,Decomposition, and Reduction

In this paper, novel multi‐functional mixed‐oxide catalysts have been rationally designed and developed for the effective abatement of NO_x. Ca_xCo_{3 – x}Al hydrotalcite‐like compounds (where x = 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0) are first synthesized by co‐precipitation and calcined at 800 °C for 4 h in air to derive the mixed oxides. The resultant mixed oxides are generally of spinel phase, where the CaO phase is segregated when x ≥ 2.5. It has subsequently been found that the derived oxides are catalytically multi‐functional for NO_x decomposition, capture, and reduction. For example, the mixed Ca₂Co₁Al₁‐oxide can decompose 55 % NO at 300 °C in 8 % oxygen, completely trap NO for 750 s, and capture 12.88 and 18.06 mg g^–1 NO within 30 and 60 min, respectively. The catalytic activities of the Ca₂Co₁Al₁‐oxide catalyst have been further improved by incorporating La to form a quaternary catalyst Ca₂Co₁La_0.1Al_0.9‐oxide. This catalyst significantly enhances the NO decomposition to 75 %, extends the complete trapping time to 1100 s, and captures more NO at 300 °C in 8 % O₂ (19.02 mg g^–1 NO within 60 min). The in‐situ IR spectra of the catalysts with adsorbed NO indicates that the major nitrogen species formed on the catalysts are various kinds of nitrites and nitrates, which can be readily reduced by H₂ within 6 min at 350 °C. Therefore, the excellent catalytic activity of layered double hydroxide (LDH)‐based mixed oxides for NO decomposition, storage, and reduction can be achieved by the elegant combination of normal transition metals.     

Modifying Electronic Structure of Cation-Exchanged Bimetallic Sulfide/Metal Oxide Heterostructure through In Situ Inclusion of Silver (Ag) Nanoparticles for Extrinsic Pseudocapacitor

The inferior electrical conductivity of conventional electrodes and their slow charge transport impose limitations on the electrochemical performance of supercapacitors (SCs) using those electrodes, necessitating strategies to overcome the limitations. An in situ Ag ion-incorporated cation-exchanged bimetallic sulfide/metal oxide heterostructure (Ag-Co_9-xFe_xS₈@α-Fe_xO_y) is synthesized using a two-step hydrothermal method. The coordination bond formation and Ag nanoparticle (NP) incorporation improve the electrical conductivity and adhesion of the heterostructure and reduce its interface resistance and volume expansion throughout the charge/discharge cycles. Density functional theory investigations indicate that the remarkable interlayer and interparticle conductivities of the heterostructure resulting from Ag doping have changed its electronic states, leading to an enhanced electrical conductivity. The optimized electrode has an excellent specific capacity (213.6 mA h g⁻¹ at 1 A g⁻¹) and can maintain 93.2% capacity retention with excellent Coulombic efficiency over 20 000 charge/discharge cycles. A flexible solid-state extrinsic pseudocapacitor (EPSC) is fabricated using Ag-Co_9-xFe_xS₈@α-Fe_xO_y and Ti₃C₂T_X electrodes. The EPSC has specific and volumetric capacitances of 259 F g⁻¹ and 2.7 F cm⁻³ at 0.7 A g⁻¹, respectively, an energy density of 80.9 Wh kg⁻¹ at 525 W kg⁻¹, and a capacity retention of 92.8% over 5000 charge/discharge cycles.     

Ferroelectric and Magnetic Properties in Room‐Temperature Multiferroic GaxFe2−xO3 Epitaxial Thin Films

GaFeO₃‐type iron oxide is a promising room‐temperature multiferroic material due to its large magnetization. To expand its usability, controlling the ferroelectric and magnetic properties is crucial. In this study, high‐quality Ga_xFe_2–xO₃ (x = 0–1) epitaxial films are fabricated and their properties are systematically investigated. All films exhibit room‐temperature out‐of‐plane ferroelectricity, showing that the coercive electric field (E_c) decreases monotonically with x. Additionally, the films show in‐plane ferrimagnetism with a Curie temperature (T_C) >350 K at x = 0–0.6. The coercive magnetic field (H_c) decreases with x at x ≤ 0.6, but shows a constant value at x > 0.6, whereas the saturated magnetization (M_s) increases with x at x ≤ 0.6, but decreases with x at x > 0.6. X‐ray magnetic circular dichroism reveals that the large magnetization at x = 0.6 is derived from Fe³⁺ (3d⁵) at octahedral sites. The controllable range of the E_c, H_c, and M_s values at room temperature (400–800 kV cm^?1, 1–8 kOe, and 0.2–0.6 µ_B/f.u.) is very wide and differs from those of well‐known multiferroic BiFeO₃. Furthermore, the Ga_xFe_2?xO₃ films exhibit room‐temperature magnetocapacitance effects, indicating that adjusting T_C near room temperature is useful to achieve large room‐temperature magnetocapacitance behavior.     

A High‐Performance Binary Ni–Co Hydroxide‐based Water Oxidation Electrode with Three‐Dimensional Coaxial Nanotube Array Structure

Developing nanostructured Ni and Co oxides with a small overpotential and fast kinetics of the oxygen evolution reaction (OER) have drawn considerable attention recently because their theoretically high efficiency, high abundance, low cost, and environmental benignity in comparison with precious metal oxides, such as RuO₂ and IrO₂. However, how to increase the specific activity area and improve their poor intrinsic conductivity is still challenging, which significantly limits the overall OER rate and largely prevent their utilization. Thus, developing effective OER electrocatalysts with abundant active sites and high electrical conductivity still remains urgent. In this work, a scrupulous design of OER electrode with a unique sandwich‐like coaxial structure of the three‐dimensional Ni@[Ni^(2+/3+)Co₂(OH)_6–7]_x nanotube arrays (3D NNCNTAs) is reported. A Ni nanotube array with open end is homogeneous coated with Ni and Co co‐hydroxide nanosheets ([Ni^(2+/3+)Co₂(OH)_6–7]_x) and is employed as multifunctional interlayer to provide a large surface area and fast electron transport and support the outermost [Ni^(2+/3+)Co₂(OH)_6–7]_x layer. The remarkable features of high surface area, enhanced electron transport, and synergistic effects have greatly assured excellent OER activity with a small overpotential of 0.46 V at the current density of 10 mA cm^?2 and high stability.     

Phase-Modulation of Iron/Nickel Phosphides Nanocrystals “Armored” with Porous P-Doped Carbon and Anchored on P-Doped Graphene Nanohybrids for Enhanced Overall Water Splitting

Transition metal phosphides (TMPs) nanostructures have emerged as important electroactive materials for energy storage and conversion. Nonetheless, the phase modulation of iron/nickel phosphides nanocrystals or related nanohybrids remains challenging, and their electrocatalytic overall water splitting (OWS) performances are not fully investigated. Here, the phase-controlled synthesis of iron/nickel phosphides nanocrystals “armored” with porous P-doped carbon (PC) and anchored on P-doped graphene (PG) nanohybrids, including FeP–Fe₂P@PC/PG, FeP–(Ni_xFe_1-x)₂P@PC/PG, (Ni_xFe_1-x)₂P@PC/PG, and Ni₂P@PC/PG, are realized by thermal conversion of predesigned supramolecular gels under Ar/H₂ atmosphere and tuning Fe/Ni ratio in gel precursors. Thanks to phase-modulation-induced increase of available catalytic active sites and optimization of surface/interface electronic structures, the resultant pure-phase (Ni_xFe_1-x)₂P@PC/PG exhibits the highest electrocatalytic activity for both hydrogen and oxygen evolution in alkaline media. Remarkably, using it as a bifunctional catalyst, the fabricated (Ni_xFe_1-x)₂P@PC/PG || (Ni_xFe_1-x)₂P@PC/PG electrolyzer needs exceptional low cell voltage (1.45 V) to reach 10 mA cm⁻² water-splitting current, outperforming its mixed phase and monometallic phosphides counterparts and recently reported bifunctional catalysts based devices, and Pt/C || IrO₂ electrolyzer. Also, such (Ni_xFe_1-x)₂P@PC/PG || (Ni_xFe_1-x)₂P@PC/PG device manifests outstanding durability for OWS. This work may shed light on optimizing TMPs nanostructures by combining phase-modulation and heteroatoms-doped carbon double-confinement strategies, and accelerate their applications in OWS or other renewable energy options.     

Bimetal–Organic Framework: One‐Step Homogenous Formation and its Derived Mesoporous Ternary Metal Oxide Nanorod for High‐Capacity,High‐Rate,and Long‐Cycle‐Life Lithium Storage

Metal–organic frameworks (MOFs) and relative structures with uniform micro/mesoporous structures have shown important applications in various fields. This paper reports the synthesis of unprecedented mesoporous Ni_xCo_3?xO₄ nanorods with tuned composition from the Co/Ni bimetallic MOF precursor. The Co/Ni‐MOFs are prepared by a one‐step facile microwave‐assisted solvothermal method rather than surface metallic cation exchange on the preformed one‐metal MOF template, therefore displaying very uniform distribution of two species and high structural integrity. The obtained mesoporous Ni_0.3Co_2.7O₄ nanorod delivers a larger‐than‐theoretical reversible capacity of 1410 mAh g^?1 after 200 repetitive cycles at a small current of 100 mA g^?1 with an excellent high‐rate capability for lithium‐ion batteries. Large reversible capacities of 812 and 656 mAh g^?1 can also be retained after 500 cycles at large currents of 2 and 5 A g^?1, respectively. These outstanding electrochemical performances of the ternary metal oxide have been mainly attributed to its interconnected nanoparticle‐integrated mesoporous nanorod structure and the synergistic effect of two active metal oxide components.     

Anchoring Polysulfides and Accelerating Redox Reaction Enabled by Fe-Based Compounds in Lithium–Sulfur Batteries

The synergetic mechanism of chemisorption and catalysis play an important role in developing high-performance lithium–sulfur (Li–S) batteries. Herein, a 3D lather-like porous carbon framework containing Fe-based compounds (including Fe₃C, Fe₃O₄, and Fe₂O₃), named FeCFeOC, is designed as the sulfur host and the interlayer on separator. Due to the strong chemisorption and catalytic ability of FeCFeOC composite, the soluble lithium polysulfides (LiPSs) are first adsorbed and anchored on the surface of the FeCFeOC composite and then are catalyzed to accelerate their conversion reaction. In addition, the Fe_xO_y in Fe-based compounds can spontaneously react with LiPSs to form magnetic FeS_x species with a larger size, further blocking the penetration of LiPSs cross the separator. As a result, the assembled Li–S cells show excellent long-term stability (748 mAh g⁻¹ over 500 cycles at 1.0 C, and ≈0.036% decay per cycle for 1000 cycles at 3.0 C), a superb rate capability with 659 mAh g⁻¹ at 5.0 C, and lower electrochemical polarization. This work introduces a feasible strategy to anchor and accelerate the conversion of LiPSs by designing the multifunctional Fe-based compounds with high chemisorption and catalytic activity, which advances the large-scale application of high-performance Li–S batteries.     

Synthetic Routes and Formation Mechanisms of Spherical Boron Nitride Nanoparticles

A new concept is proposed to explain the formation of spherical boron nitride (BN) nanoparticles synthesized by the chemical vapor deposition (CVD) reaction of trimethoxyborane (B(OMe)₃) with ammonia. The intermediate phases formed during the CVD under different reaction conditions are analyzed by X‐ray diffraction, electron microscopy, thermogravimetry, and spectroscopy techniques. The transition mechanism from an intermediate B(OMe)_3–xH_3–xN (x < 2) phase having single B? N bonds to the BN nanoparticles is elucidated. This particularly emphasizes the CVD temperature effect governing the conversion of the N? H···O? B hydrogen bonds in (OMe)₃B · NH₃ into the N? B bonds in B(OMe)_3–xH_3–xN. The spherical morphology strongly depends on the remnant impurity oxygen formed upon Me₂O group elimination in the intermediate. Two types of spherical BN nanoparticles primarily attractive for immediate commercialization (with C and H impurities at a level less than 1 wt %) are synthesized by the adjustment of experimental parameters: high oxygen‐containing (～6.3 wt %) BN spheres with a diameter of ～90 nm and a specific surface area of 26.8 m² g^?1; and low oxygen‐containing (<1 wt %) BN spheres with a diameter of ～30 nm and a surface area of 52.7 m² g^?1. Finally, the regarded synthetic techniques are fully optimized in the present work.     

Lithiation‐Induced Vacancy Engineering of Co3O4 with Improved Faradic Reactivity for High‐Performance Supercapacitor

Transition metal oxides are promising electrode candidates for supercapacitor because of their low cost, high theoretical capacity, and good reversibility. However, intrinsically poor electrical conductivity and sluggish reaction kinetics of these oxides normally lead to low specific capacity and slow rate capability of the devices. Herein, a commonly used cobalt oxide is used as an example to demonstrate that lithiation process as a new strategy to enhance its electrochemical performance for supercapacitor application. Detailed characterization reveals that electrochemical lithiation of Co₃O₄ crystal reduces the coordination of the Co? O band, leading to substantially increased oxygen vacancies (octahedral Co²⁺ sites). These vacancies further trigger the formation of a new electronic state in the bandgap, resulting in remarkably improved electrical conductivity and accelerated faradic reactions. The lithiated Co₃O₄ exhibits a noticeably enhanced specific capacity of 260 mAh g^?1 at 1 A g^?1, approximately fourfold enhancement compared to that of pristine Co₃O₄ (66 mAh g^?1). The hybrid supercapacitor assembled with lithiated Co₃O₄//N‐doped activated carbon achieves high energy densities in a broad range of power densities, e.g., 76.7 Wh kg^?1 at 0.29 kW kg^?1, 46.9 Wh kg^?1 at a high power density of 18.7 kW kg^?1, outperforming most of the reported hybrid supercapacitors.