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Nickel ferrites have served as electrode materials in energy storage applications such as batteries and supercapacitors in comparison to other metal oxides, they have a higher theoretical capacitance range. Pristine metal oxides are poor candidates as electrode components in electrochemical applications because of their tendency to aggregate and their less specific surface areas. Herein, we reported wet impregnation method to incorporate Nickel Ferrite (NiFe2O4) to multiwalled carbon nanotubes (MWCNTs) for improved electrochemical performance of nickel ferrites (NiFe2O4). The synthesized materials attained good crystallinity confirmed by X-ray diffraction (XRD). NiFe2O4 nanoparticle adhesions on multiwalled carbon nanotubes have been confirmed by scanning electron microscopy (SEM). UV-DRS was used to measure the bandgap for optical studies. Cyclic Voltammetry (CV), Galvanostatic Charge/Discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS) investigations for supercapacitor applications revealed that synthesized materials demonstrated good electrochemical potential, but MWCNTs supported NiFe2O4 composite attained exceptionally high specific capacitance (CV: 830 F g−1 at 5 mV s−1, GCD:343 F g−1 at current density of 0.1 A g−1) with capacitance retention of 98% at the current density of 0.8 A g−1 after 3500 stability cycles. [ABSTRACT FROM AUTHOR]

In this work, we have successfully formulated a single-step hydrothermal synthesis of mixed transition metal oxide nanocrystals (ZnMn 2 O 4) strongly coupled on carbon support (MWCNTs) that acts as an efficient electrocatalyst for the electrochemical oxygen reduction reaction (ORR). The results depict that the composite, MWCNTs@ZnMn 2 O 4 shows better electrocatalytic activity as compared to the activity exhibited by its individual components MWCNTs and ZnMn 2 O 4 combined, attributed to the strong coupling between the two components. Transmission electron images of the composite depict that ZnMn 2 O 4 nanocrystals have been successfully integrated on MWCNTs resulting in high conductivity and activity. The composite, MWCNTs@ZnMn 2 O 4 exhibits an onset potential of 0.9 V vs. RHE, 99 % four-electron ORR selectivity, and high stability. The high selectivity and stability are assigned due to the strong coupling of ZnMn 2 O 4 to MWCNTs through Zn/Mn–O–C bonds which are proved from DFT studies. The presence of Zn/Mn–O–C bonds is verified from X-ray photoelectron spectroscopy. [Display omitted] • MWCNTs@ZnMn 2 O 4 is synthesized by a one-step hydrothermal route. • MWCNTs@ZnMn 2 O 4 exhibits a highly four-electron selective oxygen reduction. • High selectivity is attributed to the strong covalent interaction through M-O-C bonds. • Presence of M-O-C bonds is supported by XPS analysis. • Weakening of O–O bond leading to the selective four-electron reduction is proved by computational studies also. [ABSTRACT FROM AUTHOR]

[Display omitted] Carbonaceous materials are extensively utilized to optimize the electrochemical performance of the transition metal oxides as anode for lithium-ion batteries. However, the in-depth mechanism of the synergistic effect and the interfacial interaction between transition metal oxides and conductive carbon material has not been elucidated clearly. Herein, by using the oxidized multi-walled carbon nanotubes (oMWCNTs), an advanced MnO 2 /(Co, Mn)(Co, Mn) 2 O 4 /oMWCNTs (MO/CMO/oMWCNTs) nanocomposite with abundant metal−oxygen−carbon (Me−O C) bonds as linkage bridge is fabricated for the first time. The strong covalent bonds interactions can simultaneously enhance the intrinsic sluggish kinetics and structural stability of MO/CMO/oMWCNTs nanocomposite. Meanwhile, the mixed transition metal oxides featuring mix valence state can significantly promote the electrode material activity. Consequently, the newly prepared MO/CMO/oMWCNTs electrode displays superior long-term durability with the capacity of 897 mAh g−1 over 1000 cycles at 2 A g−1 and ultrafast charging/discharging capability of 673 mAh g−1 at 5 A g−1. Detailed electrochemical kinetic analysis reveals that over 70% of the energy storage of MO/CMO/oMWCNTs electrode is dominated by the pseudocapacitive behavior. This work demonstrates an easily scalable approach for constructing high-performance transition metal oxides/carbon electrode materials through interfacial regulation. [ABSTRACT FROM AUTHOR]

Herein, we present an efficient non‐enzymatic electrochemical sensor for H2O2 detection based on the catalytic‐reduction of H2O2 on ZnMn0.5Co1.5O4. The ZnMn0.5Co1.5O4 derived from ZnCo2O4 by the partial substitution of Co with Mn was synthesized via sol‐gel combustion method. The catalytic performance of ZnMn0.5Co1.5O4 for the reduction of H2O2 is better than that of ZnCo2O4, attributing to the synergetic effects of electronic structure, lattice distortion, and multivalent state of Mn. Specifically, as‐fabricated ZnMn0.5Co1.5O4‐based electrochemical sensor shows an excellent quantitative detection capability toward H2O2 in a wide range of 5 to 7585 μM, with a theoretical detection limit of 0.12 μM (3S/N). Moreover, the excellent reproducibility and selectivity for H2O2 sensing was also verified. The excellent recoveries from 94.4 to 103.2 % were obtained for H2O2‐spiked orange juice and beer. More importantly, the sensor exhibits desirable performance in the real‐time monitoring of H2O2 released from living human colon cancer cell (HCT116 cells). The results indicate that the as‐presented sensor is a promising candidate for the H2O2 determination in food safety and clinical diagnose. [ABSTRACT FROM AUTHOR]

Mixed transition metal oxides (MTMOs) with high conductivity and multiple metal centers are promising for energy storage. We synthesized self-assembled three-dimensional (3D) flower-like NiCoMnO 4 (NCMO) and cube-like ZnCoMnO 4 (ZCMO) microstructures via the hydrothermal method. These structures effectively utilize synergistic interactions among MTMOs, offering abundant electro-active sites, and enabling efficient redox reactions. The influence of the metal cation (Ni/Zn) on the physicochemical attributes of the synthesized materials was comprehensively investigated using a diverse set of analytical techniques. When assessing their electrochemical performance in the context of battery-type supercapacitors at a current density of 1 A g−1, the NCMO electrode outperformed with a significantly higher specific capacity of 170.2 mAh g−1 (612.2 C g−1) in contrast to the 145 mAh g−1 (522 C g−1) for the ZCMO electrode. Remarkably, the NCMO electrode displayed exceptional cyclic stability, preserving 91% of its capacity even when subjected to a high current density of 20 A g−1 over 5000 cycles. This innovative approach holds substantial potential for advancing energy storage technologies. [Display omitted] • Microstructures of MCoMnO 4 (M = Ni and Zn) were synthesized through a hydrothermal method. • Flower-like NiCoMnO 4 had a surface area six times larger than cube-like ZnCoMnO 4. • NiCoMnO4 achieved a specific capacity of 170.2 mAh g−1 at 1 A g−1. • NiCoMnO 4 demonstrated excellent stability performance compared to ZnCoMnO 4. [ABSTRACT FROM AUTHOR]

• Unique three-dimensional graphene/mixed transition metal oxides modified activated carbon was prepared and characterized. • The nanocomposite electrode shows low charge transfer resistance and high specific capacitance. • Analysis of synchrotron-based hard X-ray absorption spectroscopy. • The fabricated nanocomposite exhibits a high electrosorption capacity of 9.34 mg g−1. Over the last two decades, the capacitive deionization (CDI) technique has been developed into a high performance, low-cost, and environmental-friendly desalination technology. The development of novel advanced nanostructures via the hybridization of diverse carbon materials to improve the performance of CDI technology has attracted considerable attention. In this study, the combination of graphene hydrogel and ZrO 2 -doped TiO 2 nanofibers as efficient dopants into activated carbon (AC), has been achieved through a simple electrospinning technique followed by a post annealing process. The strong interactions between the graphene hydrogel, nanofibers and AC were found to enhance the wettability as well as the electrical conductivity of the AC. The morphology and electrochemical performance of the as-synthesized composite were characterized by field-emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). What's more, the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and synchrotron X-ray absorption structures (XAS) are performed to investigate the atomic and electronic structure of titania and zirconia in order to understand their phase stability. We observed the appearance of anatase structure of titania and cubic structure of zirconia after doping the AC and graphene hydrogel with the nanofibers. The water contact angle of the composite was examined and found to be less than 3°. The introduced nanocomposite showed high electrosorption capacity of 9.34 mg g−1 at the initial solution conductivity of ∼100 μS cm−1, which is much higher compared to the other surveyed materials; these results should be attributed to its significant hydrophilicity, high specific capacitance, and reduced charge transfer resistance. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Petal-like NiCo/NiO-CoO/NPCC nanocomposites synthesized based on bimetallic MOF. • The NiCo/NiO-CoO/NPCC used as a non-precious electrocatalyst for MOR. • NiCo/NiO-CoO/NPCC showed excellent catalytic activity and durability. • Unique Petal-like structures offer large surface area and accessible active site. • Synergistic effect between metal oxides/metals enhanced the catalyst activity. Abstract Porous carbon template decorated with mixed transition metals/metal oxides with tunable architecture is becoming increasingly important and attractive as a kind of novel electrode materials. In this way, mixed-metallic metal-organic frameworks (MOFs) provide an opportunity for fabrication of homogeneous mixed metals/metal oxides distribution in the porous carbon frame without any carbon precursor additive. Also, structures, dimensions and electrochemical performance of MOFs can be readily manipulated by simply tuning the metals molar ratio. In this study, we demonstrate the design and fabrication of petal-like NiCo/NiO-CoO metal/metal oxides with a rational composition embedded in 3D ultrathin nanoporous carbon composite)NiCo/NiO-CoO/NPCC(. This nanocomposite is synthesized by a two-steps procedure involving preparation of bimetallic MOFs by partially substituting Ni2+ in the Ni-MOF structure with Co2+ (Ni-Co/BDC [BDC = 1,4-Benzene dicarboxylic acid]) and direct carbonization process in the N 2 atmosphere at 900 °C. The prepared nanocomposite was used directly as a non-precious electrocatalyst for methanol oxidation reaction. The results indicated that, in comparison to the monometallic metal/metal oxides distributed in nanoporous carbon composite (Ni/NiO/NPCC and Co/CoO/NPCC), the mixed metals/metal oxides NiCo/NiO-CoO/NPCC exhibits excellent electrochemical performance toward the anodic oxidation of methanol. The unique ultrathin porous petal-like structure with free pores and the enlarged specific surface area provides fast ion/electron transfer, leading to faster kinetics, lower over-potential, and higher electro-catalytic reactivity. Besides their intriguing structural features, the excellent conductivity of carbon frame, as well as a rational composition of two constituents and synergistic effects from cobalt, nickel and their oxides provides favorable catalytic activity for the electro-oxidation of methanol. Therefore, it is believed that this novel multi-component composites demonstrates good electrocatalytic activity and suitable stability towards the methanol oxidation. [ABSTRACT FROM AUTHOR]

A tremella-like NiCo 2 O 4 @graphene quantum dots (GQDs) composite is prepared where the tremella-like NiCo 2 O 4 is homogeneously encapsulated by GQDs. Herein, the GQDs based on π-conjugated core with abundant edge sites, make NiCo 2 O 4 favorable for advanced electric energy storage (EES). In terms of the synergistic effect between the conductive GQDs and tremella-like NiCo 2 O 4 , the as prepared NiCo 2 O 4 @GQDs composite exhibits an excellent specific capacitance of 1242 F g−1 at 30 A g−1 in 2.0 M KOH electrolytes, much higher than that of pristine NiCo 2 O 4 (790 F g−1 at 30 A g−1). Also, it manifests outstanding cycle stability (99% capacitance retention after 4000 cycles). Furthermore, an asymmetric supercapacitor (ASC) is assembled by pairing NiCo 2 O 4 @GQDs composite as positive electrode and activated carbon (AC) as negative electrode (NiCo 2 O 4 @GQDs//AC), and its specific energy density is as high as 38 W h kg−1 at a power density of 800 W kg−1. Image 1 [ABSTRACT FROM AUTHOR]

The preparation of nanostructured hierarchical Mn 1−x Ni x Co 2 O 4 metal oxides as efficient supercapacitors of different structures and configurations especially for the miniaturized electronics is still a challenge. In this context, we report template free facile hydrothermal synthesis of hierarchical nanostructured Mn 1−x Ni x Co 2 O 4 with excellent supercapacitive performance. Significantly, the morphology of pure MnCo 2 O 4 transformed from 3D microcubes to 1D nanowires with incorporation of Ni. The electrochemical study shows highest specific capacitance i.e. 1762 F/g for Mn 0.4 Ni 0.6 Co 2 O 4 with high cycling stability of 89.2% which is much higher than pristine MnCo 2 O 4 and NiCo 2 O 4 . Later, asymmetric capacitor has been fabricated successfully using Mn 0.4 Ni 0.6 Co 2 O 4 nanowires as positive electrode and activated carbon (AC) as negative electrode in a KOH aqueous electrolyte. An asymmetric cell could be cycled reversibly in the high-voltage range of 0–1.5 V and displays intriguing performances with a specific capacitance of 112.8 F/g (6.87 F/cm 3 ) and high energy density of 35.2 Wh/kg (2.1 mWh/cm 3 ). Importantly, this asymmetric capacitor device exhibits an excellent long cycle life along with 83.2% specific capacitance retained after 2000 cycles. [ABSTRACT FROM AUTHOR]

In the present work, we described a green and facile fabrication of mixed manganese-iron oxide loaded carbon fibers (Mn 2 O 3 -Fe 2 O 3 /CFs) through electrospinning and subsequent heat treatment processes. For optimal performance, a series of samples were synthesized by the same way with varying Mn/Fe molar ratios (1:0, 3:1, 1:1, 1:3, 0:1) in precursors. The composition, morphology and catalytic property of as-prepared samples were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), X-ray photo-electron spectroscopy (XPS) and electrochemical methods. Mn 2 O 3 -Fe 2 O 3 /CFs (3:1) exhibits the highest catalytic ability towards hydrogen peroxide (H 2 O 2 ) reduction and hydrazine (N 2 H 4 ) oxidation. Furthermore, Mn 2 O 3 -Fe 2 O 3 /CFs/GCE (3:1) displays remarkable analytical performances for the detection of H 2 O 2 and N 2 H 4 in terms of wide linear range, low limit of detection, short current response time, excellent anti-interference ability, good repeatability and long-time stability. In addition, it can be applied to the analysis of real samples with satisfactory results. [ABSTRACT FROM AUTHOR]

Abstract: The energy profiles of the di-hydroxo – di-oxo – peroxo pathway are discussed for a set of 3d transition metal oxides comprising V(III–V), Cr(III–V), Mn(II–IV, Mn(III–V), Fe(II–IV), Co(II–IV) and Ni(II–IV) using density functional theory (DFT). Two classes of oxides were identified. The first class, comprising V(III–V), Cr(III–V) and Fe(II–IV), displays exothermicity for the oxidation of di-hydroxo to di-oxo versus the tyrosine/tyrosyl-radical (TyrOH/TyrOand endothermicity for the subsequent Ormation ([−/+] class), while the second class, comprising Mn(III–V), Co(II–IV) and Ni(II–IV), shows endothermicity with respect to the oxidation step and exothermicity for the Ormation ([+/−] class). The energetics of the endothermicity (exothermicity) for the oxidation step is reflected in the exothermicity (endothermicity) of the subsequent Ormation step. Mn(II–IV) is not part of any of the two classes. Instead it shows zero exothermicity with respect to TyrOH/TyrOoxidation step and a small endothermicity for the Ormation step. Despite the promising energy profile Mn(II–IV) is argued to be inactive due to a large activation barrier. A set of improved hetero-nuclear candidate catalysts is predicted by mixing [−/+] with [+/−] transition metal oxides. A simple and efficient method to estimate the energy profile of mixed transition metal oxides from the homo-nuclear systems is demonstrated. The validity of this procedure is checked and agreement with the explicitly calculated values is found. All considered heteronuclear candidate catalysts display enhanced performance compared to the pure homonuclear systems. [Copyright &y& Elsevier]

Many methods exist for the synthesis of lithium metal oxides for use as positive electrode materials in lithium-ion batteries; however, no such method to date is both combinatorial (able to process broad ranges of compositional space quickly and efficiently) and well-studied to ensure confidence in the procedure. This study develops a procedure for microliter-scale solution-processing synthesis using a combinatorial solutions-processing robot. Two compositional systems (LiNixMn2-xO4 and Li-Al-Mn oxide) were synthesized to compare the method to existing syntheses to ensure confidence in the procedure. Samples produced by this new synthetic procedure have crystal structures and lattice constants that closely match those of bulk-prepared samples found in the literature. [ABSTRACT FROM AUTHOR]

Abstract: The possibility of spin-coating crystalline multi-element oxide model catalysts using citrate complexes of Bi3+ and Mo6+ solutions was studied. The characterization of obtained thin films was performed by XRD, Raman spectroscopy, SEM and XPS. XRD and confocal Raman data indicated that Bi2O3–MoO3 mixed systems behaved as dictated by the composition of the starting solutions, and pure α-Bi2Mo3O12, β-Bi2Mo2O9, and γ-Bi2MoO6 phases were obtained without any heterogeneity. XPS confirmed that Bi:Mo ratios at the surface of the films never differed from those in the bulk, namely that of the starting co-solutions. SEM revealed that the thickness of the films could be tuned in the range 40–140nm via adjustment of the spin-rate (2, 3, or 5krpm) and the concentration of the precursors solution (0.24 or 0.48M in Mo), without any disturbance of crystallinity, the Bi:Mo ratio or the homogeneity of the films. Performed studies suggested that spin-coating of mixed citrate complexes appears as a versatile and easy route to prepare homogenous films of multi-element transition metal oxides with controlled formulation and crystalline structure. [Copyright &y& Elsevier]

NiMn 2 O 4 (NMO) powders are synthesized by the sol–gel route and the NMO1 electrode is fabricated from the powder synthesized at a calcination temperature of 500 °C. The specific capacitance of the NMO1 electrode is improved from 571 Fg−1 to 762 Fg−1 at a scan rate of 5 mVs−1 , with an increase in the concentration of KOH electrolyte from 1 M to 6 M. [Display omitted] NiMn 2 O 4 (NMO) powders have been prepared by facile sol–gel route, and the effect of annealing temperature and the concentration of KOH electrolyte on its electrochemical performance has been investigated. The electrochemical performance of the NMO electrodes is tested via a three electrode arrangement in KOH electrolyte. The NMO electrode (NMO1) prepared from the powder synthesized at a temperature of 500 °C with an approximate crystallite size of 10 nm exhibits maximum specific capacitance of 571 Fg−1 at a scan rate of 5 mVs−1 in 1 M KOH electrolyte. The specific capacitance of the NMO1 electrode is found to be improved from 571 Fg−1 in 1 M KOH to 762 Fg−1 in 6 M KOH electrolyte. The improvement in the specific capacitance of the NMO1 working electrode in 6 M KOH electrolyte can be attributed to good electrochemical utilization and an effective charge storage mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • A one-step facile synthetic strategy for spinel/carbon composites is proposed. • Graphite nanoflakes matrix is obtained via the low-cost physical exfoliation. • The introduction of GNF significantly enhances the performance of spinels. • Good electrochemical performances are achieved in the MXO/GNF//rGO ACS devices. We put forward a facile one-pot hydrothermal strategy to synthesize the MnX 2 O 4 (X = Co, Ni) spinel/graphite nanoflakes (GNF) composites. Note that the physical exfoliation toward GNF frees the method from the complex and expensive conventional chemical treatments. The obtained MnCo 2 O 4 /GNF (MCO/GNF) and MnNi 2 O 4 /GNF (MNO/GNF) exhibit high specific capacitance (1712 F g−1 for MCO/GNF and 1622 F g−1 for MNO/GNF at 1 A g−1) and good cycling performance (almost 80 % capacitance retention after 3500 cycles at 5 A g−1 for both MCO/GNF and MNO/GNF). Furthermore, the asymmetric supercapacitor (ASC) with MCO/GNF or MNO/GNF as positive electrode and rGO as the negative electrode is assembled. The optimized ASC is able to show high energy density up to 22.5 Wh kg−1. Together with the facile synthetic strategy, such good electrochemical performance may promote the spreading of the next-generation energy storage electrodes. [ABSTRACT FROM AUTHOR]

• A novel design of multi-shell hollow structure dual MTMOs nanomaterial is proposed. • The unique multi-shell hollow structure buffers volume expansion and enhances the storage of lithium ions. • The integration of dual active MTMOs increases lithium storage capacity. • The coating of the outermost carbon improves the conductivity and prevents the agglomeration. • The resultant composite shows excellent cycling stability and lithium storage capacity. Mixed transition metal oxides (MTMOs) are deemed as promising anode materials for lithium-ion batteries (LIBs) because of the high theoretical capacity and low cost. However, the low electrical conductivity, agglomeration effects, and huge volume variation during discharging/charging still seriously restrict the actual applications of MTMOs as anode materials. Herein, a novel core-shell structure of CoSnO 3 @carbon-caged NiCo 2 O 4 nanobox (CNC) is rationally designed. It starts from the preparation of CoSnO 3 @ZIF-67 core-shell nanocubes, followed by chemical etching/anion exchange, dopamine coating and carbonization at high temperature in sequence. It is shown that the CNC achieves high activities from the applied MTMOs components, excellent relief of volume variation from the unique double hollow structure, improved conductivity and inhabited aggregations from the uniform-coated outmost carbon shell, and effective ion/electron transfer rates from the synergetic effects. As a result, the CNC exhibits a discharge capacity of 1548 mA h g−1 at the first cycle and a retention capacity of 992 mA h g−1 after 100 cycles at 0.1 A g−1. In addition, it exhibits a high reversible capacity of about 670 mA h g−1 after 500 cycles at a current density of 1 A g−1. The improved Li+ storage performances of CNC demonstrates that such rational design of double hollow structure could be a novel strategy to apply MTMOs as anode materials of LIBs. [ABSTRACT FROM AUTHOR]

• Nanoporous-structured nickel–cobalt oxides (NP-NCO) have been considered as the emergent nanomaterials. • The NP-NCO have effectively been employed as the promising catalysts for numerous catalysis. • Synthesis, properties, and electrocatalytic performance of the NP-NCO are highlighted. • Present challenges, and future outlook of NP-NCO in electrochemical energy conversion reactions are also described. Emergent nanomaterials of porous-structured mixed transition metal oxides have demonstrated to be promising nanomaterials for various electrochemical energy conversion reactions, including oxygen reduction reaction (ORR), hydrazine oxidation reaction (HOR), glucose oxidation reaction (GOR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), etc. In this featured letter, I intend to present the synthesis, properties, electrode fabrication methodologies, and the applications in electrochemical energy conversion technological performance of the nanoporous-structured nickel–cobalt oxide (NP-NCO) nanomaterials mainly based on our very recent research. The present challenges, and future outlook of the NP-NCO in electrochemical energy conversion reactions are also described on the basis of present attainment. [ABSTRACT FROM AUTHOR]