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In this study, NiO-added NiCo 2 O 4 composite samples were prepared using three distinct synthesis methods to study the impact of synthesis technique and NiO addition on the electrochemical performance of NiCo 2 O 4. The chosen methods, sol-gel, co-precipitation, and ultrasonication, represent a range of approaches that yield different particle structures and morphologies. The structural and morphological studies of composite samples were investigated using X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM), respectively. XRD analysis revealed the crystalline composition, revealing the presence of two distinct phases: NiO and NiCo 2 O 4. The Rietveld analysis of the composite samples supports the dual phases in the samples. FESEM analysis confirms the change in size and shape of the particles with the synthesis procedure. Optical properties, measured via UV–visible absorbance spectra, demonstrated that the energy gap varied with the synthesis method. The sol-gel samples exhibited the highest energy gap at 2.20 eV. The magnetic properties were measured using the vibration sample magnetometer (VSM), and the results confirm that the synthesis procedure influences magnetic loops and coercivity. The electrochemical performance of the samples in a 3 M potassium hydroxide electrolyte revealed that the co-precipitation method produced the highest capacitance of 398 Fg-1 at a 10 mV/s sweep rate, indicating superior energy storage capacity compared to pure NiCo 2 O 4. Adding NiO phase to the NiCo 2 O 4 matrix is believed to enhance electrochemical performance by creating additional charge at the grain boundaries, leading to a synergistic effect and improved electron and ion transport. The exceptional electrochemical performance of these composite materials suggests that the synthesis methods and the addition of NiO play a critical role in determining the overall efficiency and applicability of battery-type supercapacitors. These findings pave the way for further research into optimizing synthesis parameters to enhance energy storage capacity and inspire the development of advanced spinel metal oxide composite electrodes for supercapacitors and other energy storage applications. [ABSTRACT FROM AUTHOR]

A simple solid-state method was developed for large-scale growth of spinel nickel cobaltite (NiCo2O4) nanoparticles on the surface of N-doped reduced graphene oxide nanosheet (N-rGO) as the enhanced performance electrode for electrochemical capacitors. The synthesis involves the room-temperature solid state reaction of a bimetallic (Ni, Co) hydroxide precursor and subsequent thermal transformation to NiCo2O4 nanoparticles on the N-rGO support. Morphological analyses reveal that, with loading rate 49 wt%, NiCo2O4 nanoparticles with an average size of around 12 nm are formed and uniformly dispersed on the surface of N-rGO nanosheets (NiCo2O4/N-rGO). Electrochemical measurements of NiCo2O4/N-rGO composites display a high specific capacitance of 1135 F g− 1 (based on NiCo2O4) at a current density of 1 A g− 1, and excellent cycling performance (100% capacitance retention after 2000 cycles) even at a very high current density of 8 A g− 1, which are significantly higher than that of NiCo2O4 nanoparticles prepared without using N-rGO. This much enhanced electrochemical performance is enabled by both the well-dispersed NiCo2O4 nanoparticles that offer large accessible surface area and the mesoporous structure of NiCo2O4/N-rGO composites that facilitate electrons/ions transport. The facile two-step synthesis process developed in this work is promising to prepare electrode materials for high-performance electrochemical capacitors. [ABSTRACT FROM AUTHOR]

Due to their high energy density and cost‐effectiveness, lithium–sulfur batteries (LSBs) are considered highly promising for the next generation of energy storage technologies. However, the soluble lithium‐polysulfides (LiPSs) notorious for causing the shuttle effect and the sluggish redox kinetics have hindered their practical commercialization. To tackle these challenges, a heterostructural catalyst featuring NiS‐NiCo2O4 interfaces is developed, which serves as an interlayer for LSBs. These interfacial sites leverage the advantages of polar NiCo2O4 and conductive NiS, enabling smooth Li+ diffusion, rapid electron transport, and effective immobilization of LiPSs. This synergistic approach promotes the conversion of sulfur species, resulting in a high discharge capacity of 526 mAh g−1 at 3 C for cells with the NiS‐NiCo2O4 interlayer. Additionally, remarkable cycling stability is achievable with an areal sulfur loading of ≈5.0 mg cm−2. It is believed that this research paves the way for practical applications of LSBs. [ABSTRACT FROM AUTHOR]

[Display omitted] The efficiency of photocatalytic hydrogen evolution can be significantly enhanced while maintaining cost-effectiveness through the synergistic effect of defect surface engineering and multi-component heterojunctions. The structure and properties of NiCo 2 O 4 nanorods were modified by inducing oxygen vacancies at different temperatures in this study, resulting in improved optical properties and electron adsorption capacity. The presence of oxygen vacancies leads to a reduction in the band gap of NiCo 2 O 4 , thereby enhancing electron transport efficiency through band gap engineering. Simultaneously, surface properties undergo changes, and vacancy defects serve as electron trapping centers, facilitating an increased participation of electrons in the hydrogen evolution reaction process. The dodecahedron KMP with a cavity structure is additionally introduced to form an S-scheme heterojunction with NiCo 2 O 4. This establishes a novel mechanism for electron transport, which effectively enhances the separation of electron-hole pairs and improves the redox capacity of the photocatalytic system. The adsorption of intermediates in the hydrogen production process is enhanced through synergistic regulation of d-band centers via surface defect engineering and S-scheme heterojunction. Additionally, this approach improves the separation efficiency of electron-hole pairs and accelerates electron transfer dynamics, significantly enhancing hydrogen production efficiency. [ABSTRACT FROM AUTHOR]

This paper presents a complete analysis of the electrical and dielectric characteristics of N i C o 2 O 4 (NCO) bulk ceramic synthesized by the co-precipitation process as a future electronic device material. The structural analysis following the synthesis process revealed the formation of cubic-phase spinel NCO in the shape of nanospheres, with an approximate diameter of 25 nm. The present study aimed to examine the relationship between capacitance and conductance for the NCO under investigation, focusing on their frequency and temperature dependencies. The frequency range of interest ranged from 100 Hz to 1.5 MHz, while the temperature range considered was from 300 K to 450 K. The C/f plot has exhibited the phenomenon of negative capacitance, which may be attributed to the augmentation of polarization and the incorporation of additional minority carriers inside the structure. The dielectric parameters, such as permittivity, dielectric loss, alternating current conductance, and electrical modulus, were determined by capacitance and conductance measurements, taking into account their frequency and temperature reliance. All dielectric calculations were influenced by negative capacitance measurements. The negative capacitance feature of N i C o 2 O 4 is attributed to the ferroelectric properties of the Ni and Co elements in its composition. In conclusion, this paper has made a valuable contribution to the existing body of literature by enhancing our comprehension of the negative capacitance behavior and dielectric characteristics of the NCO. [Display omitted] [ABSTRACT FROM AUTHOR]

Energy storage technology plays a critical role in integrating variable energy sources into the grid and ensuring energy consistency. Electrochemical supercapacitors are one of the most promising energy storage devices, as they present multiple advantages of high power density, rapid charge/discharge characteristics, and long‐term cycle stability. Herein, the NiCo2O4/molybdate nanocomposites are developed as electrode materials for supercapacitor applications. The NiCo2O4/molybdate nanocomposites are synthesized by a facile single‐pot hydrothermal method and are coated on a carbon cloth substrate to form flexible supercapacitor electrodes. The structures, chemical compositions, morphologies, and textural properties of these materials are carefully studied by X‐Ray diffraction, X‐Ray absorption spectroscopy, scanning electron microscopy/energy‐dispersive X‐Ray spectroscopy mapping, and N2 adsorption–desorption isotherms. The formation of spinel NiCo2O4 nanorods decorated with molybdate (AMoO4, A = Co, Ni) particles is confirmed for all samples. The NiCo2O4/CoMoO4 electrode exhibits pseudocapacitive behavior and provides the highest specific capacitance (287.28 F g−1 at current density 6 A g−1), about 5.5 times as high as that of NiCo2O4, with excellent cycle stability (107% specific capacitance retention after 1000 charge/discharge cycles at 1 A g−1). Therefore, the NiCo2O4/CoMoO4 composites can be considered as a promising pseudocapacitor electrode material. [ABSTRACT FROM AUTHOR]

Herein, the single‐phase Ni‐based bimetallic spinel oxide (NiM2O4, M = Mn, Fe, Co) nanoparticles are successfully synthesized by sol–gel method and coated on a carbon cloth substrate to form flexible electrodes for supercapacitor applications. The effects of transition metal activity, calcination temperature, surface, and textural properties on the electrochemical properties of spinel electrode materials are demonstrated. It is found that lowering the calcination temperature results in a decrease in crystallite size and particle size, leading to an increase in surface area and pore volume. X‐Ray absorption spectroscopy reveals the presence of Mn2+/3+, Fe2+/3+, and Co2+/3+ in materials. According to the electrochemical studies, NiMn2O4 electrode in Na2SO4 electrolyte exhibits electrical double‐layer capacitance behavior, while NiFe2O4 and NiCo2O4 electrodes in KOH electrolyte exhibit pseudocapacitive behavior. All electrode materials have low solution resistance and charge transfer resistance. NiCo2O4 provides the highest specific capacitance (85.60 F g−1 at 2.5 A g−1) followed by NiFe2O4 and NiMn2O4. It seems likely that the high electrochemical activity of Co2+/3+ and small particle size of NiCo2O4 nanoparticles play an important role in improving the redox process and charge transfer, which may enhance the electrochemical performance of this electrode material. [ABSTRACT FROM AUTHOR]

The paper reports the development of Cu-doped NiCo 2 O 4 ternary inverse spinel oxides through microwave-assisted hydrothermal method as effective catalysts for alkaline hydrogen evolution reaction (HER). The effective and controlled doping of Cu to NiCo 2 O 4 lattice by the partial replacement of Ni2+/Ni3+ with Cu+/Cu2+ results in the fine-tuning of structural, morphological, and electronic characteristics, favourable for electrocatalytic HER. The study effectively correlates the influence of variation in the percentages of Cu-doping on the material properties and thereby the electrocatalytic characteristics. The experimental results indicate that Cu 0.10 Ni 0.90 Co 2 O 4 electrode having optimum Cu-doping (10%) as the best electrocatalyst with the lowest onset potential for hydrogen evolution (242.7 mV) and reduced overpotential (72.5 mV) values by following a Volmer – Heyrovsky mechanism during HER. The improvement in HER performance after Cu-doping is due to the generation of greater number of active sites and reduction in electronic band gap. The present work advantageously utilises the scope of microwave-assisted transition metal doping strategy to fine tune the physicochemical and electronic characteristics, favourable for electrocatalytic HER, and this may pave a new way for tuning the electrochemical properties of metal oxides for various applications. • Microwave-assisted hydrothermal synthesis is used effectively to develop Cu-doped NiCo 2 O 4. • Cu-doping to NiCo 2 O 4 lattice creates more oxygen vacancies and improves electronic conductivity. • Cu 0.10 Ni 0.90 Co 2 O 4 with 10% Cu-doping exhibits promising electrocatalytic activity towards HER. • Cu-doped NiCo 2 O 4 follows Volmer – Heyrovsky mechanism during alkaline HER. [ABSTRACT FROM AUTHOR]

In the quest for the development of thermally stable, highly active and low-cost catalysts for use in catalyzed diesel particulate filter, nano-composites are new areas of research. Therefore, we reported the easy synthesis of spinel NiCo 2 O 4 /perovskite LaCoO 3 nano-composite, and its individual oxides NiCo 2 O 4 and LaCoO 3 for comparison. The detailed insights into the physio-chemical characteristics of formed NiCo 2 O 4 / LaCoO 3 nano-composite were done based on various characterization analysis such as X-ray diffraction (XRD), Fourier transform infrared (FT-IR), N 2 physiosorption, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDX), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The characterization analysis of NiCo 2 O 4 /LaCoO 3 revealed the successful formation of a chemical interface possessing strong interfacial interaction, resulting in desirable physicochemical characteristics such as small crystallite size, abundant mesoporosity, high specific surface area and activation of surface lattice oxygen. Owing to the desirable characteristics, the activity results over NiCo 2 O 4 /LaCoO 3 nano-composite showed the excellent CO oxidation performance and high soot oxidation activity, recyclability and thermal stability. This work mainly attempts to emphasize the effectiveness of the facile, inexpensive and conventionally used precipitation method for the successful formation of highly efficient nano-composites. [ABSTRACT FROM AUTHOR]

The intercalation pseudocapacitance mechanism holds the potential to significantly narrow the gap between supercapacitors and lithium-ion batteries, particularly in terms of energy density and power density properties. Herein, 1D nanorod and 2D nanoflake mixed structures of nickel cobaltite (NiCo2O4) were prepared for asymmetric supercapacitor application. For comparison, the NiO and Co3O4 materials were also prepared, and examined their supercapacitor properties. The NiCo2O4 store charges through the diffusion-controlled process and delivers the specific capacity of 347 C g−1 (694 F g−1) at 1 A g−1 and it withstands 96% of initial capacity after 5000 cycles at a current density of 10 A g−1. Furthermore, the asymmetric supercapacitor device (NiCo2O4//AC) exhibits the specific capacity of 141 C g−1 (88 F g−1) at 1 A g−1, with an excellent energy and power density of 31.3 Wh kg−1 and 800 W kg−1 respectively. The device retained 86% of its initial capacity after 5000 GCD cycles at 10 A g−1. Therefore, the 1D/2D mixed morphologies with diffusion-controlled charge storage process are guaranteed to achieve superior electrochemical performance. [ABSTRACT FROM AUTHOR]

The magnetic spinel cobalt ferrite (CoFe 2 O 4) powders had the high microwave absorption performance at the large thicknesses on account of the low permittivity. Combining the CoFe 2 O 4 powders with other dielectric loss materials had been suggested to improve their impedance matching and microwave absorption performance. In this work, the microwave absorption performance of the CoFe 2 O 4 powders was enhanced by adding the various amounts of the NiCo 2 O 4 nanoparticles as dielectric loss material. The CoFe 2 O 4 -x NiCo 2 O 4 composite powders (x = 0, 12.5, 25, and 50 wt %) were prepared by a facile two-pot solution combustion synthesis method. Although the X-ray diffraction peaks of NiCo 2 O 4 phase were absent, but the decrease of saturation magnetization from 61 to 30 emu/g was related to the amount of NiCo 2 O 4 material. Furthermore, the NiCo 2 O 4 nanoparticles were nucleated and grown on the surface of spongy CoFe 2 O 4 powders because the synthesized CoFe 2 O 4 powders were added to the precursor solution of NiCo 2 O 4 material containing the nickel and cobalt nitrates as oxidants and glycine as organic fuel. The microwave absorption performance was analyzed by measuring the permittivity and permeability spectra which were applied for evaluating the reflection loss versus frequency and thickness. The CoFe 2 O 4 -25 wt % NiCo 2 O 4 composite powders had the higher microwave absorption performance including the high reflection loss of −40 dB and broad effective bandwidth of 5.6 GHz of Ku band (12–18 GHz) at a small matching thickness of 1.9 mm. The high microwave absorption performance of the x = 25 wt % sample was attributed to its better impedance matching via a proper combination of the permittivity and permeability values. [ABSTRACT FROM AUTHOR]

Transition bimetal oxides are widely used in the field of electrochemical sensing because of their variable valence and bimetallic synergies. In this work, we demonstrate the facile synthesis of snow-cake like NiCo2O4 nanostructures and its application as a working electrode modification material in enzyme-free glucose electrochemical sensing field. In a three-electrode system, the electrocatalytic oxidation activity for glucose of NiCo2O4 nanostructures is tested. The snow-cake like NiCo2O4 nanostructures are endowed with superior electron-transfer capability, large surface area, and abundant intrinsic redox couples of Ni2+/Ni3+ and Co2+/Co3+ ions. The modified electrode exhibits excellent glucose-sensing properties, such as detection of wide range of glucose concentrations with good linearity and high sensitivity of 983 μA mM−1 cm−2 at 0.45 V operating potential. Moreover, the interference from the commonly interfering species such as ascorbic acid (AA), sodium chloride (NaCl) and uric acid (UA) can be effectively avoided. [ABSTRACT FROM AUTHOR]

The phenomenon of poor cycle stability can be effectively solved by using metal–organic frameworks (MOFs) as precursor to obtain oxides. In this work, a layered NiO@NiCo2O4 nanocomposite electrodes were designed from bimetallic (Ni/Co) based bimetallic metal–organic framework (Ni/Co-MOF) by simple hydrothermal method followed by subsequent controlled calcination under air atmosphere at various temperatures for the transition process. XRD and FE-SEM studies were substantiating the formation of MOF derived NiO@NiCo2O4 nanocomposite with layered structure. Interestingly, electrochemical studies shows that MOF derived NiO@NiCo2O4 nanocomposite achieved at the calcination temperature at 300 °C and 400 °C demonstrates high specific capacitance of 2461 F/g and 2180 F/g at the current density of 1 A/g, which keeps the precursor Ni/Co-MOF with high specific capacitance peculiarity of 2250 F/g at 2 A/g. In terms of cycle retention rate, the NiO@NiCo2O4 nanocomposite obtained at 400 °C still has a high retention rate of 78% under the current density of 15 A/g for 4500 cycles. It significantly improved the precursor Ni/Co-MOF low cycle retention rate of only 56% after 1000 cycles. The results show that the metal oxide nanocomposites calcined with MOFs as sacrificial template not only retain the high specific capacitance characteristics of MOFs, but also improve its low cycle stability, which has great potential in electrochemical supercapacitor electrode materials and provides a certain useful reference for the direction of global energy demand. [ABSTRACT FROM AUTHOR]

In this work, the one-dimensional (1D) Ni–Co–Se nanowire arrays with rich grain-boundaries were prepared through the solvothermal method and gas-phase selenizaiton. The results showed that the structure and crystallization of the Ni–Co–Se nanowire arrays could be modulated through the optimization of selenizaiton time. The optimal Ni–Co–Se electrode sample displayed an area specific capacitance of 242.6 μ Ah cm−2 at 30 mA cm−2 with a current retention rate of 68.34%. The assembled Ni–Co–Se/Active carbon (AC) electrode-based asymmetric supercapacitor (ASC) showed the area specific capacitances of 329.2 μ Ah cm−2 and 225.8 μ Ah cm−2 at 3 mA cm−2 and 30 mA cm−2, respectively. A 73.33% retention rate of capacitance was observed after 8000 charge/discharge cycles. Besides, the further fabricated all-solid ASC delivered the power densities of 342.94 W kg−1 and 3441.33 W kg−1 at the energy densities of 37.62 Wh kg−1 and 25.81 Wh kg−1, respectively. Those results suggested the potentials of the obtained Ni–Co–Se nanowire arrays as electrode material for the high-performance pseudocapacitors. [ABSTRACT FROM AUTHOR]

The lithium-air battery is a new type of secondary battery technology that is currently receiving a lot of attention in the field of power storage technology. These batteries are known to offer high energy densities and potentially longer driving ranges. In this study, NiCo2O4 and CNTs were used to create a composite for use as the cathode of a Li-air battery. Improving the 3D needl-like structure that provides extensive transport channels for electrolyte infiltration and numerous sites facilitated charge transfer reactions and the synergistic effect of highly electrocatalytic NiCo2O4 with pronounced activity and high conductive CNTs, with the synthesized NiCo2O4@CNTs composites exhibiting active catalytic performance for both OER and ORR reactions. It also showed improved cycle performance at high current densities. NiCo2O4@CNTs composites were successfully fabricated using a hydrothermal method together with a sequential annealing treatment. The components of the completed composite were confirmed using TGA, XRD, and SEM, and the specific surface area was analyzed using BET. The composite was performed for over 120 cycles at a current density of 200 mA∙g−1, and 500 mA∙g−1 was achieved under the capacity limiting condition of 500 mAh∙g−1. The charging/discharging characteristics were compared under various current densities, exhibiting stable cyclability. The high catalytic activity of NiCo2O4 oxide supports its potential use as a cathode in Li-air batteries. [ABSTRACT FROM AUTHOR]

Electromagnetic pollution could harm sensitive electronic equipment due to the rising use of electronic devices and communication infrastructure. The supercapacitor's electrochemical performance should be enhanced, and electromagnetic damage should be prevented. This study proposes NiCo2O4/CF composites for supercapacitors and microwave absorption. They are made by combining hydrothermal and annealing processes. Dense NiCo2O4 nanoneedles were uniformly grown on the outer layer of carbon foam (CF) as a growth skeleton, preventing the agglomeration of NiCo2O4. The composite had a specific capacitance of 537.5 F/g at 1 A/g. When the current density was set to 1 A/g, the supercapacitor that used NiCo2O4/CF as the cathode had a specific capacitance of 70.7 F/g, and when the current density was increased to 10 A/g, the original specific capacitance of 87.2 % could still be maintained after 5000 charge‐discharge cycles. At a power density of 3695.5 W/kg, an energy density of 22.1 Wh/kg could be maintained. Furthermore, we performed a microwave absorption test and determined its reflection loss curve for various sample thicknesses. Recombination enhanced the composite material's microwave absorption capability by greatly reducing the dielectric loss and the magnetic loss. [ABSTRACT FROM AUTHOR]

Radiation exposure induces defects in the crystal structure, leading to alterations in the structural, optical, and morphological properties of metal oxides. These irradiated metal oxides have found extensive use in various household applications. In this particular investigation, carbon-coated nickel cobalt oxide/rGO nanocomposites were synthesized through ultrasonication. Subsequently, these nanocomposites were subjected to three different doses of gamma radiation using a 60Co source. Both un-irradiated and irradiated samples were subjected to characterization using FTIR, SEM, XRD, and UV-Vis spectroscopy. The FTIR analysis confirmed the presence of a spinel-type structure in NiCo2O4. SEM analysis revealed the presence of crumbled sheets of rGO, and the irradiation process caused a transformation of these stacked sheets into thinner sheets. XRD analysis indicated a decrease in crystalline size and an increase in dislocation density with higher doses of gamma irradiation. UV-Vis spectroscopy demonstrated a reduction in both direct and indirect optical band gaps as a result of gamma irradiation. Furthermore, it was observed that Urbach energy and refractive index increased with gamma irradiation. Based on these findings, it can be concluded that gamma irradiation has a significant impact on the morphological, structural, and optical properties of NiCo2O4/rGO@C nanocomposites. [ABSTRACT FROM AUTHOR]

Among the many methods of hydrogen production, the electrolysis of water has a broad prospect. In this experiment, NiCo 2 O 4 nanosheets with different degrees of oxidation were synthesized on nickel foam by the hydrothermal method, air calcination and reduction steps. The experimental results show that reduction treatment significantly improved the catalytic activity of NiCo 2 O 4 materials under alkaline medium conditions of 1.0 mol/L KOH. V–NiCo 2 O 4 -4 shows better catalytic activity with an overpotential of 285 mV and 340 mV for the oxygen evolution reaction (OER) at 10 mA cm−2 and 50 mA cm−2, respectively. The better catalytic activity of V–NiCo 2 O 4 -4 is mainly assigned to the flower-like structure of the catalyst surface and the moderate reduction of NaBH 4 , resulting in more oxygen vacancies and active sites. Density functional theory calculation also indicates that the V–NiCo 2 O 4 -4 material has a stronger water absorption energy (0.75 eV) compared to the V–NiCo 2 O 4 -2 and V–NiCo 2 O 4 -6 materials, which provides a new foundation for the construction of binder-free high-performance electrodes for water splitting. The V–NiCo 2 O 4 -4 showed better results at 50 mA cm−2, which required an overpotential of 340 mV for oxygen evolution reaction (OER). [Display omitted] • A series of NiCo 2 O 4 nanosheets were synthesized by hydrothermal method. • This V–NiCo 2 O 4 -4 exhibits enhanced activity for OER. • DFT show that the V–NiCo 2 O 4 -4 exhibits the stronger water absorption energy. • This V–NiCo 2 O 4 -4 material exhibits relatively good stability for OER. [ABSTRACT FROM AUTHOR]

In this study, we investigated the phase transition of cobalt spinel (Co3O4) nanoparticles into Co3−xNixO4/CoO heterostructures by introducing varying amounts of nickel (x = 0.0–0.16) and subjecting the particles to high annealing temperatures of 1000 ℃. X-ray diffraction (XRD) analysis confirmed the Co3−xNixO4CoO structure for all samples. Transmission electron microscopy (TEM) provided further insights into the phase or heterostructure of the samples after annealing, revealing the arrangement of the two phases. Fourier-transform infrared spectroscopy measurements demonstrated a band shift around 537 cm−1 with increasing Ni content, while ultraviolet-visible (UV-Vis) measurements indicated the energy band (Eg). Significant morphological changes were observed in scanning electron microscope (SEM) measurements at 0.16 Ni, displaying irregular agglomerates. Our findings suggest that introducing Ni into the Co3O4 structure and increasing the annealing temperature to 1000 ℃ can lead to the formation of a heterostructured system. Furthermore, our study’s significance is highlighted by the streamlined synthesis of NiCo2O4/CoO using the sol-gel method followed by calcination. This departure from complex techniques provides an efficient route to acquiring the NiCo2O4/CoO system, a promissory material for advancing supercapacitor research. [ABSTRACT FROM AUTHOR]

Exploring highly efficient electrocatalysts (OER) is critical for oxygen evolution reaction. Herein, for the first time, P-doped NiCo 2 O 4 nanosheet arrays generated on nickel foam (namely P–NiCo 2 O 4 /NF) were constructed via a feasible protocol. Notably, the etching treatment can open the internal structure of ZIF-67 to offer more electrocatalytically active surface area, and obtained NiCo 2 O 4 showed great electrocatalytic performance in OER. The introduction of P can effectively reduce the charge transfer resistance of NiCo 2 O 4 and boost OER kinetics. More importantly, doping P not only improved the hydrophilicity of NiCo 2 O 4 , but also reduced its surface potentials, which provided convenience for the adsorption of OH− over P–NiCo 2 O 4 /NF electrode. As expected, the P–NiCo 2 O 4 /NF electrode with good long-term durability displayed excellent performance for OER in alkaline solution, and an overpotential of 121.6 mV was achieved at a current density of 10 mA/cm2. To sum up, current work can provide a meaningful reference to prepare electrocatalyst for efficient OER. [Display omitted] • The P-doped NiCo 2 O 4 nanosheet array grown on nickel foam was first constructed. • An overpotential of 121.6 mV for OER was achieved at a current density of 10 mA/cm2. • Doping P improved affinity of NiCo 2 O 4 for OH− and reduced charge transfer resistance. • As-prepared P–NiCo2O4/NF electrode showed excellent long-term durability for OER. [ABSTRACT FROM AUTHOR]

[Display omitted] Flexible supercapacitors have received considerable attention for their potential application in flexible electronics, but usually suffer from relatively low energy density. Developing flexible electrodes with high capacitance and constructing asymmetric supercapacitors with large potential window has been considered as the most effective approach to achieve high energy density. Here, a flexible electrode with nickel cobaltite (NiCo 2 O 4) nanowire arrays on nitrogen (N)-doped carbon nanotube fiber fabric (denoted as CNTFF and NCNTFF, respectively) was designed and fabricated through a facile hydrothermal growth and heat treatment process. The obtained NCNTFF-NiCo 2 O 4 delivered a high capacitance of 2430.5 mF cm−2 at 2 mA cm−2, a good rate capability of 62.1 % capacitance retention even at 100 mA cm−2 and a stable cycling performance of 85.2 % capacitance retention after 10,000 cycles. Moreover, the asymmetric supercapacitor constructed with NCNTFF-NiCo 2 O 4 as positive electrode and activated CNTFF as negative electrode exhibited a combination of high capacitance (883.6 mF cm−2 at 2 mA cm−2), high energy density (241 μW h cm−2) and high power density (80175.1 μW cm−2). This device also had a long cycle life after 10,000 cycles and good mechanical flexibility under bending conditions. Our work provides a new perspective on constructing high-performance flexible supercapacitors for flexible electronics. [ABSTRACT FROM AUTHOR]

The three-dimensional (3D) nanostructured binary metal oxides have a massive prospect in energy-related applications owing to their outstanding electrochemical performance and stability. 3D hierarchical tremella-like nickel cobaltite (NiCo 2 O 4) has been successfully synthesized by a hydrothermal method coupled with an annealing treatment process. The effects of temperature and reaction time in hydrothermal process on crystal structure, morphology, particles size, surface area and pore size distribution were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Brunauer–Emmett–Teller analysis (BET) and Barrett-Joyner-Halenda (BJH) analysis. The results showed that 3D hierarchical nanoporous structures composed of interconnected thin nanoflakes with thickness of about 20 nm began to form when the mixture was heated for 6 h at 180 °C with considerably high specific surface area of 169.61 m2/g. On the other hand, the highest surface area (203.21 m2/g) and narrowest pore size distribution (9.13 nm) are achieved by the sample heated at a temperature of 160 °C for 12 h. These findings indicated that temperature and reaction time parameters in hydrothermal process play a major role in producing different quality and altered morphological structures of NiCo 2 O 4 powders which later will affect the electrochemical performance of fuel cell. • 3D nanostructures of NiCo 2 O 4 was successfully synthesized by hydrothermal method. • Hydrothermal temperature and reaction time affected the morphologies of NiCo 2 O 4. • The desired nanostructures began to form when sample was heated for 6 h at 180 °C. • The highest specific surface area was obtained by sample heated at 160 °C for 12 h. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) exhibit many structural advantages, such as large specific surface area and abundant active sites, which make them promising candidates as electrode materials for non-enzymatic glucose sensors. In this work, using MOFs as templates, MOFs derived Co 3 O 4 nanoparticles (NPs) were in-situ synthesized on the surface of NiCo 2 O 4 nanowires (NWs), forming a self-supporting electrode based on nickel foam (NF), which was directly used for the detection of glucose. Because of the presence of MOFs derivatives and self-supporting structures, NF/NiCo 2 O 4NWs @Co 3 O 4NPs electrode exhibits good structural stability and high conductivity, which ensure the excellent electrocatalytic performance. The NF/NiCo 2 O 4NWs @Co 3 O 4NPs electrode shows prominent electrocatalytic performance toward glucose with a wide testing range (0.001–1.7 mmol/L), high sensitivity (8163.2 μA cm−2 mM−1), fast response time (within 1 s), high anti-interference ability and long-term stability. Further, the electrode was used to test different glucose levels in live mouse serum samples, showing acceptable reliability and high accuracy comparing with blood glucose meter test (medical test method). Thus, NF/NiCo 2 O 4NWs @Co 3 O 4NPs electrode with self-supporting core-shell nanostructure will be a promising candidate applied in non-enzymatic glucose sensors. [ABSTRACT FROM AUTHOR]

Urchin-like NiCo2O4 was synthesized onto flexible carbon felt (CF) substrate via facile hydrothermal process as a high performed electrode for supercapacitors. The hydrothermal temperature was varied from 140 to 200 °C in order to investigate its effect on the morphological, structural, and electrochemical properties of the as-synthesized NiCo2O4@CF. Moreover, X-ray diffraction analysis revealed the formation of NiCo2O4 composite with polycrystalline nature. The SEM images demonstrate the development of NiCo2O4 structure from nanowires to a combination between nanowires and urchin like during the increasing of the hydrothermal temperature. This combination is extremely advantageous in accomplishing an exceptional electrochemical capacity by virtue of the high surface area of interaction with electrolyte and the decrease in the ion transport path. Indeed, the double nanostructured NiCo2O4 synthesized at 200 °C allowed to obtain excellent electrochemical performance with high specific capacity of 243.1 mAh.g−1(0.278 mAh.cm−2) at current value of 2 mA and capacity retention of ~ 91.3% after 5000 cycles in 6-M KOH aqueous electrolyte. As a consequence, the obtained double nanostructured NiCo2O4@CF flexible electrode is well suited for use in hybrid devices and flexible electronic devices. [ABSTRACT FROM AUTHOR]

The hydrothermal synthesis of a nanosized NiCo2O4 oxide with several levels of hierarchical self-organization was studied. Using X-ray diffraction analysis (XRD) and Fourier-transform infrared (FTIR) spectroscopy, it was determined that under the selected synthesis conditions, a nickel-cobalt carbonate hydroxide hydrate of the composition M(CO3)0.5(OH)·0.11H2O (where M–Ni2+ and Co2+) is formed as a semi-product. The conditions of semi-product transformation into the target oxide were determined by simultaneous thermal analysis. It was found by means of scanning electron microscopy (SEM) that the main powder fraction consists of hierarchically organized microspheres of 3–10 μm in diameter, and individual nanorods are observed as the second fraction of the powder. Nanorod microstructure was further studied by transmission electron microscopy (TEM). A hierarchically organized NiCo2O4 film was printed on the surface of a flexible carbon paper (CP) using an optimized microplotter printing technique and functional inks based on the obtained oxide powder. It was shown by XRD, TEM, and atomic force microscopy (AFM) that the crystalline structure and microstructural features of the oxide particles are preserved when deposited on the surface of the flexible substrate. It was found that the obtained electrode sample is characterized by a specific capacitance value of 420 F/g at a current density of 1 A/g, and the capacitance loss during 2000 charge–discharge cycles at 10 A/g is 10%, which indicates a high material stability. It was established that the proposed synthesis and printing technology enables the efficient automated formation of corresponding miniature electrode nanostructures as promising components for flexible planar supercapacitors. [ABSTRACT FROM AUTHOR]

Herein, hierarchical Ni/Co-layered double hydroxide decorated NiCo 2 O 4 electrocatalyst (NiCo-LDH@NCO) on nickel foam (NF) was synthesized using a facile hydrothermal method with electrochemical reconstruction. By converting the already existing NCO surface to hierarchical NiCo-LDH, a larger surface area and high electrical conductivity are obtained. Both structure and morphology of fabricated electrocatalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM) techniques. The electrochemical reconstruction process is accompanied by changes in the morphology of the NCO that significantly increase accessibility to the electrolyte and active surface area. Therefore, the as-obtained electrocatalyst exhibits excellent oxygen evolution reaction (OER) activity and long-term stability for 35 h continuous reaction, superior-performing the reported other OER catalysts. In addition, this work opens a new path for the development of highly efficient and innovative low-cost OER electrocatalysts able to replace Pt-based metals for energy conversion devices. [Display omitted] • NiCo-LDH@NCO was synthesized via a facile two-step method. • Synthesized electrocatalyst shows the lowest Tafel slope value (61 mVdec−1). • Synergistic effect of NiCo-LDH and NCO increases the OER activity. [ABSTRACT FROM AUTHOR]

Sulfite (S(IV)) is a promising substitute for sulfate radical-based advanced oxidation processes. Here, a composite of in-situ anchoring NiCo 2 O 4 nanosheets on biochar (BC) was firstly employed as a heterogeneous activator for sulfite (NiCo 2 O 4 @BC-sulfite) to degrade atrazine (ATZ) in the neutral environment. The synergistic coupling of BC and NiCo 2 O 4 endows the resulting composite excellent catalytic activity. 82% of the degradation ratio of ATZ (1 mg/L) could be achieved within 10 min at initial concentrations of 0.6 g/L NiCo 2 O 4 @BC, 3.0 mmol/L sulfite in neutral environment. When further supplementing sulfite into the system at 20 min (considering the depletion of sulfite), outstanding degradation efficiency (∼ 100%) were achieved in the next 10 min without any other energy input by the NiCo 2 O 4 @BC-sulfite system. The features of the prepared catalysts and the effects of some key parameters on ATZ degradation were systematically examined. A strong inner-sphere complexation (Co2+/Ni2+-SO 3 2−) was explored between sulfite and the metal sites on the NiCo 2 O 4 @BC surface. The redox cycle of the surface metal efficiently mediated sulfite activation and triggered the series radical chain reactions. The generated radicals, in particular the surface-bound radicals were involved in ATZ degradation. High performance liquid chromatography-tandem mass spectrometry (LC-MS) technique was used to detect the degradation intermediates. Density functional theory (DFT) calculations were performed to illustrate the possible degradation pathways of ATZ. Finally, an underlying mechanism for ATZ removal was proposed. The present study offered a low-cost and sustainable catalyst for sulfite activation to remove ATZ in an environmentally friendly manner from wastewater. [Display omitted] [ABSTRACT FROM AUTHOR]

Sheet-like NiCo 2 O 4 and ZnCo 2 O 4 spinels were prepared by metal-organic framework (MOF) as sacrificial template to derive into porous microwave absorber materials. The NiCo and ZnCo MOFs obtained by using 2-methylimidazole linker were decomposed to the sheet-like NiCo 2 O 4 and ZnCo 2 O 4 powders, respectively, with the similar specific surface area of 75 m2/g and the pore volume of 0.31 cm3/g. However, the NiCo 2 O 4 and ZnCo 2 O 4 absorbers had the distinct microwave absorption performance on account of their various physicochemical properties caused by the nature of Ni and Zn elements. From the practical viewpoint, the MOF-derived NiCo 2 O 4 sample had the broader effective absorption bandwidth (>3 GHz) at smaller thicknesses (<3 mm) in the Ku and X bands, whereas a significant fraction of C2, C1, and S bands could be absorbed by the MOF-derived ZnCo 2 O 4 sample. [ABSTRACT FROM AUTHOR]

Environmental problems caused by the utilization of fossil energy are becoming more and more serious, so now more attention has been paid to the use of renewable energy. Pyrolysis of biomass is a method that convert biomass energy into hydrogen, but this method is subject to the performance of the catalyst for the pyrolytic reaction. In this study, NiCo 2 O 4 was synthesized by coprecipitation method and examined by microstructure and textual characterizations. The ability of NiCo 2 O 4 to pyrolyze toluene and produce hydrogen was evaluated by temperature-programmed experiment and lifetime test. It was found that the sample could pyrolyze toluene at the concentration of 1500 ppm at 300 °C with a hydrogen production of 0.6%, suggesting toluene was completely pyrolyzed. In the longevity test, toluene can be completely pyrolyzed for at least 5 h at 400 °C, with a high hydrogen yield of above 80% maintained during the pyrolysis process. As the pyrolysis reaction progresses, NiCo 2 O 4 was gradually reduced to nickel-cobalt alloy by hydrogen from the pyrolysis of toluene, indicating the actual active site of nickel-cobalt alloy. This study gives a hint for developing a good catalyst for the ultra-low temperature biomass pyrolysis to produce hydrogen. • NiCo 2 O 4 was successfully synthesized by coprecipitation method. • High toluene pyrolysis performance and promising stability of NiCo 2 O 4 were examined. • NiCo 2 O 4 maintained good product selectivity in catalytic pyrolysis of toluene. • NiCo 2 O 4 was gradually reduced to nickel-cobalt alloy by hydrogen from the pyrolysis of toluene. [ABSTRACT FROM AUTHOR]

The morphology of nanomaterials plays an important role in the electrochemical sensing performance. Herein, the morphology-dependent electrochemical sensing properties of NiCo2O4 for glucose were studied. NiCo2O4 with one-dimensional (1D) rod structure or two-dimensional (2D) sheet structure was synthesized by just changing solvent composition. The morphology, structure and electrochemical sensing performance of NiCo2O4 were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and amperometric methods. The results of CV characterization show that the magnitude of the oxidation peak current increase obtained on rod-like NiCo2O4 is nearly two times higher than that of sheet-like NiCo2O4, which is due to the faster electron transfer rate of rod-like NiCo2O4. Rod-like NiCo2O4 exhibited higher electrocatalytic activity toward glucose oxidation with a wide linear range of 0.02–5.1 mM, a low detection limit of 2.0 μ M and an ultrahigh sensitivity of 2040 μ A ⋅ mM − 1 ⋅ cm − 2 . Our findings offer a novel morphology-controllable synthesis strategy to understand the morphology impact on the electrochemical performances of NiCo2O4, and represent a facile design of electrocatalysts for sensors. Two kinds of NiCo2O4 nanomaterials with different morphologies were synthesized by adjusting the composition of the solvent. The effect of morphology of NiCo2O4 on the electrocatalytic activity was studied. A novel sensor based on rod-like NiCo2O4 was fabricated for electrochemical sensing of glucose. [ABSTRACT FROM AUTHOR]

In this work, a nanocomposite electrode of MWCNT nanoneedles decorated on spheres like NiCo 2 O 4 /MnO 2 on NF is designed by a hydrothermal method and ultrasonication technique. The resulting interconnected network has an open geometric structure and a porous nature. Furthermore, NiCo 2 O 4 /MnO 2 @MWCNT's greater surface area (174.2 m2/g) promoted ion diffusion and transport, which enhanced specific capacitance. Consequently, this hybrid composite demonstrates a remarkable specific capacitance of 1728 F/g at 1 A/g, in addition to outstanding durability, maintaining 93.83 % of its capacitance after 10,000 cycles. A NiCo 2 O 4 /MnO 2 /MWCNT hybrid composite is used as the positive electrode, while Activated carbon serves as the negative electrode in an asymmetric supercapacitor. This configuration achieves an energy density of 55.8 Wh kg−1 and a maximum power density of 4099 W kg−1. This outcome indicates that the NiCo 2 O 4 /MnO 2 /MWCNT hybrid composite shows promise as highly efficient electrodes in energy storage devices. [Display omitted] • A facile, controllable and low cost hydrothermal method has been used to fabricate MWCNT derived NiCo 2 O 4 /MnO 2 on Ni foam. • NiCo 2 O 4 /MnO 2 @MWCNT electrode displays higher specific capacitance of 1728 Fg-1 than bare NiCo 2 O 4 /MnO 2 @MWCNT (1164 Fg-1). • The fabricated NiCo 2 O 4 /MnO 2 @MWCNT //AC ASC device showed outstanding energy density of 55.8 Whkg−1, power density of 4099 Wkg-1 and good cycle stability (remaining at 93.8% after 10000 cycles) [ABSTRACT FROM AUTHOR]

Transition metal oxides are a promising class of electrode materials for pseudocapacitors due to their high electrochemical activity and eco-friendly nature. However, they possess poor intrinsic conductivity which results in the low energy density of the assembled supercapacitors. In this study, electrodes composed of amorphous C-modified NiCo 2 O 4 (C/NiCo 2 O 4 /NF) on nickel foam substrate were prepared by electrochemical deposition and thermostatic heating method. The incorporation of amorphous C compensates for the low electrical conductivity of NiCo 2 O 4 materials, thereby significantly enhancing the electrochemical performance. The galvanostatic charge-discharge (GCD) test results reveal an impressive specific capacitance of 379.4 mF/cm2 at a current density of 1.5 mA/cm2, and with a capacitance retention rate of 87.1 %. In addition, the symmetric supercapacitor assembled using C/NiCo 2 O 4 electrode materials exhibits exceptional energy density and power density, reaching maximum values of 522.3 μWh/cm2 and 900 μW/cm2 respectively. The device is capable of illuminating LED for up to 8 min, further demonstrating its practical applicability. These results underscore the feasibility and promise of C/NiCo 2 O 4 as an electrode material for the advancement of high-performance supercapacitors. C/NiCo 2 O 4 -50/NF nanomaterials were prepared on nickel foam by electrochemical deposition and constant temperature heating treatment. The symmetric water system and solid-state supercapacitors were assembled with them, and the devices can light up LED lamps. [Display omitted] • Amorphous C was compounded on the surface of NiCo 2 O 4 using thermostatic heating treatment. • Amorphous C composite improves electrode material properties. • Symmetric supercapacitors assembled with C/NiCo 2 O 4 -50/NF have good performance and can light LEDs. [ABSTRACT FROM AUTHOR]

Metal oxide electrode material NiCo 2 O 4 has significant potential for application as an Electrode material due to its excellent electrochemical performance and environmentally friendly characteristics. This paper utilizes a unique airflow-coaxial electrospinning technique combined with a simple one-step solution reaction to prepare NiCo 2 O 4 nanotubes with a complex double-walled hollow structure. The XPS and XRD results demonstrated the synthesis of the NiCo 2 O 4 materials, while the SEM and TEM results verified the presence of a double-walled hollow structure in the NiCo 2 O 4 nanotubes. The electrochemical performance of the NiCo 2 O 4 double-walled hollow nanotubes is significantly improved compared to those single-layer hollow nanotubes. The maximum specific capacitance of those two kinds of nanotubes is 437.5 F/g and 336.7 F/g under the current density of 1 A/g, respectively. The origin of the electrochemical performance improvement can be attributed to the increased specific surface area and the presence of interlayer ion transport channels in the double-walled hollow structure. The study is very helpful in improving the application prospect of NiCo 2 O 4 material as the electrode material of supercapacitors. Equally important, this study also presents an efficient method to fabricate double-walled hollow nanostructures based on special templates. • One-step solution reaction has been used to prepare NiCo 2 O 4 nanotubes with a complex double-walled hollow structure. • A unique airflow-coaxial electrospinning technique has been used to prepare hollow PAN templates. • Electrochemical performance of the NiCo 2 O 4 double-walled hollow nanotubes is significantly improved. [ABSTRACT FROM AUTHOR]

In this study, urchin and tremella-like NiCo 2 O 4 was synthesised by adopting a facile hydrothermal method using green solvents (water and ethanol). Using different ratios and pure forms of green solvents has a direct impact on materials synthesised. Ethanol based NiCo 2 O 4 (NCO-E) illustrated tremella like microspheres with a specific surface area of 260.8 m2 g−1. The electrochemical performance confirmed that the NCO-E has a maximum specific capacitance of 2271 F g−1 at a current density of 1 A g−1. Further, as-fabricated NCO-E//AC-ASC device delivers a C s value of 96.6 F g−1 at 1 A g−1 and a cyclic stability of 99.68 % over 5000 cycles. The device exhibited a high energy density of 30.19 Wh kg−1 at a power density of 749.48 W kg−1 and a high power density of 7542.61 W kg−1 at energy density 18.43 Wh kg−1 owing to the working electrode's effective electrochemical usage and excellent ion transfer mechanism. [Display omitted] [ABSTRACT FROM AUTHOR]

This study employed three-dimensional porous carbon with high surface area as the conductive substrate for composite electrode materials, aiming to facilitate rapid charge transfer and ion diffusion to increase the specific capacitance of pseudo-capacitive materials. We employed an in-situ hydrothermal method to anchor NiCo 2 O 4 onto the porous carbonized verbena leaves, yielding nanostructured VC@NiCo 2 O 4 -8 composite electrode materials. At a current density of 1.0 A g-1, VC@NiCo 2 O 4 -8 exhibited a high specific capacitance of up to 2061.8 F g−1 and remarkable cycling stability (with only 7.8 % capacitance loss after 10000 cycles). Additionally, we assembled VC@NiCo 2 O 4 -8//VC asymmetric all-solid-state flexible supercapacitors, attaining a significant energy density of 54.0 Wh kg−1 at a power density of 695 W kg−1, while maintaining good flexibility and stability. This study provides a simple and effective method for the design and construction of high-performance electrode materials for flexible energy storage devices. [Display omitted] • VC@NiCo 2 O 4 -8 synthesized by in-situ hydrothermal method with carbonized verbena. • VC@NiCo 2 O 4 -8 showed a high specific capacitance of 2061.8 F g−1 at 1.0 A g−1. • All-solid-state SCs exhibited an energy density of 54.0 Wh kg−1 at 695 W kg−1. • VC@NiCo 2 O 4 -8//VC device demonstrated excellent flexibility and stability. [ABSTRACT FROM AUTHOR]

Irradiation is thought to be the most effective approach to change the crystal structure and properties of solid materials. Higher energy gamma-irradiation may change the physical properties of semiconductor materials. Gamma irradiation is recognized as an effective method for altering the crystal structure and properties of solid materials. The primary goal of this study was to assess how gamma irradiation affects different properties of spinel nickel cobaltite. The co-precipitation technique was operated to synthesize spinel nickel cobaltite. The synthesized spinel nickel cobaltite nanoparticles were subjected to gamma irradiation. The study employed gamma doses ranging from 40 KGy to 60 KGy. A gamma irradiator was used for this purpose. Changes induced in the structural, optical, and morphological properties of spinel nickel cobaltite had been investigated by XRD, UV–Vis spectroscopy, SEM, and FTIR. XRD revealed that the average crystalline size of nanoparticles was decreased with gamma irradiation. The band gap, Urbach energy, and extinction coefficient, real and imaginary components of dielectric constant using absorbance and transmittance spectra. The refractive index evaluated from the Moss relation increased from 2.31 to 2.46. The refractive index calculated from Van Vechan's relation increased from 2.60 to 2.78. Urbach energy values increased from 2.14 eV to 2.89 eV with an increased dosage of gamma. It was observed that all parameters were changed by gamma irradiation. SEM study showed that the grain size of particles was decreased with gamma doses. FTIR study verified the spinel-type structure of nickel cobaltite. The study aimed to shed light on the effects of gamma irradiation on spinel nickel cobaltite, with a focus on its structural, optical, and morphological properties. By using a combination of characterization techniques, the researchers can assess how gamma irradiation alters the material's properties and potentially tailor it for specific applications. • Nickel cobalt oxide were synthesized by co-precipitation. • Prepared nanoparticles were irradiated with three different doses of gamma using gamma irradiator. • It was seen that structural and optical parameters of nanoparticles were decreased with increased doses of gamma. • Morphology of nanoparticles changed after gamma irradiation. [ABSTRACT FROM AUTHOR]

The presence of antibiotics in wastewater threatens the human living environment. Activated peroxymonosulfate (PMS) method is often used for catalytic degradation of antibiotics. However, how to reduce catalyst cost and ensure efficient degradation of antibiotics at the same time is a sticky issue for the activated PMS method. Two-dimensional vermiculite flakes (2D-VMT) is cost-effective and can be used as catalyst carriers for PMS activation. Hence, we exfoliated 2D-VMT from natural vermiculite and prepared NiCo 2 O 4 loaded 2D-VMT (NiCo 2 O 4 /2D-VMT) catalyst. Levofloxacin (LVX), as a normal antibiotic, was used to evaluate the catalytic capacity of NiCo 2 O 4 /2D-VMT in PMS systems. Also, LVX degradation mechanism through NiCo 2 O 4 /2D-VMT activated PMS were explored here. XRD, EDS, TEM, and HRTEM analysis all demonstrated NiCo 2 O 4 nanoparticles were successfully anchored on 2D-VMT. NiCo 2 O 4 /2D-VMT had a high specific surface area and abundant active sites. The NiCo 2 O 4 /2D-VMT/PMS system, with a 15% mass ratio of NiCo 2 O 4 to 2D-VMT (15%-CN/2D-VMT), achieved LVX removal efficiency of 87% and LVX removal rate of 0.034 min−1. 1O 2 and SO 4 ·- were the major ROS for LVX degradation. The reversible redox cycle between Co(III)/Co(II) and Ni(III)/Ni(II) played a crucial role in activating PMS to generate ROS for LVX degradation process. Also, based on intermediates identification by LC-MS, possible degradation pathways of LVX were proposed and their ecotoxicological evolution was assessed by using the ECOSAR software. 15%-CN/2D-VMT may be a worth recommended loaded catalyst for antibiotics removal in environmental remediation, owing to its high reusability and excellent renewability. • The cost-effective 2D-VMT derived from simple liquid-phase exfoliation of vermiculite (VMT) as catalyst carriers. • 15%-CN/2D-VMT achieved an LVX removal efficiency of 87% and a LVX removal rate of 0.034 min−1. • 1O 2 and ·SO 4 − were the major ROS for LVX degradation. • 15%-CN/2D-VMT had good performances in stability, reusability, and renewability. [ABSTRACT FROM AUTHOR]

The temporal and spatial segregation of the hydrogen and oxygen evolution reactions (HER and OER) are essential for advancing membrane-free electrolysis technology in H 2 production through water splitting. This investigation employed a two-step fabrication approach to craft a three-dimensional self-supporting buffered electrode. This method involved utilizing a Ni(OH) 2 @NiCo 2 O 4 core-shell nanoneedle array as the active material and nickel foam (NF) as the substrate. Remarkably, the H 2 production at the cathode displayed remarkable efficiency, maintaining an uninterrupted operation duration of 1500 s at a current of 100 mA. Simultaneously, the Ni(OH) 2 @NiCo 2 O 4 mediator on the anodic electrode underwent oxidation during this process, leading to the generation of its respective oxidized state, accompanied by a noteworthy operating voltage of 1.50 V. Afterwards, the second step of the OER involved the recovery of the buffered electrode and the generation of O 2 at an operational voltage of 0.46 V, with the O 2 -production duration being equivalent to that of the first step in the HER process. Interestingly, the revival process of the buffered electrode in the second step can also be coupled with zinc sheets, thereby constructing a battery. During the discharge process of the battery, the regeneration of the buffered electrode was achieved, and this discharge process could also provide a power supply for the first step of H 2 -evolution. Therefore, this decoupled water electrolysis system presents a promising avenue for facilitating the effective transformation of renewable sources into hydrogen. [Display omitted] • Ni(OH) 2 @NiCo 2 O 4 core-shell nanoneedle as a highly-efficient capacitive electrode. • Ni(OH) 2 @NiCo 2 O 4 heterojunction reduces electron transfer resistance. • Decoupled water electrolysis enabled sequential O 2 and H 2 generations. [ABSTRACT FROM AUTHOR]

High-conductive composite fabrics are one class of lightweight, wearable electromagnetic interference (EMI) shields. However, such materials frequently suffer from extremely high reflectivity. Carbon fabric (CF)–NiCo composites were fabricated via hydrothermal and sintering processes with CF as conductive matrix and NiCo compounds as microwave-absorbing agents, and the influences of the morphologies (nanoparticles, nanowire or/and sheets) and structures (NiCo(OH) 6 , NiCo 2 O 4 and NiCo alloy) of NiCo compounds on the EMI shielding properties of CF were investigated. The results revealed that NiCo 2 O 4 sheets not only could improve the impedance matching of CF with electromagnetic waves, but also enriched its interfacial structures, leading to the enhanced internal absorption loss and reduced surface reflection loss simultaneously. Consequently, the CF-NiCo 2 O 4 composite in thickness only of 0.34 mm showed the shielding effectiveness of 53 dB, reflectivity of ∼0.85 and absorptivity of ∼0.15, much better than ∼45 dB, ∼0.97 and ∼0.03 for CF, highlighting the advantages of NiCo 2 O 4 sheets in the fabrication of lightweight, green EMI shielding fabrics. [Display omitted] [ABSTRACT FROM AUTHOR]

The large-scale practical application of cost-efficient lithium sulfur (Li–S) battery with high energy density is impeded due to the shuttle effect and torpid kinetics of polysulfides. Hence, it is significant for Li–S battery to solve these disadvantages to boost the electrochemical performances and facilitate the popularization in various fields. Herein, we synthesized a conductive NiCo 2 O 4 @PPy micro-flower-like material via hydrothermal technique followed by subsequent in-situ vapor phase polymerization, and the material was assembled into Li–S batteries to obtain satisfactory electrochemical performances. Flower-like NiCo 2 O 4 expedites the conversion of polysulfides through both physical adsorption and chemical anchoring. Polypyrrole can efficaciously confine polysulfides shuttling, increase the conductivity and concurrently promote lithium ions diffusion. NiCo 2 O 4 @PPy is simultaneously served as the effective cathode material and multi-functional interlayer for anchoring-catalyzing polysulfides, which can exhibit a satisfying initial capacity of 1588 mAh g−1 at 0.1C, and the average coulomb efficiency is 95.2%. The highest discharge specific capacity of 740 mAh g−1 is displayed at 2C and the capacity decay rate is 0.107% per cycle after 400 cycles. NiCo 2 O 4 @PPy composite is a favorable sulfur host material intimated by these new results, and it is also a competent candidate of interlayer in high-performance Li–S batteries. [Display omitted] • NiCo 2 O 4 @PPy (NCOP) micro-flower-like composite is rationally devised and synthesized. • NCOP composite displays superior conductivity and lithium ion diffusion capability. • NCOP composite can physically adsorb and chemically anchor polysulfides effectively. • NCOP composite efficiently catalyzes the conversion of polysulfide to Li 2 S and Li 2 S 2. • NCOP as sulfur host and interlayer jointly inhibits shuttle effect of polysulfides. [ABSTRACT FROM AUTHOR]

Generally, C3N4 was widely used in the field of photocatalytic hydrogen production, but only few studies focused on electrocatalytic hydrogen production field in Ni/Co based systems. Herein, to investigate the enhanced HER property of C3N4, NiCo2O4@C3N4 were fabricated successfully via a simple mixture method. With the introduction of C3N4, NiCo2O4@C3N4 showed better HER property with small overpotential (89 mV, η10 mA cm−2), low Tafel slope (146 mV dec−1) and superior long‐term stability, thereby indicating the excellent synergistic effect between NiCo2O4 and C3N4. Besides, compared with NiCo2O4, the large electrochemically active surface areas of NiCo2O4@C3N4 (ca. 126 cm2) indicated the abundant active sites, directly proofing the HER enhancement of C3N4. According to Density Functional Theory (DFT) calculation results, when NiCo2O4 combined with C3N4, the EH2O* of NiCo2O4@C3N4 decreased from 3.80 to 2.76 eV and, accordingly, the heterostructure possessed an appropriate ΔGH* (0.19 eV, close to Pt), suggesting the unique synergistic effect between NiCo2O4 and C3N4. Meanwhile, H2O interacted with the d orbital of the Co atom and induced more electrons to transfer from NiCo2O4 to C3N4 and H2O sequentially, thereby accumulating plenty of electrons on H2O molecule and further activating H2O molecule. Accordingly, the H−O−H bond angle of H2O was narrowed from 104.3° to 103.2°, meanwhile, the O−H bond length was extended from 0.975 to 0.989 Å, demonstrating the HER enhancement of C3N4. [ABSTRACT FROM AUTHOR]

Nano-sized NiCo 2 O 4 powders were prepared by a facile hydrothermal method. The phase structure, particle morphology, specific surface area and pore size distribution of the powders were examined as a function of their calcination temperature. In view of utilization in supercapacitors, the electrochemical properties of the electrodes prepared from the powders were investigated by means of cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy techniques. In addition, the electrochemical properties of the electrodes were tentatively interpreted with respect to the kinetics parameters of electrons and ions involved in the electrode reaction. The NiCo 2 O 4 powder calcined at 350 °C displayed nanorod morphology (30–50 nm in diameter and 200–400 nm in length) and optimal electrochemical properties among the investigated specimens. The electrode prepared from the powder displayed an outer voltammetric charge of 113 C/g and a charge transfer resistance of 0.39 Ω together with a specific capacitance of 343 C/g under current density of 1 A/g and a capacitance retention of 108% after 5000 charge/discharge cycles measured at 20 A/g. [ABSTRACT FROM AUTHOR]

Multichannel-porous carbon derived from wood can serve as a conductive substrate for fast charge transfer and ion diffusion, supporting the high-theory capacitance of pseudocapacitive materials. Herein, NiCo2O4 nanosheets, which are hierarchically porous, anchored on the surface of carbonized wood via electrodeposition for free-binder high-performance supercapacitor electrode materials, were proposed. Benefiting from the effectively alleviated NiCo2O4 nanosheets accumulation and sufficient active surface area for redox reaction, a N-doped wood-derived porous carbon-NiCo2O4 nanosheet hybrid material (NCNS–NCW) electrode exhibited a specific electric capacity of 1730 F g−1 at 1 A g−1 in 1 mol L−1 KOH and splendid electrochemical firmness with 80% capacitance retention after cycles. Furthermore, an all-wood-based asymmetric supercapacitor based on NCNS–NCW//NCW was assembled and a high energy density of 56.1 Wh kg−1 at a watt density of 349 W kg−1 was achieved. Due to the great electrochemical performance of NCNS–NCW, we expect it to be used as an electrode material with great promise for energy storage equipment. [ABSTRACT FROM AUTHOR]

The development of a high-performance electromagnetic microwave (EMW) absorber is pivotal for the practical realization of EMW pollution issues. However, the design of EMW absorbers with ultra-high reflection loss (R L < −70 dB) at ultrathin matching thickness (<2 mm) still faces daunting challenges. Herein, a NiCo 2 O 4 nanosheets-covered Ti 3 C 2 T x MXene (NiCo 2 O 4 NSs-MXene) heterostructure with multi-layered MXene and vertically grown ultrathin NiCo 2 O 4 nanosheets prepared by detachment process, reflux reaction, and heat-treatment is introduced as a new EMW absorber; this heterostructure enables a shocking EMW absorption performance with R L value of −72.3 dB at a thickness of 1.7 mm. The effective absorption bandwidth (EAB, R L < −10 dB) can also reach a relatively impressive 3.6 GHz. Furthermore, the NiCo 2 O 4 NSs-MXene heterostructure shows large dielectric loss derived from conductive loss, interface polarization, and dipolar polarization. The high magnetic loss in the heterostructure originates from natural resonance and eddy current loss. Hence, the synergistic effect of dielectric loss, magnetic loss, and impedance matching promote the superior EMW absorption performance of NiCo 2 O 4 NSs-MXene heterostructure. This achievement paves the way for the exploitation of heterostructure as an ultrathin and super-strong EMW absorption performance. [Display omitted] [ABSTRACT FROM AUTHOR]

Construction of micro-flower NiCo 2 O 4 oxides assembled from ultrathin nanosheets effectively enhanced electrocatalysis of water. [Display omitted] • NiCo 2 O 4 catalyst with microflower structure was constructed by self-assembly methods. • Reaction kinetics of F-NCO were significantly improved compared with B-NCO. • F-NCO achieved overall water splitting at 10 mA cm−2 with an overpotential of 1.74 V. • Ultra-high durability of F-NCO electrode. Effective regulation of transition metal spinel morphology is crucial for stable bifunctional catalysts in the electrocatalysis of water. In this work, we crafted a fine NiCo 2 O 4 (F-NCO) microflower structure assembled by nanosheet arrays, which exhibited highly efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), outperforming most of the previous transition metal catalysts. Electronic microscope analysis revealed that the thickness of the F-NCO catalyst was only 1.6 nm, much smaller than that (58.8 nm) of bulk NiCo 2 O 4 (B-NCO), and the ultrathin lamellar structure facilitated the exposure of active sites and improved the reaction kinetics. Compared with the B-NCO catalyst, the overpotential of the F-NCO catalyst in HER and OER was reduced by 36 and 82 mV, the active surface area increased by 2.68 and 4.16 times, and the charge transfer resistance values were reduced by 0.42 and 0.61 times, respectively. In the assembled cell, F-NCO/CFP(+)||F-NCO/CFP(−) electrolyzer was able to achieve 10 mA cm−2 at a low cell voltage of 1.74 V, which was much lower than B-NCO/CFP(+)||B-NCO/CFP(−) electrolyzer. In the 12-hour stability test, the potentiometric time dropped by only 30 mV, lower than 70 mV of the B-NCO catalyst. This work presents a facile strategy for developing a bifunctional catalyst for the electrocatalysis of water. [ABSTRACT FROM AUTHOR]

The electromagnetic wave absorption performance of NiCo 2 O 4 nanomaterials revealed a strong dependence on the calcination temperature. In particular, NiCo 2 O 4 sample obtained through calcination at 400 °C have a remarkable maximum reflection loss (−53.93 dB). A wide absorption bandwidth of 6.24 GHz can also be founded. [Display omitted] This study addresses a scientific challenge by elucidating the influence of calcination temperature on the properties and electromagnetic wave absorption capabilities of NiCo 2 O 4 , a material whose performance is inherently tied to its preparation process. Specifically, we systematically investigate how varying calcination temperatures not only diversify the material's composition and morphology but also enhance its electromagnetic wave absorption properties. By controlling the calcination temperature, we not only achieve the successful synthesis of NiCo 2 O 4 but also unravel intricate correlations among calcination conditions, material composition, and wave absorption performance. Notably, NiCo 2 O 4 sample calcined at 400 °C exhibits remarkable electromagnetic wave absorption, marked by an exceptional maximum reflection loss of −53.93 dB and a broad absorption bandwidth spanning 6.24 GHz. These insights contribute to advancing the frontiers of NiCo 2 O 4 utilization, particularly in the realm of electromagnetic wave absorption and beyond, underscoring the novelty and impact of our research. [ABSTRACT FROM AUTHOR]

[Display omitted] A new ZnO/NiCo 2 O 4 photocatalyst was synthesized to develop systems for removing pharmaceutical pollutants. Various properties of the synthesized nanocomposite such as crystal structure, morphology, optical activity, chemical composition, electrochemical functions, and energy band structure were investigated. The study on tetracycline removal showed that the catalytic activity of the ZnO/NiCo 2 O 4 nanocomposite (0.0426 min−1) is significantly higher compared to ZnO and NiCo 2 O 4 individually. Morphology images confirmed the creation of a heterojunction between rice-shaped ZnO and NiCo 2 O 4 nanoparticles. In photoluminescence and electrochemical impedance analyses, the nanocomposite displayed the weakest signal among its components, suggesting effective control of recombination and charge carrier transfer. The combination of NiCo 2 O 4 with ZnO resulted in increased light absorption in the visible spectrum, contributing to its photocatalytic performance. The energy band structure of ZnO and NiCo 2 O 4 was examined, presenting a detailed explanation of the most likely mechanism for the improved photocatalytic activity. [ABSTRACT FROM AUTHOR]

NiO is widely used in supercapacitors because of its low toxicity, low price and environmental friendliness. In this study, NiO/NiCo 2 O 4 composites were prepared on nickel foam substrates using a simple electrochemical deposition technique. By adjusting the deposition time in the electrochemical parameters, the optimum conditions for the deposition process can be fine-tuned. Characterization techniques such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) confirmed the synthesis of NiO/NiCo 2 O 4 composites. The electrochemical properties of the composite electrode NiO/NiCo 2 O 4 /NF were evaluated by cyclic voltammetry (CV), electrostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). The specific capacitance (Cs) of the prepared composite electrode NiO/NiCo 2 O 4 /NF electrode was 717.8 mF/cm2 at 2 mA/cm2 with a capacitance retention of 74.8 %. In addition, Aqueous symmetric supercapacitors (SSCs) and all-solid symmetric supercapacitors were assembled based on the composite NiO/NiCo 2 O 4 /NF electrode, respectively. The aqueous SSCs have a power density of 880 μW/cm2 and an energy density of 123.0 μWh/cm2, the all-solid symmetric supercapacitors have a power density of 960 μW/cm2 and an energy density of 24.27 μWh/cm2. The series connection of two identical capacitors can light up light-emitting diodes (LEDs). This research presents a promising technique for producing Ni-based electrode material for supercapacitors. [Display omitted] • NiO/NiCo 2 O 4 composites were prepared by a simple electrodeposition method. • Specific capacitance of NiO/NiCo 2 O 4 /NF electrode: 717.8 mF/cm2 at 2 mA/cm2, with 74.8 % retention. • Aqueous SSCs based on NiO/NiCo 2 O 4 /NF: power density 880 μW/cm2, energy density 123.0 μWh/cm2. • All-solid supercapacitors based on NiO/NiCo 2 O 4 /NF: power density 960 μW/cm 2 , energy density 24.27 μWh/cm2. [ABSTRACT FROM AUTHOR]

Different concentrations of zirconium with a fixed quantity (4 wt%) of chitosan (CS) doped nickel cobaltite (NiCo 2 O 4) nanorods were synthesized using a co-precipitation approach. This cutting-edge research explores the cooperative effect of Zr-doped CS-NiCo 2 O 4 to degrade the Eriochrome black T (EBT) and investigates potent antibacterial activity against Staphylococcus aureus (S. aureus). Advanced characterization techniques were conducted to analyze structural textures, morphological analysis, and optical characteristics of synthesized materials. XRD pattern unveiled the spinal cubic structure of NiCo 2 O 4 , incorporating Zr and CS peak shifted to a lower 2θ value. UV–Vis spectroscopy revealed the absorption range increased with CS and the same trend was observed upon Zr, showing a decrease in bandgap energy (Eg) from 2.55 to 2.4 eV. The optimal photocatalytic efficacy of doped NiCo 2 O 4 within the basic medium was around 96.26 %, and bactericidal efficacy was examined against S. aureus , revealing a remarkable inhibition zone (5.95 mm). [ABSTRACT FROM AUTHOR]

Undoubtedly, the counter electrode (CE) plays a dominant role on the power conversion efficiency (PCE) of Dye Sensitized Solar Cells (DSSCs), as it regenerates the redox couple and responsible for the continuous activity of the device. Yet, the conventional platinum CE is highly expensive and needs to be replaced with equivalent material to achieve low-cost devices. Aiming this, fabricated DSSCs with Cubic - Copper Cobalt Oxide (C-CCO), Cubic - Nickel Cobalt Oxide (C-NCO) and the composite of C-CCO and C-NCO [i.e C-(CCO/NCO)] as CEs. The Cyclic Voltammetry analysis shows that the minimum peak to peak separation (E pp) value of 0.34 V was obtained for C-(CCO/NCO), indicating that the composite shows excellent catalytic activity. Further, the charge diffusion coefficient and charge transfer resistance of C-(CCO/NCO) composites significantly favour the DSSCs performance. As our main result, we obtained a maximum PCE of 4.56% for C-(CCO/NCO), whereas the efficiency of C-CCO and C-NCO are 3.66% and 3.71%, respectively. The fabricated DSSCs show relatively better performance than contemporary spinel-oxide based DSSCs. The synergetic effect of the composite materials is analysed extensively to understand the improved performance. [Display omitted] • We report the counter electrode performance of CuCo 2 O 4 / NiCo 2 O 4 in the DSSC applications. • Dual oxidation state of CuCo 2 O 4 and NiCo 2 O 4 plays a major role on the counter electrode. • Electrochemical performance confirms the catalytic activity of composites towards iodide electrolyte. • Fabricated device with the prepared counter electrode exhibits a maximum efficiency of 4.56 %. • The mechanism behind the enhanced PCE has been discussed. [ABSTRACT FROM AUTHOR]