Porous NiCo2O4 nanostructures as bi-functional electrocatalysts for CH3OH oxidation reaction and H2O2 reduction reaction

Morphology-Tunable Binary Transition Metal Oxide Heterostructure@Carbon Composites for Lithium-Ion Batteries

Heterostructures of binary and unary transition metal oxides (B and UTMOs) have demonstrated excellent electrochemical performance in lithium-ion batteries (LIBs) due to synergistic effects; however, there remains a lack of research combining multiple strategies for synergy enhancement. Herein, we present the development of crystallinity-controlled heterostructures based on nickel and cobalt oxides (NiCo2O4/NiO and NiO/Co3O4) with different morphologies (urchin- and flower-like structures, e.g., U-NiCo2O4/NiO and F-NiCo2O4/NiO) to investigate the influence of heterostructure combinations and morphologies on electrochemical performance in LIBs. The morphologies of the heterostructures were controlled by adjusting the fluoride concentration during the synthesis of the nickel-cobalt (Ni-Co) precursor, while heterostructure combinations were regulated by heat treatment under specific conditions. When used as anodes for LIBs, electrochemical analyses revealed that the carbon-coated urchin-like U-NiCo2O4/NiO (U-NiCo2O4/NiO@C) sample provided more efficient charge transfer and a shorter Li-ion transport pathway compared to its counterpart (F-NiCo2O4/NiO@C) due to its high surface area and distinctive morphological features. In addition, U-NiCo2O4/NiO@C exhibited superior electrochemical performance as an anode in LIBs than U-NiO/Co3O4@C, indicating that the advantageous effects of BTMO over UTMO can effectively enhance LIB performance. This facile synthesis approach provides a foundation for morphology-controlled heterostructures in the development of high-performance anode materials for LIB applications.

Nickel and cobalt-based tungstate nanocomposites as promising electrocatalysts in alkaline direct methanol fuel cells

In this work, a non-precious group metal (non-PGM) electrocatalyst based on transition metals is introduced as a promising solution for enhancing the efficiency of direct methanol fuel cell (DMFC). Nickel-cobalt mixed tungstate was prepared using a simple co-precipitation method with different molar ratios of Ni, Co and W. The prepared materials were tested and validated using different characterization techniques. It was observed using SEM that the materials are agglomerated amorphous random circular nanocomposite structures. The electrochemical performance of the prepared electrocatalysts revealed that the best nanocomposite was the one with the Ni : Co : W ratio of 1 : 1 : 1.5 (W1.5). This composite showed a higher current density of 229 mA cm-2 towards methanol oxidation at a scan rate of 50 mV s-1 in 1 M methanol at 0.6 V, with the lowest onset potential of 0.33 V. The obtained results present a new strong non-PGM material for direct methanol electro-oxidation reactions and open new doors for economic and earth-abundant electrocatalysts as an alternative to expensive commercially available catalysts.

Alveoli-Like Multifunctional Scaffolds for Optical and Electrochemical In Situ Monitoring of Cellular Responses from Type II Pneumocytes

While breathing, alveoli are exposed to external irritants, which contribute to the pathogenesis of lung disease. Therefore, in situ monitoring of alveolar responses to stimuli of toxicants under in vivo environments is important to understand lung disease. For this purpose, 3D cell cultures are recently employed for examining cellular responses of pulmonary systems exposed to irritants; however, most of them have used ex situ assays requiring cell lysis and fluorescent labeling. Here, an alveoli-like multifunctional scaffold is demonstrated for optical and electrochemical monitoring of cellular responses of pneumocytes. Porous foam with dimensions like the alveoli structure is used as a backbone for the scaffold, wherein electroactive metal-organic framework crystals, optically active gold nanoparticles, and biocompatible hyaluronic acid are integrated. The fabricated multifunctional scaffold allows for label-free detection and real-time monitoring of oxidative stress released in pneumocytes under toxic-conditions via redox-active amperometry and nanospectroscopy. Moreover, cellular behavior can be statistically classified based on fingerprint Raman signals collected from the cells on the scaffold. The developed scaffold is expected to serve as a promising platform to investigate cellular responses and disease pathogenesis, owing to its versatility in monitoring electrical and optical signals from cells in situ in the 3D microenvironments.

Advanced Urea Precursors Driven NiCo2O4 Nanostructures Based Non-Enzymatic Urea Sensor for Milk and Urine Real Sample Applications

The electrochemical performance of NiCo2O4 with urea precursors was evaluated in order to develop a non-enzymatic urea sensor. In this study, NiCo2O4 nanostructures were synthesized hydrothermally at different concentrations of urea and characterized using scanning electron microscopy and X-ray diffraction. Nanostructures of NiCo2O4 exhibit a nanorod-like morphology and a cubic phase crystal structure. Urea can be detected with high sensitivity through NiCo2O4 nanostructures driven by urea precursors under alkaline conditions. A low limit of detection of 0.05 and an analytical range of 0.1 mM to 10 mM urea are provided. The concentration of 006 mM was determined by cyclic voltammetry. Chronoamperometry was used to determine the linear range in the range of 0.1 mM to 8 mM. Several analytical parameters were assessed, including selectivity, stability, and repeatability. NiCo2O4 nanostructures can also be used to detect urea in various biological samples in a practical manner.

Non-enzymatic disposable electrochemical sensors based on CuO/Co3O4@MWCNTs nanocomposite modified screen-printed electrode for the direct determination of urea

A new electrochemical impedimetric sensor for direct detection of urea was designed and fabricated using nanostructured screen-printed electrodes (SPEs) modified with CuO/Co3O4 @MWCNTs. A facile and simple hydrothermal method was achieved for the chemical synthesis of the CuO/Co3O4 nanocomposite followed by the integration of MWCNTs to be the final platform of the urea sensor. A full physical and chemical characterization for the prepared nanomaterials were performed including Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), contact angle, scanning electron microscope (SEM) and transmission electron microscopy (TEM). Additionally, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to study the electrochemical properties the modified electrodes with the nanomaterials at different composition ratios of the CuO/Co3O4 or MWCNTs. The impedimetric measurements were optimized to reach a picomolar sensitivity and high selectivity for urea detection. From the calibration curve, the linear concentration range of 10-12-10-2 M was obtained with the regression coefficient (R2) of 0.9961 and lower detection limit of 0.223 pM (S/N = 5). The proposed sensor has been used for urea analysis in real samples. Thus, the newly developed non-enzymatic sensor represents a considerable advancement in the field for urea detection, owing to the simplicity, portability, and low cost-sensor fabrication.

Carbon nanocoils decorated with a porous NiCo2O4 nanosheet array as a highly efficient electrode for supercapacitors

Well-organized substrate materials are of considerable significance in the development of energy-efficient pseudocapacitor electrodes. Herein, functionalized three-dimensional (3D) carbon nanocoils on nickel foam (CNCs/NF) have been used as the substrate to grow faradaic nickel cobaltite (NiCo2O4) via a solvothermal method. The arrays of NiCo2O4 were assembled by interconnected ultrathin nanosheets with random inter-particle pores. The number of electroactive sites increased specifically because of the porous feature of NiCo2O4 nanosheets and the 3D structure of CNCs/NF. Moreover, the CNCs/NF network aided the electrolyte ions in diffusing deeply within the architecture. The NiCo2O4/CNCs/NF composite exhibited an outstanding specific capacitance of 2821 F g-1 at the current density of 1 A g-1, a remarkable rate capability (82.4%) and long cyclic stability (91.7% after 3000 cycles). Such encouraging electrochemical performance was attributed mainly to the synergistic interactions of NiCo2O4 arrays and CNCs/NF substrate that helped achieve efficient redox reactions, enhanced ion diffusivity and excellent electron conductivity. In summary, this binder-free NiCo2O4/CNCs/NF composite electrode paves a way towards the synthesis of highly efficacious electrodes for supercapacitors.

Effect of Anode Material on Electrochemical Oxidation of Low Molecular Weight Alcohols-A Review

The growing climate crisis inspires one of the greatest challenges of the 21st century-developing novel power sources. One of the concepts that offer clean, non-fossil electricity production is fuel cells, especially when the role of fuel is played by simple organic molecules, such as low molecular weight alcohols. The greatest drawback of this technology is the lack of electrocatalytic materials that would enhance reaction kinetics and good stability under process conditions. Currently, electrodes for direct alcohol fuel cells (DAFCs) are mainly based on platinum, which not only provides a poor reaction rate but also readily deactivates because of poisoning by reaction products. Because of these disadvantages, many researchers have focused on developing novel electrode materials with electrocatalytic properties towards the oxidation of simple alcohols, such as methanol, ethanol, ethylene glycol or propanol. This paper presents the development of electrode materials and addresses future challenges that still need to be overcome before direct alcohol fuel cells can be commercialized.

High activity of NiCo2O4 promoted Pt on three-dimensional graphene-like carbon for glycerol electrooxidation in an alkaline medium

Spinel oxide NiCo₂O₄ supported on a three-dimensional hierarchically porous graphene-like carbon (3D HPG) material has been firstly used to enhance the activity of Pt for glycerol electrooxidation. The addition of NiCo₂O₄ into the Pt/HPG catalyst can significantly improve the catalytic performance for glycerol oxidation. When NiCo₂O₄ is added to the Pt/HPG catalyst, the onset potential is 25 mV more negative than that on the Pt/HPG catalyst without NiCo₂O₄. The current density at -0.3 V on the Pt-NiCo₂O₄ (wt 10 : 1)/HPG electrode is 1.3 times higher than that on the Pt (30 wt%)/HPG electrode. The Pt-NiCo₂O₄ electrode presented in this work shows great potential as an electrocatalyst for glycerol electrooxidation in an alkaline medium.

NiCo2O4 Nano-/Microstructures as High-Performance Biosensors: A Review

Non-enzymatic biosensors based on mixed transition metal oxides are deemed as the most promising devices due to their high sensitivity, selectivity, wide concentration range, low detection limits, and excellent recyclability. Spinel NiCo2O4 mixed oxides have drawn considerable attention recently due to their outstanding advantages including large specific surface area, high permeability, short electron, and ion diffusion pathways. Because of the rapid development of non-enzyme biosensors, the current state of methods for synthesis of pure and composite/hybrid NiCo2O4 materials and their subsequent electrochemical biosensing applications are systematically and comprehensively reviewed herein. Comparative analysis reveals better electrochemical sensing of bioanalytes by one-dimensional and two-dimensional NiCo2O4 nano-/microstructures than other morphologies. Better biosensing efficiency of NiCo2O4 as compared to corresponding individual metal oxides, viz. NiO and Co3O4, is attributed to the close intrinsic-state redox couples of Ni3+/Ni2+ (0.58 V/0.49 V) and Co3+/Co2+ (0.53 V/0.51 V). Biosensing performance of NiCo2O4 is also significantly improved by making the composites of NiCo2O4 with conducting carbonaceous materials like graphene, reduced graphene oxide, carbon nanotubes (single and multi-walled), carbon nanofibers; conducting polymers like polypyrrole (PPy), polyaniline (PANI); metal oxides NiO, Co3O4, SnO2, MnO2; and metals like Au, Pd, etc. Various factors affecting the morphologies and biosensing parameters of the nano-/micro-structured NiCo2O4 are also highlighted. Finally, some drawbacks and future perspectives related to this promising field are outlined.

Co-Ni Alloy Encapsulated by N-doped Graphene as a Cathode Catalyst for Rechargeable Hybrid Li-Air Batteries

A hybrid Li-air battery uses a protected lithium anode and a porous air cathode in an aqueous electrolyte, based on a 4-e oxygen reduction reaction/oxygen evolution reaction (ORR/OER). It avoids the insoluble and insulating Li₂O₂ product in a typical nonaqueous Li-air battery, and it owns unique advantages. A bifunctional cathode catalyst is crucial to battery performance. Here, we synthesize an ultrathin N-doped graphene-encapsulated nanosphere Co-Ni alloy (Co-Ni@NG). It has hierarchical architecture consisting of a uniform Co-Ni nanoalloy coated with a thin layer of N-doped graphene, showing high activity, high stability, and lower overpotential between the ORR and OER (0.55 V between onset potentials). It exhibited a discharge/charge voltage gap of 0.55 V at a current density of 1.4 mA cm^-2, which is much smaller than the commercial Pt/C catalyst. It delivered an energy density of 3158 Wh kg^-1 and a power density as high as 134.2 W m^-2 at a current density of 7 mA cm^-2. The graphene shells protect the alloy catalyst and improve the durability of the catalyst. One hundred cycles were demonstrated without significant deterioration. It was testified as a promising energy storage system with high energy density, efficiency, reliability, and durability.

A practical non-enzymatic urea sensor based on NiCo2O4 nanoneedles

We propose a new facile electrochemical sensing platform for determination of urea, based on a glassy carbon electrode (GCE) modified with nickel cobalt oxide (NiCo₂O₄) nanoneedles.

Synthesis of hierarchical Co3O4@NiO core-shell nanotubes with a synergistic catalytic activity for peroxidase mimicking and colorimetric detection of dopamine

Fabrication of core-shell nanostructured catalyst is a promising way for tuning its catalytic performance due to the highly active interface and rich redox properties. In this work, hierarchical Co₃O₄@NiO core-shell nanotubes are fabricated by the deposition of NiO shells via a chemical bath treatment using electrospun Co-C composite nanofibers as templates, followed by a calcination process in air. The as-prepared Co₃O₄@NiO core-shell nanotubes exhibit a uniform and novel hollow structure with Co₃O₄ nanoparticles attached to the inner wall of NiO nanotubes and excellent catalytic activity toward the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂. Due to the synergistic effect, the peroxidase-like activity of the Co₃O₄@NiO core-shell nanotubes is much higher than that of individual Co₃O₄ and NiO components. Owing to the superior peroxidase-like activity, a simple and rapid colorimetric approach for the detection of dopamine with a detection limit of 1.21µM and excellent selectivity has been developed. It is anticipated that the prepared Co₃O₄@NiO core-shell nanotubes are promising materials applied for biomedical analysis and environmental monitoring.

Chemical bath deposition of NiCo2S4 nanostructures supported on a conductive substrate for efficient quantum-dot-sensitized solar cells and methanol oxidation

Hierarchical nanostructures have recently attracted massive attention due to their remarkable performances in energy conversion, storage systems, catalysis, and electronic devices.

Ordered Mesoporous NiCo2O4 Nanospheres as a Novel Electrocatalyst Platform for 1-Naphthol and 2-Naphthol Individual Sensing Application

The novel ordered mesoporous NiCo₂O₄ (meso-NiCo₂O₄) nanospheres were synthesized by the nanocasting strategy followed by a calcination process for 2-naphthol (2-NAP) and 1-naphthol (1-NAP) individual sensing application. The as-obtained meso-NiCo₂O₄ material possesses mesoporous structure in spinel crystalline type with a larger specific surface area than other structures. The meso-NiCo₂O₄-modified carbon paste electrode exhibited excellent electrocatalytic performance for NAP detection by amperometry measurement. The fabricated sensor of 2-NAP and 1-NAP has a wide linear detection range (0.02-300 and 0.02-20 μM) with high sensitivity (1.822 and 1.510 μA μM^-1 cm^-2) and low limit of detection (0.007 and 0.007 μM), respectively. In addition, the NAP sensors possess excellent reproducibility, stability, and selectivity.

Facile Synthesis of Core/Shell-like NiCo2O4-Decorated MWCNTs and its Excellent Electrocatalytic Activity for Methanol Oxidation

The design and development of an economic and highly active non-precious electrocatalyst for methanol electrooxidation is challenging due to expensiveness of the precursors as well as processes and non-ecofriendliness. In this study, a facile preparation of core-shell-like NiCo₂O₄ decorated MWCNTs based on a dry synthesis technique was proposed. The synthesized NiCo₂O₄/MWCNTs were characterized by infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and selected area energy dispersive spectrum. The bimetal oxide nanoparticles with an average size of 6 ± 2 nm were homogeneously distributed onto the surface of the MWCNTs to form a core-shell-like nanostructure. The NiCo₂O₄/MWCNTs exhibited excellent electrocatalytic activity for the oxidation of methanol in an alkaline solution. The NiCo₂O₄/MWCNTs exhibited remarkably higher current density of 327 mA/cm² and a lower onset potential of 0.128 V in 1.0 M KOH with as high as 5.0 M methanol. The impressive electrocatalytic activity of the NiCo₂O₄/MWCNTs is promising for development of direct methanol fuel cell based on non-Pt catalysts.

MnO2 nanosheets as a high-efficiency electrocatalyst for H2O2 reduction in alkaline medium

Considering the good ability of MnO₂ for the breakage of the HO–OH bond in H₂O₂, we employed C@TiO₂ nanowire supported MnO₂ as a novel catalyst for H₂O₂ electroreduction.

Hierarchical nickel oxide nanosheet@nanowire arrays on nickel foam: an efficient 3D electrode for methanol electro-oxidation

Hierarchical nickel oxide nanosheet@nanowire arrays hydrothermally grown on nickel foam behave as an efficient 3D anode for electro-catalytic oxidation of methanol in alkaline media.

Template-free synthesis of 3D hierarchical nanostructured NiCo2O4 mesoporous ultrathin nanosheet hollow microspheres for excellent methanol electrooxidation and supercapacitors

Novel 3D hierarchical NiCo₂O₄ mesoporous ultrathin nanosheets hollow microspheres upon a facile template-free solvothermal method followed air-annealing shows excellent methanol electrooxidation and supercapacitors performance.

Nickel Cobaltite Nanostructures for Photoelectric and Catalytic Applications

Bimetallic oxide nickel cobaltite (NiCo2 O4 ) shows extensive potential for innovative photoelectronic and energetic materials owing to their distinctive physical and chemical properties. In this review, representative fabrications and applications of NiCo2 O4 nanostructures are outlined for photoelectronic conversion, catalysis, and energy storage, aiming to promote the development of NiCo2 O4 nanomaterials in these fields through an analysis and comparison of their diverse nanostructures. Firstly, a brief introduction of the spinel structures, properties, and morphologies of NiCo2 O4 nanomaterials are presented. Then, the advanced progress of NiCo2 O4 nanomaterials for both photoelectronic conversion and energy fields is summarized including such examples as solar cells, electrocatalysis, and lithium ion batteries. Finally, further prospects and promising developments of NiCo2 O4 nanomaterials in these significant fields are proposed.

Nickel foam supported mesoporous NiCo2O4 arrays with excellent methanol electro-oxidation performance

Schematic of the electro-oxidation reaction process of NiCo₂O₄ nanocloth arrays on nickel foam. The unique morphological features can afford efficient 3D electron transport during the redox reaction.

Reduced graphene oxide (RGO)-supported NiCo₂O₄ nanoparticles: an electrocatalyst for methanol oxidation

The design and development of cheap, highly active, and durable non-platinum (Pt)-based electrocatalysts for methanol electrooxidation is highly desirable, but is a challenging task. In this paper, we demonstrate the application of a hydrothermally synthesized NiCo₂O₄-reduced graphene oxide (RGO) composite as an electrocatalyst for the electrochemical oxidation of methanol in alkaline pH. The physicochemical properties of the NiCo₂O₄-RGO composite were investigated via Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. The physical characterization methods confirm the deposition of NiCo₂O₄ nanoparticles on the RGO surface. The TEM image shows that the NiCo₂O₄ nanoparticles with an average size of ∼10 nm are distributed over the RGO surface. Compared to RGO and NiCo₂O₄ nanoparticles, the NiCo₂O₄-RGO-based electrode shows excellent electrocatalytic activity for the oxidation of methanol in alkaline pH. On the NiCo₂O₄-RGO-based electrode, the oxidation of methanol occurs at ∼0.6 V with a higher catalytic current density, and the response is highly stable. The excellent electrocatalytic activity of the NiCo₂O₄-RGO composite is attributed to the synergistic effects between the NiCo₂O₄ nanoparticles and RGO. Since the NiCo₂O₄-RGO composite shows a highly stable response during methanol oxidation reaction, it is a very promising material to be used as an electrocatalyst in the development of high performance non-Pt based alkaline fuel cells.