The first structural, morphological and magnetic property studies on spinel nickel cobaltite nanoparticles synthesized from non-standard reagents

In this paper, using a molten salt process, nickel cobaltite nanoparticles were successfully synthesized for the first time from non-standard reagents.

Stimulation of ethylene glycol electrooxidation on electrodeposited Ni–PbO2–GN nanocomposite in alkaline medium

In this work, a novel system composed of non-precious nickel-based metal oxide/reduced graphene oxide nanocomposite (Ni–PbO2–GN) is used for electrooxidation of ethylene glycol (EG) in 1.0 M NaOH solution and compares its activity with that of Ni, Ni–GN, and Ni–PbO2. The facile electrodeposition technique is used to prepare the catalysts on glassy carbon (GC) substrates. The outcomes of electrochemical measurements show a high performance towards EG oxidation is obtained for Ni-nanocomposite electrodes compared to that of Ni mainly due to their higher surface areas. The excellent electrocatalytic properties of the Ni-nanocomposite could be ascribed to the synergistic contributions of PbO2 and graphene (GN) nano-sheets that help the reduction of Ni grains. A smaller charge transfer resistance value of 34.5 Ω cm2 for EG oxidation reaction at + 360 mV is recorded for GC/Ni–PbO2–GN compared to the other prepared electrodes. Moreover, it exhibits higher kinetic parameters of EG such as diffusion coefficient (D = 3.9 × 10–10 cm2 s−1) and charge transfer rate constant (ks = 32.5 mol−1 cm3 s−1). The overall performance and stability of the prepared catalysts towards EG electrooxidation have been estimated to be in the order of GC/Ni–PbO2–GN > GC/Ni–GN > GC/Ni–PbO2 > GC/Ni.

Graphical abstract

Mesoporous K-doped NiCo2O4 derived from a Prussian blue analog: high-yielding synthesis and assessment as oxygen evolution reaction catalyst

The conversion and storage of clean renewable energy can be achieved using water splitting. However, water splitting exhibits sluggish kinetics because of the high overpotentials of the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) and should therefore be promoted by OER and/or HER electrocatalysts. As the kinetic barrier of the former reaction exceeds that of the latter, high-performance OER catalysts are highly sought after. Herein, K-doped NiCo₂O₄ (HK-NCO) was hydrothermally prepared from a Prussian blue analog with a metal–organic framework structure and assessed as an OER catalyst. Extensive K doping increased the number of active oxygen vacancies and changed their intrinsic properties (e.g., binding energy), thus increasing conductivity. As a result, HK-NCO exhibited a Tafel slope of 49.9 mV dec⁻¹ and a low overpotential of 292 mV at 10 mA cm⁻², outperforming a commercial OER catalyst (Ir) and thus holding great promise as a component of high-performance electrode materials for metal-oxide batteries and supercapacitors.

OER characteristics of K-doped NiCo₂O₄ catalyst and K doping control through simple hydrothermal synthesis.

Molybdenum doped induced amorphous phase in cobalt acid nickel for supercapacitor and oxygen evolution reaction

Reasonable structural design and metal-doping play significant roles in the optimization of electrochemical energy storage and conversion. Herein, in situ growth of Molybdenum-doped amorphous cobalt acid nickel nanoneedles on Ni foam (Mo-NiCo₂O₄/NF) has been successfully synthesized by a simple hydrothermal-annealing strategy. Benefiting from the unique hierarchical nanostructures and doping-optimized electronic structural configuration, the cross-link network structure of Mo-doped amorphous NiCo₂O₄ with large specific surface areas exhibit excellent supercapacitor performance and electrocatalytic activity. As expected, the optimized Mo-doped NiCo₂O₄ samples possess a specific capacitance of 3970 mF cm^-2 at 1 mA cm^-2 and remarkable rate performance. The assembled hybrid supercapacitor obtains a maximum energy density of 35 Wh kg^-1 (420 W kg^-1) and keeps a capacitance retention of 107% after 5000 cycles. As an electrocatalyst, Mo-NiCo₂O₄/NF shows a rapid self-reconstruction process during oxygen evolution reaction (OER) that produces rich oxygen vacancies and thus exhibits remarkable long-term stability. The nanocomposites exhibit small overpotential (280 mV at 10 mA cm^-2) and Tafel slope (43 mV dec^-1). These results strongly demonstrate that both local amorphous phase and porous hierarchical structure design from Mo dopant provide superiorities for the synthesis of efficient and stable multifunctional electrode materials for energy storage and conversion.

Preparation and electrochemical properties of nanostructured porous spherical NiCo2O4 materials

Porous spherical NiCo₂O₄ powders with a micro–nano structure were prepared by the spray drying method using citric acid as the chelating agent and soluble salts as cobalt and nickel sources. By calcination at 300 °C, spherical and single-phase spinel-type NiCo₂O₄ powders were obtained. The powders with particle sizes of 0.5–3 μm were aggregations of nano-sized grains (about 15–30 nm). The electrical property tests demonstrated that the synthesized NiCo₂O₄ has a specific capacitance of 430.67 F g⁻¹ at a current density of 1 A g⁻¹ and a capacitance retention rate of 100% after 3000 cycles at a current density of 4 A g⁻¹, indicating excellent cycling stability. On assembly into an asymmetric supercapacitor device, a specific capacitance of 37.06 F g⁻¹ and energy density of 13.18 W h kg⁻¹ at a power density of 800 W kg⁻¹ and a current density of 1 A g⁻¹ were demonstrated. The micro–nano structured porous NiCo₂O₄ powders have a larger specific surface area, which can allow the sample to come in full contact with the electrolyte. The nanopore channels are favourable for releasing the lattice distortion stress during the charge–discharge process, maintaining the structural stability of the crystal and improving the cycle life.

Porous NiCo₂O₄ microspheres with a micro–nano structure, prepared by the spray drying method, have excellent cycle stability and 100% capacitance retention.

Reduced Graphene Oxide-Conjugated Urchin-Like NiCo2O4 Nanostructures for Individual Detection of o-Nitro and p-Amino Phenol

This work introduced a facile synthesis method of reduced graphene oxide-conjugated urchin-like NiCo2O4 nanostructures via a simple, cost-effective, and environmental-friendly one-pot hydrothermal method. The as-prepared rGO-NiCo2O4 nanocomposites were used to fabricate 3-aminopropyltriethoxysilane-modified glassy carbon electrode (GCE/APTES/rGO-NiCo2O4) for ultrasensitive electrochemical detection of o-nitro (o-NP) and p-amino (p-AP) phenols. The structure and morphology of the nanocomposite were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Electrochemical experiments revealed that the nanocomposite exhibited remarkable electrochemical performances. A linear relationship is observed with the differential pulse voltammetry experiment between the peak currents and the concentrations in the ranges of 5.0 × 10-9 to 5.0 × 10-7 M (R 2 = 0.996) and 1.0 × 10-6 to 2.5 × 10-5 M (R 2 = 0.992) for o-NP and of 1.0 × 10-8 to 5.0 × 10-7 M (R 2 = 0.996) and 1.0 × 10-6 to 1.0 × 10-4 M (R 2 = 0.987) for p-AP. The calculated detection limits (S/N = 3) are 5.0 × 10-9 M and 1.0 ×10-8 M for o-NP and p-AP, respectively. Furthermore, a very high recovery percentage is obtained with the proposed sensor after successful application in the determination of target analytes in tap water samples.

NiCo2O4 nanosheets grown on interconnected honeycomb-like porous biomass carbon for high performance asymmetric supercapacitors

An interconnected honeycomb-like structure of the HLPBC/NiCo₂O₄ composite was successfully prepared by carbonization combined with a facile hydrothermal process.

Multifunctional porous NiCo2O4 nanorods: sensitive enzymeless glucose detection and supercapacitor properties with impedance spectroscopic investigations

Multifunctional NiCo₂O₄ nanorods fabricated by a simple two-step method exhibit excellent performance in glucose sensors as well as supercapacitors.

Interconnected hierarchical NiCo2O4 microspheres as high-performance electrode materials for supercapacitors

Hierarchical NiCo₂O₄ microspheres with large tunnels and abundant mesopores have been prepared, and they exhibit excellent performance in supercapacitor applications.