Hybrid two-dimensional nickel oxide-reduced graphene oxide nanosheets for supercapacitor electrodes

In situ synthesis of europium oxide (Eu2O3) nanoparticles in heteroatom doped carbon nanofibers for boosting the cycling stability of supercapacitors

Maintaining a high specific energy without losing cycling stability is the focus of the supercapacitor field. In this study, carbon nanofibers including europium oxide nanoparticles (CNF/Eu2O3) have been synthesized in the presence of thiourea via a simple approach and applied for the first time as an electrode for SCs. The CNF/Eu2O3-1 electrode doped with nitrogen and sulfur heteroatoms possessed a favorable specific capacitance of 183.2 F g-1, a specific energy of 9.15 W h kg-1, and an excellent capacitance retention of 94.8% even after 10 000 cycles at 1 A g-1. Such excellent performance is ascribed to the surface functionalities, high surface area, and good interaction of Eu2O3 with CNFs. This strategy will provide guidance for other rare element-based electrodes in the field of energy storage.

Advancing Nanoelectronics Applications: Progress in Non-van der Waals 2D Materials

Extending the inventory of two-dimensional (2D) materials remains highly desirable, given their excellent properties and wide applications. Current studies on 2D materials mainly focus on the van der Waals (vdW) materials since the discovery of graphene, where properties of atomically thin layers have been found to be distinct from their bulk counterparts. Beyond vdW materials, there are abundant non-vdW materials that can also be thinned down to 2D forms, which are still in their early stage of exploration. In this review, we focus on the downscaling of non-vdW materials into 2D forms to enrich the 2D materials family. This underexplored group of 2D materials could show potential promise in many areas such as electronics, optics, and magnetics, as has happened in the vdW 2D materials. Hereby, we will focus our discussion on their electronic properties and applications of them. We aim to motivate and inspire fellow researchers in the 2D materials community to contribute to the development of 2D materials beyond the widely studied vdW layered materials for electronic device applications. We also give our insights into the challenges and opportunities to guide researchers who are desirous of working in this promising research area.

Natural resource-derived NiO nanoparticles via aloe vera for high-performance symmetric supercapacitor

This investigation reported a one-step green synthesis of nickel oxide nanoparticles (NiO NPs) using aloe vera leaves extract solution for their application in a supercapacitor. This method used aloe vera leaves as a reducing agent, which is very simple and cost-effective. The synthesized NPs were thoroughly characterized using various techniques. The X-ray diffraction analysis unequivocally confirmed the crystalline nature; field emission scanning electron microscopy and transmission electron microscopy images showed different shapes and forms of an agglomerated cluster of synthesized NPs. The absorption spectra were recorded from UV visible spectroscopy, while Fourier transform infrared spectroscopy provided insights into the functional groups present. Electrochemical assessments were carried out via cyclic voltammetry, galvanostatic charging-discharging and electrochemical impedance spectroscopy. These experiments were performed using a 2 M KOH electrolyte within a 1.0 V potential window. Impressively, the single electrode displayed a remarkable specific capacitance of 462 F g-1 at a scan rate of 1 mV s-1 and 336 F g-1 at a current density of 0.76 A g-1. Further, a symmetric two-electrode device (NiO||NiO) has been successfully fabricated by employing a separator between the electrodes. The device exhibited an exceptional specific capacitance of approximately 239 F g-1, along with an energy density of 47.8 Wh kg-1 and a power density of 545 W kg-1 at 1 A g-1 current density within a 1.2 V potential window. The fabricated device also shows a retention capacity of 89% at 10 A g-1 after 2000 cycles with 114% of columbic efficiency. The present study underscores the effectiveness of the green synthesis approach in producing NiO NPs and establishes their potential as highly promising candidates for supercapacitor applications, showcasing both excellent electrochemical performance in a three-electrode system and remarkable stability in a practical two-electrode device. The results collectively highlight the efficacy of the green approach in producing NiO NPs, establishing its potential as a highly promising candidate for supercapacitor application.

Engineering of nickel, cobalt oxides and nickel/cobalt binary oxides by electrodeposition and application as binder free electrodes in supercapacitors

Cobalt oxide, nickel oxide and cobalt/nickel binary oxides were synthesised by electrodeposition. To fine tune composition of CoNi alloys, growth parameters including voltage, electrolyte pH/concentration and deposition time were varied. These produced nanomaterials were used as binder free electrodes in supercapacitor cells and tested using three electrode setup in 2 MKOH aqueous electrolyte. Cyclic voltammetry and galvanostatic charge/discharge were used at different scan rates (5-100 mV/s) and current densities (1-10 A/g) respectively to investigate the capacitive behaviour and measure the capacitance of active material. Electrochemical impedance spectroscopy was used to analyse the resistive/conductive behaviours of these electrodes in frequency range of 100 kHz to 0.01 Hz at applied voltage of 10 mV. Binary oxide electrode displayed superior electrochemical performance with the specific capacitance of 176 F/g at current density of 1 A/g. This hybrid electrode also displayed capacitance retention of over 83% after 5000 charge/discharge cycles. Cell displayed low solution resistance of 0.35 Ω along with good conductivity. The proposed facile approach to synthesise binder free blended metal electrodes can result in enhanced redox activity of pseudocapacitive materials. Consequently, fine tuning of these materials by controlling the cobalt and nickel contents can assist in broadening their applications in electrochemical energy storage in general and in supercapacitors in particular.

Honeycomb-like nickel oxide-reduced graphene oxide based sensor for the electrochemical tracking of norepinephrine in neuronal cells

Highly sensitive and specific detection and monitoring of trace norepinephrine (NE) in biological fluids and neuronal cell lines is essential for the investigation of pathogenesis of certain neurological diseases. Herein, we constructed a novel electrochemical sensor for real-time monitoring of NE released by PC12 cells based on glassy carbon electrode (GCE) modified with honeycomb-like nickel oxide (NiO)-reduced graphene oxide (RGO) nanocomposite. The synthesized NiO, RGO and the NiO-RGO nanocomposite were characterized using X-ray diffraction spectrogram (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The porous three-dimensional honeycomb-like structure of NiO and high charge transfer kinetics of RGO endowed the nanocomposite with excellent electrocatalytic activity, large surface area and good conductivity. The developed sensor exhibited superior sensitivity and specificity towards NE in a wide linear range from 20 nM to 14 μM and 14 μM-80 μM, with a low detection limit of 5 nM. The performances of the sensor in terms of excellent biocompatibility and high sensitivity allow it to be successfully employed in the tracking of NE release from PC12 cells under the stimulation of K⁺, providing an effective strategy for the real-time monitoring of cellular NE.

Core-Shell Carbon Nanofibers@Ni(OH)2/NiO Composites for High-Performance Asymmetric Supercapacitors

The application of transition metal oxides/hydroxides in energy storage has long been studied by researchers. In this paper, the core-shell CNFs@Ni(OH)₂/NiO composite electrodes were prepared by calcining carbon nanofibers (CNFs) coated with Ni(OH)₂ under an N₂ atmosphere, in which NiO was generated by the thermal decomposition of Ni(OH)₂. After low-temperature carbonization at 200 °C, 250 °C and 300 °C for 1 h, Ni(OH)₂ or/and NiO existed on the surface of CNFs to form the core-shell composite CNFs@Ni(OH)₂/NiO-X (X = 200, 250, 300), in which CNFs@Ni(OH)₂/NiO-250 had the optimal electrochemical properties due to the coexistence of Ni(OH)₂ and NiO. Its specific capacitance could reach 695 F g^-1 at 1 A g^-1, and it still had 74% capacitance retention and 88% coulomb efficiency after 2000 cycles at 5 A g^-1. Additionally, the asymmetric supercapacitor (ASC) assembled from CNFs@Ni(OH)₂/NiO-250 had excellent energy storage performance with a maximum power density of 4000 W kg^-1 and a maximum functional capacity density of 16.56 Wh kg^-1.

Facile One-Step Microwave-Assisted Method to Synthesize Nickel Selenide Nanosheets for High-Performance Hybrid Supercapacitor

Nanosheets structures can be employed as the most promising electrode material to enhance electrochemical performance for supercapacitors. Nickel Selenide (Ni_0.85Se) nanosheets are synthesized using a rapid microwave synthesis method in a single step. The Ni_0.85Se nanosheets possess a high surface area (125 m²g^-1) with a hexagonal crystalline structure. It shows magnificent electrochemical properties, such as splendid specific capacitance (2530 Fg^-1 at 0.5 Ag^-1). An asymmetric hybrid supercapacitor is fabricated with nickel selenide nanosheets as a positive electrode and activated carbon as a negative electrode. The assembled hybrid supercapacitor displays a high energy density of 63.5 WhKg^-1 at a power density of 404 WKg^-1, and after 8000 cycles, only 5% capacitance is lost along with the better voltage window at 0-1.6 V.

Microwave heating followed by a solvothermal method to synthesize nickel–cobalt selenide/rGO for high-performance supercapacitors

Efficient microwave heating followed by a solvothermal method is used to synthesize (Ni0.85Se)3(Co0.85Se)/rGO nanorods with an ultrahigh specific capacitance of 2009 F g−1 at a current density of 2 A g−1.