Facile hydrothermal synthesis of NiCo2O4- decorated filter carbon as electrodes for high performance asymmetric supercapacitors

Chitosan-derived carbon and NiCo2O4 aerogel composite for high-performance supercapacitors

This work presents a multi-step strategy to fabricate chitosan-derived nitrogen-doped carbon (CCS) and CCS/NiCo2O4 (CNCO) aerogels for supercapacitor application. The various mass fractions of NiCo precursors and chitosan as well as different carbonization temperatures, were investigated. The best rationally designed aerogel carbonized at 300 °C (CNCO-2) had the highest specific surface area and nitrogen content. It exhibited a high capacitance of 1200 F g-1 at 1.0 A g-1 as an active electrode material for supercapacitors. In addition, the fully solid-state CCS//CNCO-2 device had a high capacitance of 172 F g-1 at 1.0 A g-1 and excellent cyclic stability (over 87 % capacitance retention after 10,000 cycles). This device displayed a maximum energy density of 53 Wh kg-1 at 750 W kg-1. Furthermore, two devices connected in series and parallel indicate typical voltage and capacitance expansion, highlighting practicable applications of chitosan-derived aerogel composites to meet different requirements in energy storage.

Nickel Cobaltite: A Positive Electrode Material for Hybrid Supercapacitors

The increased demand of energy due to the recent technological advances in diverse fields such as portable electronics and electric vehicles is often hindered by the poor capability of energy-storage systems. Although supercapacitors (SCs) exhibit higher power density than state-of-the art batteries, their insufficient energy density remains a major challenge. An emerging concept of hybrid supercapacitors (HSCs) with the combination of one capacitive and one battery electrode in a single cell holds a great promise to deliver high energy density without sacrificing power density and cycling stability. This Minireview elaborates the recent advances of use of nickel cobaltite (NiCo₂ O₄ ) as a potential positive electrode (battery-like) for HSCs. A brief introduction on the structural benefits and charge storage mechanisms of NiCo₂ O₄ was provided. It further shed a light on composites of NiCo₂ O₄ with different materials like carbon, polymers, metal oxides, and others, which altogether helps in increasing the electrochemical performance of HSCs. Finally, the key scientific challenges and perspectives on building high-performance HSCs for future-generation applications were reviewed.

Marigold micro-flower like NiCo2O4 grown on flexible stainless-steel mesh as an electrode for supercapacitors

Nanostructured NiCo₂O₄ is a promising material for energy storage systems. Herein, we report the binder-free deposition of porous marigold micro-flower like NiCo₂O₄ (PNCO) on the flexible stainless-steel mesh (FSSM) as (PNCO@FSSM) electrode by simple chemical bath deposition. The SEM and EDS analysis revealed the marigold micro-flowers like morphology of NiCo₂O₄ and its elemental composition. The porous nature of the electrode is supported by the BET surface area (100.47 m² g⁻¹) and BJH pore size diameter (∼1.8 nm) analysis. This PNCO@FSSM electrode demonstrated a specific capacitance of 530 F g⁻¹ at a high current density of 6 mA cm⁻² and revealed 90.5% retention of specific capacitance after 3000 cycles. The asymmetric supercapacitor device NiCo₂O₄//rGO within a voltage window of 1.4 V delivered a maximum energy density of 41.66 W h kg⁻¹ at a power density of 3000 W kg⁻¹. The cyclic stability study of this device revealed 73.33% capacitance retention after 2000 cycles. These results indicate that the porous NiCo₂O₄ micro-flowers electrode is a promising functional material for the energy storage device.

Binder-free marigold micro-flower like NiCo₂O₄ deposited on FSSM as electrode in ASC device (NiCo₂O₄//rGO) is a promising functional material for energy storage device.

Reagent-assisted hydrothermal synthesis of NiCo2O4 nanomaterials as electrodes for high-performance asymmetric supercapacitors

Spinel nickel cobaltate nanoneedle arrays in situ synthesized by a CTAB assisted hydrothermal method show an energy density of 22.5 W h kg⁻¹ at 800 W kg⁻¹.

Designing vertically aligned porous NiCo2O4@MnMoO4 Core@Shell nanostructures for high-performance asymmetric supercapacitors

NiCo₂O₄@MnMoO₄ core@shell nanostructures are synthesized as electrode material using hydrothermal method for the fabrication of asymmetric supercapacitor (ASC) device. The NiCo₂O₄@MnMoO₄ electrode shows better electrochemical performance with specific capacitance (SC) of 1821 F/g at current density of 5 A/g and cycling stability of 94%. The NiCo₂O₄@MnMoO₄ core@shell electrode shows better SC compared to pure NiCo₂O₄ and MnMoO₄ electrodes. An ASC device is fabricated using NiCo₂O₄@MnMoO₄ as a positive and rGO/Fe₂O₃ as negative electrode materials. Remarkably, the fabricated device shows a SC of 294 F/g at current density 4 A/g, with an energy density of 91.87 Wh/kg at a power density of 374.15 W/kg. The device shows good reversibility with cycling stability of 68% after 2,000 cycles. The ASC device is used to illuminate nine green color LEDs for 35 min. Therefore, the present report provides a simple method to fabricate efficient and stable energy storage devices for industrial applications.

Activated Carbon/MnO2 Composites as Electrode for High Performance Supercapacitors

Activated carbon (AC) was synthesized with various weight ratios of manganese dioxide (MO) through a simple hydrothermal approach. The electrochemical performance of the synthesized activated carbon/MnO2 composites was investigated. The effect of the activated carbon/MnO2 (AM) ratio on the electrochemical properties of the activated carbon/MnO2 composites and the pore structure was also examined. The results show that the specific capacitance of the activated carbon material has been improved after the addition of MO. The as-synthesized composite material exhibits specific capacitance of 60.3 F g−1 at 1 A g−1, as well as stable cycle performance and 99.6% capacitance retention over 5000 cycles.

A Facile Method of Preparing the Asymmetric Supercapacitor with Two Electrodes Assembled on a Sheet of Filter Paper

An asymmetric supercapacitor was prepared on a sheet of filter paper with two modified surfaces acting as electrodes in 1 M potassium hydroxide aqueous solution. By choosing carbon nanotubes and two different kinds of metal oxides (zinc oxide and ferro ferric oxide) as electrode materials, the asymmetric supercapacitor was successfully fabricated. The results showed that this device exhibited a wide potential window of 1.8 V and significantly improved electrochemical performances of its counterparts. Particularly, the one-sheet asymmetric supercapacitor demonstrated high energy density of 116.11 W h/kg and power density 27.48 kW/kg, which was attributed to the combined action and shortened distance between the two electrodes, respectively. Besides, it showed superior electrochemical cycling stability with 87.1% capacitance retention under room temperature. These outstanding results can not only give researchers new insights into compact energy storage systems, but they also provide a good prospect for flexible asymmetric supercapacitors.

Conventional and Microwave Hydrothermal Synthesis and Application of Functional Materials: A Review

With the continuous development and progress of materials science, increasingly more attention has been paid to the new technology of powder synthesis and material preparation. The hydrothermal method is a promising liquid phase preparation technology that has developed rapidly during recent years. It is widely used in many fields, such as the piezoelectric, ferroelectric, ceramic powder, and oxide film fields. The hydrothermal method has resulted in many new methods during the long-term research process, such as adding other force fields to the hydrothermal condition reaction system. These force fields mainly include direct current, electric, magnetic (autoclaves composed of non-ferroelectric materials), and microwave fields. Among them, the microwave hydrothermal method, as an extension of the hydrothermal reaction, cleverly uses the microwave temperature to compensate for the lack of temperature in the hydrothermal method, allowing better practical application. This paper reviews the development of the hydrothermal and microwave hydrothermal methods, introduces their reaction mechanisms, and focuses on the practical application of the two methods.