Advanced flower-like Co3O4 with ultrathin nanosheets and 3D rGO aerogels as double ion-buffering reservoirs for asymmetric supercapacitors

Ribbon-like Nickel Cobaltite with Layer-by-Layer-Assembled Ordered Nanocrystallites for Next-Generation All-Solid-State Hybrid Supercapatteries

In the context to develop ultra-efficient electrode materials with good physicoelectrochemical and electrostructural properties, for their application in high-performance supercapatteries, herein, a facile tartrate-mediated inhibited crystal growth method is reported to engineer thoroughly uniform ribbon-like nickel cobaltite (NiCo₂O₄) microstructure with unique layer-by-layer-assembled nanocrystallites. This material demonstrates significant kinetic reversibility, good rate efficiency and bulk diffusibility of the electroactive ions, and a predominant semi-infinite diffusion mechanism during the redox-based charge storage process. This material also shows bias-potential-independent equivalent series resistance, very low charge-transfer resistance, and diagonal Warburg profile, corresponding to the ion diffusion occurring during the electrochemical processes in supercapacitors and batteries. Further, the fabricated NiCo₂O₄-based all-solid-state supercapattery (NiCo₂O₄||N-rGO) delivers excellent rate-specific capacity, very low internal resistance, good electrochemical and electrostructural stability (∼94% capacity retention after 10,000 charge-discharge cycles), energy density (31 W h kg^-1) of a typical rechargeable battery, and power density (13,003 W kg^-1) of an ultra-supercapacitor. The ultimate performance of the supercapattery is ascribed to low-dimensional crystallites, ordered inter-crystallite and channel-type bulk and boundary porosity, multiple reactive equivalents, enhanced electronic conductivity, and "ion buffering pool" like behavior of ribbon-like NiCo₂O₄, supplemented with enhanced electronic and ionic conductivities of N-doped rGO (negative electrode) and PVA/KOH gel (electrolyte separator), respectively.

A Simple Route to Produce Highly Efficient Porous Carbons Recycled from Tea Waste for High-Performance Symmetric Supercapacitor Electrodes

High-performance porous carbons derived from tea waste were prepared by hydrothermal treatment, combined together with KOH activation. The heat-treatment-processed materials possess an abundant hierarchical structure, with a large specific surface of 2235 m² g⁻¹ and wetting-complemental hydrophilicity for electrolytes. In a two-electrode system, the porous carbon electrodes’ built-in supercapacitor exhibited a high specific capacitance of 256 F g⁻¹ at 0.05 A g⁻¹, an excellent capacitance retention of 95.4% after 10,000 cycles, and a low leakage current of 0.014 mA. In our work, the collective results present that the precursor crafted from the tea waste can be a promising strategy to prepare valuable electrodes for high-performance supercapacitors, which offers a practical strategy to recycle biowastes into manufactured materials in energy storage applications.

Mesoporous NiCo2Se4 tube as an efficient electrode material with enhanced performance for asymmetric supercapacitor applications

• One-component NiCo₂Se₄ is synthesized. • The unique mesoporous tubular micro-nanostructure greatly improves the electrochemical performance. • Selenium with high electrical conductivity is beneficial for improving the energy density and power density.

High Electrochemical Performance of Bi2WO6/Carbon Nano-Onion Composites as Electrode Materials for Pseudocapacitors

Bi₂WO₆/CNO (CNO, carbon nano-onion) composites are synthesized via a facile low-cost hydrothermal method and are used pseudocapacitor electrode material. X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption-desorption techniques, and X-ray photoelectron spectroscopy (XPS) measurements are used to characterize the synthesized composite powders. The electrochemical performances of the composite electrodes are studied by cycle voltammetry, charge-discharge, and electrochemical impedance spectroscopy. The results indicate that the specific capacitance of the Bi₂WO₆/CNO composite materials reaches up to 640.2 F/g at a current density of 3 mA/cm² and higher than that of pristine Bi₂WO₆, 359.1 F/g. The capability of the prepared pseudocapacitor remains 90.15% after 1,000 cycles of charge-discharge cycling measurement. The cell performance and stability can be enhanced by further optimization and modification of the composition and microstructure of the electrode of the cell.

High-performance double ion-buffering reservoirs of asymmetric supercapacitors based on flower-like Co3O4-G>N-PEGm microspheres and 3D rGO-CNT>N-PEGm aerogels

Novel 3D flower-like Co3O4-G>N-PEGm composites have been synthesized by employing a solvothermal method, in which the incorporating graphene nanosheets are modified with methoxypolyethylene glycol (mPEG) via nitrene chemistry to form 2D macromolecular brushes. In Co3O4-G>N-PEGm, the flower-like Co3O4 microspheres can anchor on the G>N-PEGm nanosheets, corresponding to the coordination bonds between the lone pair of electrons on the mPEG polymer chains of the G>N-PEGm macromolecular brushes and cobalt ions. Owing to the novel structure, a high specific capacitance value of 1625.6 F g-1 at a current density of 0.5 A g-1 can be achieved in KOH solution. Meanwhile, 3D rGO-CNT>N-PEGm aerogels (GCA), as the negative electrode of electrical double-layer capacitor materials, exhibit a high reversible specific capacitance of 313.8 F g-1 at a current density of 2 A g-1. Based on the high electrochemical performance of both electrode materials, the double ion-buffering reservoirs of asymmetric supercapacitors configured with the Co3O4-G>N-PEGm as the positive electrode and 3D GCA as the negative electrode can deliver a high energy density of 34.4 W h kg-1 at a power density of 400 kW kg-1.