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The rapid development of economy and technology caused numerous irreversible effects on the environment, and the rational use and storage of existing resources have became an indispensable process in modern development. Energy storage through supercapacitors can effectively alleviate part of the energy crisis. Here, the effects of heating rates on the morphology of carbonized bacterial cellulose (CBC) carbon and its electrochemical properties were studied and CBC-5 (heating rate of 5 ℃/min) with porous structure was confirmed to be supporting material for loading MnO 2. The specific capacitance of CBC-5@MnO 2 composites was high up to 190 F g−1 at 1 A g−1, and its capacitance retention rate was up to 96.6% after 8000 cycles. The superior electrochemical performance cannot be achieved without the cooperative effect among the metal oxides and carbon materials, which also benefits from the fast transport of ions and electrons in solution. The assembled CBC-5//CBC-5@MnO 2 -6 h hybrid supercapacitors exhibited largest energy density and power density values of 44.5 Wh kg−1 (at 0.2 A g−1) and 11111.1 W kg−1 (at 10 A g−1), respectively. The assembled button cells can light up small LED bulbs for at least 10 min. The porous bacterial cellulose carbon can provided possibilities for high electrode design. [Display omitted] • Morphology change of carbonized bacterial cellulose (CBC) affected by heating rate was clarified. • CBC-5 exhibited a three-dimensional channel structure and large specific surface area. • Homogeneous MnO 2 nanospheres were loaded onto CBC by adjusting hydrothermal time. • The device shows energy density of 44.5 Wh kg−1and power density of 11,111.1 W kg−1. • A button cell was assembled to light an LED lamp for nearly 20 min [ABSTRACT FROM AUTHOR]

A nanocomposite containing three-dimensional (3D) flower-like MoS 2 nanosheets and two-dimensional (2D) interconnected carbon nanosheets was successfully prepared by a facile hydrothermal method. The nanocomposite (MC-2) containing 6% surface-functional carbon nanosheets are beneficial to inhabit the restacking of MoS 2 nanosheets and form curved MoS 2 nanosheets, which are grown along the vertical orientation on the carbon nanosheets. The curved MoS 2 nanosheets could provide more suitable ion transport channels. The carbon nanosheets can enhance the electronic conductivity and keep the integrity of the nanocomposites. MC-2 exhibits the highest specific capacitance of 381 F/g at the current density of 1 A/g, as well as superior cyclic stability with 92% capacitance retention over 3000 cycles in KOH electrolyte. The excellent electrochemical performance of MC-2 as supercapacitor electrode is attributed to the 3D/2D structure and the synergistic effects between MoS 2 nanosheets and carbon nanosheets. [ABSTRACT FROM AUTHOR]

Porous carbons have recently drawn extensive attention in energy conversion and storage devices. Boosting energy densities of carbon family is still a challenge due to their limited surface area and accessible active sites. In this work, porous carbons with hierarchically structures were prepared from natural Juncus effuses (CJE) and homogeneous MnO 2 layer was successfully incorporated on their surfaces without changing their original porous structure. The CJE/MnO 2 composite showed large specific capacitance (283 F/g at 1 A/g), which was on account of high specific surface area (1283 m2/g) and abundant active sites for pseudocapacitance, particularly, resulted from the introduction of MnO 2. Significantly, the assembled symmetric supercapacitor from CJE/MnO 2 in Na 2 SO 4 aqueous electrolyte delivered high energy/power densities (19.13 Wh/kg at 225 W/kg and 13.73 Wh/kg at 8984 W/kg) and good cyclic performance (86.2% capacitance retention over 5000 cycles at 10.0 A/g). These results demonstrate the CJE/MnO 2 composite can be a potential candidate for supercapacitors. • The surfaces of porous carbons from Juncus effuses are functioned. • Oxygen-containing functional groups facilitate the formation of MnO 2 layer. • Prepared CJE/MnO 2 composites show high specific surface area and capacitance. • The supercapacitor from CJE/MnO 2 delivers excellent energy-power output. [ABSTRACT FROM AUTHOR]

A MoS 2 /CNT nanocomposite containing three-dimensional (3D) flower-like MoS 2 nanospheres and interconnected carbon nanotubes (CNTs) has been successfully synthesized by using MoO 3 and KSCN as reactants and deionized water as solvent with the presence of CNTs through a facile one-step hydrothermal method. The nanocomposite was applied as an electrode material for the supercapacitors with excellent energy storage performance. The structure and morphology of the nanocomposite were characterized by scanning electron microscopy and transmission electron microscopy, which show that MoS 2 nanospheres are about 300 nm in diameter and interconnected by CNTs. The special capacity of the nanocomposites can reach 74.05 F/g at a high current density of 2 A/g, which is higher than those of the flower-like MoS 2 and MoS 2 nanosheets at the same current density. Furthermore, the specific capacitance of the MoS 2 /CNT nanocomposite still maintains 80.8% of initial capacitance over 1000 cycles at the current density of 2 A/g. The excellent electrochemical performance and long cycle life of the nanocomposite are attributed to the synergetic effect between CNTs and ultrathin MoS 2 nanosheets grown vertically on the flower-like MoS 2 . [ABSTRACT FROM AUTHOR]

Two-dimensional Ti 3 C 2 MXene with high bulk density can act as prospective electrode material to construct high volumetric energy density supercapacitors. Herein, a series of nitrogen-doped Ti 3 C 2 (N-Ti 3 C 2) films are successfully synthesized by adjusting the quantity of urea using a facile solvothermal method. The incorporation of nitrogen atoms can enlarge interlayer spacing and diminish -F terminal groups of Ti 3 C 2 to promote the diffusion and intercalation of electrolyte ions, and bring about defect sites to provide more electrochemical reactive sites, thus improving the specific capacitance of N-Ti 3 C 2. As a result, the 2.0 N-Ti 3 C 2 film shows the highest volumetric capacitance of 2898.5 F cm−3 at scan rate of 2 mV s−1 in 3 M H 2 SO 4 solution, which is mainly attributed to its high pyridinic N content and low -F terminal groups. Density functional theory (DFT) calculations indicate that the doped N atoms have a higher adsorption energy for protons to enhance the pseudocapacitance of 2.0 N-Ti 3 C 2 electrode, and the increased density of states demonstrate the improvement of its electric conductivity after N doping, which promotes the rate performance of 2.0 N-Ti 3 C 2 electrode. The assembled symmetric supercapacitor based on 2.0 N-Ti 3 C 2 film delivers a high volumetric energy density of 40.8 Wh L−1 and good cycling stability. Our work provides an effective and alternative strategy to improve capacitance of other MXenes for high-performance supercapacitors. [Display omitted] • Flexible nitrogen-doped Ti 3 C 2 films are synthesized by a solvothermal method. • Nitrogen atoms can enlarge interlayer spacing and generate defect sites in Ti 3 C 2. • High pyridinic N can act as electron-donors to absorb more electrolyte ions of H+. • Low -F terminal groups are beneficial to enhance pseudocapacitance of N-Ti 3 C 2. • Optimal 2.0 N-Ti 3 C 2 shows a volumetric capacitance of 2898.5 F cm−3 at 2 mV s−1. [ABSTRACT FROM AUTHOR]