Search

[Display omitted] Among many supercapacitor electrode materials, carbon materials are widely used due to their large specific surface area, good electrical conductivity and high economic efficiency. However, carbon-based supercapacitors face the challenges of low energy density and limited operating environment. This work reports a facile self-assembled method to prepare three-dimensional carbon nanotubes/reduced graphene oxide (CNTs/rGO) aerogel material, which was applied as both positive and negative electrodes in a symmetric superacapacitor. The fabricated supercapacitor exhibited prominent capacitive performance not only at room temperature, but also at extreme temperatures (−20 ∼ 80 °C). The specific capacitances of the symmetric supercapacitors based on CNTs/rGO at a weight ratio of 2:5 respectively reached 107.8 and 128.2 F g−1 at 25 °C and 80 °C with KOH as the electrolyte, and 80.0 and 144.6 F g−1 at −20 °C and 60 °C with deep eutectic solvent as the electrolyte. Notably, the capacitance retention and coulombic efficiency of the assembled supercapacitors remained almost unchanged after 20,000 cycles of charge/discharge test over a wide temperature range. The work uncovered a possibility for the development of high-performance supercapacitors flexibly operated at extreme temperatures. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) transition metal carbon/nitrogen compound (MXene) and graphene are popular energy storage materials. Still, the electrochemical performance and application of those 2D materials are severely limited due to their easy self-stacking. In this article, three-dimensional (3D) hybrid porous aerogel made of sulfur and nitrogen doped reduced graphene oxide and MXene (S,N-rGO@MXene) is successfully self-assembled via a simple hydrothermal method. The reductive nature of MXene positively tune the hydrophilicity of rGO, thus leading to a controllable formation of 3D mutual cross-linking rGO/MXene. The involvement of elemental S and N additionally promotes electrochemical performance. The specific capacitances of 85.4 and 88.9 F g−1 in symmetric liquid- and all-solid-state supercapacitors assembled with S,N-rGO@MXene are achieved at the current density of 1 A g−1, respectively. Notably, the capacitance retention and Coulombic efficiency remain almost unchanged after 20,000 and 10,000 charge/discharge cycles in the respective systems. In particular, the all-solid-state supercapacitor achieves a high energy density of 24.2 Wh kg−1 at the power density of 1400.6 W kg−1, outperforming most of the MXene-based all-solid-state supercapacitors reported so far. Practically, the constructed supercapacitor is applicable to light up LED lamps. Our self-assembled 3D aerogel provides a valuable reference for the fabrication of efficient symmetric supercapacitors. [Display omitted] • S,N co-doped rGO/MXene aerogel is self-assembled via simple hydrothermal method. • MXene favors the formation of porous network and enhances the strength of aerogel. • Heteroatoms S and N strengthen chemical reactivity and charge transfer capability. • Both liquid- and all-solid-state supercapacitors show ca. 100% Coulombic efficiency. • Both supercapacitors enable LED powering. [ABSTRACT FROM AUTHOR]

Two-dimensional graphene and metal carbide/nitride/carbonitride compounds (MXene) are widely recognized as promising electrode materials for electrochemical energy storage systems. Herein, MXene was hydrothermally self-assembled with graphene oxide to form three-dimensional porous aerogels, which were applied as electrode materials in symmetrical supercapacitors with both liquid and solid electrolytes. The fabricated supercapacitors exhibited excellent supercapacitive performances including superior capability, coulombic efficiency, and cycle stability. The specific capacitance of the aerogel-based supercapacitor assembled with liquid KOH electrolyte reached as high as 158.6 F g−1, while the fabricated all-solid-state supercapacitor displayed a power density of 1398.8 W kg−1 and an energy density of 33.3 Wh kg−1 at a current density of 1 A g−1. Notably, MXene was prepared via a more enviromentally friendly route by using molten Lewis acid instead of the traditional fluorine-involved agent as the etchant, thus efficiently limiting the hazardous chemicals to pollute the environment. This work provides a strong motivation for applying graphene and MXene composite materials in sustainable energy storage systems. • MXene was greenly prepared by fluorine-free Lewis acid-etched method. • Lewis acid-etched MXene was self-assembled with rGO to form three-dimensional porous aerogel. • Lewis acid-etched MXene was rarely reported as electrode material in all-solid-state supercapacitor. [ABSTRACT FROM AUTHOR]

It is indeed particularly important in aqueous supercapacitors to avoid any gas evolution due to safety concerns. Nevertheless, limited research has been concentrated on those side reactions, but with more focus on the advancement of the intrinsic electrochemical properties of supercapacitor electrode materials. Herein, we report for the first time to apply high-resolution scanning electrochemical microscopy (SECM) in elucidating hydrogen evolution side reaction occurred during the charge process of supercapacitor electrodes. By taking CNTs functionalized with or without oxygen groups as the exemplary electrode materials, at first we applied conventional analytical methods to demonstrate their difference in supercapapcitor behavior. Subsequently, SECM was specifically introduced to investigate the local reactivity and conductivity of the CNT samples at submicrometer scale. Prominently, SECM was demonstrated to be capable of in-depth understanding the type of side reactions taken placeon the CNT surfaces. This report offers a new avenue to extend SECM application into assessment of supercapacitor safety performance. [ABSTRACT FROM AUTHOR]

Three-dimensional structural materials with sufficient reactive contact surface to the electrolyte can significantly improve the capacitance performance of supercapacitors. Herein, we report a facile method to fabricate a hierarchical carbon nanofibers (CNFs) modified Cu-foam supported Co@CoO hybrid as a free-standing and binder-free electrode for supercapacitor application. The optimized Co@CoO/CNFs/Cu-foam shows a high specific capacitance of 19.2 F cm−3 at the current density of 50 mA cm−3 and a remarkable capacitance retention of 97.5% after 5000 cycles in a 3-electrode system. A button-type asymmetric supercapacitor was additionally constructed by using Co@CoO/CNFs/Cu foam as the positive electrode and activated carbon electrode as negative electrode to examine its practical application. The stored energy density reached to 180.5 mWh cm−2 with the corresponding power density of 6000 mW cm−2 at a discharging current density of 4 mA cm−2. An excellent cycling life of retention 100% was maintained after 5000 cycles. The high-surface area and conductivity of the CNFs played a positive role as support to highly-dispersed Co@CoO nanoparticles. The pulsed electrodeposition additionally favored the controllable fabrication of Co@CoO nanoparticles with homogeneously distribution and uniform sizes. The hierarchical hybrid electrode with porous architecture eventually allowed good access of electrolyte and efficient charge storage and transfer, which concomitantly improved its overall electrochemical performance. Co@CoO nanoparticles supported on CNFs modified Cu-foam prepared by chemical vapor deposition and electrodeposition method exhibited high supercapacitive performance. ga1 • Free-standing Co@CoO/CNFs/Cu-foam supercapacitor electrode is successfully fabricated. • CNFs favor the homogeneous distribution of metal catalysts and efficient charge and ion transportation. • Electrochemical deposition method is applied to controllable synthesize metal catalyst nanoparticles with uniform sizes. [ABSTRACT FROM AUTHOR]