Amorphous MnO_x Nanostructure/Multiwalled Carbon Nanotube Composites as Electrode Materials for Supercapacitor Applications

Abstract

Disordered nanostructures with abundant defects and porous microstructures have drawn tremendous interest in the energy storage application. Herein, a simple synthesis of amorphous MnO x nanostructures (AMO-S) is demonstrated by a redox reaction between carbon dots (CD-S, derived from sucrose via hydrothermal method) and KMnO 4 at room temperature. The obtained AMO-S displays a nanoparticulate/nanorod-like irregular morphology and mesoporous structure. Experimental observations illustrate that the presence of CD-S is essential for the precipitation of AMO-S under ambient conditions. Afterward, a small amount of multiwalled carbon nanotubes (MWCNTs) is incorporated before (in situ) and after (ex situ) the formation of AMO-S, which resulted in AMO/MWCNT-in and AMO/MWCNT-ex nanocomposites, respectively. Electrochemical tests of the synthesized materials are conducted to evaluate their charge storage characteristics. It is found that the AMO/MWCNT-in nanocomposite with a small MWCNT content (∼3.0 wt %) exhibits a high specific capacitance of 580.2 F g −1 at 1.0 A g −1 based on the total mass of electrode material, promising rate capability (57.1% retention after 6-fold increase in the current density), and high cycling stability (96.9% @ 3000 charge−discharge cycles at 1.0 A g −1 ). The excellent electrochemical performance of the AMO/MWCNT-in electrode is mainly attributed to the better intermixing of two components along with the synergistic contributions of CD-S, resulting in a high electronic conductivity, fast ion diffusion ability, abundant electroactive sites, and mesoporosity. Moreover, the assembled aqueous AMO/MWCNT-in//activated carbon asymmetric supercapacitor can work properly in a significantly large potential window of 0−2.2 V, which delivers a high specific capacitance (76.2 F g −1 @ 1.0 A g −1 ) and excellent energy density (51.2 Wh kg −1 ) at a power density of 1100 W kg −1 . This study suggests that the in situ incorporation of a small amount of MWCNTs may be an effective approach to improve the energy storage ability of pseudocapacitive AMO-S.

Manganese–cobalt hydroxide nanosheets anchored on a hollow sulfur-doped bimetallic MOF for high-performance supercapacitors and the hydrogen evolution reaction in alkaline media

“…The b values indicate that the diffusion-controlled process is more dominant than the surface-controlled process. The ratio of capacitive and diffusion-controlled contributions can be calculated by using the following equation: 63 i = i cap + i diff = k 1 ν + k 2 ν 1/2 where k 1 ν and k 2 ν 1/2 represent the charge contributions from the capacitive and diffusion-controlled process, respectively. Fig.…”

Nanotexturing TiO2 over carbon nanotubes for high-energy and high-power density pseudocapacitors in organic electrolytes

“…Multiwalled carbon nanotubes (CNTs) have been chosen as nanotexturing agents because of their morphology and high conductivity. It has already been proven that their high aspect ratio and extended graphitic layers allow better percolation of the active particles in an electrode than materials with other carbonbased particles such as carbon black (Raymundo-Piñero et al, 2005;Raymundo-Piñero et al, 2011;Zhu et al, 2020;Kazari et al, 2022;Keshari and Dubey, 2022).…”

CNTs-Supercapacitors: A Review of Electrode Nanocomposites Based on CNTs, Graphene, Metals, and Polymers

“…As can be observed from Figure 3, the electrode nanocomposite based on the CNTs/graphene, CNTs/metal, and CNTs/polymer are more highlighted in the co-occurrence keywords analysis. Other characterizations such as symmetric [9][10][11], flexible [12,13], wearable electronic [14,15], cellulose [16][17][18], cycling stability [19,20], pseudocapacitor [21,22], solid-state supercapacitor [23][24][25], activated carbon [26][27][28], polymers [29][30][31], MXene [32,33], and CNTs [34][35][36][37][38][39][40][41][42][43][44][45][46] were mentioned in Figure 3. Nanomaterials are widely used for industrial applications such as supercapacitors, batteries, antibacterial activity, nano-membranes, and sensors [47][48][49][50][51][52]…”