Search

Disordered nanostructures with abundant defects and porous microstructures have drawn tremendous interest in the energy storage application. Herein, a simple synthesis of amorphous MnOx nanostructures (AMO-S) is demonstrated by a redox reaction between carbon dots (CD-S, derived from sucrose via hydrothermal method) and KMnO4 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. [ABSTRACT FROM AUTHOR]

Herein, hierarchical sheet-like assemblies of interfacially coupled NiO/NiMoO4 (NNMO) nanocomposites are prepared by a simple and cost-effective one-step aqueous reflux method followed by post-thermal treatment. The reaction time is optimized for a high precursor yield and the homogeneity of the final product. The fabricated electrodes with varying amounts of active material and conducting carbon show better electrochemical activity for 50 : 50 weight ratio combinations as extrinsic pseudocapacitors. The optimized NNMO-3 electrode (obtained from the Ni–Mo hydroxide precursor during the 10 h reaction time) exhibits superior performance among all the tested nanocomposite electrodes like a high specific capacity of 649.8 C g−1 (1624.5 F g−1) and 73.5% retention of capacity after 2200 cycles at a specific current of 1.0 A g−1 along with satisfactory rate capability (42.5% retention after a ten-times increment in specific current), which may be attributed to the abundant electroactive sites due to the high bulk as well as electrochemically active surface area, mesoporous structure, and synergistic coupling between the optimum compositions of NiO and NiMoO4 within the sheet-like networks. Moreover, an aqueous asymmetric supercapacitor is assembled by employing NNMO-3 and activated carbon as the positive and negative electrodes, respectively, and exhibits a maximum specific capacity of 216.2 C g−1 (144.1 F g−1), specific energy of 45.0 W h kg−1 at a specific power of 750.0 W kg−1, promising rate capability of 58.5%, and good cycling stability with 86.2% capacitive retention after 2500 charge–discharge cycles. Based on the overall performance, we can infer that the NNMO-3 nanocomposite may be a promising electrode material for high-performance supercapacitor applications. [ABSTRACT FROM AUTHOR]

Herein, hierarchical sheet-like assemblies of interfacially coupled NiO/NiMoO 4 (NNMO) nanocomposites are prepared by a simple and cost-effective one-step aqueous reflux method followed by post-thermal treatment. The reaction time is optimized for a high precursor yield and the homogeneity of the final product. The fabricated electrodes with varying amounts of active material and conducting carbon show better electrochemical activity for 50 : 50 weight ratio combinations as extrinsic pseudocapacitors. The optimized NNMO-3 electrode (obtained from the Ni-Mo hydroxide precursor during the 10 h reaction time) exhibits superior performance among all the tested nanocomposite electrodes like a high specific capacity of 649.8 C g -1 (1624.5 F g -1 ) and 73.5% retention of capacity after 2200 cycles at a specific current of 1.0 A g -1 along with satisfactory rate capability (42.5% retention after a ten-times increment in specific current), which may be attributed to the abundant electroactive sites due to the high bulk as well as electrochemically active surface area, mesoporous structure, and synergistic coupling between the optimum compositions of NiO and NiMoO 4 within the sheet-like networks. Moreover, an aqueous asymmetric supercapacitor is assembled by employing NNMO-3 and activated carbon as the positive and negative electrodes, respectively, and exhibits a maximum specific capacity of 216.2 C g -1 (144.1 F g -1 ), specific energy of 45.0 W h kg -1 at a specific power of 750.0 W kg -1 , promising rate capability of 58.5%, and good cycling stability with 86.2% capacitive retention after 2500 charge-discharge cycles. Based on the overall performance, we can infer that the NNMO-3 nanocomposite may be a promising electrode material for high-performance supercapacitor applications.