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This work relates to the preparation of CNT-MnO 2 hybrid electrode by a simple solvent-assisted synthesis. This one-step method is also cost-effective, scalable, and addition of surfactant or other additives for carrying out the synthesis is not necessary.The effect of selected solvents (DMF vs. ethanol) on the properties and performance of the prepared materials is depicted during this work using XRD, Raman, TEM, SEM and porosity estimation by nitrogen adsorption-desorption isotherm at 77 K. The electrochemical behavior was studied using cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy in a K 2 SO 4 aqueous electrolyte. The superior electrochemical performance of the CNT-MnO2 hybrid obtained by DMF assisted synthesis were explicated by its favorable texture and morphology. Furthermore, an asymmetric 2 V aqueous supercapacitor was assembled and tested using hybrid CNT-MnO 2 and reduced graphene oxide (rGO) as positive and negative electrodes respectively. The supercapacitor showed an excellent stability under cycling (6000 cycles) with a specific energy of 14 Wh/kg at a power density of 3000 W kg −1 . [ABSTRACT FROM AUTHOR]

Herein, synthesis and characterization of amorphous MnO 2 and application in asymmetric aqueous ultracapacitors are reported. Different amorphous manganese oxide (MnO 2 ) materials were synthesized from the reduction of KMnO 4 in different media such as ethanol (EtOH) or dimethylformamide (DMF). The electrochemical behavior of amorphous MnO 2 , labeled MnO 2 -Et and MnO 2 -DMF, were studied by using cyclic voltammetry, impedance spectroscopy, and galvanostatic cycling in aqueous electrolyte. XRD, BET, TEM, and SEM characterizations highlighted the amorphous nature and the nanostructuration of these MnO 2 materials. BET measurement established that these amorphous MnO 2 are mesoporous. In addition, MnO 2 -Et exhibits a larger specific surface area (168 m 2 g −1 ), a narrower pore diameters distribution with lower diameters compared to MnO 2 -DMF. These results are in agreement with the electrochemical results. Indeed, MnO 2 -Et shows a higher specific capacitance and lower impedance in aqueous K 2 SO 4 electrolyte. Furthermore, aqueous asymmetric ultracapacitors were assembled and studied using amorphous MnO 2 as positive electrode and reduced graphene oxide (rGO) as negative electrode. These asymmetric systems exhibit an electrochemical stability for more than 20,000 galvanostatic cycles at current density of 1 A g −1 with an operating voltage of 2 V. [ABSTRACT FROM AUTHOR]