Rational design of binder-free materials with high cyclic stability and high conductivity is a great need for high performance supercapacitors. We demonstrate a facile one-step synthesis method of binder-free MnO@C nanofibers as electrodes for supercapacitor applications. The topology of the fabricated nanofibers was investigated using FESEM and HRTEM. The X-ray photoelectron spectroscopy (XPS) and the X-ray diffraction (XRD) analyses confirm the formation of the MnO structure. The electrospun MnO@C electrodes achieve high specific capacitance of 578 F/g at 1 A/g with an outstanding cycling performance. The electrodes also show 127% capacity increasing after 3000 cycles. An asymmetric supercapacitor composed of activated carbon as the negative electrode and MnO@C as the positive electrode shows an ultrahigh energy density of 35.5 Wh/kg with a power density of 1000 W/kg. The device shows a superior columbic efficiency, cycle life, and capacity retention.
A facile one-step method was demonstrated for the electrodeposition of manganese−nickel sulfide (Mn−Ni−S) 3D interconnected sheets on nickel foam substrates. The assynthesized materials were characterized using field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) techniques. Upon their use as supercapacitor electrodes, the electrodeposited Mn−Ni−S showed exceptionally high specific capacitance (2849 and 1986 F/g at 1 and 5 A/g, respectively) and an excellent rate capability. Using Fe 3 O 4 -GR as the negative electrode and the Mn−Ni−S 3D interconnected sheets as the positive electrode to assemble an asymmetric supercapacitor device revealed high power density (800 W kg −1 ) and energy density (40.44 Wh kg −1 ) with 90% capacitance retention and a Columbic efficiency of 100% after 11 000 cycles, indicating the high potential of the fabricated materials for practical energy storage devices.
Supercapacitors (SCs) are being considered the next-generation power storage devices due to the many favorable properties. In this regard, mesoporous nanostructures are excellent supercapacitor electrodes as they enjoy a large number of active sites and high surface area promising the utilization of the full capacitance of the active materials. In this study, we report on the assembly of electrospun, binder-free mesoporous Mn 0.56 V 0.42 O@C fibrous electrodes. The morphological and structural analyses of the fabricated Mn 0.56 V 0.42 O@C electrodes were investigated using field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and glancing angle X-ray diffraction (GAXRD). The X-ray photoelectron spectroscopy (XPS) and GAXRD confirm the formation of Mn 0.56 V 0.42 O nanofibers and their successful bonding to carbon during crystal growth. Those fibrous composite electrodes showed excellent specific capacitance of 668.5 F g −1 at 1 A g −1 . The highly obtained capacitance is attributed to the multiple oxidation states of the Mn−V oxides, the binder-free electrodes, surface roughness, and the mesoporous nature of the fabricated nanofibers. The asymmetric supercapacitor composed of the mesoporous Mn 0.56 V 0.42 O@C nanofibers as the positive electrode and graphene hydrogel as the negative electrode possesses ultrahigh energy density of 37.77 W h kg −1 and a power density of 900 W kg −1 with superior Coulombic efficiency over 13 000 charge−discharge cycles.
We demonstrate the fabrication of binder-free electrospun nickel− manganese oxides embedded into carbon-shell fibrous electrodes. The morphological and structural properties of the assembled electrode materials were elucidated by high-resolution transmission electron microscopy (HR-TEM), field-emission scanning electron microscopy, and glancing-angle X-ray diffraction. The fibrous structure of the electrodes was retained even after annealing at high temperatures. The X-ray photoelectron spectroscopy and HR-TEM analyses revealed the formation of nickel and manganese oxides in multiple oxidation states (Ni 2+ , Ni 3+ , Mn 2+ , Mn 3+ , and Mn 4+ ) embedded in the carbon shell. The embedded nickel−manganese oxides into the carbon matrix fibrous electrodes exhibit an excellent capacitance (1082 F/g) in 1 M K 2 SO 4 at 1 A/g and possess a high rate capability of 73% at 5 A/g. The high rate capability and capacitance can be attributed to the presence of carbon crosslinked channels, the binder-free nature of the electrodes, and various oxidation states of the Ni−Mn oxides. The asymmetric supercapacitor device constructed of the asfabricated nanofibers and the bio-derived microporous carbon as the positive and negative electrodes, respectively, sustains up to 1.9 V with a high specific capacitance at 1.5 A/g of 108 F/g. The nanofibrous//bio-derived device exhibits an outstanding specific energy of 54.2 W h/kg with a high specific power of 1425 W/kg. Interestingly, the tested device maintains a high capacitive retention of 92% upon cycling over 10,000 charging/discharging cycles.
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