Abstract
The carbon onion/birnessite-type manganese oxide nanohybrid symmetric pseudocapacitor exhibits excellent capacitive properties compared to the conventional carbon onion symmetric supercapacitor.
Highlights
Previous studies related to MnO2 with “carbon onions” were carried out using low-graphitized materials obtained from either clari ed butter (“Ghee”)[30] or phenolicformaldehyde resins with much larger particle diameters.[42]. Whilst these initial reports are encouraging, we show in this study that by using highly graphitized onion-like carbon (OLC), OLC/MnO2 nanohybrids exhibit a very high power density ($75 kW kgÀ1)
The surface morphologies of OLC and the OLC/MnO2 nanohybrid studied using scanning electron microscope (SEM) are shown in Fig. 1a and c and using Transmission electron microscopy (TEM) in Fig. 1b and d
The primary particle size of carbon onions is in the range of a few nanometers as seen from the TEM images in agreement with our previous ndings.[47]. This primary particle size is maintained for the OLC/MnO2 nanohybrid
Summary
Non-porous carbon onions, known as onion-like carbon (OLC), have attracted major research interest as electrode materials for energy storage, for example, advanced anode electrodes for lithium ion batteries,[19,20] pseudocapacitors,[21,22] and ultrahigh-power electrical double-layer capacitors.[23,24,25] The major attractions stem from the ability to prepare them on a large scale by thermal annealing of nanodiamonds and the superior power handling ability.[26]. The working electrode was prepared by drop-casting 7.1 mg mLÀ1 OLC colloidal dispersion (10 mass% polyvinyliden uoride, PVDF in ethanol) or 9.0 mg mLÀ1 OLC/MnO2 nanohybrid colloidal dispersion (in anhydrous N-methyl-2-pyrrolidone, NMP) onto a Pt disc (diameter: 12 mm, thickness: 100 mm, purity 99.99%, Carl Schaefer) and dried at 80 C overnight in a vacuum oven at 20 mbar to remove the solvent. For the nickel foam based three-electrode con guration, the nickel foam (Celmet: thickness 1⁄4 1.6 mm, surface area 1⁄4 7500 m2 mÀ3, cell size 1⁄4 0.5 mm, 48–52 cells per inch) was cleaned prior to use, in a 1 M HCl solution, washed with a copious amount of deionized water to a neutral pH, and dried under vacuum It was pasted with a mixture of OLC/MnO2 nanohybrid, carbon black (CB, Degussa), and polyvinylidene uoride (PVDF) Where i (A) is the applied current, DV (V)/Dt (s) the slope of the discharge curve and m (g) the total mass of both electrodes, C (F) the calculated capacitance, V (V) is the maximum voltage obtained during charge, and Rs is the equivalent series resistance (ESR)
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