Abstract
Symmetric supercapacitors are fabricated by carbon nanofibers (CNF) and activated carbon (AC) using similar proportions of 7 wt% polyvinylidene fluoride (PVDF) polymer binder in an aqueous electrolyte. In this study, a comparison of porous texture and electrochemical performances between CNFs and AC based supercapacitors was carried out. Electrodes were assembled in the cell without a current collector. The prepared electrodes of CNFs and AC present Brunauer-Emmett-Teller (BET) surface area of 83 and 1042 m2/g, respectively. The dominant pore structure for CNFs is mesoporous while for AC is micropore. The results showed that AC provided higher specific capacitance retention up to very fast scan rate of 500 mV/s. AC carbon had a specific capacitance of 334 F/g, and CNFs had 52 F/g at scan rate 5 mV/s in aqueous solution. Also, the results indicate the superior conductivity of CNFs in contrast to AC counterparts. The measured equivalent series resistance (ESR) showed a very small value for CNFs (0.28 Ω) in comparison to AC that has an ESR resistance of (3.72 Ω). Moreover, CNF delivered higher specific power (1860 W/kg) than that for AC (450 W/kg). On the other hand, AC gave higher specific energy (18.1 Wh/kg) than that for CNFs (2 Wh/kg).This indicates that the AC is good for energy applications. Whereas, CNF is good for power application. Indeed, the higher surface area will lead to higher specific capacitance and hence higher energy density for AC. For CNF, lower ESR is responsible for having higher power density.Both CNF and AC supercapacitor exhibit an excellent charge-discharge stability up to 2500 cycles.
Highlights
Supercapacitors or electrochemical capacitors have attracted much interest due to their high power density and long cycling capabilities
The specific capacitance decreased to 32 F/g at 500 mV/s scan rate. These results indicate the moderate decrease in specific capacitance, and at even higher scan rates, most of the surface area and pores of carbon nanofibers (CNF) are accessible to the ions
These results show an increase of specific power; the specific energy only decreases a little, which is a signature of excellent electrochemical properties of high energy density and power output, very promising for application in the scenarios where high power output as well as high energy capacity is required [25]
Summary
Supercapacitors or electrochemical capacitors have attracted much interest due to their high power density and long cycling capabilities. Surface Characterization The porous texture and specific surface area and pore size distribution of CNF and AC electrodes were obtained by physical adsorption of gasesN2 at 77 K using Micromeritics TriStar 3000 V6.04 A .All samples were outgassed at 100 ° C for 4 h prior to the adsorption measurements.
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