Abstract
Pastes containing reduced graphene oxide (rGO) and SnCl2 solution were screen printed on carbon cloth and then calcined using a CO2 tornado-type atmospheric-pressure plasma jet (APPJ). The tornado circulation of the plasma gas enhances the mixing of the reactive plasma species and thus ensures better reaction uniformity. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) were performed to characterize the synthesized rGO-SnO2 nanocomposites on carbon cloth. After CO2 tornado-type APPJ treatment, the pastes were converted into rGO-SnO2 nanocomposites for use as the active electrode materials of polyvinyl alcohol (PVA)-H2SO4 gel-electrolyte flexible supercapacitors (SCs). Various APPJ scanning times were tested to obtain SCs with optimized performance. With seven APPJ scans, the SC achieved the best areal capacitance of 37.17 mF/cm2 in Galvanostatic charging/discharging (GCD) and a capacitance retention rate of 84.2% after 10,000-cycle cyclic voltammetry (CV) tests. The capacitance contribution ratio, calculated as pseudocapacitance/electrical double layer capacitance (PC/EDLC), is ~50/50 as analyzed by the Trasatti method. GCD data were also analyzed to obtain Ragone plots; these indicated an energy density comparable to those of SCs processed using a fixed-point nitrogen APPJ in our previous study.
Highlights
A supercapacitor (SC) is a passive energy storage device that has a higher energy density than conventional capacitors and a higher power density than batteries [1]
The reduced graphene oxide (rGO) was used as an active material to provide electric double-layer capacitance (EDLC); SnCl2 solution was used as a precursor for converting to SnO2 ; ethyl cellulose was used as a binder, and the ethanol and terpineol were used as solvents
The temperature is slightly higher than 50 ◦ C before atmospheric-pressure plasma jet (APPJ) scanning because of the residual heat left by the warm-up scan
Summary
A supercapacitor (SC) is a passive energy storage device that has a higher energy density than conventional capacitors and a higher power density than batteries [1]. RGO and SnO2 were combined and processed using a scan-mode CO2 tornado-type atmospheric-pressure plasma jet (APPJ). Atmospheric pressure plasma (APP) can be processed on large scale in a regularpressure environment without using a vacuum system CO2 DBD plasma has been used for oxidizing carbon-based materials for use as the electrodes of SCs [45]. Our subsequent study indicated that a higher SC specific capacitance value could be achieved by replacing 50 wt% of CNTs with reduced graphene oxides (rGOs) [8,48], possibly owing to the higher specific surface area of rGOs. we used rGOs with SnO2 for the direct APPJ processing of rGO pastes containing SnCl2 solution, and this approach resulted in promising adhesion between SnO2 and rGOs [49]. The SCs fabricated by the CO2 tornado-type APPJ show comparable performance to those fabricated by the nitrogen fixed-point APPJ
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