Fig. 4.

Electrochemical performance of two-terminal symmetric supercapacitor devices. a CV curves of the symmetric supercapacitor device at scan rates from 2 to 100 mV s⁻¹ with a voltage range between 0 and 1 V in 1 M H₂SO₄. b Galvanostatic charge/discharge curves of the present device at low current densities from 3 to 12 mA cm⁻² in the voltage range between 0 and 1 V. c Capacitance of the device as a function of scan rate. d Nyquist plot for the present symmetric device recorded from 0.1 Hz to 1 MHz with an AC perturbation amplitude of 5 mV. e Cyclic stability and coulombic efficiencies of the present supercapacitor. f Comparative Ragone plot of a typical electrolytic capacitor, a Li-ion thin-film battery, a commercial supercapacitor (from ref. ³⁹), contemporary energy devices [44–46], and the present symmetric device