# Porous Doped Carbons from Anthracite for High-Performance Supercapacitors
## Materials and Methods
### Electrochemical Analysis  
The electrochemical measurements were carried out at room temperature in both three-electrode and two-electrode configurations. In the three-electrode system, all the electrochemical measurements were conducted on the CHI660e electrochemical workstation in 6 M KOH aqueous solution with Pt wire as counter electrodes and a Hg/HgO electrode as reference electrodes. The working electrodes were prepared by mixing the porous carbons, acetylene black, and polyvinylidene fluoride binder together in a weight ratio of 8:1:1 in _N_-methyl-2-pyrrolidone. The mixture was then pasted onto on the  
Figure 1: Schematic diagram for the synthesis of porous carbon from anthracite.  
\(1\) cm \(\times\) 1 cm nickel foam and dried at 100 \({}^{\circ}\)C overnight. The electrochemical cyclic voltammetry (CV) curves were recorded between a potential range of \(-\)1 and 0 V at various sweep rates. Galvanostatic charge-discharge cycling (GCD) tests were implemented at different current densities from 0.5 to 20 A g\({}^{-1}\). Electrochemical impedance spectroscopy (EIS) was monitored in the frequency range of 10 mHz to 100 kHz with an amplitude of 5 mV. The cycling stability test was evaluated by GCD measurements at a current density of 10 A g\({}^{-1}\) for 5000 cycles. The specific capacitance was computed according to Equation (1):  
\[C=\frac{I\Delta t}{m\Delta V} \tag{1}\]  
wherein \(C\) (F g\({}^{-1}\)) represents the specific capacitance, \(I\) (A) is the discharge current, \(\Delta t\) (s) is the discharge time, \(m\) (g) stands for the mass of active material in a single electrode, and \(\Delta V\) refers to the voltage change during the discharge process.  
In the two-electrode symmetrical supercapacitor cells, the electrodes were prepared by applying the previous method. The symmetric supercapacitors were built utilizing two equal electrodes equipped with a separator and nickel foam current collector and appraised in 6 M KOH (voltage range of 0-1 V) and 1 M Na\({}_{2}\)SO\({}_{4}\) (voltage range of 0-1.8 V). Cyclic voltammetry (CV) was assessed at various scan rates. Galvanostatic charge/discharge curves were obtained at diversifying current densities to estimate the specific capacitance. The specific capacitance of the two-electrode symmetrical supercapacitor cell was gauged using the following Equation (2):  
\[C_{cell}=\frac{I\Delta t}{M\Delta V} \tag{2}\]  
where \(C_{cell}\) (F g\({}^{-1}\)) means the total cell specific capacitance, \(I\) (A) deals with the current density, \(\Delta V\) appertains to the potential change (V) within the discharge time \(\Delta t\) (s), and M concerns the total mass (g) of active materials in both electrodes.  
The energy density and power density were calculated by using the following Equations (3) and (4):  
\[E=\frac{1}{2}C_{cell}(\Delta V)^{2}\times\frac{1}{3.6} \tag{3}\]  
\[P=\frac{E}{\Delta t}\times 3600 \tag{4}\]  
where \(E\) (Wh kg\({}^{-1}\)) is representative of specific energy density; \(P\) (W kg\({}^{-1}\)) signifies the specific power density of the symmetrical supercapacitor setup; \(\Delta V\) (V) means the operation voltage for charging and discharging; and \(\Delta t\) (s) stands for the discharge time.