## 3 Results and Discussions
As shown in Figure 9, the specific capacitance of the corn stalks nanocomposite practically does not decrease, while for the beet pulp nanocomposite the decrease for 8000 cycles was of the magnitude of 3%. The Impedance spectra of the tested supercapacitors are shown as Nyquist diagrams and Bode diagrams (Figure 10). All curves have a typical appearance for the dominant process of electric double layer formation at the carbon electrode/electrolyte interface. The Nyquist diagrams at high frequencies look like straight lines at an angle close to 90\({}^{\circ}\) to the axis of the real component of the complex resistance, while the Bode diagrams show a phase angle of about \(-80^{\circ}\) at a frequency of 10\({}^{-2}\) Hz. According to [57], such behaviour of a supercapacitor may be due to the presence of Faraday processes, the contribution of which may be as high as 5-10%. However, studies by [PERSON] and [PERSON] in [58] showed that quasi-reversible Faraday processes of electrochemical reduction of oxygen-containing surface groups in alkaline electrolytes appear in Nyquist diagrams only at sufficiently low frequencies of the order of 10\({}^{-3}\) Hz. Therefore, for our chosen frequency range (10\({}^{-2}\)-10\({}^{5}\) Hz), the influence of such Faraday processes can be neglected. This conclusion is confirmed by the calculation of the specific capacitance at 10\({}^{-2}\) Hz using the following formula [50]:  
\[C=-\frac{1}{2\pi fZ^{\prime\prime}} \tag{5}\]  
A value of 94.5 F/g in terms of specific value is obtained for the beet pulp nanocomposites, and 91.6 F/g for the corn stalks nanocomposites. These values are quite close to those obtained using Equation (4) for galvanostatic charging/discharging. Impedance data were modelled with Zwiew 3.4 software using an electrical equivalent circuit based on a linear model of de Levy with the addition of an R4C4 coupler, which corresponds to the resistance and capacitance of the space charge region in the AC [59; 60]. The calculated parameters of the elements in the electrical equivalent circuits are shown in Table 3. The contribution of pores of a certain size to the formation of an electrical double layer corresponds to a certain RC cell. In the circuit shown in the insert in Figure 10a, the resistance R1 corresponds to the internal resistance of the supercapacitor, R2 and C2 are the electrolyte resistance and capacitance in the mesopores, and R3 and C3 are the electrolyte  
Figure 9: Dependence of specific capacitance on the number of charge-discharge cycles for supercapacitors made from carbon composites made from beet pulp (1) and from corn stalks (2). resistance and capacitance in the micropores. In modelling the impedance of the studied carbon nanocomposites in aqueous electrolyte, a capacitive phase constant element (CRE1) was also used [61]. It simulates the distributed capacitance resulting from the presence of vacancies or impurity defects that provide conductivity to the carbon material at room temperature. The C3/C2 ratio for composites from beet pulp is 2.35, and for composites from corn stalks it is 2.67, indicating the main influence of micropores in shaping the capacitance of the electrical double layer. Similar conclusions were made in [62], where the C3/C2 ratio was about 2.75. Another parameter that can be calculated from the model applied is the relaxation time of the charging/discharging process of a porous structure with different pore sizes, in which an electrical double layer is formed. The relaxation time can be calculated using the following formula [50]:  
Figure 5:0  
where \(C\) is the electrical capacitance, \(R\) is the resistance. Figure 5:1 The Nyquist (**a**) and Bode diagrams (**b**,**c**) for supercapacitors made of carbon composites from beet pulp (1) and corn stalks (2). The insert (**a**) shows the electrical equivalent circuit for the supercapacitor.