## 3 Results and Discussion
### Electrochemical Properties  
The CV curves presented in Figure 9a regardless of the scan rate exhibit two pronounced redox peaks in the 0-0.5 V (vs. Ag/AgCl) potential region. This form of the curve indicates that the electrochemical capacity of the studied sample is mostly determined by the faradaic processes' contribution. The reversible transformations of electrode material occurring during electrochemical testing proceed in two stages: at the first stage, carbonate hydroxide hydrates of nickel and cobalt are transformed into metahydroxides (reactions 7 and 8 [25; 68]), followed by the appearance of reversible transitions Ni\({}^{2+}\leftrightarrow\)Ni\({}^{3+}\) and Co\({}^{2+}\leftrightarrow\)Co\({}^{3+}\leftrightarrow\)Co\({}^{4+}\) (reactions 9-11 [69]):  
\[\text{Ni}_{2}(\text{CO}_{3})(\text{OH})_{2}+4\text{OH}^{-}\leftrightarrow 2 \text{NiOOH}+\text{CO}_{3}^{2-}+2\text{H}_{2}\text{O}+2\text{e}^{-} \tag{7}\]  
\[\text{Co}_{2}(\text{CO}_{3})(\text{OH})_{2}+4\text{OH}^{-}\leftrightarrow 2 \text{CoCOOH}+\text{CO}_{3}^{2-}+2\text{H}_{2}\text{O}+2\text{e}^{-} \tag{8}\]  
\[\text{NiOOH}+\text{H}_{2}\text{O}+\text{e}^{-}\leftrightarrow\text{Ni}( \text{OH})_{2}+\text{OH}^{-} \tag{9}\]  
\[\text{CoOOH}+\text{H}_{2}\text{O}+\text{e}^{-}\leftrightarrow\text{Co}( \text{OH})_{2}+\text{OH}^{-} \tag{10}\]  
\[\text{CoOOH}+\text{OH}^{-}\leftrightarrow\text{CoO}_{2}+\text{H}_{2}\text{O }+\text{e}^{-} \tag{11}\]  
Figure 9: Electrochemical performance of materials in a three-electrode system with 3 M KOH electrolyte: CV curves at different scan rates (**a**), GCD curves at different current densities (**b**) and rate capabilities (inset: cycle performance of the film at 0.300 mA/cm\({}^{2}\) for 2000 cycles) (**c**), and the EIS spectrum for the material under study (inset: enlargement of high-frequency part and equivalent circuit model) (**d**). Since the nickel and cobalt redox processes have sufficiently close potential ranges, in our case, they probably overlap, and only two distinct peaks are observed on the CV curves. It should be noted that the shape of the curves remained practically unchanged as the scanning speed increased; only a slight shift of the anodic peaks towards more positive potential and cathodic peaks towards more negative potential was observed, which was additionally accompanied by the increase in the current value. This trend indicates the energy storage possibility, as well as the reproducibility and reversibility of the processes that cause the occurrence of the material electrochemical capacitance [69]. According to the galvanostatic charge-discharge tests at different current densities, the discharge curves were plotted (Figure 9b), which have a non-linear range and a plateau, which agrees well with the CV curves and further confirms the faradaic mechanism of capacitance in the studied sample. Based on the GDC data, and using Equation (2), the areal specific capacitance (C\({}_{\text{s}}\)) values were calculated, and it was found that increasing the current density from 0.030 mA/cm\({}^{2}\) to 0.300 mA/cm\({}^{2}\) leads to a 5% decrease in the C\({}_{\text{s}}\) value from 10.1 to 9.6 mF/cm\({}^{2}\) (Figure 9c). Such a decrease in capacitance is typical for supercapacitor electrodes and related to the fact that at higher current densities, electrolyte ions involved in the charge transfer process do not have time to penetrate into the material pores and interact only with a limited number of the surface active centers, while at lower density, the charged particles reach a greater material depth, providing the most effective interaction of electrolyte with active centers of the surface. Cyclic stability tests of the investigated electrode material allowed us to determine that the capacitance value at 0.300 mA/cm\({}^{2}\) is retained by 93% after 2000 charge-discharge cycles (Figure 9c, inset).