## 3 Results and Discussion
### XPS Studies of the Electrode Materials  
Figure 6a shows the XPS spectrum of copper obtained on the samples with high copper content NCNCO02-NCNCO04. We failed to obtain similar spectra on the samples with lower copper content. As it is known, in the process of photoelectron emission, a \(2p\) hole appearing in the core level of bivalent copper can lead to a complex type of relaxation of the electronic structure--a charge transfer from the ligand to the metal with the final state \(d^{10}L^{-1}\). The location of the bottom of the hybridized O \(2p\) band relative to the Fermi level determines the distance between \(d^{10}L^{-1}\)and the satellite shake-up peak in the Cu \(2p\) spectrum [72]. Due to the presence of an intense calcium Auger peak in the spectrum, which overlaps with the shake-up satellite, the image of the latter in Figure 6 is given with a certain degree of conventionality. As follows from [73], the obtained binding energies of 933.7 and 935.1 eV for the \(d^{10}L^{-1}\) peaks of the Cu \(2p_{3/2}\) electronic level correspond, respectively, to the main compound and copper hydroxide. Figure 6b shows the XPS spectrum of nickel. The NiO spectrum has been studied by many authors, who have stated that, in addition to the spin-orbit splitting, its complex structure also contains multiplets and shake-up satellites [74, 75, 76, 77]. In ref. [75], the XPS method was used to study the defect structure of NiO after the heat treatment. It was shown that the specific changes occurring in the Ni \(2p\) and O \(1s\) spectra upon heating, in particular, the appearance of a peak at 856.1 eV, can be interpreted as the appearance of the Ni(III) state in the oxide. It was shown in [76] that Ni(III) can form on a Ni(110)-O surface doped with potassium. This is due to the presence of a strong electropositive element near the Ni atoms. In this and otherworks [77], the subtraction method was used to determine the presence of Ni(III) in the overlapping of its spectrum with the NiO shake-up satellite. Figure 5: Concentration dependencies of the lattice parameters (**a**) and the unit cell volume (**b**) of the NCNCO00-NCNCO04 samples after the treatment in the synthetic air flow and in the He flow (error bars are not visible on the graph asthey are of the size of the symbols for the data points). Referring to the Ni 2\(p\) spectra obtained in this study and taking into account the data of other authors, it can be concluded that in the spectrum of the samples with a copper content of 0.1-0.4, along with the Ni(II) state, there was also the Ni(III) state, which corresponds to the main peakII and, in one case of the NCNCO02 sample, to the satellite IV, as shown in Figure 6b. The XPS data obtained on the Ni and Cu states in the series correlate well with the in-situ XRD data (Section 3.2). Figure 6c shows the XPS spectrum of oxygen in which peaks I and II correspond to metal-oxygen bonds and high-energy peaks III, IV, and V correspond to CO\({}_{3}\) and OH groups as well as other organic impurities contained on the surface of the samples. The number of holes per formula unit in the NCNCO00-NCNCO04 samples in the sublattice of the 3d element can be expressed as: \(n=\alpha(1-\mathrm{x})\), where \(\alpha\) is the fraction of Ni(III) (Table 5).This fraction can be determined from the obtained XPS spectra related to the Ni 2\(p\) electronic level (see Figure 6b) by the ratio of the corresponding intensities, taking into account that doublets I and III refer to the signals from Ni(II), while doublets II and IV refer to the signals from Ni(III). It can be seen from the calculation results (Table 5) that the amount of the hole charge increases with a decrease in the amount of copper down to 0.2 and then decreases. It corresponds to the results of the conductivity study, presented in our earlier work [49],  
Figure 6: XPS spectra obtained in air at room temperature for the NCNCO samples with different Cu content: Cu 2\(p_{3/2}\) (a); Ni 2\(p\) (b); and O 1s (c).