## 3 Results and Discussion
### Further Considerations  
The results of the electrochemical experiments evidence the superior properties of the Gr4P11+CB electrode. Compared with the Gr4P11, Gr4P14, and Gr4P14+CB samples, Gr4P11+CB displays higher OER electrocatalytic activity, higher ECSA, and D values, a lower Tafel slope value, and is more electrochemically stable. The higher OER catalytic activity of the electrode modified with the P11 perovskite material, Carbon Black, and Nafion is probably the outcome of structural and transport effects [48]. However, it should also be pointed out that the higher ECSA value estimated for this sample indicates its surface is more discontinuous, probably due to features including edges and defects that generate more catalytically active centers [49]. Furthermore, it is sometimes the case that electrodes manufactured us  
Figure 5: The graphical representation of the dependence between the peak current densities of the anodic and cathodic peaks corresponding to the ferrocyanide/ferricyanide redox couple and the square root of the scan rate for the Gr4P11 (**a**), Gr4P14 (**b**), Gr4P11+CB (**c**), and Gr4P14+CB (**d**) electrodes.  
ing compositions containing at least two materials benefits from improved charge transfer and adjusted electron density at the catalytic centers as a result of their interplay [50]. The acquired experimental data implies this is not the case with Gr4P14+CB and Gr4P11+CB which were manufactured using the perovskite oxides mixed with Carbon Black. At i = \(-\)10 mA/cm\({}^{2}\) the \(\eta_{\text{OER}}\) values for these samples are very close to those determined for the electrodes obtained without utilizing Carbon Black. This observation is rather unexpected since the material in question was added for electron transfer enhancement purposes. A potential explanation has to do with the way in which the particles constituting the solid phase of the suspension applied on the surface of the carbon substrate were arranged. Arrangements in the shape of thick layers prevent the electrolyte solution from reaching the pores situated deep into the deposited material. The result is a decrease in the number of catalytically active centers that would otherwise participate in the electrochemical reaction [24; 51]. According to this explanation, the ECSA values of Gr4P14+CB and Gr4P11+CB could have been higher and the same is true of their OER electrocatalytic activity.  
Figure 6: The Tafel plots were obtained for the O\({}_{2}\) evolution reaction on the Gr4P11, Gr4P14, Gr4P11+CB, and Gr4P14+CB electrodes, in 1 M KOH solution.  
Figure 7: The graphical representation of the dependence between current density and time for the Gr4P11+CB and Gr4P14+CB electrodes immersed in 1 M KOH solution. Insets: (**a**) The overlap between the polarization curves obtained on the Gr4P11+CB electrode before and after the chronoamperometric experiment, denoted as Gr4P11+CB and Gr4P11+CB’, respectively; (**b**,**c**) enlarged areas from the overlapped i vs. time curves.  
While Gr4P11+CB possesses superior OER electrocatalytic properties compared with the electrodes investigated during the present study the same cannot be said regarding other electrodes reported in the scientific literature, including other perovskite-based ones [52; 53; 54; 55]. The OER catalytic activity of Gr4P11+CB is not as high and its electrochemical stability is not as good as those of the electrodes from recently published studies. In light of this observation, the future water electrolysis studies that will be performed on P11, P14, and other novel perovskite oxide structures will probably involve a more complex electrode manufacturing method than drop-casting (e.g., pulsed laser deposition and spray pyrolysis).