## 3 Results and Discussion
### Electrochemical Experiments  
The OER studies performed on the electrodes modified with Procedure 1 revealed GC1P11+CB and GC1P14+CB as the only samples having higher electrocatalytic activity than the sample modified only with Carbon Black (GC1 CB). The polarization curves recorded on these electrodes are shown in Figure 4a. At i = 10 mA/cm\({}^{2}\)--the current density value  
Figure 3: SEM images for (**a**) PVP; (**b**) LaMnO\({}_{3}\):Ag; (**c**) LaMnO\({}_{3}\):Ag/PVP (P11), (**d**) LaMnO\({}_{3}\):Pd, and (**e**) LaMnO\({}_{3}\):Pd/PVP (P14). The samples obtained using Procedure 1 did not exhibit electrocatalytic activity for the HER, and those obtained by applying Procedure 2 exhibited negligible water-splitting activity. In light of these results subsequent investigations focused only on the OER, and the electrodes manufactured with Procedures 3 and 4 were evaluated in terms of their electrocatalytic activity for this half-reaction. Figure 4b presents the LSVs recorded on the most catalytically active samples modified using Procedure 3. It can be observed that at current densities >25 mA/cm\({}^{2}\) the polarization curves traced on Gr3P1 and Gr3P14+CB overlap, but at lower values of this parameter \(\eta_{\text{OER}}\) for the former electrode is <\(\eta_{\text{OER}}\) for the latter. However, at I = 10 mA/cm\({}^{2}\), the \(\eta_{\text{OER}}\) value determined for the sample obtained using only Carbon Black is higher than for Gr3P14+CB and very close to that of Gr3P11 (0.91 V vs. 0.9 V). Considering this, the OER catalytic activity of Gr3P11 is too low to be considered significant. The linear voltammograms shown in Figure 4c were traced on the unmodified graphite electrode and on the samples modified according to Procedure 4. Perovskite-containing electrodes exhibited higher OER electrocatalytic activity compared with Gr0 and the Carbon  
Figure 4: (**a**) Anodic LSVs recorded on the unmodified glassy carbon electrode (GC0) and on the modified electrodes GC1 CB, GC1P11+CB, and GC1P14+CB, in 1 M KOH solution, at \(v\) = 5 mV/s. (**b**) Anodic polarization curves recorded on the unmodified graphite electrode (Gr0) and on the modified electrodes Gr3 CB, Gr3P11, and Gr3P14+CB, in 1 M KOH solution, at \(v\) = 5 mV/s. (**c**) Anodic polarization curves recorded on Gr0, Gr4 CB, Gr4P11, Gr4P14, Gr4P11+CB, and Gr4P14+CB electrodes, in 1 M KOH solution, at \(v\) = 5 mV/s. Black-only modified graphite sample (Gr4 CB). At i = 10 mA/cm2 \({}^{2}\)\({}_{\text{IOER}}\) = 0.875 V for Gr4P11, 0.84 V for Gr4P14 and Gr4P14+CB, and 0.83 for Gr4P11+CB. At higher i values, it is observed that the polarization curves are very close to each other and in some cases even overlap. By comparing the LSVs traced on the perovskite-containing electrodes manufactured via the four procedures it can be concluded that the best results were obtained for the samples resulted by using Procedure 4. Because of the closeness of the \(\eta\)OER values Gr4P11, Gr4P14, Gr4P11+CB, and Gr4P14+CB were all considered for the further evaluation of their electrochemical properties, including their OER electrocatalytic ones. Firstly, their ECSA and the diffusion coefficient of the hexacyanoferrate (III) ions (D) were estimated. To do so, the Randles-Sevcik equation was employed together with data from experiments performed as described in Section 2.5. The obtained values are presented in Table 3.  
High values for both parameters are to be desired since a higher D indicates a faster diffusion process while a higher ECSA implies a larger number of catalytic active centers involved in an electrochemical process [45]. As can be seen in Table 3, the highest values were found for the Gr4P11+CB electrode. The data acquired during the cyclic voltammetry experiments were used to plot 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 (Figure 5).