## 3 Results and Discussion
### Electrochemistry
The appearance of CII and CIII cathodic peaks at \(-\)0.50 V and \(-\)1.00 V vs. SCE are ascribed to the reduction of the inner and dissolved outer O2, which could occur by 4-electron pathway (reaction 1) and two successive 2-electron pathways, according to the reactions (reactions 2 and 3):  
\[\text{O}_{2}+2\text{H}_{2}\text{O}+4\text{e}^{-}\to 4\text{HO}^{-} \tag{1}\]  
\[\text{O}_{2}+\text{H}_{2}\text{O}+2\text{e}^{-}\to\text{HO}_{2}^{-}+\text{HO} ^{-} \tag{2}\]  
Figure 5: Cyclic voltammograms recorded in 0.1 M NaOH supporting electrolyte at a scan rate of 0.05 V\(\cdot\)s\({}^{-1}\) with **GC** electrode (black line), **Zn_p/GC** (red line) and **Zn_typ/GC** electrode (blue line) within the potential range of \(-\)1.5 to \(+\)1.5 V/SC; Inset: details of CVs, including the anodic and cathodic peaks marking. \[\text{HO}_{2}{}^{-}+\text{H}_{2}\text{O}+2\text{e}^{-}\to 3\text{HO}^{-} \tag{3}\]  
Moreover, under the potential range of CIII, the hydrogen evolution reaction (HER) occurred onto **GC** electrode, which is partially overlapping with ORR. All cathodic and anodic peaks were influenced by the presence of **Zn_typ**. Thus, a slight polarization effect towards the OER is noticed and the shoulder recorded at +1.25 V/SCE is higher due to zinc oxide dissolution overlapping with O2 evolution. Considering the literature data related to zinc deposition and zinc oxide formation [55; 56; 57], during cathodic direction scanning, starting with \(-\)0.760 V, metallic zinc is deposited, which can continue at more negative potentials than \(-\)1.5 V vs. SCE. Moreover, under this negative potential range of ORR, ZnO can be formed based on EC (electrochemical/chemical) mechanism by coupling the zinc ions with peroxide and superoxide ions, which are generated from oxygen reduction reaction, according with reactions (4 and 5):  
\[\text{Zn}^{2+}+\text{O}_{2}{}^{2-}\rightarrow\text{ZnO}_{2}\rightarrow\text{ ZnO}+\frac{1}{2}{}_{2} \tag{4}\]  
\[\text{Zn}^{2+}+2{}^{\circ}{}_{2}{}^{-}\rightarrow\text{ZnO}_{4}\rightarrow \text{ZnO}+3/2{}^{\circ}{}_{2} \tag{5}\]  
These processes are proved by the CII cathodic peak increasing, which is related with the anodic peak from +1.25 V/SCE, considering both the higher concentrations of Zn\({}^{2+}\) and ORR products. Another alternative considers the conversion of metallic zinc deposit into ZnO through peroxide ions generated by ORR, based on reaction (6):  
\[\text{Zn}+\frac{1}{2}\text{O}_{2}{}^{2-}\rightarrow\text{ZnO}+1\text{e}^{-} \tag{6}\]  
This process occurred at a more negative potential, at which zinc ions are reduced to metallic deposits that can be oxidized via peroxide generated from ORR, which is evidenced by CIII cathodic peak increasing. During anodic scanning, the first anodic peak (A0) appeared only in the presence of **Zn_typ** at about \(-\)0.55 V vs. SCE, being a characteristic feature of the stripping of Zn deposited onto a GC electrode. At more positive scanning, the AI anodic peak increased due to the dissolution of metallic zinc and zinc oxide. A new anodic peak is evidenced at the potential value of about +0.65 V vs. SCE (A II), which can be attributed to the zinc oxide dissolution with the zincate formation (reaction (7)), which is controlled by the HO\({}^{-}\) anions diffusion at the electrode surface. \[\text{ZnO}+\text{H}_{2}\text{O}+2\text{HO}^{-}\rightarrow\text{Zn}(\text{ OH})_{4}{}^{2-} \tag{7}\]  
To further elucidate several mechanistic aspects, the influence of the scan rate on CV shape recorded at **Zn_typ/GC** electrode was studied. The family of CVs recorded for the scan rate, ranged between 0.01 to 0.20 V-s\({}^{-1}\), are presented in Figure 5.0 When the scan rate is ranged from 0.01 to 0.10 V-s\({}^{-1}\), the usual behaviour characteristics to the diffusion-controlled processes is observed for all cathodic and anodic peaks.