## 4 Discussion
### Materials and Electrochemical Characterization
Firstly, the Ni(II)/Ni(III) transformation potential is negatively shifted by about 0.2 V in comparison to NiOx@CNTs/GCE (d), and this is attributed to the influence of a partial alloy or alloy structure, where the peaks of Ni(II)/Ni(III) and Co(II)/Co(III) of the formed alloy shifted negatively and positively, respectively [19]. 2. Secondly, the charging current of the Ni(II)/Ni(III) transformation increased dramatically compared to the case of NiOx@CNTs/GCE, and this may be due to the synergism between NiOx and the other two oxides present at the same time that resulted in more transformation of Ni(II) to Ni(III). This enhanced transformation can be explained in the view of the results recorded in the literature previously, which assumed that mixing NiOx with other oxides to form binary alloys, for example MnOx, CoOx, or CuOx, causes an noticeable increase in the Ni(II)/Ni(III) transformation reaction [24; 28; 30]. This can be represented by Equation (6). \[\text{Ni}^{2+}+\text{Cu}^{2+}\text{and/or Co}^{3+}\Rightarrow\text{Ni}^{3+}+ \text{Cu}^{1+}\text{ and/or Co}^{2+}\] (5)
3. Thirdly, the charging current for both CuOx and CoOx, observed in the potential range 0.3 V to 0.55 V in curve b and c, decreased slightly in the same potential range in the case of CuCoNiOx@CNTs/GCE; this is certainly due to the last-mentioned feature in point II. Where, the high charging current in the mentioned potential range for both CuOx and CoOx is attributed to the conversion of Cu(II) and Co(III) to the higher oxidation states mentioned in Equations (3) and (4), and immediately the produced higher oxidation states are consumed in the Ni(II)/Ni(III) transformation according to Equation (6), so that no high charging current is observed. The effect of the scan rate on the CuCoNiOx@CNTs/GCE electrode has been studied by recording CVs in 0.5 M NaOH at different scan rates (see Figure 4A). An increase in the peak currents was observed with increasing the potential scan rate. Figure 4B shows the variation of both anodic and cathodic peak currents with the scan rate. A linear relation between the peak current and the scan rate is obtained, indicating that the transformation process is a surface redox reaction [19]. Figure 5 shows the CVs for CuCoNiOx@CNTs/GCE at different deposition times in 1 M NaOH at a scan rate of 100 mV/s. In the case of CuCoNi@CNTs/GCE, as the deposition time of CuCoNi increases, the current for the redox transformation increases regularly, except for the last two deposition times, 1200 s and 1500 s, where the current difference is small. This may be due to the increase of the amount of deposit increases the time needed for the surface enrichment with oxides during the passivation step in alkaline medium. Also, by increasing the deposition time, the rate of crystal growth exceeds that of nucleation and results in the formation of bigger deposits rather than the formation of new crystals, which has a negative effect on the deposits' accessible surface area, so the current does not increase directly [24]. On the other hand, with increasing the loading level of the deposit, the peak potential shifts slightly positive, and this could be attributed to the higher potential required for the nucleation of the upper oxides at these high loading levels [24]. Moreover, the peak of the transformation became sharp (i.e., small potential window of the peak) instead of broad at low loading levels, which confirms a fast kinetics of the transformation process.