## 4 Discussion  
### Materials and Electrochemical Characterization  
Figure 1 represents the FE-SEM for CuCoNiOx@CNTs/GCE at (A) 600 s; (B) 900 s; and (C) 1200 s deposition time; as well as the (D) EDX analysis for sample (C). The SEM micrographs reveal that CuCoNi alloy is deposited throughout the CNTs' texture as rough sphere-like shapes with poor distribution on the entire surface (SEM A, 600 s). When increasing the deposition time to 900 s, the rough sphere-like deposits' diameter increases with enhancement of the deposits' distribution through the surface. At 1200 s, the texture of the rough sphere starts to change to a cauliflower-like shape with noticeable high and uniform distribution. On the other hand, EDX is an important tool to quantify the deposits and to confirm the deposition of the different ingredients in the catalyst. The EDX chart (D) confirms the deposition of the three metal simultaneously by the revealed peaks of cobalt, nickel, and copper at 7.0 keV, 7.7 keV, and 8.1 keV, in weight percent quantities of 3.34, 3.47, and 1.5, respectively [8; 19]. The mapping EDX (inset of (D) depicts the uniform distribution of the three metals inside the sample. The wide-angle XRD patterns of the prepared CuCoNiOx@CNTs/GCE were also carried out to explain the existing forms of the metal elements. As shown in Figure 2, the sharp peak located at around 25\({}^{\circ}\) corresponds to the (002) diffraction of the carbon substrate. According to the literature, Co, Ni, and Cu elements have similar negative electrons and atomic radiuses. Therefore, they can easily form the similar cubic structure. The (111), (200), and (220) peaks belonging to cubic system of Co, Ni, and Cu are 44.2\({}^{\circ}\), 44.3\({}^{\circ}\), 43.3\({}^{\circ}\), 51.5\({}^{\circ}\), 51.7\({}^{\circ}\), 50.4\({}^{\circ}\), and 76.0\({}^{\circ}\). The XRD pattern revealed that the ternary alloy deposited has a cubic crystalline structure since the peaks from the characteristic cubic planes of (111), (200), and (220) were observed at 26 \(\approx\) 44.0, 51.0, and 76.0, respectively, suggesting that the CuCoNi system is a solid solution [26; 27]. In addition, the peaks located around 20 \(\approx\) (37.0, 42.0) and 55.0 are attributed to NiOx and Co(OH)\({}_{2}\) formation, respectively [27; 28]. Figure 3 shows the CVs of (a) CNTs/GCE and (b-d) metal oxide modified CNTs/GCE in 1 M NaOH solution at a scan rate of 100 mV/s. The Voltammetric behavior of CNTs/GCE is featureless in the operating conditions of both potential and pH. While on the modification of CNTs/GCE with CoOx (CoOx@CNTs/GCE, curve b) reveals an anodic peak around +0.07 V and the corresponding small cathodic peak at the same value, and this can be attributed to the redox reaction [19],  
\[\mathrm{Co_{3}O_{4}+OH^{-}+H_{2}O\Leftrightarrow 3 CoOOH+}e^{-} \tag{1}\]  
\[\mathrm{CoOOH+OH^{-}\Leftrightarrow CoO_{2}+H_{2}O\ +}e^{-} \tag{2}\]  
as long as there is a redox couple at about +0.45 V, which is related to the oxidation process of CoOOH to CoO\({}_{2}\) following the equation [19]. On the other hand, CuOx@CNTs/GCE (curve c) shows a significant increase in the CV current starting around 0.25 V in the forward and backward directions, which is caused by conversion of the already formed Cu(II) at more negative potentials to Cu(III) according to the following equation [29],  
\[\mathrm{CuO+OH^{-}\Leftrightarrow CuOOH+}e^{-} \tag{3}\]  
At the NiOx@CNTs/GCE (curve e), the well-defined redox waves of the Ni(II)/Ni(III) transformation in alkaline medium is observed around 0.4 V, which leads to the formation of NiOOH according to [24],  
\[\mathrm{Ni(OH)}_{2}+\mathrm{OH^{-}\Leftrightarrow NiOOH+H_{2}O+}e^{-} \tag{4}\]Furthermore, on the deposition of the tertiary metal oxides (CuCoNiOx@CNTs/GCE, curve d) several interesting features can be observed,  
1.