# Concentration Influence of Complexing Agent on Electrodeposited Zn-Ni Alloy
## 3 Results and Discussion
### Electroplating Performance
The content of coulomb (q) was fixed (2.5 C), and the current density (i\({}_{\text{a}}\)) of alloy deposition was varied (0.1, 0.2, 0.5, 1, 2, 5, 10, 20, and 50 ASD); hence, the deposition time was determined as follow t = q/i\({}_{\text{a}}\). By applying the determined time and current density, the potential could be recorded using the potentiostat. The partial current densities of each Zn and Ni electrodeposition were calculated from the element mass obtained by AAS and the chemical composition of the coating according to [PERSON]'s laws of electrolysis using the formula: i = \(\frac{m\pi\
u}{ATM}\), where i is the partial current density of element (A.cm\({}^{-2}\)), m is the amount of element (g), M is the molecular weight of element (g/mol), v is the valency of the ions, A is the surface area of the cathode (cm\({}^{2}\)) t is the time of electrodeposition of electrodeposition (s), and F is Faraday constant (96,500 s.A/mol). For each sample, the electrochemical test was carried out 3 times, and the average values were calculated. Figure 8 displays  
Figure 6: Content of (a) Zn, (b) Ni, and (c) Fe obtained by EDS mapping as a function of current density with different TEPA concentrations. the partial polarization curves of Zn and Ni during Zn-Ni alloy electroplating at room temperature. For ease of visibility, the current density is presented as a function of potential on a logarithmic scale. The equilibrium potential of Zn \(E_{Zn}^{eq}\) is \(-1.27\) V with pure Zn depositing at room temperature [17]. The Zn polarization curve rose at approximately \(-1.0\) V, which is nobler than \(E_{Zn}^{eq}\), suggesting underpotential deposition of Zn. The cathode potential subsequently shifted to the negative direction, which is less noble than \(E_{Zn}^{eq}\), and the current density increased with shifting potential. A similar trend occurred during Ni deposition. Specifically, the partial current density for Ni deposition constantly increased from \(-1.0\) V to potentials less noble than \(E_{Zn}^{eq}\). Both the partial current densities of Zn and Ni depositions reached constant values at potentials more negative than \(-1.8\) V, indicating that the deposition limitations of Zn\({}^{2+}\) and Ni\({}^{2+}\) ions are at \(-1.8\) V. This agrees with the Butler-Volmer equation [37], which predicts four regions of a polarization curve, including a linear increase of current density with overpotential, exponential increase indicating pure activation, mixed control of activation and mass transportation, and a limiting diffusion current density. Furthermore, the current density of Zn deposition was higher than that of Ni deposition at all TEPA concentrations, which is constant to what was stated about the anomalous co-deposition. Additionally, the partial polarization curve did not significantly change with the change of TEPA concentration in both Zn and Ni deposition cases, indicating that TEPA did not significantly influence the electrochemical behavior of partial Zn and Ni deposition. Figure 7: EDS mapping of Zn-Ni coating surface with TEPA concentrations of (**a**) 0 M, (**b**) 0.035 M, (**c**) 0.07 M, and (**d**) 0.1 M.