Quantum Chemistry Research on Iron-Zinc Alloy Electrodeposition

Employing gaussian 09 Software, and using ub3lyp/6-311 (3df) method, first do research on iron-zinc alloy electrodeposition, indicating that this method is in good agreement with the experimental data. The result has shown that at the electrode surface, the HOMO of Fe atoms is much higher than that of Zn atoms, the HOMO of Fe atoms is close to the LUMO of Fe² , and these make Fe atoms easy to transfer electrons to Fe² , and the Fe atoms formed on the electrode surface are not stable enough and are easy to dissolve again, and the polarization process adsorbs the positive ions and repels negative ions, and this makes LUMO of Zn² almost equal to LUMO of Fe² , even greater at the electrode surface, although the standard electrode potential of Fe is higher than that of Zn, the Fe² has no priority to get electrons, these are the reasons of abnormal co-deposition in zinc-iron alloy coating; while the HOMO energy level of Zn atoms is much lower than LUMO energy level of Zn² , so the Zn atoms are not easy to lose electrons, and are relatively stable and can move and spread on the electrode surface. Electroplating additives can affect the electronic energy level of atoms or ions on the surface of the electrode, and so affect the tunnel electron transfer between atoms and ions, and influence electrode deposition velocity. No less than 4 Zn atoms or no less than 2 Fe atoms forms a stable nucleus, so zinc is more prone to nuclear deposition at higher current density. The electric deposition process is divided into de-solvation of ions (also includes eliminating negative-ion effects), electron transferring and atoms forming nuclei then forming coating, deciding the free energy change (electrode potential) of one metal element. The content of each metal element in the alloy coating is not only related to its free energy change (electrode potential) but also related to its corresponding reaction speed. From the electrical point of view, it depends not only on the electrode potential factor but also on the resistance factor. Therefore, the electrode potential alone cannot determine the metal element content of the alloy coating.