Quantum Chemistry Research on Zinc Electrodeposition in KCl Solution

Employing ub3lyp/6-311 (3df, 2p) method in gaussian 09 Software, first do research on zinc electrodeposition in KCl solution. The result has shown that at the electrode surface when electrodepositing, the HOMO of Zn atom is much lower for the impact of k (the cathode adsorbs the positive ions and repels negative ions in polarization process), also the LUMO of Zn² (ZnCl₂) is much lower for the impact of k , and this makes Zn² is easier to get electrons. So KCl can increase Zn² (ZnCl₂) electrodepositing speed. When the distance from k to Zn ² is at the range of 3.5 - 4.5 angstrom, the value of LUMO(Zn² )-HOMO(Zn) (Zn² and Zn at the same location) is the highest, and is much higher than the value of LUMO(Zn² )-HOMO(Zn) without KCl in water solution. And this makes Zn atoms more stable and moving freely on the electrode surface, making electroplating layer more smooth and flat. When the electroplating additive O-Chlorobenzaldehyde is absorbed on Zn atoms, accumulating within 3 - 5 angstrom from electroplating surface, the energy of the system formed by Zn and O-Chlorobenzaldehyde decreases, the HOMO of Zn atom and the LUMO of Zn² also decrease. The HOMO of Zn atom decreases more, the value of LUMO(Zn² )-HOMO(Zn) (Zn² and Zn at the same location) is higher than the value of LUMO(Zn² )-HOMO(Zn) without O-Chlorobenzaldehyde. This makes the Zn atoms more stable and move freely on the electrode surface, and helps to form a smooth and flat electroplating surface. However, if o-chlorobenzaldehyde is directly adsorbed on the electrode surface, it means o-chlorobenzaldehyde and Zn on the same surface, the HOMO energy of the nearby Zn atom may be decreased, or may be increased; that is, it is possible for o-chlorobenzaldehyde to stabilize or destabilize the Zn atoms. Therefore, the direct adsorption of o-chlorobenzaldehyde on the electrode is not as effective as the enrichment in the range of 3 - 5 angstroms from the electrode surface. The stabilizing effect on Zn atom is by the whole O-chlorobenzaldehyde molecule. A large number of electroplating additives contain O and N, which may be related to their stabilizing effect on the atoms formed by electrodeposition. The KCl and electroplating additives are substances other than Reactants and products in chemical reaction, their action principle is that intermolecular force by KCl and electroplating additives can affect the HOMO and LUMO of reactants and products, so can affect electron transfer rate and process. This principal is similar to catalysts, so can be applied to select catalysts of chemical reaction. Some molecules may increase the HOMO energy of the molecular which gets electron and reduce the LUMO energy of the molecular which give electron. Such molecules can increase electrons transfer rate to the product orbital and speed up chemical reaction. Such molecules have catalytic effect. Therefore, the catalysts for chemical reactions can be preliminarily selected by calculating and analyzing the catalytic properties of molecules. And the corrosion inhibitor increases the LUMO energy of the molecular which gets electron and reduces the HOMO energy of the molecular which give electron. Also the polarization process when electroplating is researched. When Zn² approaching to the electrode surface, Zn² interacts with atom, atom cluster on electrode surface and interacts with metal surface, the LUMO energy of Zn² which gets electrons rises, and the HOMO energy of atom, atom cluster on electrode surface and metal surface which give electrons decreases, these two aspects of reason cause electroplating more difficult, we must give higher voltage when electroplating.