Electrodeposition Behavior of Zn-Polyethyleneimine Composite from Sulfate Solution and Its Micro Structure

Abstract

Electrodeposition of Zn-polyethyleneimine composite was performed at 100–12000 A·m⁻² and 4.8 × 10⁵ C·m⁻² in agitated sulfate solutions containing 1.84 mol·dm⁻³ of ZnSO₄ and 4 g·dm⁻³ of polyethyleneimine at pH 1.8 and at 313 K: the composite’s deposition behavior and the relevant deposits’ micro-structure were investigated. The films obtained at current densities above 4000 A·m⁻² from solutions containing polyethyleneimine exhibited gloss, and the gloss was highest for solutions containing polyethyleneimine with the highest molecular weight (70000). The preferred orientation of deposited Zn crystals changed from {0001} to {1120} and {1010} in the presence of polyethyleneimine, and the size of the platelet-shaped Zn crystals decreased as the polyethyleneimine molecular weight and current density increased. The deposition of Zn was polarized in the presence of polyethyleneimine, and the degree of polarization increased with the current density and with polyethyleneimine’s molecular weight. The C and N contents in deposited films increased as the polyethyleneimine molecular weight and current density increased, indicating an increase in the tendency of polyethyleneimine to be adsorbed onto the cathode. During deposition, polyethyleneimine buffered somewhat the pH increase in the layer of the electrolyte solution in contact with the cathode. At this time, H⁺ ions are released from polyethyleneimine because of an increase in pH in the cathode’s vicinity, and consequently, the number of electron lone-pairs in N atoms of polyethyleneimine increased, resulting in an increase in the adsorption ability of polyethyleneimine onto the cathode.