Electrodeposition behavior of Zn-polyethyleneimine composite from sulfate solution and its micro structure

Electrodeposition of Zn-polyethyleneimine composite was performed at current density of 100-12000 A.m^-2 and a charge of 4.8 × 10⁵ C.m^-2 in an agitated sulfate solution containing 1.84 mol.dm^-3 of ZnSO₄ and 4 g.dm^-3 of polyethyleneimine at pH 1.8 and at 313 K, and the deposition behavior and its micro structure were investigated. The films deposited at current densities above 4000 A.m^-2 from the solution containing polyethyleneimine exhibited the gloss, and the gloss was highest with polyethyleneimine of higher molecular weight of 70000. The preferred orientation of deposited Zn changed from {0001} to {1120} and {1010} with polyethyleneimine, and the size of Zn platelet crystals deceased with increasing the molecular weight of polyethyleneimine and current density. The deposition of Zn was polarized with polyethyleneimine, and the degree of polarization became larger at higher current density region with polyethyleneimine of higher molecular weight of 70000. With increasing the molecular weight of polyethyleneimine and current density, the content of C and N in deposited films increased, indicating the increase in adsorption ability of polyethyleneimine onto cathode. Polyethyleneimine somewhat suppressed the rise of pH at cathode layer during deposition, or showed the buffer action of pH. During deposition, H⁺ ions are detached from the polyethyleneimine due to rise of pH at cathode layer and, as a result, the lone pairs of electron in N atom increased, which resulted in increase in adsorption ability of polyethyleneimine onto cathode.