Electrocrystallizations of copper from both CuCl2 silica sol and aqueous solutions were studied by the chronoamperometry technique.It was found that current density contributions of the double-layer charging (iDL) in current-time transients (CTTs) from both of the solutions were large.An adsorption-nucleation based model was proposed to analyze quantitatively the CTTs,by which copper electrocrystallization mechanism was characterized as progressive nucleation with 3D growth (3DP) under diffusion control.The diffusion coefficient of copper ions and the AN∞ products in aqueous solutions were larger than that in silica sols,which indicated that copper nucleation was inhibited in sol solution.The large iDL may be resulted from the adsorption of chloride ions on the electrode surface.