Aluminum Electrochemical Nucleation and Growth onto a Glassy Carbon Electrode from a Deep Eutectic Solvent

Abstract

This paper deals with the aluminum nanoparticles nucleation and growth kinetics and electrodeposition mechanism onto a glassy carbon electrode from Al(III) ions dissolved in a deep eutectic solvent based on choline chloride: urea. The cyclic voltammetry and chronoamperometry analyses indicate that the Al electrodeposition was attained directly from Al(III) ions that formed metallic Al, of which the nuclei provoked, in turn, residual water reduction on their growing surfaces. Consequently, hydroxide ions formed and reacted with Al(III) ions in the DES, originating thus insoluble Al(OH)3 onto the Al nuclei surfaces. Therefore, oxidation currents were absent during the backward scan of the cyclic voltammetry due to passivation of the Al deposits with the Al(OH)3 formed during the direct scan. Analyses of the experimental potentiostatic current density transients were carried out by means of a theoretical formalism, comprising the simultaneous presence of Al diffusion-controlled 3D nucleation and growth and residual water reaction over the Al nuclei growing surfaces. This model helps explaining clearly the contribution of the residual water during the aluminum electrodeposition and determining the charge percentages due to each individual contribution to the total process. Evidence of the aluminum, nanoparticles, deposits was obtained by means of SEM, EDX and XPS.