Preparation of Ni and Ni-Al Alloys from 2AlCl<sub>3</sub>/Et<sub>3</sub>NHCl Ionic Liquid by Electrodeposition

Abstract

Nickel and nickel-aluminum alloy were successfully electrodeposited on Cu electrodes from 2: 1 molar ratio aluminum chloride (AlCl3)/triethylamine hydrochloride (Et3NHCl) ionic liquids containing Ni2+ by constant potential electrolysis. The nucleation mechanism of nickel electrodeposition on Cu was investigated by cyclic voltammograms and chronoamperometry. The mechanism and the influence of experimental conditions on the current efficiency and the surface morphology of nickel-aluminum alloy electrodeposition on Cu electrodes were studied. The electrodeposition of nickel on Cu electrodes was controlled by three-dimensional instantaneous nucleation with diffusion-controlled growth. The Ni-Al alloy composition did not become independent of the deposition charge until at least 3.0 C had been accumulated. The mechanism of Ni-Al alloy formation appears to involve the underpotential deposition of aluminum on the developing nickel deposit and alloy formation must be kinetically hindered because the aluminum content is always less than that predicted from theoretical considerations. The Ni-Al alloy that was obtained on the Cu electrode was dense, continuous, and well adherent when the deposition current was small and stationary. If these conditions were not met, a nodule surface morphology appeared. The current efficiency of the Ni-Al alloy electrodeposition was greater than 90% and the deposition composition was close to that of the Ni3Al alloy.