(Invited) Innovations in Ionic Liquids Electrodeposition of Metals

Abstract

A novel pathway for the high energy efficiency electrodeposition of metals from metal oxides and metal compounds by means of electrolysis in ionic liquids at low temperatures was investigated. Experimental results for electrochemical deposition of Zn from ZnO and Cu from Cu2O, Pb from PbO using Urea ((NH2)2CO) and Choline chloride (HOC2H4N(CH3)3 +Cl-) or (ChCl) are discussed. The results showed that pure metal was deposited on the cathode. Successful deposition of metal from metal oxide dissolved in Urea/ChCl (2:1) was accomplished with efficiency greater than 87%. Electrodeposition of aluminium and titanium using imidazolium chloride ionic liquids with the addition of AlCl3 and TlCl4 were carried out at low temperatures. The cathode deposits obtained were dendrite free pure aluminium (>99.9% pure) and Al-Ti (up to 37 wt %) alloy. Cathode current densities of up to 500 A/m2for electrowinning of aluminium were achieved. The surface modification of electrodes not only improved the cathode current density but also eliminated the dendritic deposition of metals. Use of glassy surface finish, aluminum cathode and aluminum alloy anode improved the current density of the process. The critical cathode overpotential and limiting current density at which aluminum dendritic growth begins was determined as -0.53 V and 518 A/m2, respectively. Lower overpotentials (<0.42 V) prevent the dendrite formation in the aluminum deposits. It was concluded that the overpotential is the key in preventing dendrite formation. A 3-D mathematical model (CFD) was developed for the batch reactor electrodeposition of metals process. The optimum conditions for electrodeposition of metals and alloys were determined. The model results are in good agreement with the experimental data for the Al electrowinning process. The advantages of the electrodeposition of metals using ionic liquids compared to industrial aqueous metals processes are low temperature, low energy consumption, and low pollutant emissions.