Open AccessAluminum Deposition and Dissolution in [EMIm]Cl-Based Ionic Liquids–Kinetics of Charge–Transfer and the Rate–Determining Step
Author(s) -
René Böttcher,
Sebastian Mai,
Adriana Ispas,
Andreas Bund
Publication year - 2020
Publication title -
journal of the electrochemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.258
H-Index - 271
eISSN - 1945-7111
pISSN - 0013-4651
DOI - 10.1149/1945-7111/ab9c84
Subject(s) - tafel equation , chemistry , inorganic chemistry , overpotential , dissolution , chloride , double layer capacitance , ionic liquid , electrochemistry , charge transfer coefficient , electron transfer , dielectric spectroscopy , analytical chemistry (journal) , electrode , cyclic voltammetry , organic chemistry , catalysis
The kinetics of the dissolution and deposition of aluminum from a first generation ionic liquid consisting of AlCl 3 /1-ethyl-3-methylimidazolium chloride (molar ratio 2:1) was studied. Electrochemical impedance spectroscopy shows that the double layer capacitance and the charge–transfer resistance depend on the state of the electrode surface. The impedance spectra are strongly influenced by mass transport. The rate–determining step of the aluminum deposition, as determined from the cathodic Tafel slope evaluated from current step experiments, was found to be either a chemical step, releasing the complexing agent chloride, while aluminum is in the divalent oxidation state (AlCl 3 − → AlCl 2 + Cl − ) or an electron transfer from the divalent to the monovalent aluminum occurring twice for the overall reaction to occur once (Al 2+ + e − → Al + ). The rate–determining step for aluminum dissolution was found to be the transfer of an electron from elemental aluminum to the monovalent oxidation state (Al 0 → Al + + e − ). A linear slope in the low cathodic overpotential region of the Tafel plot suggests a change in the cathodic rate–determining step. The Tafel slope indicates a chemical step, releasing the complexing agent chloride, after the last electron transfer (AlCl − → Al 0 + Cl − ) to be the rate–determining step for overpotentials below 50 mV. Density functional theory calculations support the proposed reduction and oxidation mechanisms.