TY - JOUR
T1 - Electrochemical stability of quaternary ammonium cations
T2 - An experimental and computational study
AU - Mousavi, Maral P.S.
AU - Kashefolgheta, Sadra
AU - Stein, Andreas
AU - Bühlmann, Philippe
N1 - Publisher Copyright:
© The Author(s) 2015. Published by ECS.
Copyright:
Copyright 2015 Elsevier B.V., All rights reserved.
PY - 2016
Y1 - 2016
N2 - Quaternary ammonium ions, NR4+, are among the most electrochemically stable organic cations. Because of their wide electrochemical windows, they are frequently used in batteries and electrochemical capacitors. Improving the electrochemical stability and expanding the electrochemical windows of quaternary ammonium ion is highly desired. In this work, we investigated the electrochemical stability of quaternary ammonium ions and showed that the chain length, type (primary vs. secondary), size, and steric hindrance of the saturated alkyl substituents have only a very small effect (less than 150 mV) on their electrochemical stability toward reduction. To provide a molecular understanding of substituent effects on electrochemical stability, quantum calculations were performed employing density functional theory, and it was shown that the structure of saturated aliphatic alkyl substituents has only minimal effects on the electronic environment around the positive nitrogen center and the LUMO energy level of quaternary ammonium cations. Moreover, a linear correlation between the cathodic limit and the LUMO energy levels of the NR4+, N-butylpyridinium, and 1-ethyl-3-methylimidazolium ions was found, suggesting that electrochemical stabilities of new cations may be computationally predicted on the basis of LUMO energies of these systems.
AB - Quaternary ammonium ions, NR4+, are among the most electrochemically stable organic cations. Because of their wide electrochemical windows, they are frequently used in batteries and electrochemical capacitors. Improving the electrochemical stability and expanding the electrochemical windows of quaternary ammonium ion is highly desired. In this work, we investigated the electrochemical stability of quaternary ammonium ions and showed that the chain length, type (primary vs. secondary), size, and steric hindrance of the saturated alkyl substituents have only a very small effect (less than 150 mV) on their electrochemical stability toward reduction. To provide a molecular understanding of substituent effects on electrochemical stability, quantum calculations were performed employing density functional theory, and it was shown that the structure of saturated aliphatic alkyl substituents has only minimal effects on the electronic environment around the positive nitrogen center and the LUMO energy level of quaternary ammonium cations. Moreover, a linear correlation between the cathodic limit and the LUMO energy levels of the NR4+, N-butylpyridinium, and 1-ethyl-3-methylimidazolium ions was found, suggesting that electrochemical stabilities of new cations may be computationally predicted on the basis of LUMO energies of these systems.
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U2 - 10.1149/2.0671602jes
DO - 10.1149/2.0671602jes
M3 - Article
AN - SCOPUS:84949580209
VL - 163
SP - H74-H80
JO - Journal of the Electrochemical Society
JF - Journal of the Electrochemical Society
SN - 0013-4651
IS - 2
ER -