Investigation of the Effect of Functional Group Substitutions on the Gas-Phase Electron Affinities and Ionization Energies of Room-Temperature Ionic Liquids Ions using Density Functional Theory

• Published in: Electrochimica acta Vol. 55; no. 11; pp. 3804 - 3811
• Main Authors: Ong, Shyue Ping, Ceder, Gerbrand
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 15.04.2010; Elsevier
• Subjects: Anions; Anodic; Atomic and molecular physics; Cations; Density functional theory; Electrochemical stability; Electron affinities; Exact sciences and technology; Functional group; Functional groups; Ionic liquids; Ionization; Ionization energies; Ionization potentials, electron affinities, molecular core binding energy; Mathematical analysis; Molecular properties and interactions with photons; Physics; Properties of molecules and molecular ions; Ionic liquids; Density functional theory; Ionization energies; Electron affinities; Electrochemical stability; Functional group; Stability; Electron affinity; Theoretical study; Hexafluophosphates; Acidity; Tetrafluoborates; Quaternary phosphonium compound; Ionic liquid; Quaternary ammonium compound; Density functional method; Electrolytes; Ionization potential; Gas phase; Chemical properties
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2010.01.091

The cathodic and anodic stabilities of room-temperature ionic liquids (ILs) are important factors in their applications in electrochemical devices. In this work, we investigated the electron affinities of cations and ionization energies of anions for ionic liquids by density functional theory (DFT) calculations at the B3LYP/6-311+G(2d,p)//B3LYP/6-31+G(d) level. Over 200 unique cations and anions, formed from a set of six base cation structures, three base anion structures, and seven functional groups, were investigated. We find the trends in calculated EAs of alkylated cations and IEs of alkylated anions to be in good agreement with observed experimental trends in relative cathodic and anodic stabilities of various ILs. In addition, we also investigated the effect that functional group substitution at distinct positions in the ions have on the EA of the 1,2,3-trimethylimidazolium cation and the IE of the PF 5CF 3 anion. The overall impact on the EA or IE can be explained by the known electron-donating and electron-withdrawing inductive and resonance effects of the attached functional group, and the relative strength of the effect depends on the substitution position.