Electrochemical reduction mechanisms and stabilities of some cation types used in ionic liquids and other organic salts

Interfaces between Charged Surfaces and Ionic Liquids: Insights from Molecular Simulations

“…3, the formation of the monolayer structure both in the cathodic and anodic regimes can be expected at realistic electrode charge densities (~±35 μC/cm 2 ) 24,26 for a number of relatively large ions such as C n MIm + and C n MPyr + with n ≥ 4, TFSA − , FAP − , etc. These ions are electrochemically stable due to the presence of stabilizing functional groups and larger contact distances from the electrode 40,41 and, therefore, relatively high electrode charge densities necessary for the formation of the monolayer structures can be achieved experimentally in these systems.…”

Electrochemical studies of acetonitrile based supercapacitor electrolytes containing alkali and alkaline earth metal cations

“…Quaternary ammonium and quaternary phosphonium cations are the most reductively stable organic cations available, they typically undergo gross reduction at or beyond À2.8 V (vs. SHE) [7], and in some situations the stability may be extended to nearly À3 V (vs. SHE) such as when the materials are of exceptional purity or when large alkyl groups are used. Although phosphonium cations have been studied as potential electrolyte salts [4,8,9], and have even been proven to be of equal stability to quaternary ammonium cations in some cases [4], to the best of our knowledge phosphonium cations are not being used in commercial supercapacitors, instead quaternary ammonium cations are preferred.…”

“…The overall effect would most likely be the passivation of the electrode. In the case of a non-spiro quaternary ammonium cation, reduction by the Hoffman elimination route will liberate gaseous products (increasing pressure in the cell), unsaturated hydrocarbons as well as a tertiary amine [7]. The amine will likely cross the separator and undergo oxidation at the positive electrode at about 1 V (vs. SHE) [12], or react with any H + generated at the positive electrode.…”

Reactivity of the Ionic Liquid Pyr14TFSI with Superoxide Radicals Generated from KO2or by Contact of O2with Li7Ti5O12

“…1,2 In this last category, ionic liquids with cyclic quaternary ammonium cations such as pyrrolidinium or piperidinium have become especially popular due to their outstanding stability at reducing potentials, which renders them suitable for highly negative battery electrodes. 3 Even though their cathodic stability is superior to, e.g., imidazolium-based ionic liquids, there are doubts as to whether they are indeed stable at the lithium potential. While Kroon et al 4 and Markevich et al 5 reported the instability of the 1-butyl-1-methylpyrrolidinium cation (Pyr 14 , often also referred to as BMP or BMPyr) employing quantum chemical calculations, GC-MS and FTIR analysis, others observed high cycling stability for lithium plating 6,7 as long as the ionic liquid was sufficiently clean and dry.…”