title: Alkaline stability of quaternary ammonium cations for alkaline fuel cell membranes and ionic liquids.
abstract: The alkaline stability of 26 different quaternary ammonium groups (QA) is investigated for temperatures up to 160 °C and NaOH concentrations up to 10 mol L(-1) with the aim to provide a basis for the selection of functional groups for hydroxide exchange membranes in alkaline fuel cells and of ionic-liquid cations stable in basic conditions. Most QAs exhibit unexpectedly high alkaline stability with the exception of aromatic cations. β-Protons are found to be far less susceptible to nucleophilic attack than previously suggested, whereas the presence of benzyl groups, nearby hetero-atoms, or other electron-withdrawing species promote degradation reactions significantly. Cyclic QAs proved to be exceptionally stable, with the piperidine-based 6-azonia-spiro[5.5]undecane featuring the highest half-life at the chosen conditions. Absolute and relative stabilities presented herein stand in contrast to literature data, the differences being ascribed to solvent effects on degradation.
authors.affiliation: Max Planck Institute for Solid State Research, Heisenbergstraße 1, 70569 Stuttgart (Germany). m.marino@fkf.mpg.de.
authors.forename: M G
authors.initials: MG
authors.lastname: Marino
authors.forename: K D
authors.initials: KD
authors.lastname: Kreuer
mesh_terms: D004355:Drug Stability; D011211:Electric Power Supplies; D052578:Ionic Liquids / Q000737:chemistry*; D007700:Kinetics; D008567:Membranes, Artificial; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013696:Temperature
chemical_list: D052578:Ionic Liquids; D008567:Membranes, Artificial; D000644:Quaternary Ammonium Compounds; D012997:Solvents
keywords: alkaline fuel cells; alkaline stability; anion exchange; ionic liquids; membranes