title: A New Alkali-Stable Phosphonium Cation Based on Fundamental Understanding of Degradation Mechanisms.
abstract: Highly alkali-stable cationic groups are a critical component of hydroxide exchange membranes (HEMs). To search for such cations, we studied the degradation kinetics and mechanisms of a series of quaternary phosphonium (QP) cations. Benzyl tris(2,4,6-trimethoxyphenyl)phosphonium [BTPP-(2,4,6-MeO)] was determined to have higher alkaline stability than the benchmark cation, benzyl trimethylammonium (BTMA). A multi-step methoxy-triggered degradation mechanism for BTPP-(2,4,6-MeO) was proposed and verified. By replacing methoxy substituents with methyl groups, a superior QP cation, methyl tris(2,4,6-trimethylphenyl)phosphonium [MTPP-(2,4,6-Me)] was developed. MTPP-(2,4,6-Me) is one of the most stable cations reported to date, with <20 % degradation after 5000 h at 80 °C in a 1 m KOD in CD3 OD/D2 O (5:1 v/v) solution.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE, 19716, USA.
authors.forename: Bingzi
authors.initials: B
authors.lastname: Zhang
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE, 19716, USA.
authors.forename: Robert B
authors.initials: RB
authors.lastname: Kaspar
authors.affiliation: Department of Mechanical Engineering, Wichita State University, Wichita, KS, 67260, USA.
authors.forename: Shuang
authors.initials: S
authors.lastname: Gu
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE, 19716, USA.
authors.forename: Junhua
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE, 19716, USA.
authors.forename: Zhongbin
authors.initials: Z
authors.lastname: Zhuang
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE, 19716, USA. yanys@udel.edu.
authors.forename: Yushan
authors.initials: Y
authors.lastname: Yan
mesh_terms: D000468:Alkalies / Q000737:chemistry*; D004355:Drug Stability; D007700:Kinetics; D009943:Organophosphorus Compounds / Q000737:chemistry*; D013696:Temperature
chemical_list: D000468:Alkalies; D009943:Organophosphorus Compounds; C405845:tris(trimethoxyphenyl)phosphonium acetyl
keywords: alkali-stable; degradation mechanisms; hydroxide exchange membrane; phosphonium cation