Hydroxide based Benzyltrimethylammonium Degradation: Quantification of Rates and Degradation Technique Development

Abstract

Anion exchange membranes (AEMs) are of interest as hydroxide conducting polymer electrolytes in electrochemical devices like fuel cells and electrolyzers. AEMs require hydroxide stable covalently tetherable cations to ensure required conductivity. Benzyltrimethylammonium (BTMA) has been the covalently tetherable cation that has been most often employed in anion exchange membranes because it is reasonably basic, compact (limited number of atoms per charge), and easily/cheaply synthesized. Several reports exist that have investigated hydroxide stability of BTMA under specific conditions, but consistency within these reports and comparisons between them have not yet been made. While the hydroxide stability of BTMA has been believed to be a limitation for AEMs, this stability has not been thoroughly reported. We have found that several methods reported have inherent flaws in their findings due to the difficulty of performing degradation experiments at high temperature and high pH. In order to address these shortcomings, we have developed a reliable, standardized method of determining cation degradation under conditions similar/relevant to those expected in electrochemical devices. The experimental method has been employed to determine BTMA stabilities at varying cation concentrations and elevated temperatures, and has resulted in improved experimental accuracy and reproducibility. Alkaline membrane fuel cells (AMFCs) employing anion exchange membranes (AEMs) are of increasing interest in fuel cell research as they potentially enable the use of non-Pt fuel cell catalysts, a primary cost limitation of proton exchange membrane fuel cells.

Electrospun Ionomeric Fibers with Anion Conducting Properties

“…The nonacidic environment of AEMFCs allows the use of nonprecious metal catalysts, which intensely reduces the cost per kilowatt of power of fuel cell devices . In spite of the latest technological progress related to electrocatalysts and to the understanding of carbonation issues, one of the main remaining challenges in the AEMFCs is the availability of good, stable anion conducting membranes that enable the hydroxide anion and water conduction through the polymeric network, both as an anion exchange membrane (AEM) and as anion exchange ionomers (AEIs).…”

Novel Processing of a Poly(phenyleneoxide) −b–Poly(vinylbenzyltrimethylammonium) Copolymer Anion Exchange Membrane; The Effect On Mechanical And Transport Properties

“…Smaller cationic head groups such as those formed by quaternization with trimethlyamine (TMA), especially benzyltrimethyl amine (BTMA) are easy to tether to the polymer backbone and are stable at low temperatures [21,22]. Quaternary ammonium cations have actually shown great chemical stability and high ionic conductivity in alkaline environments when operated at 80 °C in some cases [1,7,12,21,23,24].…”

“…Quaternary ammonium cations have actually shown great chemical stability and high ionic conductivity in alkaline environments when operated at 80 °C in some cases [1,7,12,21,23,24]. Deavin et al and several other groups have used different experimental techniques to show very little to no degradation of benzyl trimethyl ammonium groups in their systems when operated at 60-80 °C and alkaline environments [22,25,26].…”

Experimental Evaluation of Effective Parameters for the Synthesis of Polysulfone‐Based Anion Exchange Membrane

“…A considerable amount of literatures have been published on post‐functionalization (chemical modification) of existing polymers which is a routine and effective method for AEMs preparation 6, 7. Various polymers such as polysulfone 8–15, poly(2,6‐dimethyl‐phenylene oxide) 16–19, poly(vinyl alcohol) 20, 21, poly(ether ether ketone) 22, 23, polybenzimidazole 24, 25, poly(ether imide) 26, 27, poly(phenylene) 28, poly(vinylbenzyl chloride) 29, poly(ether sulfone) 30, poly(propylene) 31 can be quaternized with ammonium 16, 32–34, imidazolium 35–37, phosphonium 22, 38, guanidinium 39, 40 and pyridinium 41 cationic groups.…”