Counter‐Anion Effect on the Properties of Anion‐Conducting Polymer Electrolyte Membranes Prepared by Radiation‐Induced Graft Polymerization

Abstract

Graft‐type anion‐conducting polymer electrolyte membranes (AEMs) are prepared by the radiation‐induced graft polymerization of chloromethylstyrene into poly(ethylene‐co‐tetrafluoroethylene) (ETFE) films and subsequent quaternization with trimethylamine. AEMs in the hydroxide form (AEM‐OH) are prepared by immersing the chloride form (AEM‐Cl) in 1 M potassium hydroxide (KOH) solution, followed by KOH and washing with nitrogen‐saturated water to prevent bicarbonate formation (AEM‐HCO3). The AEM‐OH shows conductivity and water uptake four and two times higher than AEM‐Cl and ‐HCO3 and is thermally and chemically less stable, resulting in the tendency to absorb water and to convert to the bicarbonate form.

Synthesis and characterization of aniline‐containing anion‐conducting polymer electrolyte membranes by radiation‐induced graft polymerization

“…The yields of the conversion of An‐AEM/OH from the chloride to the hydroxide were 75–87% as determined by titrimetric analysis, as shown in Table . In our previous article, the conversion of BA‐AEM/OH was 88–92%; namely, the IEC of the membrane was approximately 90% on the basis of the expected IEC calculated using a millimolar amount of a quaternary ammonium salt in a unit weight (1 g) of the AEM . However, the IECs of An‐AEM/OH were slightly lower than those of previously reported membranes, although the SEM–EDX clearly did not show a chlorine peak.…”

“…In the previous article, the basicity of the counter anion of the graft‐type AEMs appeared to strongly affect the conductivity and water uptake . It can be assumed that the large differences in water uptake when different counter anions are used result from the different stabilities of the quaternary ammonium salts of the AEMs.…”

“…According to the procedure in a previous article, the ETFE films were preirradiated with a dose of 30 kGy in the presence of argon gas at room temperature, and subsequently, the films were immersed in a 33 vol % solution of DMASt in 1,4‐dioxane at 60 or 80°C to yield DMASt‐g‐ETFE [Scheme (a)]. As shown in Figure , in the graft polymerization of DMASt at 80°C, the GD initially increased rapidly for grafting times of up to 8 h, and then reached a plateau at 27–42%.…”

“…Recently, we prepared poly(vinylbenzyltrimethylammonium hydroxide)‐grafted ETFE membrane (BA‐AEM/OH) by the radiation‐induced graft polymerization of chloromethylstyrene into ETFE films and subsequent quaternization with trimethylamine (Figure ) . Although, BA‐AEM/OH with a high IEC maintained a conductivity above 90% of the initial value in 1 M KOH at 80°C, the films broke into several pieces after 3 days and exhibited low‐mechanical stability in alkaline solution at high temperature (unpublished data).…”

A review of radiation-grafted polymer electrolyte membranes for alkaline polymer electrolyte membrane fuel cells

“…Walsby et al [201] used this technique to examine the solvent effects of toluene and n-propanol in the grafting of styrene to PVDF. Koshikawa et al [202] used 60 Co g-rays to pre-irradiate ETFE films, which were then treated by chloromethyl styrene and trimethylamine to prepare modified ETFE membranes (AEM-Cl). In their study, the quantitative conversion from Cl À to HCO 3 À forms was confirmed by analysis using energy-dispersive X-ray spectroscopy and SEM (EDX-SEM).…”