Imidazolium Cation Based Anion-Conducting Electrolyte Membranes Prepared by Radiation Induced Grafting for Direct Hydrazine Hydrate Fuel Cells

Abstract

Graft-type anion-conducting electrolyte membranes (AEMs) with imidazolium cations on graft polymers were synthesized through radiation-induced graft polymerization of N-vinylimidazole (NVIm) on poly(ethylene-co-tetrafluoroethylene) (ETFE) films, followed by N-propylation and ion-exchange reactions. The N-propylation proceeded quantitatively, whereas the ion-exchange reactions in 1 M KOH at 60 • C were accompanied by partial β-elimination of the imidazolium cations to yield copolymer grafts consisting of poly-(1-vinyl-3-propylimidazolium hydroxide) and double bonds (polyethyne) (AEM2), which exhibited an ion-exchange capacity (IEC) of 0.85 mmol g −1 and ionic conductivity of 10 mS cm −1 . AEM2 showed alkaline stability at 60 • C but it gradually degraded at 80 • C for ca. 150 h. The copolymer-type AEM (AEM3) with an IEC of 1.20 mmol g −1 was prepared through the copolymerization of NVIm with styrene on ETFE films, followed by the same N-propylation and ion-exchange reactions. AEM3 was characterized to be a terpolymer, owing to partial β-elimination and showed higher alkaline durability in 1 M KOH at 80 • C. As a result, it exhibited higher conductivity (>10 mS cm −1 ) for 250 h. Therefore, alkylimidazolium cations in copolymer grafts are a promising anion conducting group for alkaline-durable AEMs. A maximum power density of 75 mW cm −2 is obtained for AEM3 in a direct hydrazine hydrate fuel cell.

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

“…Since the ion‐exchange reaction from iodide to hydroxide in the grafted‐type AEM was very slow, requiring 48 h to ensure complete reaction, we conducted the ion‐exchange reaction in two steps: from An‐AEM/I to the chloride form, followed by transformation of the obtained chloride form to the hydroxide form to attain a high exchange degree, as shown in Scheme (b). First, the An‐AEM/I were transformed to the corresponding chloride form by soaking in 1 M HCl and 1,4‐dioxane at 60°C to facilitate the ion‐exchange reaction.…”

“…This might be due to the decomposition of ETFE and/or the grafted chains due to the high basicity of tetramethylammonium hydroxide. On the other hand, low basicity poly(1‐vinyl‐3‐propylimidazolium hydroxide)‐grafted ETFE (Im‐AEM/OH) was prepared to prevent the decomposition of ETFE in 1 M KOH at 80°C (Figure ) . However, an Im‐AEM/OH with an IEC = 0.85 mmol/g did not show conductivity after 150 h in 1 M KOH at 80°C because of ring‐opening hydrolysis of the imidazolium groups and β‐elimination of the imidazolium groups from the graft chains.…”

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

“…This result confirms the presence of N,Ndimethylethanolamine in the degradation products. Yoshimura et al [172] prepared a series of imidazolium-type AEMs through radiation grafting ways and used 13 C NMR to investigate the grafting result. NMR technology has also been used to investigate alkaline membranes prepared by chemical modification.…”

Imidazolium-based anion exchange membranes for alkaline anion fuel cells: elucidation of the morphology and the interplay between the morphology and properties

“…In a previous study, we reported the synthesis and characterization of a series of newly developed imidazolium cation based anion exchange membranes (AEMs) made by radiation-induced grafting of 1-vinylimidazole and styrene into poly(ethylene-cotetrafluoroethylene) (ETFE) films, and followed by N-alkylation with methyliodide. 1 These AEMs were characterized to be terpolymers, and showed better alkaline durability in 1 M KOH at 80 1C. Most lately, we have further modified the grafted imidazole group to 2-methyl-1-vinylimidazole, and the resultant AEMs (hereafter named 2Me-AEM) exhibit even higher ion conductivity (4100 mS cm À1 ) and longer alkaline durability, owing to the fact that the methyl protecting group at the 2-imidazole position prevents ring-opening degradation.…”