Hierarchical Structure–Property Relationships in Graft-Type Fluorinated Polymer Electrolyte Membranes Using Small- and Ultrasmall-Angle X-ray Scattering Analysis

Abstract

The hierarchical structures of graft-type poly(ethylene-co-tetrafluoroethylene) (ETFE)-based polymer electrolyte membranes (ETFE-PEMs) were investigated using small- and ultrasmall-angle X-ray scattering experiments. The ETFE-PEMs with ion exchange capacities (IECs) <2.4 mmol/g possessed conducting graft domains around lamellar crystals, with a d-spacing of 21.8–29.1 nm, and oriented crystallites (lamellar grains) with short and long correlation distances of 218–320 and 903–1124 nm, respectively. The membranes with IECs > 2.7 mmol/g showed a new phase of crystallite network domains with a d-range of 225–256 nm, indicating a phase transition from oriented crystallite to crystallite network structures in the IEC range of 2.4–2.7 mmol/g. Noted that for the ETFE-PEMs with high IECs higher conductivity at 30% RH and compatible tensile strengths at 100% RH and 80 °C, compared with Nafion, originated from the well-interconnected ion channels around the crystallites and the remaining lamellar crystals and crystallites, respectively.

Anion‐Exchange Membranes for Fuel Cells: Synthesis Strategies, Properties and Perspectives

“…But the studies about morphologies of grafted AEMs derived from pre‐irradiated films are still scarce. Some insight to them might be given through the reports about the hierarchical structures of graft‐type PEMs 86, 87. Based on the results of FSANS, SANS and SAXS, Iwase and coworkers thought that the hierarchical structure of cPTFE‐g‐PSSA membranes could be regarded as being composed of conducting layers (graft domains) in lamellar stacks with 48–57 nm spacing on the surfaces of 480 nm diameter crystallites and ultrasmall structures with 1.7 nm correlation distance of the sulfonic acid groups in the conducting layers (Figure 6).…”

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

“…[16][17][18] For the first time, our group tried to develop a new type of 2Me-AEM by radiation grafting of imidazole/styrene on mechanically tough poly(ethylene-co-tetrafluoroethylene) (ETFE) films. 1,19 There have been intensive reports including our previous studies [20][21][22] on the radiation grafting technique, which has been successfully applied for the preparation of PEMs, where grafts containing an ion-conducting group (i.e. sulfonic acid) grafted onto fluorinated polymer films such as cross-linked polytetrafluoroethylene (cPTFE), ETFE, and poly(vinylidene fluoride) (PVDF) or fully aromatic hydrocarbon polymers such as poly-(ether ether ketone).…”

“…sulfonic acid) grafted onto fluorinated polymer films such as cross-linked polytetrafluoroethylene (cPTFE), ETFE, and poly(vinylidene fluoride) (PVDF) or fully aromatic hydrocarbon polymers such as poly-(ether ether ketone). [20][21][22][23][24][25][26][27][28][29] Therefore, we believe that this technique may allow the introduction of a large amount of grafts containing ion-conducting groups into the AEMs, and thus the resultant AEMs are expected to possess both high ion conductivity and good mechanical properties.…”

“…The morphology of the crystalline domains for polystyrene-grafted PEMs prepared by the radiation grafting technique has been intensively investigated using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and small-angle scattering methods. [20][21][22][23][24][25][26][27][28][29] For instance, the crystallinity of the grafted films was found to decrease with an increase in the grafting degree by many researchers in different fluoropolymer bases. [27][28][29] In our previous work, we studied the hierarchical structure of PEMs consisting of poly(styrenesulfonic acid) and the PTFE base by using small angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) methods.…”

“…20,21 Most recently, we investigated the hierarchical structures of graft-type ETFE-based PEMs by using the Ultra-SAXS technique, and found that when the IEC is low, the conducting graft domains are around the ETFE lamellar crystals, however, when the IEC is high, new amorphous hydrated and crystallite network domains are formed independently. 22 According to the previous studies on graft-type PEMs, ETFE was regarded as the most promising base material because of its well-balanced properties. Thus, we selected ETFE as the base material to develop a new type of imidazolium cation-grafted AEM.…”