Humidity and temperature effects on mechanical properties and conductivity of graft-type polymer electrolyte membrane

Macro Chemistry & Physics

Nguyen

Zhao³

et al. 2019

Self Cite

their advantages over other fuel cells in terms of the clean and efficient power generation and lower operating temperature. [1] They are expected to reduce the fossil fuel consumption, which is believed to be the primary sources causing the climate change. PEM, which consists of super acid groups (i.e., sulfonic acid), has been considered as one of the key components in achieving the high fuel cell performance because of its unique fuel cell properties such as ionic conductance, mechanical strength, and thermal and chemical stabilities. When a dry PEM is immersed in water, the hydrophilic chains with sulfonic ion groups can absorb water and consequently form the interconnected ion channels inside the hydrated regions. The macro and microphase separations, viz., crystalline morphologies, conducting layers (ion channels), characteristic domain sizes, and the connection and distribution of the ionic groups and water in the conducting layers and around the crystalline phases are believed to play an important role in the conductivity and mechanical integrity of the PEMs. [2][3][4] Currently, the main challenges to improve the conductivity and mechanical strength of the PEMs are the lack of detailed informationThe changes of the lamellar periods (L 1D ), thickness of lamellar crystals (L c ), and amorphous layers (L a ) within the stacked lamellae of poly(styrenesulfonic acid)-grafted poly(ethylene-co-tetrafluoroethylene) polymer electrolyte membranes (ETFE-PEMs), induced by the preparation and water-absorbing steps are investigated using the small-angle X-ray scattering method. The L 1D values of all the samples quickly increase at a grafting degree (GD) range of less than 19% and then level off. The solvent-induced recrystallization is observed at the early stage of grafting (GD < 10%) and at successive sulfonation and hydration steps. The L 1D , L a , and L c of dry and hydrated PEMs show similar values at higher GD ranges (>34%), leading to the conclusion that most water molecules in the PEMs with higher GDs exist at the outside of the lamellar stacks. Accordingly, for the PEMs with low GD (<19%), all the hydrophilic graft-polymers (ion-channels) locate in the lamellar stacks and are strongly restricted by lamellar crystalline layers, which suppress the swelling of the PEMs. The unique lamellar structures of ETFE-PEMs characterized by L a and L c are well connected with the high conductance and mechanical properties of the membranes, and are suitable for fuel cell applications.

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

“…Details on the materials were described in the authors' previous studies . The equipments and procedures for the SAXS measurements were also described explicitly in the recent work .…”

Section: Methodsmentioning

confidence: 99%

“…The term γ( 0 ) in Equation is the so‐called scattering invariant, which is often defined based on the invariant Q of the form as

Q = \int_{0}^{\infty} I (q) q^{2} d q \equiv 2 π^{2} v {(ρ_{1} - ρ_{2})}^{2} W_{c} (1 - W_{c})

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

SAXS Investigation on Morphological Change in Lamellar Structures During Propagation Steps of Graft‐Type Polymer Electrolyte Membranes for Fuel Cell Applications

Macro Chemistry & Physics

Nguyen

Zhao³

et al. 2019

Self Cite

Internal and interfacial structure analysis of graft‐type fluorinated polymer electrolyte membranes by small‐angle X‐ray scattering in the high‐q range

J of Applied Polymer Sci

Nguyen

Hasegawa

et al. 2020

The hierarchical structures of poly(styrenesulfonic acid)‐grafted poly(ethylene‐co‐tetrafluoroethylene) polymer electrolyte membranes (ETFE‐PEMs) with different scale ranges including lamellar spacing, interfacial thickness, and intra‐structure of conducting layers were evaluated by small‐angle X‐ray scattering in terms of background scattering (I B(q)). First, I B(q) was roughly estimated by modifying Ruland's method and then optimized to avoid overestimation using a “contribution factor,” which is defined as the contribution of I B(q) to the observed scattering intensities over the entire q range. Then, I B(q) was optimized again by using the model for the deviation from Porod's law also proposed by Ruland to select proper q‐range for interfacial thickness evaluation. The lamellar spacing, which is observed in the low‐q range, was not altered by background correction. In contrast, in the high‐q range, the interfacial thickness and the internal structures can be estimated only after correction for the background scattering data. The interfacial thickness of the final membranes (ETFE‐PEMs) is affected by both the graft‐polymerization and sulfonation processes and because the change in membrane structures is observed during propagation steps at lower ion exchange capacity (IEC) range (IECs < 2.4 mmol/g), which should affect the mechanical strength of graft‐type PEMs.

Morphological characterization of grafted polymer electrolyte membranes at a surface layer for fuel cell application

Hao

J of Applied Polymer Sci

Hieu

et al. 2021

Self Cite

The morphology and elemental compositions at the surface of poly(styrene sulfonic acid) (PSSA) grafted poly(ethylene‐co‐tetrafluoroethylene) polymer electrolyte membranes (ETFE‐PEMs) in a grafting degree (GD) range of 0%–127% are investigated by using FE‐SEM and XPS analyses. The concentrations of elemental components at the surface are not a linear function of GDs, resulting from different grafting speeds at the surface and bulk. In addition, low accumulation of PSSA grafts on the surface of ETFE‐PEMs in the low GDs of 0%–19%, as well as their homogeneous distribution through the membranes at least at a GD of 19% are observed. At higher GDs of 19%–127%, the PSSA accumulation on the surface is relatively limited, indicating the presence of more PSSA grafts inside the bulk than on the surface. The surface signatures of ETFE‐PEMs over the entire GD range can be determined based on the grafting process. These interesting observations suggest the significant advantages of interfacial properties of ETFE‐PEMs for fuel cell applications.