Understanding of Nanophase Separation and Hydrophilic Morphology in Nafion and SPEEK Membranes: A Combined Experimental and Theoretical Studies

Abstract

The understanding of the relationship between the chemical structure and the hydrophilic structure is crucial for the designing of high-performance PEMs. Comparative studies in typical Nafion and sulfonated poly (ether ether ketone) (SPEEK) were performed using a combined experimental and theoretical method. SPEEK showed suppressed fuel crossover and good mechanical property but low water uptake, weak phase separation, and inadequate proton conductivity. Molecular dynamics (MD) simulation approaches were employed to get a molecular-level understanding of the structure–property relationship of SPEEK and Nafion membranes. In SPEEK membranes, the local aggregation of hydrophilic clusters is worse, and much stronger electrostatic interaction between Os–Hh was verified, resulting in less delocalized free H3O+ and much lower DH3O+. In addition, the probability of H2O–H3O+ association varied with water content. Particularly, SPEEK exhibited much lower H9O4+ probability at various relative water contents, leading to lower structural diffusivity than Nafion. Eventually, SPEEK possessed low vehicular and structural diffusivities, which resulted in a low proton conductivity. The results indicated that the structure of hydrated hydronium complexes would deform to adapt the confining hydrophilic channels. The confinement effect on diffusion of H2O and H3O+ is influenced by the water content and the hydrophilic morphologies. This study provided a new insight into the exploration of high-performance membranes in fuel cell.

Synthesis of Sulfonated Poly(Arylene Ether Sulfone)s Containing Aliphatic Moieties for Effective Membrane Electrode Assembly Fabrication by Low-Temperature Decal Transfer Methods

“…If the IEC values are similar, the conductivity of the Nafion 212 is higher than that of the synthesized SPAES membranes. Fluorinated groups of Nafion have higher electronegativity than the hydrogen of hydrocarbon-based membranes; therefore, it is known that Nafion is more conductive than general hydrocarbon-based membranes [ 26 ]. Hex-SPAES-40 showed a higher conductivity value, even though it had a lower IEC value than Phe-SPAES-40.…”

“…There are many research papers that consider the degree of hydrophilic–hydrophobic phase separation in TEM images with respect to ion conduction channels [ 16 , 26 ]. This is because when the moisture content of the polymer electrolyte membrane increases, adjacent hydrophilic clusters connect to each other to form ion-conducting channels that promote ion diffusion [ 26 ].…”

“…There are many research papers that consider the degree of hydrophilic–hydrophobic phase separation in TEM images with respect to ion conduction channels [ 16 , 26 ]. This is because when the moisture content of the polymer electrolyte membrane increases, adjacent hydrophilic clusters connect to each other to form ion-conducting channels that promote ion diffusion [ 26 ]. Previously, Zhao et al reported that the presence of a flexible aliphatic chain in the rigid aromatic polymer backbone increases the mobility of the polymer chain and contributes to the formation of a larger ion-conducting channel [ 16 ].…”

Green Synthetic Fuels: Renewable Routes for the Conversion of Non-Fossil Feedstocks into Gaseous Fuels and Their End Uses

“…The low membrane thickness (120-170 µm) and the solid electrolyte reduce the ohmic overpotential and allow the operation in a load-following mode with 100% turndown potential of the specific power input since the crossover rate is low and the response to power change is rapid [199]. Nafion, generally used as a membrane polymer due to its high stability, consist of a hydrophobic poly(tetrafluoroethylene) with a lateral branch of hydrophilic sulfonic acid functional group (-SO 3 H) [200]. Proton transport across the electrolyte is a combination of proton hopping (structural diffusion) among water molecules and diffusion in solution by forming a hydrated ion [201].…”

Novel Polymeric Composite TPPS/s-PEEK Membranes for Low Relative Humidity PEFC

“…Even if Nafion ® is the most commonly used membrane, due to its high proton conductivity, some disadvantages, such as water uptake, methanol permeability and cost, have oriented research to the study of alternative polymers. Poly-ether-ether-ketone (PEEK) is a low cost thermoplastic, widely used in the space-flight, petroleum, chemical and medical industrial fields, due to its heat and corrosion resistant properties [3][4][5]. Moreover, a wide range of literature has shown that functionalized PEEK containing sulfonic groups is suitable for PEFC applications [6,7].…”