Abstract
Polymer electrolyte membrane (PEM) composed of polymer or polymer blend is a vital element in PEM fuel cell that allows proton transport and serves as a barrier between fuel and oxygen. Understanding the microscopic phase behavior in polymer blends is very crucial to design alternative cost-effective proton-conducting materials. In this study, the mesoscale morphologies of Nafion/poly(1-vinyl-1,2,4-triazole) (Nafion-PVTri) and Nafion/poly(vinyl phosphonic acid) (Nafion-PVPA) blend membranes were studied by dissipative particle dynamics (DPD) simulation technique. Simulation results indicate that both blend membranes can form a phase-separated microstructure due to the different hydrophobic and hydrophilic character of different polymer chains and different segments in the same polymer chain. There is a strong, attractive interaction between the phosphonic acid and sulfonic acid groups and a very strong repulsive interaction between the fluorinated and phosphonic acid groups in the Nafion-PVPA blend membrane. By increasing the PVPA content in the blend membrane, the PVPA clusters’ size gradually increases and forms a continuous phase. On the other hand, repulsive interaction between fluorinated and triazole units in the Nafion-PVTri blend is not very strong compared to the Nafion-PVPA blend, which results in different phase behavior in Nafion-PVTri blend membrane. This relatively lower repulsive interaction causes Nafion-PVTri blend membrane to have non-continuous phases regardless of the composition.
Highlights
This article is an open access articlePolymer electrolyte membrane (PEM) fuel cell, being more efficient, environmentally friendly, and modular, is one of the most outstanding candidates to replace the internal combustion engine [1,2,3,4]
To construct systems for the dissipative particle dynamics (DPD), copolymer Nafion is divided into three beads (A, B, and S), and homopolymers of PVPA and PVTri are represented by a single bead
Conventional perfluorinated sulfonic acid (PFSA)-based membranes’ proton conductivity highly depends on the water content in their protonated form. This dependency limits the fuel cells’ working temperature to below 100 ◦ C due to the membranes’ dehydration from hydrophilic cavities at elevated temperatures. These membranes typically show phase separation where the network of hydrophilic nanopores and nanochannels are embedded in a hydrophobic phase domain
Summary
Polymer electrolyte membrane (PEM) fuel cell, being more efficient, environmentally friendly, and modular, is one of the most outstanding candidates to replace the internal combustion engine [1,2,3,4]. Properties like high proton conductivity, thermal and chemical stability, impermeability to gases, and easier compatibility with electrodes [5,6,7] Morphological peculiarities of these materials mostly stem from the micro-phase separation of hydrophobic and hydrophilic parts of the macromolecules [8]. Many studies have displayed that the conduction of protons takes place via hydrophilic domains that are resulted from micro-phase separation [9] Morphological attributes of these membrane materials are very much affected by water and the backbone’s chemistry. These simulations are not useful to analyze the nanoscale morphology in complicated inhomogeneous phases because they require more atoms and excessive time for equilibration For this reason, many modeling methods are used on a comparable scale with experimental. We establish a connection between the simulated morphologies and experimental properties
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