Multi-Block Copolymer Membranes Consisting of Sulfonated Poly(p-phenylene) and Naphthalene Containing Poly(arylene Ether Ketone) for Proton Exchange Membrane Water Electrolysis

Abstract

Glassy hydrocarbon-based membranes are being researched as a replacement for perfluorosulfonic acid (PFSA) membranes in proton exchange membrane water electrolysis (PEMWE). Here, naphthalene containing poly(arylene ether ketone) was introduced into the poly(p-phenylene)-based multi-block copolymers through Ni(0)-catalyzed coupling reaction to enhance π-π interactions of the naphthalene units. It is discovered that there is an optimum input ratio of the hydrophilic monomer and NBP oligomer for the multi-block copolymers with high ion exchange capacity (IEC) and polymerization yield. With the optimum input ratio, the naphthalene containing copolymer exhibits good hydrogen gas barrier property, chemical stability, and mechanical toughness, even with its high IEC value over 2.4 meq g−1. The membrane shows 3.6 times higher proton selectivity to hydrogen gas than Nafion 212. The PEMWE single cells using the membrane performed better (5.5 A cm−2) than Nafion 212 (4.75 A cm−2) at 1.9 V and 80 °C. These findings suggest that naphthalene containing copolymer membranes are a promising replacement for PFSA membranes in PEMWE.

Enhancing Water Absorption in Sulfonated Poly(arylene ether sulfone) Polymer Electrolyte Membranes by Reducing Chain Entanglement through Constrained Deswelling

“…Modification of the molecular architecture could be an approach to achieving lower areal expansion of a PEM in water. Even if an ionomer has the same IEC and chemical structure, PEMs made from blocky ionomers exhibit significantly lower areal expansion. − As previously reported, PEMs with a block architecture display lower areal expansion compared to PEMs with random architecture ionomers. ,− For example, multiblock SPAES PEMs showed lower dimensional changes in length but higher changes in thickness . These characteristics led to entirely different interfacial stability after long-term exposure to water in confined electrochemical cells even when the PEMs had similar IEC values.…”

“…Both PFSA-based and HC-based PEMs consist of phase-separated hydrophilic and hydrophobic domains, providing ion-conducting path and mechanical robustness, respectively, to the PEM. Under humid conditions, phase separation is significantly enhanced by the absorption of water molecules into the hydrophilic domains. − Generally, PFSA-based PEMs, known for their excellent phase separation, feature wide water channels with continuous hydrophilic pathways. − In contrast, HC-based PEMs exhibit smaller water channels, and the partitioning difference between hydrophilic and hydrophobic segments is less pronounced due to the rigidity caused by the aromatic backbone. , Because of these differences, HC-based PEMs show less distinct phase separation and a larger average spacing between neighboring hydrophilic domains compared to PFSA-based PEMs. − Therefore, in electrochemical applications, HC-based PEMs require higher sulfonic acid group capacity (>∼1.8 mmol/g) to achieve cell performance similar to that of Nafion. − As a result, they absorb more water and exhibit greater areal expansion in aqueous environments, leading to challenges in maintaining the interfacial stability between the PEM and the electrodes. Nonetheless, the higher water uptake by a PEM can enhance mass transfer and ion conduction through the PEMs and MEA interfaces, ,, especially in the case of sulfonated HC-based PEMs, which are incompatible with the commonly used PFSA-based ionomers in the electrodes. ,, Therefore, achieving an optimal balance between water absorption and areal expansion is crucial when PEMs are exposed to water.…”

2,5-Substituted Thiophene Functionalized Semifluorinated Polytriazoles and Evaluation of Low-Temperature Proton Exchange Membrane Application with Elevated Oxidative Stability

“…Nafion and other perfluorosulfonic acid membranes are the most prevalent commercial PEMs that possess extraordinary proton conductivity and chemical durability; however, a few concerns like high permeability to fuel and loss of mechanical properties at higher temperatures have made it a formidable challenge to apply fuel cells on a broader scale in real life. , The major focus in designing alternative membranes is on sulfonic acid functionalized poly­(arylene ether ketone)­s, − poly­(arylene ether sulfone)­s, − polyimides, − polyphonylenes, − polybenzimidazoles, − and polytriazoles − as successors to perfluorinated PEMs like Nafion. Among these PEMs, sulfonated polytriazole (SPTZs) have been explored to an extent in recent times.…”

Porous Polyethylene Supports in Reinforcement of Multiblock Hydrocarbon Ionomers for Proton Exchange Membranes

“…However, HC-based membranes still have unresolved issues that need to be addressed. First, they exhibit poorer tensile properties compared to PFSA membranes. − PFSA membranes are composed of a Teflon-like tetrafluoroethylene backbone and side chains containing sulfonic acid groups, which provide both proton conduction capability along with relatively high flexibility and mechanical toughness. ,,, In contrast, HC-based membranes consist of an aromatic backbone with sulfonic acid groups . Due to these structural differences, HC-based membranes are generally brittle in the dry state and lack flexibility even in fully hydrated states. − Second, HC-based membranes display higher volume expansion compared to PFSA membranes when hydrated, owing to their greater ion exchange capacity (IEC), which is typically around twice that of PFSA membranes. , Achieving a harmonious equilibrium between elevated proton conductivity resulting from a high degree of sulfonation (DS) and minimal swelling (expansion) poses a significant challenge for HC-based membranes. , …”