Development of a Superior Anion Exchange Membrane with Hyperbranched Polymer for Anion Exchange Membrane Water Electrolysis
Authors: Palanivel Tamilazhagan , Kalanur Shankara , Rajangam Vinodh , Pollet Bruno Georges 
Published: December 2024

Hydrogen is a clean and renewable energy, that provides numerous potential benefits to industries, and households, with zero greenhouse gas emissions, and increased energy security. Mainly hydrogen energy is widely seen as a key component to combat climate change that could potentially fulfill the global energy demands in the future. Hence, hydrogen production technologies are considered an important energy and R&D sector in both academics and industries. Currently, water with its abundance in electrolysis mode is known to be an effective route of green hydrogen production. Specifically, hydrogen production via anion exchange membrane water electrolysis (AEMWE) is a promising green technology gaining significant attention in recent times owing to its advantages, efficiency, and simplicity. In AEMWE, the membranes play a crucial role in determining the efficiency, stability, and pilot scale strategies. However, AEMs face several limitations due to their linear polymer backbone structure which can lead to mechanical and chemical instability, ultimately impacting the durability and performance of the AEMWE. That is, the linear backbone which is responsible for controlling the mobility of ions, affects the ionic resistance, and mechanical strength of the membrane. Given this, the present work addresses the limitations of linear polymer backbones and proposes hyperbranched polymers and dendrimers. Generally, hyperbranched polymers have highly branched structure that offers improved mechanical and chemical stability compared to linear polymers and thus enhance the stability that could provide durability and improve the performance compared to that of linear AEMs. Furthermore, blending hyperbranched polymers with dendrimers yield a high density of functional groups that facilitate ion transport and reduce ionic resistance by allowing efficient movement of ions, leading to increased efficiency in hydrogen production. The proposed innovative strategy offers a significant advancement in AEMWE systems.

The production of hyperbranched polycarbonate was carried out via a polycondensation reaction involving dimethyl carbonate and trimethylolpropane ethoxylate, utilizing 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as the catalyst. The poly(aminoamide) dendrimer was synthesized through a step-growth polymerization process catalyzed by DBU, to form a dendritic polymer. Following the synthesis, both the hyperbranched polycarbonate and the dendrimer were individually blended with polyether sulfone. The blending step aims to augment the overall performance of the resultant materials, leveraging the unique properties of each component to achieve a synergistic effect.

The hyperbranching by polycarbonate is characterized by high branching and functionality, which is aimed at improving the mechanical strength and chemical stability of anion exchange membranes (AEMs). On the other hand, the poly(aminoamide) dendrimer structure (shown in the below Figure) is found to enhance the ion exchange capacity and water uptake properties, which are crucial for increasing the efficiency of hydrogen production via electrolysis. Overall the synthesized anion exchange membrane was characterized to confirm the incorporation of hyperbranched polycarbonate and poly(aminoamide) dendrimers within a polyethersulfone matrix. The detailed characterization confirmed a significant improvement in ionic conductivity and ion exchange capacity, which could facilitate the effective ionic pathways and the abundance of functional groups from the hyperbranched structures. Moreover, the membrane exhibited remarkable alkaline stability, maintaining its structural integrity and performance in strong alkaline environments, a crucial attribute for durability in practical applications. Furthermore, the results showed that the membrane achieves an optimal balance between water uptake and swelling, absorbing sufficient water to aid efficient ion transport while minimizing swelling, due to the precise hyperbranched and dendrimer network. Conclusively, the optimized hyperbranched membrane ensures effective functionality in operational stability under a variety of conditions without compromising its dimensional stability. Importantly, the membrane's mechanical integrity was tested and the results confirm the robust nature of the hyperbranched structure, indicating significant resistance to the physical stresses. Overall, the developed AEM exhibits a combination of enhanced ionic conductivity, optimal water uptake, superior alkaline stability, and robust mechanical properties, positioning it as a promising candidate for AEMWE.

Figure: Schematic illustration of linear polymer backbone with hyperbranched network.

Figure 1