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Development of Ether-Free Polyarylene-based Anion Exchange Membranes for Alkaline Fuel Cells through Crosslinking, Copolymerization, and Blending Strategies

Farhadpour, Mohammad | 2025

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 58337 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Bagheri, Reza; Pircheraghi, Gholamreza; Shao, Minhua
  7. Abstract:
  8. Developing high-performance anion exchange membranes (AEMs) with well-balanced properties is essential for advancing AEM fuel cell technology. However, current AEMs face performance and durability limitations due to the trade-off challenges between different properties. This work addresses these challenges through various approaches, including crosslinking, copolymerization, and blending. Firstly, we developed crosslinked ether-free polyfluorene-based AEMs using a crosslinker containing potential cationic groups. Optimizing the crosslinking degree significantly improved swelling ratio (<15.9%), water uptake (<78.0%), and mechanical properties (>35 MPa), while simultaneously enhancing hydroxide conductivity (>144.6 mS cm⁻¹). This enhancement was attributed to an improved microphase-separated morphology. Moreover, the resulting membranes exhibited exceptional alkaline and oxidative stability. They retained over 93-95% of their initial hydroxide conductivity, ion exchange capacity, and tensile strength after 1080 h in 3 M NaOH at 80 °C, representing one of the best chemical stability results reported to date. Secondly, we developed copolymer AEMs using bibenzyl (flexible) and dimethylfluorene (rigid) monomers. We demonstrated that optimizing the monomer weight percentages allows for fine-tuning AEM properties, leading to membranes with well-balanced characteristics. Finally, we fabricated blend AEMs by combining two ether-free polyarylene-based polymer phases with identical backbones but different ion exchange capacities (IECs). This strategy produced AEMs with a highly microphase-separated morphology, achieving a remarkable hydroxide conductivity of 262.9 mS cm⁻¹ at an IEC of 2.43 mmol g⁻¹. This conductivity represents a new benchmark. In AEM fuel cell tests, the blend AEM reached a peak power density of 1.36 W cm⁻² and demonstrated stable operation at 0.5 A cm⁻² for 150 hours, with a voltage decay rate of only 0.26 mV h⁻¹. This performance surpasses that of the leading commercial PiperION™ AEM under identical testing conditions
  9. Keywords:
  10. Anion Exchange Membrane ; Ion Conduction ; Nano Channel ; Alkaline Fuel Cells ; Hydroxide Conductivity ; Microphase Separation ; Ion Conductive Nano Channel

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