Synthetic design and development of sterically-protected hydroxide-conducting polymers for energy conversion devices

摘要

The production of renewable energy conversion devices is crucial in reducing greenhouse gas emissions and sustaining the energy required for future generations. However, most energy conversion devices currently available have high costs, which greatly slow down any transition from non-renewable combustion devices. The most promising low-cost, renewable energy conversion devices are based on anion-conducting membranes, such as those found in hydrogen fuel cells, water electrolyzers, redox flow batteries, and electrodialysis. Unfortunately, the current lifetime of such devices is too short for wide-spread adoption. The main issue is the instability of the alkaline anion exchange membrane towards caustic hydroxide. While a significant amount of research has been on demonstrating materials that have longer lifetimes, little work has been concentrated on investigating the degradation pathways on small molecule model compounds. By understanding the chemistry behind their weakness, materials can be specifically designed to counter such pathways. This then leads towards specifically designed polymers with high endurance. The development towards permanently-stable, alkaline anion exchange membranes is the focus of this thesis. Throughout this thesis, new model compounds are developed and extensively characterized. Using new stability tests, the degradation pathways are identified and the stability is quantitatively compared. Novel polymers are then prepared, which are designed to mimic the highest stability small molecule compounds. Steric hindrance is found to be the most promising method towards durable cationic polymers. From Chapter 2 to Chapter 5, the prepared materials become more and more resistant to hydroxide, demonstrating development in the correct direction.