基於新型氫氧根傳導雙環交聯劑之交聯聚苯乙烯-聚異戊二烯嵌段共聚物應用於陰離子交換膜

Abstract

氫能因其高能量密度與燃燒過程乾淨無碳排放等特性，已經成為未來替代能源的有力候選之一。水電解是製備綠氫的常用方法，其中陰離子交換膜水電解反應槽（Anion Exchange Membrane Water Electrolyzers, AEMWE）利用陰離子交換膜（Anion Exchange Membranes, AEM）將氫氧根離子由陰極傳導至陽極。該技術的優勢包括：析氧反應（Oxygen Evolution Reaction, OER）在鹼性環境下具備有利的動力學，能夠降低反應能耗，以及在催化劑材料選用上可避免使用昂貴的鉑族金屬，使其具備商業開發的潛力。 本研究旨在開發具高穩定性且具成本效益的陰離子交換膜，以應用於陰離子交換膜水電解槽中。我們使用陰離子聚合合成具有特定分子量與組成的聚苯乙烯-聚異戊二烯嵌段共聚物（Poly(styrene-b-isoprene), PS-b-PI）作為高分子骨架，並對PI鏈段上高反應性的垂懸雙鍵進行一系列後續化學修飾，使PI鏈段帶有可交聯之反應性官能基。而後在系統中導入直鏈型(linear type)與橋環型(bridged type)的交聯劑，並評估不同交聯系統的性能差異。以雙環戊二烯（Dicyclopentadiene, DCPD）為起始物合成之新型橋聯雙環型交聯劑具有兩個一級胺，可與PI主鏈上的溴基反應，形成交聯橋鍵，後續將交聯薄膜浸泡於碘甲烷溶液，即可在橋環位置產生具陰離子導電性的季銨官能基。而直鏈型交聯劑N,N,N’,N’-tetramethyl-1,6-hexanediamine(TMHDA)則由兩個三級胺與柔軟長碳鏈組成，可形成交聯鍵結的同時進行四級銨化。兩交聯系統皆提供薄膜良好的鹼性穩定性與剛性，其中橋環結構可引入較大自由體積以容納結合水，並誘導產生更加規整的微相分離結構，形成連續的離子傳導通道以促進氫氧根離子的傳導。直鏈結構則具有較小的離子傳導通道尺寸，且更限縮薄膜的吸水與澎潤，保有良好的結構完整性與機械性質。

Hydrogen energy has emerged as a promising candidate for future alternative energy sources due to its high energy density and carbon-free combustion process. Water electrolysis is a widely adopted method for green hydrogen production, among which anion exchange membrane water electrolyzers (AEMWE) utilize anion exchange membranes (AEMs) to transport hydroxide ions from the cathode to the anode. The advantages of this technology include the favorable kinetics of the oxygen evolution reaction (OER) under alkaline conditions, which helps reduce energy consumption, and the ability to employ non-precious metal catalysts, thus enhancing its commercial viability. This study aims to develop highly stable and cost-effective anion exchange membranes for application in AEMWE systems. Poly(styrene-b-isoprene) (PS-b-PI) block copolymers with tailored molecular weights and compositions were synthesized via anionic polymerization to serve as the polymeric backbone. The reactive pendant double bonds on the PI segments were subsequently modified through a series of post-functionalization reactions to introduce crosslinkable functional groups. Two types of crosslinkers—linear and bridged—were incorporated into the system to investigate the effects of crosslinking architectures on membrane performance. A novel bridged crosslinker derived from dicyclopentadiene (DCPD), containing two primary amine groups, was designed to react with the brominated PI backbone, forming covalent crosslinked bridges. Subsequent immersion of the crosslinked membranes in methyl iodide resulted in the formation of anion-conductive quaternary ammonium groups at the bridged sites. In contrast, the linear crosslinker N,N,N’,N’-tetramethyl-1,6-hexanediamine (TMHDA), composed of two tertiary amines and a flexible aliphatic chain, simultaneously facilitated crosslinking and quaternization. Both crosslinking systems conferred the membranes with excellent alkaline stability and rigidity. The bridged architecture introduced larger free volume, which accommodated sufficient bound water and promoted the formation of well-ordered lamellar microphase-separated structures, thereby enabling the creation of continuous ion transport channels for enhanced hydroxide ion conductivity. Conversely, the linear architecture produced smaller ionic domains and restricted water uptake and swelling, maintaining superior structural integrity and mechanical robustness.