燃料电池用共振离子型碱性电解质膜稳定性影响机制和改善策略研究

Compared with its counterpart fuel cells, alkaline anion exchange membrane fuel cell (AEMFC) has the advantages of low oxygen reduction over-potential and good compatibility with non-noble metal catalysts, but its development has been limited by the low conductivity and poor stability of conventional anion exchange membranes (AEM). Recently, membranes with imidazolium and guanidinium cations have attracted great interests because of their benefits in both conductivity and alkaline stability, the former related to the strong basicity and the latter ascribed to the resonant cation structure. Our prior research in this area suggested that the imidazolium membrane's stability is closely related to its chain structure. However, such correlation is not well understood at this moment; also, there is an urgent need to explore methodologies for membrane stability improvement. Therefore, in this project, we will first carry out systematic work to tune the chain structure of the imidazolium membrane and illuminate the correlation between chain structure and the membrane's alkaline stability; hopefully through these efforts, one or more favorable chain structures can be identified. On the basis of such a structure, we will investigate the influence mechanism and improvement strategy for AEM alkaline stability from the perspectives of cation resonance effect and hydroxide ion solvation degree in the membrane. To be specific, AEMs with enhanced or synergic cation resonance will be designed to achieve better stability than that of AEM with common resonant cations. Meanwhile, a strongly water-affinitive but swelling-resistant hybrid gel will be incorporated into the above membrane as "water collector" to boost hydroxide solvation so that the hydroxide attack on the cations can be alleviated, which is beneficial for maintaining good membrane stability. Finally, for prevention of membrane becoming brittle due to the above gel incorporation and the possible cross-links introduced when building the synergic resonance effect, a functionalized reinforcing material will be employed in which the anion conductive polymer and the water-affinitive gel form a semi-interpenetrating network; the functional reinforcing material will chemically interface the anion conductive polymer, insuring long-term integrity of the resultant composite membrane. This project will provide new idea and methodology for research and development of high-performance AEM, and is therefore of great value and importance for AEMFC technology.

碱性电解质膜燃料电池（AEMFC）氧还原过电位低、可使用非贵金属催化剂，但长期受膜稳定性差、电导率低问题困扰。咪唑和胍型电解质膜因离子交换基的强碱性和共振结构而具有电导性和稳定性上的潜在优势，近年来受到高度关注。申请者前期工作发现咪唑膜碱稳定性与其链结构密切相关，但原因尚不甚明确，其稳定性改善策略也有待深入研究。鉴于此，本项目通过系统的链结构调控揭示上述相关性的内在机理，并从离子基共振结构和水含量两方面进一步探索膜稳定性影响机制和改善途径。通过分子设计实现离子基"增强或协同共振效应"以提高电荷离域程度、弱化与氢氧根的相互作用；在膜内构筑强吸水耐溶胀型杂化凝胶"捕水剂"以促进氢氧根溶剂化、降低其对离子基的进攻强度；采用基于界面设计的化学复合方法防止捕水凝胶引起的膜韧性下降。本项目的实施将为解决碱性膜稳定性问题提供新思路、开辟新途径，其研究成果对推进AEMFC的发展具有重要科学意义和应用价值。

碱性电解质膜燃料电池氧还原过电位低、可使用非贵金属催化剂，但长期受碱性膜（AEM）稳定性差问题困扰。申请者前期工作发现咪唑膜碱稳定性与其链结构密切相关，但原因尚不甚明确，其稳定性改善策略也有待深入研究。针对此问题，本项目已完成的主要研究内容、重要结果和关键数据如下：. 1.主链结构与离子基稳定性的关系. 制备了不同主链结构的咪唑盐型聚砜AEM，包括双酚A聚砜，联苯型聚砜和六氟双酚A聚砜。经室温下3 M 碱处理168 h后，膜电导率分别下降18%、11%、7%。该差异主要源于主链供电效应与空间效应对咪唑离子基的影响：双酚A聚砜主链中亚异丙基增大了链自由体积，使氢氧根对咪唑离子的进攻加剧，造成膜的碱稳定性下降。 为弱化上述不利影响，制备了咪唑化接枝型双酚A聚砜AEM。经3 M的NaOH水溶液处理168 h后，电导率下降15%，稳定性优于非接枝AEM（18%），验证了主链结构对离子基稳定性的影响。. 2.离子基双共振结构与稳定性的关系.合成了具有双重共振结构的新型离子化试剂-咪唑胍，其增强共振效应使AEM的稳定性显著提升：其在室温3M碱性条件下能够稳定10天，而单纯的咪唑型碱性膜在同样条件下电导率下降70%。碱处理后通过红外表征，发现咪唑基团的特征峰依然存在。由密度泛函理论计算得到咪唑胍型离子基的HOMO能级为-4.4091eV，高于咪唑的-5.2387eV，从理论上证实了双共振效应对离子基团碱稳定性的促进作用。. 3.溶剂化效应对离子基稳定性的影响. 合成了二苯醚双胍，通过原位溶胶凝胶反应在膜内引入双胍化水凝胶（ODGBS）。ODGBS 中胍离子基和硅氧基能显著增大膜的吸水率（7.92%-18.97%），改善氢氧根和胍离子的溶剂化效应，弱化氢氧根对胍离子的进攻；ODGBS 结构中无β-H，可避免霍夫曼降解。引入ODGBS后，膜在60℃，3M碱处理120小时后的电导率保持率为85%，高于引入BGBS膜的72%。 . 通过本项目的研究，获得了对AEM稳定性影响因素的新认识。所提出的主链结构调控、增强共振和杂化水凝胶策略对于提高膜的碱稳定性具有重要作用，对促进碱性膜燃料电池的发展具有积极意义。