Surface Active Ionic Liquids in Ionic Liquid Solvents for Enhanced Supercapacitor Energy Storage NR

Surface active ionic liquids (SAILs) are a unique group of ionic liquids (ILs) that combine the properties of self-assembling surfactants with that of ILs. From the results of previous neutron reflectivity (NR) studies, we have found that due to their electroresponsive nature, specific phosphonium/imidazolium (Im) orthoborate SAILs (Figure 1) are able to self-assemble into multi-layered structures on a charged electrode surface. They thus display great potential as electrolytes for enhanced supercapacitor energy storage. However, this was accomplished in the organic solvent propylene carbonate (PC), limiting the applicability of such a system with its intrinsic volatility and flammability. ILs on the other hand, provide a “green” alternative with their tunable properties and proven ability to support self-assembly1. They provide a plethora of “solvents” to choose from but due to their ionic nature (Figure 1), also provide a competing molecular species for interaction with a charged electrode interface. Therefore, we propose the use of NR to study the electroresponsive SAILs interfacial assembly when combined with an IL solvent. This has significant implications for the design of future supercapacitors and will be paired with SANS experiments on SANS2D.

表面活性离子液体（Surface Active Ionic Liquids, SAILs）是一类兼具自组装表面活性剂与离子液体特性的独特离子液体（Ionic Liquids, ILs）。既往中子反射法（Neutron Reflectivity, NR）研究结果显示，得益于电响应特性，特定的鏻/咪唑鎓（Im）原硼酸酯类表面活性离子液体（图1）可在带电电极表面自组装形成多层结构，因此在高性能超级电容器储能用电解质领域展现出巨大应用潜力。然而，此类体系此前仅在有机溶剂碳酸丙烯酯（Propylene Carbonate, PC）中实现，而该溶剂固有的挥发性与易燃性限制了其实际应用范围。相较之下，离子液体凭借可调控的理化性质与已证实的自组装能力¹，成为一类"绿色"替代溶剂。其可供选择的溶剂品类极为丰富，但由于自身的离子特性（图1），也会在带电电极界面处产生竞争性相互作用的分子组分。因此，本研究拟采用中子反射法，探究电响应型表面活性离子液体与离子液体溶剂复配时的界面组装行为。该研究对下一代超级电容器的设计具有重要指导价值，且将与SANS2D平台上的小角中子散射（Small Angle Neutron Scattering, SANS）实验协同开展。