(309h) Electrical Double Layers in Double-Cationic Ionic Liquids

As a novel class of energy storage devices, electrical double layer capacitors (EDLCs), also called supercapacitors, have attracted tremendous attention in recent years as a promising type of electric energy storage (EES) device, due to their advantageous properties, such as high power density, high capacitance, and excellent durability. In view of their exceptionally wide electrochemical stability window, excellent thermal stability, non-volatility and relatively inert nature, room-temperature ionic liquids (RTILs) have emerged as a very advanced class of electrolytes for supercapacitors. In contrast to the tremendous amount of work on single-cationic ionic liquids, few efforts have been devoted to double-cationic ionic liquids used as electrolytes in supercapacitors. We performed molecular dynamics (MD) simulations to investigate the structure and capacitive behaviour of the electrical double layers (EDLs) in double-cationic ionic liquids with varying alkyl linkage chain lengths near planar carbon surfaces, for comparison with that for single-cationic ionic liquids. Different capacitance-potential relations are observed for single- and double-cationic RTILs in supercapacitor applications.