Ion-pore size match effects and high-performance cucurbit[8]uril-carbon-based supercapacitors

Abstract

The performance of supercapacitors depends on largely the efficient utilization of electrode pores. Therefore, clarifying the matching relationship between the ion size of electrolyte and the pore size of electrode is very crucial to achieve high-performance supercapacitors. Herein, we design a cucurbit[8]uril-derived hierarchical porous carbon (CB8C-Y) with primary pore size of 0.88 nm and a secondary pore size of 0.5 nm as electrode, and four ionic liquids with different cation sizes are compared and utilized as electrolytes. Among ionic liquids, 1-propyl-3-methylimidazole tetrafluoroborate (PMIMBF4) possesses a cation (PMIM+) size of 0.87 nm and an anion (BF4‒) size of 0.33 nm, which just matches with the porous carbon electrode's primary pore size and a secondary pore size, respectively. The suitable ion-pore size matching enables CB8C-2//PMIMBF4//CB8C-2 supercapacitor to achieve an excellent energy density of 89.15 Wh kg‒1. The results provide a typical documentation for high-performance supercapacitor by ion-pore size matching between electrolytes and electrodes.