Energetic influence of methylene blue on the electrochemical performance of activated carbon in a water-in-salt electrolyte

Though supercapacitors are attractive for fast charge storage, their energy densities are usually unsatisfactory owing to the low operating potential window and the low capacity. Herein, a new supercapacitor system is constructed, using a concentrated HCOOK (a water-in-salt electrolyte) and a methylene blue modified activated carbon (AC/MB) electrode. In this system, the operating window can reach − 1.6 to 0 V; Capacity can reach 608 C g−1 at 2 A g−1, which is still as high as 324 C g−1 at 10 A g−1, indicating fast charging/discharging ability. The stability of the AC/MB is obviously better than that of the pure AC, and 74% of the initial capacity remains after 10,000 cycles’ cycling at 10 A g−1 for the AC/MB. In a symmetrical cell, the working window of the system can reach 2 V; capacity retention is enhanced to be 79% after cycling, exhibiting promising prospects for stable and high energy storage.